turn 350w amp kit to class A ???

[mikefromaus]

Hi guys,

I am looking at buying a couple of amp kits based on the MJL21193/94 - it is rated at 200W into 8R and 350w into 4R - The specs in class a/b mode are

-1db at 15Hz and 60kHz
-0.002% THD at 150w 8R (10hz - 22KHz)
-SNR -122dB unweighted (22Hz - 22kHz) @ 200W into 8R
-Damping factor 75 at 10kHz with respect to 8R

Now I was wanting to know if it would be minor to bias this into class A to get around 60W into 8R - Im guessing the +-70 volt rails will need to be alot less and the bias changed but can anyone see any issues in doing this?

I have attached a schematic so you can see the design - thankyou for any input.

[myhrrhleine]

Originally posted by mikefromaus
Hi guys,

I am looking at buying a couple of amp kits based on the MJL21193/94 - it is rated at 200W into 8R and 350w into 4R - The specs in class a/b mode are

-1db at 15Hz and 60kHz
-0.002% THD at 150w 8R (10hz - 22KHz)
-SNR -122dB unweighted (22Hz - 22kHz) @ 200W into 8R
-Damping factor 75 at 10kHz with respect to 8R

Now I was wanting to know if it would be minor to bias this into class A to get around 60W into 8R - Im guessing the +-70 volt rails will need to be alot less and the bias changed but can anyone see any issues in doing this?

I have attached a schematic so you can see the design - thankyou for any input.

My thought:
you'd be better off getting an amp designed for class A rather than doing a mod like this.

[Nico Ras]

Originally posted by mikefromaus
Hi guys,
Now I was wanting to know if it would be minor to bias this into class A to get around 60W into 8R - Im guessing the +-70 volt rails will need to be alot less and the bias changed but can anyone see any issues in doing this?

I have attached a schematic so you can see the design - thankyou for any input.

Yep, totally feasible. Reduce the supply to about +-35V and turn the bias up to 3 amps total. You may have to change VR to 4K7 to reach required bias. Also you will need very beefed up heat sinks and a large power transformer with plenty of caps.

[MJL21193]

Originally posted by mikefromaus

-1db at 15Hz and 60kHz
-0.002% THD at 150w 8R (10hz - 22KHz)
-SNR -122dB unweighted (22Hz - 22kHz) @ 200W into 8R
-Damping factor 75 at 10kHz with respect to 8R

Not related to it's use as class A:
I'd have a real problem believing some of the quoted numbers, especially the THD.

[Jan Dupont]

That amp has been in the "trouble section" here before.....
Be carefull