Amp Camp Amp - ACA

[fr0sty]

tried replacing them in my working ACA channel..including considering the leads are different for J111), but did not work...

What happened when you tried a straight substitution? No audio? Quiet audio? Distorted audio? Temporal Rift?

The characteristics of the J111 and SK170 are not exacly identical, far from it, so changing Q4 to another type will require a new value for R9. The change will likely effect input sensitivity as well.

EDIT: R9 sets current through the jFET, not R6...

 

[kpsthakur]

No audio.. I did feel this would happen...but gave it a shot...headless ofcourse...its cold out here, did not want to go scratching from the start

 

[Zen Mod]

try to find T092

if not , you can put it on small smd pcb with pins , as T092 substitute

easy to made even with scalpel

 

[fr0sty]

No audio.. I did feel this would happen...but gave it a shot...

Did you re-adjust P1 to attempt get the correct voltage on the drain of Q1?

 

[kpsthakur]

fr0sty - yes, but the value was way too low around 1.2V did not move much with turns on the pot

ZM- J309 TO-92...seem so be out of production

 

[irishpatrick33]

I'll repeat someone else's question that nobody answered.

Any idea as to when the kit will be in stock again?

 

[Variac]

We haven't decided yet, still getting the final VFET amp kits finished.
Then we hope to get on a new Batch of ACAs. Probably a good 4-6 months.

 

[irishpatrick33]

We haven't decided yet, still getting the final VFET amp kits finished.
Then we hope to get on a new Batch of ACAs. Probably a good 4-6 months.

Thanks

 

[twocents]

fr0sty - yes, but the value was way too low around 1.2V did not move much with turns on the pot

ZM- J309 TO-92...seem so be out of production

Have you considered BF862? Apparently a straight substitute as reported by others. Currently there are plenty of exciting BF862 based projects happening on the forum.

Yes, it is SMT, but even I found it quite easy to solder thin copper wires to the 3 leads using 3x glasses or a magnifying glass. Then it is the same as TO-92.

I am certainly planning to use BF862's as a straight replacement for 2SK170's in my ACA build. Hope to start soon. First need to finish my B1 (also with BF862's).

Maybe the more experienced guys can confirm if this is a good option.

 

[kpsthakur]

Yes, I did read about Juma's version and got hold of plenty of BF862's....not sure if even they will be straightforward replacements like J111....saw the specs...


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[kpsthakur]

diyRookie, wishing you luck...share some good news. Meanwhile, I did read somewhere to add a resistor to gate pin of BF862...try finding bit more about it before deploying it in your ACA


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[koja]

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

I tried it today and the turn off thump of my ACA did not change . I am now thinking relays for speaker outputs but in that case, to reduce the number of switches I would probably put both ACAs in a single housing and in the process do a proper linear PS; so this is a complete rework and not something I wanted to do. I may have to put up with the current setup for a while where my B200s are popping on turn off. there is a serious DC swing as they visibly jump on flipping the switch.

 

[nzlowie]

Hi guys
Can some one please give me the measurements of the ACA kit heatsink?

I've built a 4 channel version and I'm having trouble cooling it!!

Cheers

 

[kpsthakur]

190x70x30


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[nzlowie]

Thanks, that's a lot smaller than I thought they were by looking at the photos...
So its 70mm high x 190mm deep with 30mm fins?

 

[kpsthakur]

Yup...but with ACA's kit you get Keratherm pads (Hope I spelled that right), that does a great job of transferring heat. The chips remain much cooler than other options like mica or silicon


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[HemiBooch]

KnuckleHead Rookie Mistake

ACA Trouble Shooting for a newbie, please!
Long time audiophile, first time I have ever built something on my own. Minimal practical knowledge, but I can follow instructions and am decent with a soldering iron.
> Built the first ACA, sounds terrific, no problems.
> Built the second, sounds good for 5-10 seconds, then volume drops off a cliff and output becomes very distorted, regardless of source. Gently tapping internal wires or chassis gets a blip of added, staticky distortion.
> Checked all solder joints, everything looks good
> only thing I have found out of order is this: when I test ground and Q1 center pin, DC is 10.2V or so, then takes off to 14, even 15VDC!
Not a clue what to do from here. Any help greatly appreciated.

While poking around trying to figure what was wrong, I realized I only used one layer of the Keratherm. I guess I thought the other layer was the backing, not part of the of the heat dissipation function. Rather embarrassing...
Amps now sound wonderful with both layers of Keratherm in place!

 

[Zen Mod]

????

keratherm is just grayish* thing

if anything else is there , that's protective layer

power it off immediately and check what you did , if you already didn't cook poor mosfets

*I have pinky ones

 

[noelectrix]

my diya- store keraterms are grey also. i didn´t used them and they are lying around for a while
and i just today -more by accidence- read on the store site they are named "red" appear "pinky" .....but still grey in real world.
fake news or should i rub a bit on them never tried

 

[rnjorge]

I tried it today and the turn off thump of my ACA did not change . I am now thinking relays for speaker outputs but in that case, to reduce the number of switches I would probably put both ACAs in a single housing and in the process do a proper linear PS; so this is a complete rework and not something I wanted to do. I may have to put up with the current setup for a while where my B200s are popping on turn off. there is a serious DC swing as they visibly jump on flipping the switch.

One alternative to reduce the "thump" is to switch the AC and not the DC. I removed the PSUs from their cases (which reduced their size considerably), placed them inside the housing and the switch turns THE PSU on and off. (I did this out of pure laziness, until I build a proper linear PS). The thump is minimal.