BA-3 As Preamp

Maybe....iam running a little less bias right now too. Iam going to let it play for a couple days...maybe raise the rail voltage and bias. I can take it up to 28v rails and still have 5v of drop out. Right now iam noticing more detail and less slam and bass. But it sounds extremely good, just a bit delicate. Better detail on cymbals and piano sounds more true. But perhaps not as much drive and kick. Could be the bias and rail voltage. But iam going to give it some time before making a judgement.

OK, I've given the superreg 24hrs with the BA-3. Here's what I think:

Superreg has more detail than the LM317/337 psu. This is the most obvious difference. With the volume control maxed out on the BA-3/F5 I could hear a bit of noise from a few feet away from my 91DB efficient speakers. Quiet but there. With the Superreg I have to put my ear up to tweeter to hear anything. So perhaps the noise floor has dropped a bit.

Overall it is an improvement...small but noticeable. Makes the system a little more lively and imaging seems locked in a bit better. It seems to have lost a little tonal density...sounds a little thinner, just a little. This may be due to tighter bass or less bass bloom. "Clean" is the word I would use. Seems like some of the bass and "slam" is returning as it runs in. It seems to be loosening up a little.

Also, I was running 30V rails w/the LM317/337 combo. Now I am running 25V rails due to the greater dropout of the superreg (5V or greater is recommended). I am guessing this is kind of a step backwards (I assume more rail voltage is better) then a step forwards with the superreg.

Should all you guys w/LM317/337 regs on your BA-3 ditch them for the superreg? It's your call. I am happy, glad I did it.
 
Official Court Jester
Joined 2003
Paid Member
With preamp off, should I be able to turn P1 P2 resistance to zero?
Negative rail, lowest on trimmer measures 100ohms. I ran into issue, neg rail
On power up measures -24v the becomes -5v. I pulled the board out and going through
All the part vaues and shorts.

P1 and P2 are 1K, Im using fairchild for Q3 Q4
 
Butter fingers, I shorted R10 while power on, would that kill Q3 or Q4?

I measure Q3 Q4 2 pins measure 560ohms and other 2 infinite resistance
Doesnt seem shorted

Iam no expert but I would look at the mosfets first...then jfets then trimpots. The electro caps could be damaged too. Resistors should be ok. I shorted a thermistor on my f5. Everything was fine but the trimpots...took me forever to figure out. Test the trimpots by locating the resistor effected by them and seeing if the resistance across the trimpot changes when the pot is turned.
 
I borrowed dual psu bench supply, circuit survived, each channel draws about 56mA at 24V
The psu board I have is messed up on the neg. Rail
Will get another psu board going

Thx

What shunt reg did you get off ebay? Ive heard some bad things about the ebay shunt regs.

What voltage transformer are you using? A lm317/337 setup works, is hard to mess up and is cheap. Iam using a superreg in mine, sounds good but is a little more complicated to set up. And more expensive.
 
What shunt reg did you get off ebay? Ive heard some bad things about the ebay shunt regs.

What voltage transformer are you using? A lm317/337 setup works, is hard to mess up and is cheap. Iam using a superreg in mine, sounds good but is a little more complicated to set up. And more expensive.

This one, only because you asked :)
I know many dont like to use ebay stuff.

http://www.ebay.com/itm/Class-A-Par..._Audio_Amplifiers_Preamps&hash=item4610fcc9d8

This was cheap enough to give a try. The schematic is not same as
Parts on the pcb, neg. Rail uses lm337 and some other parts,
Different from schematic. Problem with this board, they use hard to find
Toshiba parts.

yup, I have a twisted pear 317/337 probably will stuff and and use
 
This one, only because you asked :)
I know many dont like to use ebay stuff.

Class A Parallel Type Regulated Power Supply Finished Board | eBay

This was cheap enough to give a try. The schematic is not same as
Parts on the pcb, neg. Rail uses lm337 and some other parts,
Different from schematic. Problem with this board, they use hard to find
Toshiba parts.

yup, I have a twisted pear 317/337 probably will stuff and and use

$15 shipped! Too good to be true. Probably full of fake mosfets and bad caps. Ive got nothing against chinese ebay stuff...as long as its not ripping off someone elses design. But this thing is too cheap to make any sense at all.

Ive read good things about the Salas shunt. But shunts can be bad or good depending on the design.