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Old 9th October 2013, 02:57 PM   #1411
6L6 is offline 6L6  United States
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If you can get them dialed in with single turn pots, there is no need to use anything else.

Nelson used single-turn in the original, so if it's good enough for him...
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Old 9th October 2013, 03:00 PM   #1412
bcmbob is offline bcmbob  United States
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Good deal - thanks.
Bob M.
"Arrange Whatever Pieces Come Your Way."
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Old 10th October 2013, 08:17 AM   #1413
AndrewT is offline AndrewT  Scotland
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Originally Posted by Neville View Post
................................Have not messed with P3 yet, still set at zero.... oh and yes this time I did check all pots for min value before firing it up......................
Should P3 be set to middle of range, or to zero ohms?
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Old 10th October 2013, 03:17 PM   #1414
Neville is offline Neville  United States
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Originally Posted by AndrewT View Post
Should P3 be set to middle of range, or to zero ohms?
It should be set to middle of range. I just set it to zero for now but will dial it to 50 ohms, BOM asks for 100 ohms pot.

Just to make sure I was not throwing my jfets away, I put them back in and alas they were fried.....one channel completely dead and the other was very low and distorted.
Put back the jfets I had in and music. Very expensive noob mistake !!!!!! still kicking myself for this.

Loving the combo BA-3 and F4...As Backbones said.....marmite changer (ugh..hated that stuff, give me jam any day.), if I compare to my F5

Last edited by Neville; 10th October 2013 at 03:24 PM.
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Old 11th October 2013, 02:20 PM   #1415
jarkaa is offline jarkaa  Finland
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Default Cascoded hv version


I searhced for HV voltage version of BA-3. Could not find any so I decided to draw a schematic.

My aim is to drive class AB follower to with this.

I have tried many front ends before and I would like to try also this.

The rail voltage will be somewhere between +/-42V-55V

Any impressions on the design?
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Last edited by jarkaa; 11th October 2013 at 02:24 PM. Reason: Forgot to add the rail voltage
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Old 11th October 2013, 10:02 PM   #1416
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Your voltages are too high I'm pretty sure. Do read Nelson's build notes. It really doesn't take any time at all.
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Old 11th October 2013, 10:29 PM   #1417
gl is offline gl  United States
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Generally speaking your circuit should work. I've built a similar version that ran fine at 36V.

However, you will need to recalculate the power ratings on a number of the resistors.

The cascode transistors Q3 and Q7 are also too small. I would suggest the 2SA/2SC parts used in the F5 Turbo. That's what I used.

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Old 30th October 2013, 04:29 AM   #1418
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Default Need Help With BA-3 Front End Problem

I am building a push-pull BA-3. The output stage is working like a champ. The input stage is another story.

As soon as I apply power, R11 on both sides of the board smokes. I am using FQ3P20s and 1K pots. I have changed out both Q4 power FETs thinking they were bad and the same thing happened a second time. I have set P2 to zero ohms (full CCW) at start-up.

I get about 1.5 to 1.6 ohms across R10 on both sides with P1 set to zero ohms (full CCW).

I'm clearly doing something dumb but I don't know what it is.

Any thoughts?
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Old 30th October 2013, 07:57 AM   #1419
Zen Mod is offline Zen Mod  Serbia
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are you building them on store pcbs or at backyard ?

pics will help
my Papa is smarter than your Nelson !
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Old 30th October 2013, 12:25 PM   #1420
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Building them with store PCBs. :-)

My post had an error - it's 1.5-1.6V across R10, not ohms. It was a long night.....
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