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gene
03-06-2006, 11:27 AM
hello. I need a good preamp to run my nakamichi pa -7 amp. I am also thinking of buying a yamaha pc 4002m power amp. what preamp would match up with these power amp. any info

boputnam
03-06-2006, 01:31 PM
I see no-one has yet replied.

Try the SEARCH function - there's been many discussions.

kulashaker
03-06-2006, 02:13 PM
Very good match for the PA 7 would be a Nakamichi CA 5 or CA 7.
Used CA 5s can be bought for relatively little money.

jim campbell
03-06-2006, 04:28 PM
how much money do you want to spend?

jblnut
03-06-2006, 05:20 PM
You have to help us help you....

1) what is your budget?
2) Do you need/want tone controls ?
3) Do you need a phono input ? moving coil too?
4) is a remote important?
5) is having XLR outs important?
6) do you care about new versus used ?

Give us something to work with....

jblnut

Titanium Dome
03-07-2006, 01:46 AM
You have to help us help you....

1) what is your budget?
2) Do you need/want tone controls ?
3) Do you need a phono input ? moving coil too?
4) is a remote important?
5) is having XLR outs important?
6) do you care about new versus used ?

Give us something to work with....

jblnut

7) What speakers do you plan to use?
8) Do you want a simple preamplifier only or a pre with a tuner?
9) Are aesthetics important? If so, black or silver, match the amp, display or no display?

Not harassment, just trying to get to know you. :yes:

gene
03-07-2006, 06:24 AM
Hello . I have a technics su-a4 preamp that I love the way my speaker sound. but I have a problem. on the back of the preamp inputs It reads normal/dc- on the front of the preamp it has a little push button for normal or dc.keep in mind it has a loaudness control button. but when I push in the dc control button in the bass is much deeper the treble is crisp It runs or push the current even harder. Lets say I am runnuig about 80 watt rms with the dc button push in I can see the little red l.e.d. light starting to flash on and off.on the amp. ( I need more power):bouncy: Is this normal or I am over reacting

rgrjit8
03-07-2006, 06:38 AM
Someone more knowledgable should be here in a minute, but it sounds like the flashing light is a warning indicator. It has something to do with whether an amp has a capacitor in the signal path or not. Hence the normal and DC coupled switch.
Flashing red lights, is generally, not a good thing.

Someone else will have to come enligten us BOTH on this.

gene
03-07-2006, 06:43 AM
when I run about 75 watts rms or less every thing seems to work fine the amp may get a little warm but other than that it runs fine

speakerdave
03-07-2006, 07:02 AM
Hello . I have a technics su-a4 preamp that I love the way my speaker sound. but I have a problem. on the back of the preamp inputs It reads normal/dc- on the front of the preamp it has a little push button for normal or dc.keep in mind it has a loaudness control button. but when I push in the dc control button in the bass is much deeper the treble is crisp It runs or push the current even harder. Lets say I am runnuig about 80 watt rms with the dc button push in I can see the little red l.e.d. light starting to flash on and off.on the amp. ( I need more power) Is this normal or I am over reacting
This problem can't be analyzed from a distance and with this much (and partially garbled) information.

You may be under reacting. Your post is a little unclear. I'm not sure where the normal/dc switch is, preamp or power amp.

You are overloading something important.

"DC" probably means direct-coupled.

You may be activiting the protection circuitry in your amp. If so you're speakers have a lower impedance than you think and when you drive them hard your amp can't handle it.

Or, you may be over driving the amp, which may mean you are putting a lot of low frequency or direct current garbage into it with the DC switch engaged.

There is an online source that will sell you a copy of the manual for your amp. It may be overpriced, but you need it. Get it and read it. And/or take your electronics to a tech and get them checked out before you blow something expensive.

David

Robh3606
03-07-2006, 07:14 AM
Why would you be running at 75 watts???? How big is the amp?? With a 200wpc amp you have maybe 4dB of headroom left. That's virtually none at all so you are out of gas and driving the amp way too hard. The DC button is Direct Coupled. Have to see how I have my Su-A6 is set-up. I think I have it running DC.

Rob:)

gene
03-07-2006, 07:30 AM
I have the technics manual for the preamp. it reads the use of the dc direct button is for the best pure sound you can get. but I belive i am pushing to much low end . that dc dirrect button act like a booster which drive the current even harder at low or high volumes.

Rolf
03-07-2006, 07:46 AM
If I understand you right, the DC button is on the pre-amp. I do not understand that you have a warning light on the same unit. I have never seen a pre-amp with overload warning.

If the red warning light is on your power amp, then you are pushing it to hard, and if you need to play that loud, or if your speakers are that power hungry you must get a bigger amp. If your amp is 200W pc you need at least to double or triple it.



I have the technics manual for the preamp. it reads the use of the dc direct button is for the best pure sound you can get. but I belive i am pushing to much low end . that dc dirrect button act like a booster which drive the current even harder at low or high volumes.

gene
03-07-2006, 08:07 AM
Hello Rolf. the lights are on my amp. my amp is being push hard ,I hope thats the only thing I am doing. my speaker are hungry -12 cubit ft. 2245h-2202h-2425hwith a 2344a biradial horn -2424h ports are 4 inch dia and 5 5/6 lenth. I belive i need a stronger amp but with with the same balls as the nakamichi pa-7 other amps I used in the past did not do the job speakers are 8 ohms

gene
03-07-2006, 08:23 AM
Lansing member Robh 3606 has a technics su-a6 preamp. If I can get him to him to answer .And hope to shead some light on this issue:blink:

gene
03-07-2006, 09:09 AM
Robh 3606 what is the term direct coupled . I am lost what does that mean to my system. am I doing my system wrong ?

majick47
03-07-2006, 09:30 AM
Gene the Nak PA7 is a great amp but from the description of your speakers it is not up to the task. I have a Yamaha PC4002m, 420 watts x 2, powering my L300 and the amp has adequate headroom for this model JBL speaker. You probably need two (2) PC5002m amps bridged to power your speakers which would give you at least 1500 watts x 2. I'm sure LH members can suggest other sufficently powerful amps for your purposes. (Crown, MAC, Accuphase etc.)

Robh3606
03-07-2006, 10:40 AM
Direct Coupled means DC coupled meaning no capacitors in line. Not all DC amps are less capacitors and frankly it's over my head. Best thing to do is a search for Direct Coupled Amplifier in Google or MSN. You will get tons of information. The Technics give you the option to run the signal as a DC coupled or standard. Would be nice if we could get our hands on the schematic to see what the switch actually does.

Rob:)

gene
03-07-2006, 11:12 AM
thanks for all the info guys . I want to buy a yamaha pc 5002m amp the more research I do the more awesome things i hear about this amp. I just dont want to pay an arm and a leg for it.

GordonW
03-07-2006, 11:57 AM
I think the guys are onto the right track here, regarding the "DC coupling" thing.

In this case, the "DC coupling" may be effectively bypassing a blocking cap, which may be acting as a de-facto "rumble filter"... filtering out "junk" below 20 Hz, or whatnot.

If you don't hear a difference whether the "DC coupling" is in or out, I'd leave it in the NOT DC-coupled mode. More efficient use of power. However, if it sounds better in the DC-coupled mode, then just either learn to live with it running at a slightly lower volume level, or get a larger power amp...

With the speakers specified (ie, 2245 18" bass driver), you MIGHT want to just BI-AMP the system... set it up so the 2202 and horn mid-high unit (with passive crossover between them) are on one amp (possibly the Nak 7 you already have), and the 2245 is on another amp... with an active crossover between the two amps. Should be able to give the 2245 plenty of power, while still keeping the Nak's sonics in the part of the system, where it probably makes the most difference. With a system such as this, you might just want to use a JBL/Urei 6260 or 6290, or something like a Crown DC300 or such for the 2245... anything 150w/ch or over, with a BRICK WALL power supply, should work...

Regards,
Gordon.

doodlebug
03-07-2006, 01:52 PM
Ye gads! What size of room are you using this gear in?

So the DC thing was a 'feature' to remove the ouput coupling cap from the audio chain. Very popular in the early/mid-80s. The downside is that it will pass a bit more low frequency 'stuff' that's probably not wanted. This brings to mind a couple of questions for Gene:

1) What source are you using? If a phono, then I'd suspect you're doing a great job of accurately reproducing all the rumble that TT is producing. If a CD player, what's the age?

2) What are your speaker's woofers doing when the Red Light comes on? Do you hear them popping occasionally? If so, they could be 'bottoming' out. That is, if they're moving a whole lot while the music in on but you don't hear anything, there's clearly something wrong with the amp or preamp.

3) What happens when the power amp has been on for a while? With no music or sound, what happens with the woofers? Do they sit without moving or do you see them moving back and forth? Frankly, I'm suspecting you've got a problem with the power amp when it gets warm and may be getting a bit unstable. With the age of the power amp, I'd wonder about the age of the capacitors in there.......

Just my thoughts.....

Cheers,

David

Rolf
03-07-2006, 01:53 PM
If I remember correctly the Naka 7 amp was build at the same concept as Threshold at that time. (Stasis) IF it is the amp I am thinking about I tried it many years ago and remember it was quite "week" compared to the specifications.

Anybody else remember correctly?

gene
03-07-2006, 03:26 PM
Hi doodle.Im not using a turn table. my speaker are not poping. the woofer are fine, there is plenty of bass but no poping. when the amp is on, but not running any program the woofers are still. the caps are fine. I need more power I am looking to buy a yahama pc5002 power amp. my room size is 20 by20. nothing wrong with the amp. my preamp has a dc/ or normal inputs . when you push the in the dc button the bass is heaver and the treble is more crisp I belive it is just like hooking up an equalizer to your system. turn up all the controls on the equalizer than turn the volume up your system will the system will clip alot early with it than with out it I just hope i am not doing any dammage to my system.

Robh3606
03-07-2006, 04:22 PM
Hello Gene

I got home and sure enough the preamp is set for DC coupled. That's what I thought but I have broken it down a couple of times to change out speakers so I wasn't sure. I use this old warhorse to run my 2 channel rig. It has a realy nice phono section and sounds good. It runs some old crowns and my 4344 at the moment. Kind of an 80's vintage system. It all sounds good together so I like it. One of these days I should upgrade it. Let me know if you change yours out what you like.

Rob:)

jblfreeek
03-12-2006, 05:04 PM
Hi,
I own Technics SU-A6, SU-A6mk2, SU-A4mk2 pre-amps.
I always use them in DC setting.

As you can tell, I love that vintage Technics sound, it is simply superb. (I'm talking about SE-XX series)
If you like to go for the best, I recommend SU-A4mk2.


There are quite a bit of information on the web about them, here is a quote from Adrian's site (http://adrian-kingston.com/SEA5.htm).

The Technics SE-A5 is equipped with two sets of line level inputs marked "DC" and "Normal". The "Normal" inputs are coupled by a capacitor like with an ordinary amplifier. In this case, the amplifier operates as a normal AC amplifier with a low end cutoff frequency of about 2Hz. As a capacitor is a reactive device that can introduce phase changes, this is considered to be undesirable, so the SE-A5 has been designed as a DC amplifier where there are no capacitors in the signal path at all! So using the "DC" input gives a completely flat frequency response right down to 0 Hz with no reactive phase effects of any capacitors! One possible issue with doing this is in case of a fault in the device connected to the input. If for some reason there is a DC component in the input signal, this will result in the speaker cones being pushed and held there which will cause the voice coils to burn because of the very low DC resistance compared to about 8 ohms of AC resistance (or inductive reactance), although the internal output protection circuit will operate to save the speakers from this. So if it is desired to operate with such an input, the "Normal" inputs are provided to ensure compatibility and are simply coupled to the "DC" inputs via a capacitor which eliminated the DC component of the sugnal. When ever possible, the amp should be operated using the "DC" input and only one set of the inputs should be connected at one time. Some other Technics power amp designs have just one set of inputs with a switch that has the "Normal" and "DC" settings.

gene
03-18-2006, 07:22 AM
Thanks for the info guys. also thanks robd-3606 and JBL freeek. I think the technics su-a4 preamp is awesome. I just wanted some info on guys who had this preamp or know about this preamp. I will buy a bigger amp later this summer. I have a nakamichi pa-7 power amp 200 watts rms not enough power. speaker are 12 cub- ft. ports are tune I belive at 25 or 26 hz. ports size-5 inches in diam and 5/56 in lenth. woofer-2245h .mid bass 2202h seald with inside the cab.-midrange 2425h -2344a biradial horn.-tweeter -2404h crossover is rated at 600 watts per channel. crossover points 250hz-1200 khz -5000 khz this is a passive xover. my room size is 20x20. for know I am using a samsnug hdmi dvd/cd player. I also have a sony ps1 model scph-1001

duaneage
03-21-2006, 05:35 PM
DC coupled amps use an inductor on their outputs to prevent oscillating at high frequencies, usually above 50Khz. The one danger with older DC amps, especialy the crown and phase linear's, is a shorted transistor. This will send up to 65 volts DC right into the woofers. They won't survive it. Old Colony Sound Lab has a cheap effective speaker protection relay circuit for around 30 dollars that will interrupt the circuit if it detects DC voltage above a few volts. Cheap insurance for 300 dollar woofers. If your running older DC amps it is a good idea.

BMWCCA
03-21-2006, 07:56 PM
The one danger with older DC amps, especialy the crown and phase linear's, is a shorted transistor. This will send up to 65 volts DC right into the woofers. They won't survive it. Old Colony Sound Lab has a cheap effective speaker protection relay circuit for around 30 dollars that will interrupt the circuit if it detects DC voltage above a few volts. Cheap insurance for 300 dollar woofers. If your running older DC amps it is a good idea.
Is that primarily in the old D-series amps before the IOC circuitry? Not that I have any $300 woofers, but I do have four D-series Crown amps, only one that's not a "Series-II". Just curious....

Nightbrace
03-24-2006, 06:56 PM
If that doesn't pan out, try a Phase Linear preamp from the 70's.

Nightbrace
03-24-2006, 06:57 PM
DC coupled amps use an inductor on their outputs to prevent oscillating at high frequencies, usually above 50Khz. The one danger with older DC amps, especialy the crown and phase linear's, is a shorted transistor. This will send up to 65 volts DC right into the woofers. They won't survive it. Old Colony Sound Lab has a cheap effective speaker protection relay circuit for around 30 dollars that will interrupt the circuit if it detects DC voltage above a few volts. Cheap insurance for 300 dollar woofers. If your running older DC amps it is a good idea.

Hmm, the amps I run all are DC, good thought..

Ian Mackenzie
03-25-2006, 05:29 AM
While there might be some design merit in a DC coupled power amp there is the problem of Dc drift which is sometimes controlled by a servo circuit to hold the amp output at 0 volts. Unfortunately servos can intrude on the sonic attributes of the amplifier. There is also the inherent problem of real gain at Dc, typically 26 db and this means any dc in the signal path will be amplifed by this amount of gain.

It is therefore adviseable to use a high quality film foil coupling capacitor at the input of the power amplifier to block any DC, pops ect that can result from the source.

People complain about capacitors a lot.

Finch and Marsh wrote a very good article on this topic with mods than can be done to preamps and power amps to minimise most of the negative effects.

If the coupling capacitor is chose correctly (and the capacitor in the feedback path) it should introduce little phase shift in the audio passband.

It is worth noting that a typical recording is processed though many stages that introduce some phase shift so don't let anyone pull you chain about phase shift in your modern day power amp!

I would also point out that some of the most expensive pre amps and the most well regarded are capacitively coupled but of course cost is no object with the parts quality in these designs! Unfortunately mass market consumer audio equipment often uses parts chosen on price and not sonic performance.