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Excuse for a class A DIY AMP build?

It's "frowned upon" etc but in many cases will be perfectly OK. It all depends on just how long, how they are routed and above all else on the actual circuit but real world parasitics etc mean it's not possible to simulate etc and only a "suck it and see" approach can be used... If you don't have lots of test gear, the knowledge to use it and the knowledge/experience to spot incipient instability and to track the cause of any oscillation or ringing to this or a completely different cause it is best to stick to a known good layout.

The length of the wiring to the output devices in a Quad 303 is a good example of it being fine in at least this specific instance.
 
Quick update - looks like Colin has a couple of SECA amp boards for me to try, so I’m going to go that route.

I’m expecting problems with the stock heat sinking but given chassis was so cheap I’m not averse to mounting larger heat sinks internally down each side and then hacking the casework for airflow if I cannot rig up a fan solution that allows stock ones to cope.

Richard
 
Dowser said:
Quick update - looks like Colin has a couple of SECA amp boards for me to try, so I’m going to go that route.

I’m expecting problems with the stock heat sinking but given chassis was so cheap I’m not averse to mounting larger heat sinks internally down each side and then hacking the casework for airflow if I cannot rig up a fan solution that allows stock ones to cope.

Richard
Click to expand...

You will like what you hear.
 
Thanks - yep, have seen (& also pissed at photobucket shit!). Colin put my boards (v2) in post today :)
 
Recently picked up a couple of cheap fans I'm sure will be required. Checking my parts stock for transformers, I've a fair few dual secondary 24v AC items, but I think recommended values are only 15-18v AC secondaries? And as my heatsinks are likely to be too small any ways, I'm maybe better off at the lower end of the voltage range?

Does anyone know minimum and maximum AC input voltages please? Is it 15 & 18v?

Cheers, Richard
 
Do people think the amount of heatsinking shown would be enough for a pair of 25w Class A transistor designs based on the JLH 1969 design? I feel not, and the enclosure I got for my DIY stereo amp project has even less sinking, so I think it is probably time for a rethink or judicious addition of heatsinking to the chassis I bought (and silicone).
 
Millennium said:
Do people think the amount of heatsinking shown would be enough for a pair of 25w Class A transistor designs based on the JLH 1969 design? I feel not, and the enclosure I got for my DIY stereo amp project has even less sinking, so I think it is probably time for a rethink or judicious addition of heatsinking to the chassis I bought (and silicone).
Click to expand...

No.
 
But AliExpress do some impressive separate heat sinks, and one or two fans (run as suggested above at less than their nominal voltage) might do the trick on their own. Adding a couple of (fan) motors may be counter-intuitive, but they really are silent. Given that the chassis is always the most expensive part, definitely worth a try.
 
Anyone know what min and max input AC voltages are for the iss 2 SECA amp boards?

Thanks :)
 
That doesn't look like enough heat sink for anything bigger than 10-15W Class A. Looks like about half the area, maybe less, than what you'd see on one of Nelson Pass' 25W/ch amps.
 
Marra said:
I have the amp built with mk1 boards and the secondary voltages recommended are 15-18 vac.
Click to expand...

Thanks!

Yank said:
That doesn't look like enough heat sink for anything bigger than 10-15W Class A. Looks like about half the area, maybe less, than what you'd see on one of Nelson Pass' 25W/ch amps.
Click to expand...

Nope, probably not - question is whether I can use fans to control it :)
 
Richard, what about a couple of Les's new LS protection boards? They have a fan control circuit on the same board should you need it.
 
Chops54 said:
Richard, what about a couple of Les's new LS protection boards? They have a fan control circuit on the same board should you need it.
Click to expand...

Thanks - I’ll first check whether a fan can control the heat build up - I suspect I’ll need new heatsinks:)
 
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