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Old 4th November 2013, 07:21 AM   #1451
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Quote:
Originally Posted by Samuel Jayaraj View Post
Though I should have done this earlier, too many constraints had denied me the opportunity thus far; but I have now completed a single-sided PCB layout for the ACA. I am going to try an SMPS as well as a conventional one to check the sonic differences. I will be using a 18-0-18 120VA torroid. I guess it is just about sufficient. I have made the provision to switch the cap bank out when using an SMPS. Made provision for a BF862 along with a resistor in the Drain.

Questions are, the value of the resistor, assuming about a 24VDC linear supply when testing with BF862?

Although I would be driving Fostex FE168Sigmas, I just thought adding a peak power indicator or clipping indicator would be added insurance. Any pointers to a circuit?

Thanks,

Sam
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Old 12th November 2013, 06:17 AM   #1452
Variac is offline Variac  United States
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We sent a kit to Papa Pass and he wrung it out with his test gear...
Turns out it can be tweaked to have more bias and put out the full SIX watts, with less distortion!
You have to add R15, Value 2.21K
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Last edited by Variac; 21st November 2013 at 05:17 AM.
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Old 12th November 2013, 06:24 AM   #1453
Variac is offline Variac  United States
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Here's a photo of how to tweak the ACA to have 6 watts output and lower distortion! Higher bias is the ticket and it's simple!

Just use a 1/4 or 1/8w 2.21K metal film resistor and solder it in place as shown here..
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Last edited by Variac; 13th January 2014 at 06:52 AM.
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Old 12th November 2013, 07:32 AM   #1454
Zen Mod is offline Zen Mod  Serbia
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forgot to say percentage of increased bias/dissipation (40-45%) ......
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Old 12th November 2013, 08:06 AM   #1455
Variac is offline Variac  United States
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yes it will get hotter but Papa has the current kit chassis and says it isn't too hot.
I always say: Depends on where you live!
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Old 12th November 2013, 08:24 AM   #1456
Zen Mod is offline Zen Mod  Serbia
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that's easy .......

I live where amps are hot

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Last edited by Variac; 13th November 2013 at 05:48 AM.
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Old 12th November 2013, 09:11 AM   #1457
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ZM
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Old 12th November 2013, 12:14 PM   #1458
WalterW is offline WalterW  Netherlands
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Just did the tweak, it pulls instead of 0.98 A now 1.40 A, and on the AC side it pulls 34 Watt instead of 21 Watt.
Adjusted the drain of Q1 to 10 Volts.
My little red ACA chassis from the DIYAudio store can handle this extra heat very easily.

Walter
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Old 12th November 2013, 01:25 PM   #1459
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Sorry for sounding noob,but how much do we need to set bias to get 6 watts?

Regards,
Sachin
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Old 12th November 2013, 01:31 PM   #1460
Zen Mod is offline Zen Mod  Serbia
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you have explanation in few posts up

read #1452-#1458
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