Amp Camp Amp - ACA

[Zen Mod]

read #1887

 

[wcakey]

Heat sink tap sizes?

I purchased the chassis set from the diyAudio store for the ACA, but it does not come with machine screws to attach the output transistors or the standoffs needed to attach the PCB. I thought they might be 6-32, but that is not correct. Anyone know the correct sizes for those machine screws (thread size and length)?

Thanks

 

[Bones13]

It's probably metric. M3 or M4. The chasses are made in Italy. I don't know the length, but it's in the 5-8 mm range.

 

[nicoch58]

M4 is near 6-32

 

[thiagomogi]

My PCB

An externally hosted image should be here but it was not working when we last tested it.

 

[sippy]

I purchased the chassis set from the diyAudio store for the ACA, but it does not come with machine screws to attach the output transistors or the standoffs needed to attach the PCB. I thought they might be 6-32, but that is not correct. Anyone know the correct sizes for those machine screws (thread size and length)?

Thanks

M3, as are all other diyAudio 'pre drilled' heatsinks.
12.5mm or 10mm length is my guess - use a matchstick as a depth gauge.

 

[wcakey]

M3, as are all other diyAudio 'pre drilled' heatsinks.
12.5mm or 10mm length is my guess - use a matchstick as a depth gauge.

M3 it is, and thank you very much.

 

[sippy]

🙂

 

[Variac]

M3 10mm for the outputs as they use two washers, one a bigger fender washer
The board standoffs are M3 in the Lian Li spec

 

[huynavy]

Please advise me if I should use 24vdc for ACA?
Sorry for my messy English,

 

[Zen Mod]

feel free to use 24V , already done

 

[Danger Mouse]

if you use higher rail voltage you might read this

http://www.diyaudio.com/forums/pass-labs/215392-amp-camp-amp-aca-70.html#post3303906

 

[huynavy]

feel free to use 24V , already done

Many thanks, Zen

 

[wcakey]

Unequal heat production between channels...

Got my ACAs built, thanks to help from several folks. They do sound very nice with a Norh ACA 2B pre-amp (that I got very cheaply and resurrected) and a pair of speakers that I built with Audio Nirvana drivers.

Here is one weird thing I noticed: both amps constructed identically with the same parts and biased the same; however one of the amps runs very cool (just barely warm even after 3 hrs) while the other runs quite warm (probably 15 to 20 degrees warmer than the other -- not measured). I cannot think of any reason for this behavior and wonder if any of you have any suggestions of what might be causing this?

Thanks

 

[6L6]

Heat - The most likely scenarios are;

1) The cooler one has a mosfet that is not thermally coupling to the heatsink very well.

2) The cooler one has an incorrect value resistor somewhere making the bias or CCS gain lower, resulting in less heat.

 

[gideon]

Heat - The most likely scenarios are;

1) The cooler one has a mosfet that is not thermally coupling to the heatsink very well.

2) The cooler one has an incorrect value resistor somewhere making the bias or CCS gain lower, resulting in less heat.

I had a similar issue and i fixed it by replacing all the bias resistors..

 

[wcakey]

Heat - The most likely scenarios are;

1) The cooler one has a mosfet that is not thermally coupling to the heatsink very well.

2) The cooler one has an incorrect value resistor somewhere making the bias or CCS gain lower, resulting in less heat.

Thanks for the suggestions. Did a little inspection before undertaking any reworking and found one of the dreaded cold solder joints. All fixed and now it is cooking like its twin!

 

[6L6]

Fantastic news!

Enjoy your new amps!!

 

[Sprags]

Are they ever going to be in stock again as complete kits or do I need to buy the boards and chassis here then hunt for components?

 

[6L6]

If you have a good answer for chassis, they by all means get the PCB and go for it. The components for the PCB are easy to get.