T-amp capacitance

Ok i have got my T-amp up and runnign on a good quality SMPS and it really does sound good, very punchy and detailed, but very natural as well. I love it in short. Howver i fancy do a rebox into a better case and was thinking about doing a couple of tweaks to it. On this site there are a fair few post about what are the main issue that can be delt with of which the main ones seem to be better pot, shorter signal path, better wiring, increasing the input coupld caps size and adding capacitance closer to the chip.

Most of this seems pretty clear and there seems to be a consensus that a 2.2 uf is the right input coupling value however what to people thing is the right amount of added capacitance? Also is it a good idea to effectively put in 2 lots? say 2*1000uf on the chips power pins and say 10000uf elsewhere inside the box? also would this effect the punchniess of the chip like the LM series which dont seem to like too much capacitance?

Lot of questions, any help?

Fil
 

marct10

Member
2004-06-04 11:35 pm
york
Interesting question, I certainly dint like too much supply decoupling capacitance on my gainclones.
Having just finished an Amp3 and listening to it on my Swans powered by a Panasonic 17AH SLA battery, i was stunned, simply amazing for the money!

Anyhow,back to the point, I tried briefly a 68,000uf 16v 'lytic I had lying around across the battery and .....I didnt like it!, it seemed to smooth the treble slightly, but much to my disgust it seemed to smear the bass unacceptably.

The Apm 3 is standard except for some 4.7uf LCR polyprop input caps, Ill get rid of the standard electrolytics on the PCB next , probably for some Sanyo Oscons.

cheers
Marc
 
Hi Marct10,

Thanks for the response, interesting stuff. I was thinking abotu building a cascade of caps to power it going from 1000uf, 100uf, 10uf, 1uf, etc. This might bea totally [email protected] idea but the Nuuk designed psu for my preamp had something like this and i was wondering if this continuos bypassing type of thing would work in aower amp psu.

I am new to this as you might have guessed.

Thanks for sharing your experiences very usefull, at least i know not to go for just big high value caps.


The LCR caps are the big yellow polys from maplin arent they? Got some myself, how have they work in the amps 3 just interested as to much much difference they might make in my t-amp.

Cheers mate.

Fil
 

marct10

Member
2004-06-04 11:35 pm
york
yep they are the onnes, except I got them from CPC cos they are cheaper ! They sound better than the supplied 2.2uf ceramics on the PCB, perhaps just a bit too sterile in the treble, though Im quite prepared to believe a "boutique" polyprop like a Mundorf etc will sound better.
If anyone knows a good cheap UK source of "posh" caps I'd be interested.
Ive never been keen on lots of psu capacitance (when using batterys as a supply), especially if its electrolytic. I can see some marginal improvments but on average it does more wrong than right.
Ill report back when Ive changed the pcb caps.
 
I am currently drive mine using a SMPS from a router, pretty big and rated at 5amps. I tried it since Nuuk had been using some to great effect on his Lm based chipamps. I have also got a big old 7ah 12v i recently found in a skip along with about 20 others which i might try. I have to say thought that even un moddied this thing has already got me a bit worried, it sounds to me even now better than the lm3886 carlos snubberised amps i spent 3 months constructing. Actually that not quite true, but it is more detailed and not in a harsh way. Puzzling stuff. I cannot believe the power rating of the amp since it really does go as loud as need on a pair of old Koda 7's which arent exactlly sensitive.

As for cheap boutique caps in england havent found any source for poly caps but you can get starget from RS reasonably cheap and ther is a chap on pink fish media forums selling some low value silmic very cheap.

fil
 

marct10

Member
2004-06-04 11:35 pm
york
Fil,
Please give the SLA's a try and let me know what you think, I prefer them to linear supplys every time (best sounding and most cost effective) and I've never used a switchmode on an item of Hi-fi, it just seems wrong! I suppose i should put aside my prejudices and give it a try.....
I had a look at cricklewoods caps, vat and p&p bumps them up to a fiver each for a pair, I might try them sometime.
 
Hey dude,

Will do, it's on my to do list this weekend, by the way do you think i could use a car battery charger to give a bit of juice to the SLA it has some now but to give the listen test a fair chance i want it close to full it you see what i mean. sure it would be okay same things near enough arent they.

fil
 
Thanks ill give it a go

Got loads of stuff planned for these little devils. I know people are saying there are not that good but to my ears they really are. The level of minute details and the impact of stuff in just so differnt to the other amps i have heard and built and i love it.

Totally hooked on class-t now


Fil
 
filholder said:
Thanks ill give it a go

Got loads of stuff planned for these little devils. I know people are saying there are not that good but to my ears they really are. The level of minute details and the impact of stuff in just so differnt to the other amps i have heard and built and i love it.

Totally hooked on class-t now


Fil


Just wait till you have a couple hundred hours on it. Those surface mount caps need a lot of time to settle in. I personally like the amp with a SMPS and large buffer cap (at least 10,000uf). This will give considerably more power than a SLA as it can be set to a higher voltage. The amp will live with up to 13.2 volts and I wouldn’t go beyond that myself as I don’t want to have to repair it.
The input mods are almost mandatory to get good sound. The rest of the recommended changes are also an improvement and well worth doing.
You have a lot of reading to do. I would recommend looking at every SI and Amp 3 post before you start making changes, could save you a lot of time and effort.
Roger
 

!

Member
2005-06-05 12:52 am
Midwest
I was thinking abotu building a cascade of caps to power it going from 1000uf, 100uf, 10uf, 1uf, etc.

That is a good idea. You might want to choose a larger value big cap (unless you have a lot of capcitance after the PSU regulation stage already, in which case 1000uF should suffice) and skip a couple intermediary values though. For example, 4700uF, 10uF, 1uF, 0.1uF, with the latter two being film or ceramics, and with those latter two close(st) to the supply pins. Contrary to some mods I've seen, technically it is worse to try to squeeze a slow giant cap close to the 2024's supply pins rather than a small fast one. The idea should be to get lowest possible impedance close to the chip, with the large slow caps being fine a little further away. Only if you skip the smaller film/cermaic caps should the larger then be moved closest to chip pins.

IMO, linear is still the best bet but don't rely on the basic design that only puts a mere 10-100uF post-regulator. To keep PSU impedance down put plenty of capacitance after the regulator.
 

bachiano

Member
2004-07-02 2:59 am
us
How add caps to output of SMPS ?

Can someone show me a schematic.

I know this is a dumb question and I think I know how, but just want to be sure.

Are there good variations on the theme or is there "one" best way???

Bachiano

P.S. I search the forum and could not find a drawing.