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Chip Amps Amplifiers based on integrated circuits

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Old 26th May 2003, 04:54 PM   #51
mikelm is offline mikelm  England
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I wonder it bridged or paralelled can ever sound as good as single chips ?

I had good results with balanced.

When I tried paralelled without knowing quite why I could hardly bear to listen to it ! ( but I did not zero the o/p's )

( I have not tried balanced & paralelled )

Now I am running with a single chip per channel and I feel that this is the best sound that I have acheived.

I may be deluded, but if you don't find the sound quite delightful & engaging, I get the feeling that you may not be in the 'gainclone zone' Do you really need all that power ?

I wonder what others have found with this comparison

mike
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Old 26th May 2003, 05:00 PM   #52
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Default Re: Re: Re: ....Bridge/paralell ...

Koinichiwa,

Quote:
Originally posted by Cobra2
My impression now, is that it is very "correct", a bit dry, but with a slight forward soundstage. Imaging/3D is rock solid.

But it has nowhere the sheer guts and power of my N-channel-amp, not as liquid and musical...but for the price...and parts-count...I'll say I'm happy.
A small point of criticsm and also perhaps a little bit of explanation as to the "why" of the sound you describe. It seems you have literally "Bridge/Paralleled" multiple gainclones, including the local 1,000uF Caps et al. Such an approach leads invariably to problems with grounding.

I would recommend to change the grounding as follows:

1) Local 1uF/100V capacitors from +V to -V to guarantee stability, without effecting the ground routing.

2) PSU Capacitors should have a value of appx n X 1,000uF where n is the unber of chips used in the parallel/bridge system (up to 8pcs per channel can make sense) and the transformer(s) per channel (2 pcs of PSU Capacitors per channel, plus minimum 1 Transformer per channel, channels galvanically separate) should have a (total for several transformers series/parallel in low flux connection) n X 160VA power. So in your specific case I'd suggest a pair of 600VA+ transformers (one per channel) plus one pair of 3,900...4,700uF/50V main PSU Capacitors, look for low impedance and low inductances (ESR & ESL).

3) Power "Star Ground" where the supplies and PSU Capacitors meet. Seperate Input "Star Ground" where the input transformer centertap (if present) and the components from all the positive chip inputs are combined, a single wire links this to the "Kelvin Return" point of the power "Star Ground".

4) Starwire the positive and negative PSU lines to the chips using ideally twisted pairs of reasonably heavy wire, do NOT buswire the +V and -V lines.

5) If you MUST share the PSU between channels then have per channel a "input star", linked back individually to the kelvin return (the point of all flowing currents is zero) and double to quadruple the values of the PSU Capacitors, plus of course fit the biggest suckah of mains transformer you can possibly find.

You may find the results of such a rewire as suggested above rather greater than you would credit. Much (40 - 50% IMNSHO) of the sound of Solid State Amplifiers (or indeed other Amp's) is the result of correct ground routing. To put it simple, always think in loops traversed by the currents, the whole concept of "ground" in itself is highly dubious and letting yourself think that "ground is ground" rather than "ground is a convenient abstratcion" is the road to troubles.

Sayonara
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Old 26th May 2003, 05:41 PM   #53
Cobra2 is offline Cobra2  Norway
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Default Re: Re: ....Bridge/paralell ...

I have now made a few adjustments; split supply to 2x +/-10 000uF banks (one pair of caps pr. channel), and beefed up "ground-path".
(The local caps are "just" 100uF/63v Elna...)
It made it feel a bit more "bottom-solid".
Anyway, the sound is good enough for my mate ;-)
For myself, (if I make another for myself) I would do the suggested star-wiring thruout, larger heatsinks, and double trafos (or as mono-blocks).
And yes, my large living-room, and my AudioVector S-6 soaks power!

Arne K

P.S.: Thanx for your input !
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Old 28th May 2003, 05:37 PM   #54
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Default Re: Re: Re: ....Bridge/paralell ...

Koinichiwa,

Just another note, it seems you are using the Transformer 1CT : 1CT.

You CAN change that to 1CT:0.5 (or better 2:1) which will reflect around 40K input impedance and may be an easier load to preamplifiers (SE or Balanced) while reducing gain by 6db.

Simply link 6/7 and 5/8 on the Transformer, 5/8 drives the Chips that supply the "Black" (negative) speaker terminal, 6/7 drive the chips that supply the "Red" (positive) speaker terminal.

In this case the input to the Chipamps is "floating Balanced", giving an effective DC Resistance to (sort of) ground for each Chip of around 18k, so the resistors from the non-inverting input to ground (if used) should be in the same region.

Sayonara
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Old 4th June 2003, 12:03 AM   #55
Cobra2 is offline Cobra2  Norway
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Default Re: Porcupine...err...BridgeClone

More caps & tweaks later....

I'm still wondering about impedance & gain...
Changed positive input resistors, and ended up with 4,7k ( to gnd), same as neg. input resistors. 220K feedback, 0,1R output.
Changed/inverted phase on one channel, (as I wanted to keep the 600VA trafo, and not buy 2 new ones), this helped a bit, bass seems tighter & more controlled now.
But the "fun" started when I used balanced input from a "Pro" Rane BB 44x, RCA to XLR converter with the increased gain this gave.
So-far, IMO, it seems that these amps can be set up w. a lot more gain than most articles describe.

Arne K
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Old 5th June 2003, 03:36 PM   #56
Cobra2 is offline Cobra2  Norway
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Default My BC is too hot?

I think something does not "add up", it's fairly warm,(~35șC) just ideling.
No oscillation, (on scope or freq.counter) and less than 15mV DC-offset.
Any advice, please ?

Arne K
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Old 5th June 2003, 05:21 PM   #57
UrSv is offline UrSv  Sweden
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Default Re: My BC is too hot?

Quote:
Originally posted by Cobra2
I think something does not "add up", it's fairly warm,(~35șC) just ideling.
No oscillation, (on scope or freq.counter) and less than 15mV DC-offset.
Any advice, please ?

Arne K
Have you checked the values over the current sharing resistors? If so what is the current flowing at idle?
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Old 5th June 2003, 06:43 PM   #58
Cobra2 is offline Cobra2  Norway
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Default Re:....

0,015V over resistor on one pair, & 0,005V over another pair...
I guess these chip's are of the +/-10% variety....

So I would need trimpots for offset-null ?

Arne K
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Old 5th June 2003, 07:16 PM   #59
UrSv is offline UrSv  Sweden
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Default Re: Re:....

Quote:
Originally posted by Cobra2
0,015V over resistor on one pair, & 0,005V over another pair...
I guess these chip's are of the +/-10% variety....

So I would need trimpots for offset-null ?

Arne K
That's like 15 W idle then...
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Old 5th June 2003, 07:56 PM   #60
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Default Re: Re:....

Quote:
Originally posted by Cobra2

So I would need trimpots for offset-null ?
Maybe so.

One thing that puzzled me when I saw Jeff Rowland's amp using 3886 on his power amp, were the trimpots you can see on every chip.

Maybe he's using an inverted circuit on each chip and nulling offset on every one with the pot.

I can think of any reaso why he would use a pot on a non-inverting arrangement. Do you?


Carlos
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