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Ken Pachkowsky
12-18-2003, 12:05 AM
I have never heard the above. Anyone have any experience with these amplifiers? If so what were your impressions. Thinking of grabbing a couple of them.

Thinking of using the 6260's in mono mode to drive dual 2235H's per side. 4 ohm load. Would be 600 watts per side.

Thanks.

speakerdave
12-18-2003, 12:25 AM
Hey Ken,

I've been thinking along the same lines, but I haven't had a chance to check them out. Be aware that the 6290 has a two-speed fan, so you'll want to be using that in an environment where that is OK. The 6260 has a large finned heatsink at the back and no fan.

These amps seem to have a very solid build quality and are available at what seem to be very reasonable prices.

I'm thinking of them as bass and bass/mid amps, or full range in a simpler setup.

David

sa660
12-18-2003, 02:56 AM
The 6260 is very good amplifier and you will see that their is no fear that your dual 15" will be out of control.
My brother is using a 6260 on a pair of 4435. He does not feel the need to bridge it for mono mode 1x600Watt @8 Ohms.
They are very good and can be compare to the Amcrown DC300 II

Unfortunatly cannot compare with expensive high end Hi-fi model.

May be in future.

Good product and on the second hand market good value for money. I will not advise the 6290 for home use. The fan is very noisy.

Regards,

Niklas Nord
12-18-2003, 05:02 AM
A friend of mine here in Sweden uses these
models for amping 2235H and 4435 studiomonitors.

it works perfect.

right now he is upgrading to Krell KSA 250 though..

JBL Dog
12-18-2003, 08:23 AM
I have three of the 6290's and they are outstanding amplifiers, IMHO. Very clean sounding, conservatively rated and reliable. One of the few amps on the market that you will actually double your power output going from 8 ohms (300 x 2) to 4 ohms (600 x 2). I am currently using mine with some EV SX100's full range for small club gigs and as part of of tri-amped system for mids/highs.

You may not like the fan noise as previously mentioned, but a 6290 may be the best value on the Ebay market at $250 - $350. They're pretty heavy at about 70 lbs. Factor that in if you are having them shipped to you. Good Luck!

This message comes from JBL Dog :band:

Ken Pachkowsky
12-18-2003, 09:03 AM
I appeciate your input fellas.

Building a custom pair of 4355's and am shopping for new electronics.

Let me throw this out for opinion's:

Should I go quad amped with 4 way electronic crossover or bi amped with combo electronic and passive using higher end amps?

I suspect most would suggest bi amped with better amps?

Ken

JBL Dog
12-18-2003, 09:53 AM
I would go biamped. Quad sounds like too much work. Also, wouldn't you be forced to go mono with quad? Does anyone make a "stereo" 4-way active crossover?

:hmm:

This message comes from JBL Dog :band:

Ken Pachkowsky
12-18-2003, 09:58 AM
There are many 4-way electronic crossovers out there. My Westlakes are 4-way. The problem becomes groundloops if mixing balanced and unbalanced lines. I still have a slight GL problems to this date. You can of course have the same problem with a 2-way system.

boputnam
12-18-2003, 09:59 AM
Originally posted by Ken Pachkowsky
Should I go ... bi amped with combo electronic and passive using higher end amps? Hey, Ken... :wave:

Since you're largely trying to authentically replicate the 4355's, I'd do it their way: active crossover bi-amped, and then passive crossover for MF/HF/UHF, using JBL specified xover points and slopes, and bypass caps. Mr. Widget made a beauty passive with the assistance of Giskard (and others...?), and his "rig" is astonishing.

Although, I hear tell he's adding some 2245H's for the rumble... :hmm: I think it's 4345 envy, plain and simple! :yes:

Robh3606
12-18-2003, 10:30 AM
Hello Ken

I am quad amping using cascaded actives works fine. I had ground problems too then I changed amps to all Crown PS200's and got the balanced input boxes for them. As soon as I went balanced between the amps and the crossovers all my ground loop problems vanished. Made a big improvement in noise in the whole system. Didn't realize at the time how much noise I was living with that I just got used to. Cleaned up noise in my center channel too.

I would go biamp with a 5235 like Bo says. Experiment too maybe but that sure makes sense. When choosing your amps I tried to get amps I could stap easilly. With the Crowns I can strap with the flip on a switch. 2 strapped for the lowend and use a single for the highs for biamp or triamp. Gives you more flexabillity.

Rob:)

Ken Pachkowsky
12-18-2003, 10:31 AM
Originally posted by boputnam
Hey, Ken... :wave:

Since you're largely trying to authentically replicate the 4355's, I'd do it their way: active crossover bi-amped, and then passive crossover for MF/HF/UHF, using JBL specified xover points and slopes, and bypass caps. Mr. Widget made a beauty passive with the assistance of Giskard (and others...?), and his "rig" is astonishing.

Although, I hear tell he's adding some 2245H's for the rumble... :hmm: I think it's 4345 envy, plain and simple! :yes:


Well, as you know BO, I understand 4345 envy quite well.

I have always thought I would go bi-amped with a custom passive built by Widgy but was just getting some other opinions.

Earl also brought up an interesting point in one of the project threads. Why not incorporate some newer JBL technology in terms of drivers for a 43xx project. That got me to thinking.

Just did our taxes.....Julie saw what I spent last year on all this stuff. I hate the couch!!!

Gonna be fun.

Hope you and Susan are well. Julie says Hi.

Ken

Mr. Widget
12-18-2003, 10:35 AM
Next I am buying a Hummer.


What's that Mike, Big is Good?

boputnam
12-18-2003, 10:38 AM
Originally posted by Ken Pachkowsky
Just did our taxes.....Julie saw what I spent last year on all this stuff. :shock: Are you trying to deduct all this as a business expense? Whoa... Come to papa! :dancin:

Ken Pachkowsky
12-18-2003, 10:38 AM
Originally posted by Mr. Widget
Next I am buying a Hummer.


What's that Mike, Big is Good?


Speak of the devil!

Whats this " You have 18 inch envy all about?

Ken

Mr. Widget
12-18-2003, 11:10 AM
Not exactly, got a pair of 2245s for the HT set-up. At the rate I am going it'll be a year before they are in boxes. I can click "Buy it Now" much faster than I can keep up in the shop.

Oldmics
12-18-2003, 12:18 PM
I hear that disease is called "Trigger Finger"
Oldmics

Tom Loizeaux
12-18-2003, 04:56 PM
Ken,
I use a 6260 and a 6230 in a bi-amp rack, along with a 5235, to drive one of my studio monitor pairs. I also have a similar set up using a Crown PS-400 and PS-200. I find the JBL/ Ureis to be a bit stronger (louder) and sound fine, but the Crowns seem to have slighty less noise and seem a little more refined. ? I believe the protection circuits in the Crowns are a little more advanced.
I like all of these because they are big, heavy, stable and overlooked by most people today.

Tom

Ken Pachkowsky
12-19-2003, 12:16 AM
Thanks for the info guys, will let you know if I get them.

Nice to hear from you Tom.

Ken

Mike Caldwell
12-19-2003, 06:52 AM
Hello
The largest Urie amp had speaker sense line input jacks
in the form of BNC connectors.
These were for and second set of lines going to the
speaker and connecting to the main speaker cable binding post
or connectors.
The amp would then detect any voltage generated by the speaker
s voice coils and compensate for it, makeing for a very high
damping factor.
Velodyne powered sub woofers had a similar idea only they
used a velocity transducer fastened to the back of the speakers cone.
I have an old Urie catalog, I'll dig it up and see what else the
say about the sense lines.
If anyone wanted the info for a Urie amp I could scan the pages
and e-mail them to you.

Thanks
Mike Caldwell

DL2246
03-04-2009, 12:58 PM
I have a pair of 6290 amps and currently use them to power four BassTech7 ServoDrive concert subs that weigh in at almost a half ton. They are a conservatively rated amp with a conventional power supply, four rack spaces and hefty at 60 pounds or so. The fan is a bit noisy but cools the heatsinks very well. With a slew rate of 50 volts per microsecond it's an exceptional value on the used market, going for $200 to $350 bucks. Only Chevin and Lab Gruppen can match that spec and those amps are like a bazillion bucks. The 6290's are a true 600 watts per side with a 4 ohm load and sound great. With a conventional PS they retain enough reserve power and won't crap out if the AC line voltage gets a little weird. They are big and heavy but if you have the rack space probably the best deal in old power amps.

subwoof
03-04-2009, 01:23 PM
Did you realize that this thread is SIX YEARS OLD????

JBL Dog
03-04-2009, 01:37 PM
They are big and heavy but if you have the rack space probably the best deal in old power amps.

Yup. I have three 6200 series amps. No doubt one of the best values out there.

:applaud:

jbl_daddy
03-04-2009, 03:02 PM
I had a pair of 6290's a while ago, 10+ years ago, great amps very punchy. The fans were anoying and they sucked a lot of power when turned on. I had a line just for them in my electrical pannel. When turned on all at once from a remote pannel they will trip breakers in your house.:)

speakerdave
03-04-2009, 03:13 PM
I have a pair of 6290 amps and currently use them to power four BassTech7 ServoDrive concert subs that weigh in at almost a half ton. They are a conservatively rated amp with a conventional power supply, four rack spaces and hefty at 60 pounds or so. The fan is a bit noisy but cools the heatsinks very well. With a slew rate of 50 volts per microsecond it's an exceptional value on the used market, going for $200 to $350 bucks. Only Chevin and Lab Gruppen can match that spec and those amps are like a bazillion bucks. The 6290's are a true 600 watts per side with a 4 ohm load and sound great. With a conventional PS they retain enough reserve power and won't crap out if the AC line voltage gets a little weird. They are big and heavy but if you have the rack space probably the best deal in old power amps.

I agree on all counts. A musical amp.

Though this thread is six years old, the amps are older and still providing good value for money, and they still show up on the used market, although I like to advise caution when buying used pro power amps on ebay.

Mr. Widget
03-04-2009, 05:16 PM
I like to advise caution when buying used pro power amps on ebay.Over the past 6 years I have become significantly less open to the idea of buying vintage electronics. Of the basement full of older amps and other devices I have and have had like these older speakers we love, almost none of it actually works up to original specs.

As John pointed out on another thread... the amp may being "working", but sometimes it really isn't.



About a year ago people started complaining about the sound in one of the production studios here at the radio station. The studio has JBL 4412A speakers. I listened to the sound in the studio and something had changed!
There was a fuzziness to the sound, a low level distortion. The people said the speakers were bad, I doubted that it was the speakers. After checking out some things I figured out it was the old Crown DC300, I swapped it out with a different amp, sound was clean again.
I took the DC300 to the shop and hooked it up, put 8 ohm resistors on and put a 1khz sine wave in, hooked up a scope. What I saw on the scope just blew my mind! On the left channel the positive half of the sine wave was clipped about half way up, but the negative part of the sine wave was OK.
On the right channel the negative part of the sine was was clipped and the positive part was OK. This is very high amplitude distortion, but it didn't sound terrible, just kinda fuzzy. From what I saw on the scope I though it should have sounded much worse than it did! :biting:
For years I have know that speaker distortion is usually much higher than amp distortion. The reason that we love JBL is because of their low distortion. This experience has reinforced my conclusion that the quality of the speakers is far more important than the amp. I don't get hung up on amps. I use good amps but I don't go crazy over them, JBL speakers,YES!:D
I not putting down any one for their like or dislike of any brand of amp. John

Widget

westend
03-04-2009, 06:25 PM
I use a 6290, driving low end in a biamped Altec set. More than enough power, of course. I have a replacement fan sitting on a shelf as the older stock fans are a bit loud. I'm thinking the newer fan will be much quieter.

JBL's own product literature states that the 62xx series are underrated as to the amount of actual power available. I've never tested mine but with that long row of Sanken's in there I don't doubt it has a lot of power to spare.

Titanium Dome
03-04-2009, 07:25 PM
Well, well, here's a thread that's back from the dead.

This little discussion caused me to do a little research on the 6230 and 6260. They appear to be identical, spec-wise, to the Synthesis® S150 and S300 amps I got recently, which were made by UREI. :hmm: Facelift, anyone?

hjames
03-04-2009, 07:48 PM
Well, well, here's a thread that's back from the dead.

This little discussion caused me to do a little research on the 6230 and 6260. They appear to be identical, spec-wise, to the Synthesis® S150 and S300 amps I got recently, which were made by UREI. :hmm: Facelift, anyone?

Well, I'm real happy with mine ...

Mr. Widget
03-04-2009, 10:12 PM
This little discussion caused me to do a little research on the 6230 and 6260. They appear to be identical, spec-wise, to the Synthesis® S150 and S300 amps I got recently, which were made by UREI. :hmm: Facelift, anyone?Vintage gear and being up to spec aside, you might find this interesting...

Several years ago Zilch lent me a small 62XX that compared to the Hafler P3000. I compared them. Running them full range on my mini monitors, the Hafler P3000 was significantly better sounding. I suppose it also cost significantly more. Now that they are both dead lines the prices are likely more in line with each other.

Widget

JBL 4645
03-05-2009, 03:00 AM
The famous Empire Leicester Square, screen #1 at London's West End, used them for its original, JBL 13KW THX sound system during the late 1980’s though to late 1990’s. The amps where removed and replaced with QSC and Martin Audio loudspeakers during 2000. About 5 years later it was all-revamped back to JBL and Crown power amplifiers and killer 56KW THX certification. :applaud:


http://forum.ecoustics.com/bbs/messages/47069/275681.jpg


http://forum.ecoustics.com/bbs/messages/47069/275682.jpg
More over at this thread: The Empire Leicester Square London a JBL installation!
http://www.audioheritage.org/vbulletin/showthread.php?t=13057 (http://www.audioheritage.org/vbulletin/showthread.php?t=13057)

Russellc
03-12-2009, 06:17 AM
I agree on all counts. A musical amp.

Though this thread is six years old, the amps are older and still providing good value for money, and they still show up on the used market, although I like to advise caution when buying used pro power amps on ebay.
Unless something is really burned up, they are quite "fixable". subwoof walked me through the repairs to my 6230 ebay amp, and as dumb as I am, it is and has been working fine. Basically there needs to be a lot of solder reflowing, and replacement of a few small electrolitics. Then its good for another 20+ years.

Thanks again subwoof!

Russellc

Russellc
03-12-2009, 06:22 AM
I use a 6290, driving low end in a biamped Altec set. More than enough power, of course. I have a replacement fan sitting on a shelf as the older stock fans are a bit loud. I'm thinking the newer fan will be much quieter.

JBL's own product literature states that the 62xx series are underrated as to the amount of actual power available. I've never tested mine but with that long row of Sanken's in there I don't doubt it has a lot of power to spare.
You might ask subwoof about this, he once told me that the fan could be quited down considerable if need be. Lower the voltage to it maybe? I didnt inquire B/C I dont have the 6290.

Russellc

subwoof
03-12-2009, 06:32 PM
2 things would help the 6290 fan situation.

First thing is that the amp was designed to be stacked and racked and left on for a bazillion hours SO airflow through it's chassis was designed not to interfere with other rack components ( at least too much ).

If you removed the top and bottom covers, and cut out ALL the metal over *and under* the heatsink fins, and gave this a rack space above and below it would run a lot cooler and the need for high speed might never present itself.

If it did it would be the LEAST noticeable volume in that room...:)

Second is the value of the low speed resistor. The fan is a standard 120V bearing type and it needs to see 120V at start up then drop to the low speed otherwise it won't engage ( esp if worn ).

The stock value can be increased to make the fan spin slower OR not unless the "magic" temp is obtained ( rewiring required ) for home use.

I have 9 of them here from an install and later this month will be doing my analysis on this issue and will post a DIY thread.

There is also the issue of bias voltage but that is a little more advanced BUT easily checked / adjusted. This amp series tends to drift up with age and that WILL cause heat buildup and early fan engaging.

sub

Fred Sanford
03-12-2009, 06:36 PM
I remember also a small resistor that you said was a chronic problem in these amps, and should be upgraded...do you have detail on that?

Thanks,

je (6260)

John
03-13-2009, 12:22 AM
I thought the 6290 fan was always on???:hmm:

subwoof
03-13-2009, 08:41 AM
Look at the schematic and you will see a thermal switch wired across the dropping resistor. When the switch closes the resistor is shorted and the fan gets full voltage.

If you actually REMOVED the resistor the fan would stay off until that temp is achieved, then go full speed.

If you simply put the thermal switch in SERIES with the resistor ( and fan ) then the fan would go to low speed only when the temp is achieved...

secrets out.

:cheers:

http://www.jblproservice.com/pdf/Vintage%20JBL-UREI%20Electronics/JBL-6290%20manual.pdf

Russellc
03-17-2009, 06:04 PM
2 things would help the 6290 fan situation.

First thing is that the amp was designed to be stacked and racked and left on for a bazillion hours SO airflow through it's chassis was designed not to interfere with other rack components ( at least too much ).

If you removed the top and bottom covers, and cut out ALL the metal over *and under* the heatsink fins, and gave this a rack space above and below it would run a lot cooler and the need for high speed might never present itself.

If it did it would be the LEAST noticeable volume in that room...:)

Second is the value of the low speed resistor. The fan is a standard 120V bearing type and it needs to see 120V at start up then drop to the low speed otherwise it won't engage ( esp if worn ).

The stock value can be increased to make the fan spin slower OR not unless the "magic" temp is obtained ( rewiring required ) for home use.

I have 9 of them here from an install and later this month will be doing my analysis on this issue and will post a DIY thread.

There is also the issue of bias voltage but that is a little more advanced BUT easily checked / adjusted. This amp series tends to drift up with age and that WILL cause heat buildup and early fan engaging.

sub
Does the bias voltage drift on the 6230 as well? If so. I'd like to know how to measure and adjust it if possible. Thanks in advance,

Russellc

subwoof
03-17-2009, 07:02 PM
Nearly all AB output amplifiers drift with age. Some up, some down. Look at the schematic and you will see a trim pot for each channel on the output stage on ALL of the urei/jbl amps.

Connect a voltmeter ( set to 2VDC ) across any output transistor's base to emitter junction for that channel.

What you should see after the amp has been powered up ( no load / signal ) for 10 min or so is the actual bias voltage.

If it is below .200 volts the amp will have a VERY SLIGHT crossover distortion. If it goes over .500 you will have a new toaster as the output stage will go into thermal runaway..

The goal here is to give it enough bias ( like the idle on a car ) to keep the distortion low ( not stall ) while not allowing excessive heat to build up ( radiator fan on ) and cause problems.

I usually aim for .250 to .300

NOTE 1: This is a general adjustment for bipolar output stages ( no matter WHO makes it ) and is not a substitute for the manufacturers recommendation.

NOTE 2: Some "fancy" makes and models, to get that magical itty bitty low distortion level, will recommend a "high" bias. This is not a very good idea unless you are sure that it can be tolerated...heat is heat and the laws of physics cannot be changed no matter how good a companies marketing dept can write.

The difference in distortion between .01 and .001 is about the level of a mouse fart in the closet down the hall when you are at "11"


If the amp is used for sub only use, the crossover distortion is inaudible so it can be tweaked much lower however the circuit can only go down to a fixed point.

sub

kb50
09-26-2016, 07:16 PM
Does the bias voltage drift on the 6230 as well? If so. I'd like to know how to measure and adjust it if possible. Thanks in advance,

Russellc

I am working on a defective 6260 (non fan type).
Here is the scoop, I probed around the drivers and outputs to discover CHA was glitching and relay dropping out at random due to DC fluctuation on that channel. Taking my meter probe to various points in the driver stages would cause it to suddenly become stable. So I did reflow solder on all the outputs and driver stages. I noticed someone had taken a sharpie and marked around the relay and one of the transistors. Probably in the past those had been replaced. After the reflow nothing changed. Ok so now it is looking like prior stages were causing DC offsets at random, perhaps a stage breaking into oscillation? Well no, it turns out IC2 is the culprit. Ok so since IC1 and IC2 are identical and socketed, I decided to swap them around. This puts the flaky chip into CHB. This caused CHA to stabilize but now CHB is jumping around. I should have stopped here with the conclusion that the ICs will need to be replaced.
However....
Still probing around to see if it was some other component resistor etc around IC2 or a bad cap maybe? Nothing changing it still randomly jumping DC to 3 volts bios and then sometimes back to the normal bias. After being on a while POP big spark and it now has blown R19

So of course as are with most high power amps I suspect I will need to look at the schematic and replace everything connected to R19, which means the chip which was failing has now failed totally and over voltage CHB. I now also think there may be a weaker link in the chain as well.

Mostly wondering if anyone else has seen this problem, and did changing out the chips solve the problem? Is it worth the effort to repair this amp? Are their other problems being the problem and not IC2
Now of course am facing more problems that will have to be resolved before it lives and breathes right again. It looks I will be replacing that 27 ohm? R19 resistor along with the associated driver transistor to be on the safe side it would seem it popped when the IC2 finally has failed, and caused a huge voltage swing. I will be diode checking that transistor, and also shows a diode that is off the emitter that if bad will get replaced too. I am hoping it did not blow any of the output transistors.

I would love to get ahold of a parts listing to locate proper parts. The manual I found online has very little technical information to help in repair especially to have a parts list to reference.

kb50
09-26-2016, 07:38 PM
Does the bias voltage drift on the 6230 as well? If so. I'd like to know how to measure and adjust it if possible. Thanks in advance,

Russellc

It would seem to be the same design as that of Desktop Computer Power Supplies. However those use 12 volt fans with hall effect speed sensors to control the fan speed based on temperature.

I think the environment and use of the amp, will dictate noise levels, and how long it takes to get to top speed. If its in an open enclosure, and used at normal levels then cooling should not be a problem.
I am not seeing the familiar beads or thermistors, that when heat builds up on the unit, adjusts bias voltage slightly to keep things in perspective.

kb50
09-26-2016, 08:06 PM
I thought the 6290 fan was always on???:hmm:
Yes it is always on, when the amp is on. It just runs at low speed thru the current limiting resistor as shown in the schematic. Then the thermal switch when exceeded shorts the resistor giving full current to the fan. It runs on 120VAC or probably cut to 30VAC or some figure. So it stays on low speed unless the amp is driving hard, then jumps to full speed once a certain temp is reached. Most of these have a degree stamped on the side of the switch.

kb50
09-26-2016, 08:19 PM
2 things would help the 6290 fan situation.

First thing is that the amp was designed to be stacked and racked and left on for a bazillion hours SO airflow through it's chassis was designed not to interfere with other rack components ( at least too much ).

If you removed the top and bottom covers, and cut out ALL the metal over *and under* the heatsink fins, and gave this a rack space above and below it would run a lot cooler and the need for high speed might never present itself.

If it did it would be the LEAST noticeable volume in that room...:)

Second is the value of the low speed resistor. The fan is a standard 120V bearing type and it needs to see 120V at start up then drop to the low speed otherwise it won't engage ( esp if worn ).

The stock value can be increased to make the fan spin slower OR not unless the "magic" temp is obtained ( rewiring required ) for home use.

I have 9 of them here from an install and later this month will be doing my analysis on this issue and will post a DIY thread.

There is also the issue of bias voltage but that is a little more advanced BUT easily checked / adjusted. This amp series tends to drift up with age and that WILL cause heat buildup and early fan engaging.

sub

No it does not need 120 to start, and it would make no difference. If the fan did not start and then slow down, the amp will just warm up faster, and then the thermal switch will put the full 120 so then it would jump up in speed as it is intended. If the fan being ball bearing is the much worn out, or full of dust and dirt, then you should just replace it.

Touchtunes jukeboxes use a 120 fan to provide airflow, and often they wear out, and the result is the amp either shuts down, or blows something out. But they did do 1 smart thing and that was to put in an air filter to limit the dust sucked into the fan over time. But still again the operators neglect to change the filter and so it still causes early fan failure, and/or poor airflow. Its usually a no win situation.
The same problems exist in older desktop and laptop computers, the dust eventually causing overheating conditions. Annual or more cleaning will keep your equipment running for many years with proper maintenance. This is why electrolytic caps fail, because of excess heat over time.

BMWCCA
09-27-2016, 06:03 AM
Did you realize that this thread is SIX YEARS OLD????

. . . and now THIRTEEN-YEARS-OLD!

Now I have a 6260 I didn't own back then. Seems to work fine, but I've made no measurements. I do normally push decades-old Crown D and PS series amps, some of which have been returned to Crown for check-ups and most returned with minor tweaks but actually not enough out-of-spec to be a concern.

Cheap Thrills!

1audiohack
09-27-2016, 07:10 AM
I have a bunch of these and have found as subwoof said, they are biased very low. I have heard that is because they are permanent install products and that a low bias value is both energy efficient and thermally efficient as well.

They sound better the warmer they get (to me) and take 20 minutes to a couple of hours to sound their best. Biased up a bit, they come right around.

My 2 cents 13 years later. :)

Barry.

Johnny_Law
10-15-2016, 11:57 AM
Hope this is the correct place to ask this question. I have a 6260 that I used for a time in my music room, fed via an RCA to 1/4" jack cable by a McIntosh C24 which was fed by an RCA wire to my laptop streaming Tidal. The problem was that there was always a background hum, almost like a faint static, audible through the speakers, increasing as the volume knob on the C24 turned to the right. The DC offset of channel A is 24mV and channel B is 14mV which seems acceptable. But the buzz got to me and I switched back to my MC502 which is quiet as a mouse.

I'm trying to figure out whether the hum from the 6260 is due to the ungrounded RCA to 1/4" cable, or because of a problem internal to the amp, or whether that's normal. Any ideas? Thanks in advance.

robertg
10-16-2016, 10:36 AM
Hope this is the correct place to ask this question. I have a 6260 that I used for a time in my music room, fed via an RCA to 1/4" jack cable by a McIntosh C24 which was fed by an RCA wire to my laptop streaming Tidal. The problem was that there was always a background hum, almost like a faint static, audible through the speakers, increasing as the volume knob on the C24 turned to the right. The DC offset of channel A is 24mV and channel B is 14mV which seems acceptable. But the buzz got to me and I switched back to my MC502 which is quiet as a mouse.

I'm trying to figure out whether the hum from the 6260 is due to the ungrounded RCA to 1/4" cable, or because of a problem internal to the amp, or whether that's normal. Any ideas? Thanks in advance.
I turned down the gain on my amplifier, and the hum is almost gone.

Johnny_Law
10-16-2016, 02:14 PM
I turned down the gain on my amplifier, and the hum is almost gone.

So yours has the hum too? Sounds like it's normal. Problem is the feed voltage from the laptop RCA isn't scaled correctly into the C24, I don't think, so I need to have the volume way up (at around the 1:00-3:00 positions) to produce acceptable listening volumes, and turning the gain down on the 6260 wasn't an option. I wish there was a way to get rid of that hum at high gain levels.

Mike Caldwell
10-17-2016, 05:57 AM
It sounds like you may need some transformer isolation between the signal source and the amp. Something like this would be worth trying (you would need two) http://www.rdlnet.com/product.php?page=166

(http://www.radialeng.com/proav.php)
In addition to the transformer isolation it also properly converts the unbalanced signal to a fully balanced signal that the amps input is designed for.
There are also active/powered unbalanced to balanced interfaces available, something like this
http://www.rdlnet.com/product.php?page=45


(http://www.rdlnet.com/product.php?page=45)

mech986
10-20-2016, 05:02 AM
I have a bunch of these and have found as subwoof said, they are biased very low. I have heard that is because they are permanent install products and that a low bias value is both energy efficient and thermally efficient as well.

They sound better the warmer they get (to me) and take 20 minutes to a couple of hours to sound their best. Biased up a bit, they come right around.

My 2 cents 13 years later. :)

Barry.

Barry, what level do you run the bias at?


So yours has the hum too? Sounds like it's normal. Problem is the feed voltage from the laptop RCA isn't scaled correctly into the C24, I don't think, so I need to have the volume way up (at around the 1:00-3:00 positions) to produce acceptable listening volumes, and turning the gain down on the 6260 wasn't an option. I wish there was a way to get rid of that hum at high gain levels.


It sounds like you may need some transformer isolation between the signal source and the amp. Something like this would be worth trying (you would need two) http://www.rdlnet.com/product.php?page=166

(http://www.radialeng.com/proav.php)
In addition to the transformer isolation it also properly converts the unbalanced signal to a fully balanced signal that the amps input is designed for.
There are also active/powered unbalanced to balanced interfaces available, something like this
http://www.rdlnet.com/product.php?page=45
(http://www.rdlnet.com/product.php?page=45)

I agree with the transformer isolation, the laptop probably was running with a power adapter hooked up and that can cause some odd ground issues. Run it with only the batteries, or use the transformer isolation or run a fully balanced line from the isolator.

1audiohack
10-20-2016, 05:20 AM
Hi Mech;

I had a friend go over mine and I really don't know the bias value. I wish I knew enough about electronics to repair my own stuff. The pile of amps needing some help is steadily growing. :(

Barry.

Johnny_Law
01-11-2017, 01:48 PM
It sounds like you may need some transformer isolation between the signal source and the amp. Something like this would be worth trying (you would need two) http://www.rdlnet.com/product.php?page=166

(http://www.radialeng.com/proav.php)
In addition to the transformer isolation it also properly converts the unbalanced signal to a fully balanced signal that the amps input is designed for.
There are also active/powered unbalanced to balanced interfaces available, something like this
http://www.rdlnet.com/product.php?page=45

Would a pro mixer solve this issue? I recently acquired a Yamaha MV802 (https://www.manualslib.com/manual/341345/Yamaha-Mv802.html) and it seems to be able to adjust the output gain of a given input signal (for purposes of mixing instrument inputs) - but I have no experience here and thought I'd ask. Seems like I could run the laptop into the mixer and be able to adjust the gain of the output to the amp appropriately. Apologize if a silly question.

Mike Caldwell
01-14-2017, 07:12 AM
Would a pro mixer solve this issue? I recently acquired a Yamaha MV802 (https://www.manualslib.com/manual/341345/Yamaha-Mv802.html) and it seems to be able to adjust the output gain of a given input signal (for purposes of mixing instrument inputs) - but I have no experience here and thought I'd ask. Seems like I could run the laptop into the mixer and be able to adjust the gain of the output to the amp appropriately. Apologize if a silly question.

I just looked that mixer up and that would do it, just pick a pair of the line inputs to use for the lap tops input. You want to use a cable that breaks out a 1/8 tip ring sleeve head phone plug at the laptop into two
1/4 inch tip sleeve (mono) plugs to connect to the mixers inputs, do not use a straight through 1/8 inch TRS to a 1/4 inch TRS plug.

AudioFan
02-09-2017, 08:30 PM
I have a couple dozen of these JBL/UREI 62XX amps. Everything from the 6210 to 6290 models. Most were in very good functional condition and produced excellent output with no issues. A few were purchased on eBay that had no or poor output on one channel when they arrived. :( I don't have the skills to repair them myself, and I can't justify the repair rates charged locally relative to what I paid for them, but I don't want to just toss them. Do you think that there might be anyone interested in fixing two and keeping one for their services? :o:

jbl_daddy
02-21-2017, 02:10 PM
They are some of the best amps for the money out there, just picked up another 6260 today from Gordon at Northwest speaker in Marietta. Good people there.

shipping would kill you, but they do fix them there.

AudioFan
02-21-2017, 03:20 PM
Unfortunately, insured shipping both ways all the way across the country would probably exceed the amount I originally paid for the amps - let alone the price of evaluation and repair. It would actually cost less to buy another on Flea-Bay. I have 10~12 UREI/JBL and other PRO/audiophile amps sitting that probably have very fixable issues. (UREI, Ashly, Nikko, Marantz, Phase Linear, Hafler) I just hate to let these amps go to the dump because I don't have the skills to fix them. 7609476095

Johnny_Law
02-21-2017, 10:12 PM
Unfortunately, insured shipping both ways all the way across the country would probably exceed the amount I originally paid for the amps - let alone the price of evaluation and repair. It would actually cost less to buy another on Flea-Bay. I have 10~12 UREI/JBL and other PRO/audiophile amps sitting that probably have very fixable issues. (UREI, Ashly, Nikko, Marantz, Phase Linear, Hafler) I just hate to let these amps go to the dump because I don't have the skills to fix them.

Shoot, who's in Utah? That's a heck of a pile! Coming out to the SF Bay any time soon? :dont-know:

AudioFan
02-22-2017, 07:45 AM
Those pictures are actually of some of my good ones, (including around 25 Marantz MA500 mono amps - yes that was for a big PITA multi-channel system). I didn't have one of the stack of those items needing work, and I was too lazy to go out to my shop to take a picture of them. I know of only one good electronics repair shop in Salt Lake. They have been around in the same building since the 70's doing warranty repairs on most of the better lines. But their prices are high and the wait time is long.

The last time I was in your area was to pick up a Victory Motorcycle I bought from a retiring rider last year. I got stuck in traffic driving down. I think it took me over 5 hours to go 20 miles on a quiet Sunday afternoon. I also drove down to LA a couple of years ago to pick up a load of JBL speakers and components. (Another adventure - the truck's trans went out on me half way back). If I get another batch of electronics/speakers in CA to pick up, I will be back down again. I have been collecting, building, and listening to JBL speakers since the early 60's.

I am retired now, so it is easier to go where I want. I have seen where some of the LH members have had audio listening parties and get togethers in the past. I don't know if you have been a part of any of those. I was interested in going to one, but did not know if it was OK for me to attend without a specific invite. I have followed the various projects and exploits of many of the people here ever since this site went online. I built quite a few systems based upon what others were building and reporting about here. It feel like I have gotten to know some of these people well after reading about their projects and exploits for decades. It would be nice to actually meet some of them in person.

Thanks for your reply

gio brunetto
03-31-2018, 02:21 PM
80683

Hello
I bought two 6290 some days ago.
One of them need to be serviced because one channel is not working.
But my first impression after a check is that these amps are very good. The sound is clear and these amps are very good build.
Only the fan is a little bit noisy.
These amps are very current hungry especially in mono bridge operation.
G

AudioFan
03-31-2018, 03:36 PM
80683

Hello
I bought two 6290 some days ago.
One of them need to be serviced because one channel is not working.
But my first impression after a check is that these amps are very good. The sound is clear and these amps are very good build.
Only the fan is a little bit noisy.
These amps are very current hungry especially in mono bridge operation.
G

If you don't mind sharing - What did the repair cost on your 6290? What component failed? Who did you take it to?
I have seen articles in the past about slowing the fan speed on these amps. I like to use the 6260 and 6230 amps for in room installations, because they have no fan. I usually put the 6290 amps in another room or audio closet to keep noise to a minimum.

robertg
03-31-2018, 04:32 PM
I had a 6290 a couple of years ago. From what I remember I mounted a toggle switch to shut off the fan. I thought it had a two stage fan and the toggle switch shut off the first stage. Mine never even came close to getting hot.

Mike Caldwell
03-31-2018, 08:44 PM
80683

Hello
I bought two 6290 some days ago.
One of them need to be serviced because one channel is not working.
But my first impression after a check is that these amps are very good. The sound is clear and these amps are very good build.
Only the fan is a little bit noisy.
These amps are very current hungry especially in mono bridge operation.
G


I'm curious as to what you have in the Midas box!

1audiohack
03-31-2018, 10:10 PM
I'm curious as to what you have in the Midas box!

A muffler!

We maybe not in Italy.

B

gio brunetto
04-01-2018, 10:15 AM
I'm curious as to what you have in the Midas box!
Hi! in the box I have a Midas M32R mixer. It is for the theater audio equipment were I work. the amps are mine, I am a collector of vintage audio equipment from 80 and 70. Now I am setting a JBL sound system for a live show in the garden of my home. :) Bye. g

Mike Caldwell
04-01-2018, 05:04 PM
Hi! in the box I have a Midas M32R mixer. It is for the theater audio equipment were I work. the amps are mine, I am a collector of vintage audio equipment from 80 and 70. Now I am setting a JBL sound system for a live show in the garden of my home. :) Bye. g

I have one of the Allen Heath Qu-Pac32 rack digital mixers and the AR2412 expansion stage box.

Enjoy your new mixer!