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Old 8th October 2006, 10:05 PM   #1
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Default Gainclone V+ to V- capacitor?

I've added a 1.5uF ero mkt cap to each chipamp revision 3 board, from V+ to V-.

PSU is basic 220VA tranny, single MUR860 rectifier bridge, 1000uF pan FC per side per amp.

The sound seems to have lost a slight edginess but seems more focused and smoother.

Any once got any experience with a similar cap in this position? I seem to remember Carlos had a 3.3uF in his snubberized PSU setup?
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Old 9th October 2006, 03:12 AM   #2
Leolabs is offline Leolabs  Malaysia
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Have you try to add them at V+ to 0V and V- to 0V???
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Old 9th October 2006, 06:53 AM   #3
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Yes, all 1000uf caps are connected as normal. I have tried a 1.5uF cap as a bypass of these but didn't like the effect - top end became exposed.

My question relates to additional caps between V+ and V-. Why would these sound smoother?
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Old 9th October 2006, 07:16 PM   #4
owen is offline owen  United Kingdom
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You are getting two 'hits' for the price of one.

You are coupling the + and - rails at HF effectively without involving the ground circuit.

If you place capacitors from + to ground and - to ground, then rail to rail you will have 1/2 the capacitance (two capacitors in series), running them from one rail to the other will give you the *full* capacitance between rails

Caps from the + to the - rail is an old Nelson Pass trick (yes, that Nelson Pass), its a PITA to calculate using PSU designer, but it works soooo well.


Owen
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Old 9th October 2006, 07:32 PM   #5
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I guess this explanation would be consistant with the improved smoothness without loss of transparency.

Thanks for the help Owen.

Should I be using small caps like the 1.5uF I have, or look at a bigger electrolytic? I'd try a big FM but all mine are 50V, so not up to the 54V from V+ to v-.

Is there a pass labs thread that explains more?
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Old 9th October 2006, 07:59 PM   #6
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I'm being a bit spontaneous with my current amp as I have been buying bits for the next one and nd am keen to try out as many things as I can.

Anyway, I just added 4uf russian PIO caps in parallel with the 1.5uF eros. Seems like more of the same improvements! I'm loving this - I've been playing with these amps for months and it's cool to try something new that seems to work.....

I'd love to hear of other's experiences :-D

Must be one of the easist mods to try temporarily.... go on!
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Old 9th October 2006, 08:04 PM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
I think part of the success you have found is down to using a plastic film cap across the supply.
Compare what you have done to the recommended scheme for bypassing an opamp. Many go +pin to -pin. Although a few recommend asymetric bypassing and some +pin to ground and -pin to ground. It seems to depend on how the internals of the amp are designed.
Your gainclone may well suit rail to rail decoupling.
Have you tried pin to pin bypassing by moving the film cap from PSU to gainclone pins?
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Old 9th October 2006, 08:10 PM   #8
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That makes complete sense to me - best place for the cap (whatever size is optimal).

Unfortunately the base of the pcb is inaccesible - next time I build I'll do the work before final assembly.

Any suggestion for cap value? 5.5uF combo sounds better than 1.5uF, but since I don't know the maths It'll be trial and error for me...
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Old 9th October 2006, 08:34 PM   #9
AndrewT is offline AndrewT  Scotland
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Hi,
I cannot advise on cap values nor on the ideal location of the bypassing and/or decoupling.

This is down to my biassed attitude towards chip power amps.
I am a discrete man to the grave.
I have heard how bad car radios/CD players, separate amps, cassette players etc sound when compared to in house stereo systems.
It is almost certainly down to using chipamps to save space, cost and development time (=cost).
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Old 9th October 2006, 09:45 PM   #10
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Chipamps (like everything) aren't perfect. I like them a lot though.

We all have our own experience to lean on. For my part, I used to sell high end hifi etc. and believe that the gainlone is the best accessible high-end amp I've ever heard.

After I finish the next 'statement' gainclone, I want to try something like a first watt..... Already played with lots of low power class-d which is excellent for the portable kit I've built (sound quality:efficiency ratio is brilliant). A Nelson amp seems like the next project...

This mod works wonders for me though - my gainclone already bettered than the naim, classe, burmester, mf, myryad, linn, chord etc. I've used at home in the past.

Anyway, grander plans aside, TRY THIS IF YOU HAVE A GAINCLONE!!!
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