Amp Camp Amp - ACA

[ZacharyP]

And the 1.7 amp bias mod?

 

[vdi_nenna]

nothing easier than mod it and try

🙂

Wasn't expecting much of a change but there was very noticeable different between 2.21k and 2.67k. Sounds fine tuned.

Some finishing touched.

 

[poseidonsvoice]

Vince,

Awesome build dude! Nice & clean. Me like! I think this is the 1st ACA I've seen with a linear supply...nice big 3u or 4u (?) chassis, those heatsinks must be frigid 😉

Best,
Anand.

 

[vdi_nenna]

Thanks. It's 3U. Heat sinks are not very warm.
Transformer has four 15v secondaries. They are in parallel down to two. Has 60k uF per side. Bass is silly good. Hard to believe

I have two more of these tranformers. Tempted to build another ACA. 🙂
.

 

[bloozestringer]

After seeing several ACA's with linear supplies I think I'll go ahead and build a separate
PS chassis for my store kits and run umbilicals to the amps.

Anand, have you seen this one: https://www.dvatp.com/tech/aca_project

 

[poseidonsvoice]

After seeing several ACA's with linear supplies I think I'll go ahead and build a separate
PS chassis for my store kits and run umbilicals to the amps.

Anand, have you seen this one: https://www.dvatp.com/tech/aca_project

Ahh...yes, thanks for the reminder, that fella even designed his own PCB boards...I completely forgot!

Best,
Anand.

 

[koja]

gents a PS question: I put together a pair of ACA from diyaudio store kit. I used them to take a measurement on a speaker and the turn off thump is pretty bad; also there was some noise in large sensitive drivers (it could have been coming from my signal generator too, not sure yet).

> anyways I am looking at adding a large capacitor to prevent/reduce the depowering thump. I also have a pair of 0.68mH inductors lying around and they could each fit into the ACA housing; so i was wondering if I could use them in an L-C?

Can somebody recommend a capacitor size for an L-C after the SMPS DC voltage in, so the store smps can charge it and it can provide some noise attenuation with that size choke? (also if I need to add a resistor and a diode at the cap plus).

by the online calculators it looks like the LC impedance goes down with larger caps. to me 0.68mH with 22,000uf looks good, but Papa makes a reference to "lesser values"? so I have no idea if my coils could be used with what size cap to add anything to it, and how to size a resistor and a diode if I need them:
http://www.diyaudio.com/forums/pass-labs/215392-amp-camp-amp-aca-197.html#post4152611

Mucho appreciated!

 

[Zen Mod]

where are you switching power off - after SMPS or you're killing mains to SMPS ?

regarding noise - what's happening when you short inputs ?

 

[koja]

after smps at the front switch as in the ACA build guide. when taking speaker measurements I ended up trying to flip the switch as fast as possible as that seemed to help a bit, at least judging by the naked eye watching the speaker cones pop (that made me wonder if the whole approach with adding a large cap after smps would have been wrong; maybe I need something across the switch?)

I did not try shorting the inputs for noise. i am reluctant to connect them to speakers until I have figured out the turn off.

turn on was seamless though, no issue whatsoever. only the turn off was bad.

 

[Zen Mod]

I can't emulate you setup , but I believe that's already covered in this ( or any of myriad ACA) thread(s)

try with 0R1+4700uF

 

[ZacharyP]

I can't emulate you setup , but I believe that's already covered in this ( or any of myriad ACA) thread(s)

try with 0R1+4700uF

ZM. Would you mind explaining the 1.7 amp bias mid???

Thanks so much for reading looking forward to your reply.

 

[Zen Mod]

I believe it's already explained in thread

nothing more (and nothing less) than upping Iq , thus increasing power and lowering THD

 

[ZacharyP]

Is it the same as the resistmor mod? My computer is down and my phone mskes it it hard to search

 

[Zen Mod]

yup

editing/changing that resistance position , you are changing Iq

 

[ZacharyP]

yup

editing/changing that resistance position , you are changing Iq

So if I changed the R15 2,21 to say 2,6 would that increase bias? To 1.7amps?

Thanks for guiding me, I'm a total newbie to DIYaudio projects

 

[vdi_nenna]

So if I changed the R15 2,21 to say 2,6 would that increase bias? To 1.7amps?

Thanks for guiding me, I'm a total newbie to DIYaudio projects

I used 2.67k because it's what I had on hand. Switched to 2.21k this past weekend and it's noticeably better.

Trying each one is best way to know, but that was my resent experience.

Vince

 

[kpsthakur]

Ok one channel done with stock ACA kit from diystore...great sound quality...funny it works great with my floor standing Sony speakers 180W 8ohm, but pathetic with Sony bookshelf VX333 70W 6ohm...every one is just amazed with the treble mid base of this teeny 6W thingy...only bit of sound while startup...guess that are the capacitor's charging, but a very loud thump while switching it off...I read a lot of similar comments on thump issue, but no standard fix...the bleeding resistor at output was supposed to solve the power on thump...any know value of cap I can attach that will not change the audio signature...or any other suggestions


Sent from my iPhone using Tapatalk Pro

 

[ta240]

Is there an easy way to raise the input impedance without messing up anything else on the amp? Just raising R11 seems too easy.

I have a tube preamp I want to use with it but from what people have said my preamp doesn't like that low of impedance.

 

[Zen Mod]

HF performance will suffer

btw. input resistor (R11) is directly in correlation with other feedback net resistor (R12) thus defining both input impedance and gain

 

[rnjorge]

I have a tube preamp I want to use with it but from what people have said my preamp doesn't like that low of impedance

I've been using the stock ACA with a tube preamp and it sounds great.