Well, I'm stumped on the feedback cap. Thought I'd sorted it, what voltage should it be running at?
When I changed the 47 for the 100 it sorted the bass, although the reg heatsinks did seem to get alot hotter than usual but I could have just not noticed how hot they got before?
Back to caps, Nichicon MUSE seem to have a good name in diy, how's about them instead of the Silmics?? They're around a quarter of the price and available in all the values I need?????
If it measures 24.8v then that's the voltage its supposed to run at. Usually feedback caps don't have such high voltage across them so I don't think that's the FB cap after all. Like I said, leave the 25v cap there for now. Change it when you can. The regs are on big heatsinks so no problem if they are a bit warm.
Ive heard good things about muse too. All I can say is try them and see what they sound like. Remember, one change at a time, listen and evaluate.
Ive heard good things about muse too. All I can say is try them and see what they sound like. Remember, one change at a time, listen and evaluate.
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The new/old 100uf cap seems to be in the path from the speaker output through a series of resistors then to the middle pin on the transistors. Could this actually be the feedback??
That's the one I was saying was 24.8v. 50v 100uf original cheapy put in place of Nichicon FG 63v 47uf equalled much more punch/bass.
1 question......
How does feedback work??? does it take an amplified signal then pass it back into itself to give more power?? ie an amplified amplifier??
If so, I assume the 50v 100uf must be the feedback cap as that's the only one leading back from the output to the power transistors.
How does feedback work??? does it take an amplified signal then pass it back into itself to give more power?? ie an amplified amplifier??
If so, I assume the 50v 100uf must be the feedback cap as that's the only one leading back from the output to the power transistors.
Am I right????
I understand the transistors have 3 inputs; a collector, base and emmiter. The base is the 'input' from source. So if the higher 'output' is returned to the 'input' (base) then the 'input' signal is greater which in turn makes the 'output' greater????
So as the 100uf is the only cap from output signal to 'base' , I presume this must be the feedback????
Or am I wrong?
I understand the transistors have 3 inputs; a collector, base and emmiter. The base is the 'input' from source. So if the higher 'output' is returned to the 'input' (base) then the 'input' signal is greater which in turn makes the 'output' greater????
So as the 100uf is the only cap from output signal to 'base' , I presume this must be the feedback????
Or am I wrong?
In general, the feedback referred to is negative feedback. It is 180 degrees out of phase with the input signal and is used to lower distortion numbers. The more neg feedback, the lower the circuit gain and the lower the distortion, but there are so many downsides to using lots of feedback that designers use it judiciously.
Thanks. Could you tell me what the downsides are?? could higher frequencies be reduced??
Interesting links, Thanks.
From what I've read...... If the ideal feedback cap is 100uf, why do designers put 47s in?? is it because of the stability (could be why the regs are running hot) or for the wider frequency spectrum ?? (could be why the highs have dropped and there's a reduction in transparency?).
Is the above correct? Surely there must be downsides to increasing the uf??
More caps, more soldering to follow.....
I dont know enough about amplifiers to comment there.
You mention the regs. I don't think they have anything to do with the amp. The poweramp stage will most likely run on raw/smoothed DC. Its the lower voltage stuff that will have a regulated supply. Have you traced out the reg outputs to see what they are supplying? (by the way, whats the part number on these regs?)
This is where having the service/repair manual or at least the schematics comes in handy. Did you make any effort to obtain them yet?
You mention the regs. I don't think they have anything to do with the amp. The poweramp stage will most likely run on raw/smoothed DC. Its the lower voltage stuff that will have a regulated supply. Have you traced out the reg outputs to see what they are supplying? (by the way, whats the part number on these regs?)
This is where having the service/repair manual or at least the schematics comes in handy. Did you make any effort to obtain them yet?
Tried everywhere for the schematics, can't find a thing. I read that NAD do not allow their current schematics/service manuals to be available on the 'net' and if they are posted anywhere, they're quickly removed. Must have a team searching for them etc etc????
Heard you can attain them direct from NAD if you are a service/repair agent.
Also heard you can buy them direct for personal use ONLY with penalties if you publish, although they're supposed to be extremely expensive.
Cap findings
Here's a result from a test I did today regarding the folowing feedback caps I had spare........
............................Value.......Highs......Mids......Punch......Lows
Standard (JH).......47uf/63v......Poor.......OK.........Poor........OK
Nichicon FG..........47uf/63v.....Bright.....Good.......Poor........Poor
Panasonic FM.......47uf/63v......Good......Poor.......Poor.........OK
Alternative (JH)...100uf/50v.......Poor.....Poor.......V.Good....V.good
The FG's haven't had much 'burn in' time so I expect they would loosen up on the highs and better themselves in the lows in time.
The 'alternative JH' excels the others in the lows so I presume a quality cap of that value would be much better in the highs/mid too??
Here's a result from a test I did today regarding the folowing feedback caps I had spare........
............................Value.......Highs......Mids......Punch......Lows
Standard (JH).......47uf/63v......Poor.......OK.........Poor........OK
Nichicon FG..........47uf/63v.....Bright.....Good.......Poor........Poor
Panasonic FM.......47uf/63v......Good......Poor.......Poor.........OK
Alternative (JH)...100uf/50v.......Poor.....Poor.......V.Good....V.good
The FG's haven't had much 'burn in' time so I expect they would loosen up on the highs and better themselves in the lows in time.
The 'alternative JH' excels the others in the lows so I presume a quality cap of that value would be much better in the highs/mid too??
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