Further Mods to make to A400 - please advise - diyAudio
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Old 28th August 2009, 04:07 PM   #1
diyAudio Member
Join Date: Aug 2009
Location: West Midlands
Default Further Mods to make to A400 - please advise

Hi guys, newbie here but not at modding.
I have made several mods to my A400 already but am looking to go a few steps further to ring every last bit of potential out of the amp.
Firstly i am going to replace the smoothing capacitos (currently 10,000uF 50v Elna's) with either Mundorf M-lytic® SI, BHC's or Jensens -any recommendations please?
I also want to replace the other smaller caps on the board. i have read Mudan's very helpful thread on this but I am having trouble locating all the Black Gate caps i require so if anyone has any other suggestions please let me know.
I will be replacing the standard binding posts with some high quality silver plated ones.
Having removed all the RCA input plugs from the amp, and now having only one high quality set i was thinking about removing the input selector and bridging the relevant gaps in the PCB with silver wire - good idea?
thanks in advance for any assistance you can give me.
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Old 2nd September 2009, 03:24 PM   #2
diyAudio Member
Join Date: Aug 2009
Location: West Midlands
well i was hoping to get more of a response than this...
anyway, i went ahead and removed the input selector and bridged the relevant terminals with solid silver wire - WOW what a difference it made. it was like a new amp! the sound had a new level a realism and the level of detail also increased dramatically.
when i removed the selector i took it apart and found that it had quite a lot of corrosion/oxidisation on it so no doubt it was degrading the sound. obviously this tweak wont be for everyone but for me it was great!

after checking how much space i have in my case and the size of the possible replaacement smoothing caps i am limited to the Mundorfs - no bad thing i think. will be ordering them very soon.
if anyone has any advice about replacing the other caps though i would really appreciate it.
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Old 2nd September 2009, 04:19 PM   #3
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Join Date: Dec 2003
Location: earth
it would help if you said what amp it was, a400 means little,

I know the amplifier intimately, so I am guessing its a pioneer a400, post a link to the schematic, to.

you are talking snake oil, capacitor replacments are just a subjective thing, all they do is smooth psu and couple in this amplifier.

The only thinig you can do, and its a fragile board to mess with, is a larger offboard psu perhaps, with a bigger tx, same voltage, or if you are clever which I am not, is to find out the max the amplifier, output devices will take.

and build more microfarads into it, 10,000 is perhaps sufficient, but I would go for 20,000-40,000 per channel, along with a 25 amp plus bridge, that's the power supply sorted.

in a separate box, use safe connectors and thick wire links insulated.

tom evans uses a multi layer polyester for coupling, and a dc servo in parallel with the feedback to smooth the sound out sucessfully.

then only thing is bias , not much you can do to it really, just keep it running well apart from that. i dunno how much power it will be happy giving out ie volt / current/ heat ratings, upping the current capacity of the tx a bit won't hurt by double, ie same volts 500 VA plus along with bridge and psu caps like I said,

forget snake oil bespoke. concentrate on engineering, that's why you have been ignored likely 1/ none knows what an a400 is, 2/ people don't do black gates here on the whole, they are engineers, not BS'ers

ie just things that wear, like a good vol pot, try pec, or noble, too. ie just good engineering parts. maintain it in other words if you like it

a blanket recap won't help much, all amps sound different, its in the configuation and devices mostly I feel, now after decades messing like you

also, many of the caps don't even affect the circuit, eg protection, so you are wasting your time there, either they work or they don't.

an offboard psu is really the only likely change apart from worn out parts, oxidation may have something in it

Last edited by lt cdr data; 2nd September 2009 at 04:24 PM.
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Old 2nd September 2009, 07:30 PM   #4
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Join Date: Aug 2009
Location: West Midlands
thanks very much for your reply.
your right i should have written that it was the Pioneer A400 i was talking about! sorry

i didnt think capacitor replacement was regarded here like snake oil - in fact i have only ever read positive things about replacing caps- especially aged ones like mine.

unfortunately most of your reply was lost on me as it was too technical. maybe i am under the mistaken impression about what this site is about? i thought i would find modders here as well as technicians. although saying that are the two a world apart?

all i am aiming to do is (because of my lack of technical knowledge) replace (what i believe) are the weak components in the amp to improve the sound.
one thing you said that really caught my attention was moving the psu offboard. i recently scrapped a pioneer A757 mkII but i have kept a lot of the parts and casing. the 757 has a huge twin psu with sheiled transformers cased in what appears to be cast-iron. do you think i could utilise these? and maybe the sheilded 22,000uF caps from it as well?

i will also look into the vol pot as at present the output is uneven through both channels.

i was also thinking about removing/bypassing the headphone output - good idea?

the schematics for the a400 and a757 can be found here:

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