a good preamp

[gene]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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.

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]

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]

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]

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]

If that doesn't pan out, try a Phase Linear preamp from the 70's.

[Nightbrace]

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..