The BA-3 as preamp build guide

generally , I prefer regs with error amplifier ,to ones being set as sort of reference followers

also , I'm heavy biased there ..... during the years , tried most best known , and even if I was satisfied with some of them , wasn't satisfied due to feeling that pure cloning isn't enough

so , back to biased - Shunty and Good Gemini are my cup of tea ; Good Gemini, as later - even if simpler , made with even greater care of phase behavior and pcb routing , which is of same importance as electrical design

if you want simplest possible but with good performance , look at reg in PSM LS article

What is "PSM LS" article? I can't find it, or more likely I am missing something
 
Check Zen Mods footer. they are links to his PDFs.
 

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Receiving parts for my ba-3 build and some questions

I have received all the parts. Easy, Digikey had them all. For the power supply I ordered the high current module from Twisted Pear, though Tubecad does not have their ps19 kit in stock, it has been a while since that.

The enclosure is one from the store and yesterday it was still in Italy, shipping was more than the actual price.

So my first question, Antek was out of the 50 VA transformers so I got the 100va albeit with 20-20v secondaries, hope this is no problem.

2nd. Question, the light bulb procedure. 6L6 mentions a 25w bulb in this thread, and in other threads I've seen 100w bulbs. Please clarify.

3rd. I am fairly new to SS builds, although I successfully build my Twisted Pear Buffalo dac without any incident, but need to clarify the light bulb purpose and procedure. Kind of got lost in the last sentence under the F5T explanation...so, until what step of the biasing would I have to keep the light bulb?

The twisted pear ps has all the instructions to check the output voltage prior to connections to the main board.

4th. Question, when it is said that it would make it easier to bias shorting the input, is that literal, I man connecting temporarily the rca inputs from ground to
positive?

Thanks!
 
To my best knowledge:
1) 100 VA is fine (i used 80)
2) The bulb acts as a current limiter in case you have a short. If the bulb burns bright after turning on, current is wasted in the bulb rather than frying your circuit. If it lights up briefly (or not at all), and all voltages test out in your circuit, you can power up without it. As i understand it, the main rationale for a large bulb is when you have a circuit that pulls more current, e.g. a power amp, where a 25W bulb would probably just burn out.
3) You may be able to bias some of the way with the bulb in place, but if you set your pots to zero before starting you can just use the bulb to verify nothing is going to catch fire and then do the biasing without the bulb.
4) That's what i did, though the exact explanation for why this helps i am not sharp on. Might be for a similar reason that you should add a bleeder resistor from D to Gnd on the output (as pointed out by Zen Mod just a few posts back).
 

6L6

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Silas has a bunch of good information.

To expand -

1) Yes, your transformer will be fine.

2) The 25W bulb is suggested in this case as the total current draw is smaller, so in case of a problem, you need a smaller bulb, which will light up faster and limit the current and voltage to the circuit and (hopefully) keep things from burning up. Remember that the filament of the bulb is in series with the load, only when there is considerable current craw will it light up, and when it does, it will drop a bunch of voltage across the line, reducing the voltage at the load, and saving the project. If you use a 100w bulb, he amount of current passed before it limits voltage is much, much larger.

3) Use the bulb for initial testing and power up in case you've got a short. If the bulb stays dim and your PSU voltages are good, proceed to starting the bias procedure with the bulb in place... Once you have 10-15% or recommended bias and zero offset, and everything seems to be reacting properly, remove the bulb and continue. The Bias will most likely measure higher than the setting previously as the bulb will not be there reducing the psu voltage. This is normal.

4) Yes, RCA plugs with pin connected to barrel are fine to short the input. This gives the Jfets something to look at (zero signal) during bias. In addition, a load on the output helps stabilize the circuit during bias, I have found a 20K resistor from output to ground is very useful to keep bias measurements from drifting.
Zen Mod's suggested 100K from output to ground to bleed the output cap is a very good one, I think it's a great idea.
 
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Could one use a twisted pear placid bipolar hd power supply?
Placid HD Bipolar Power Supply

From manual:
The Placid HD BP is a shunt regulated bipolar DC power supply designed for low noise and excellent line and
load regulation. It is primarily intended for ±10-20VDC supplies using transformers with 12-20VAC
secondaries.

The Placid HD PS is limited to DC equal to or less than 20v. You might have to see what changes need to be made to the BA-3 circuit to perform at it's best.

http://www.twistedpearaudio.com/docs/power/placid_hd_bp_1.0_manual.pdf
 
From manual:





The Placid HD PS is limited to DC equal to or less than 20v. You might have to see what changes need to be made to the BA-3 circuit to perform at it's best.



http://www.twistedpearaudio.com/docs/power/placid_hd_bp_1.0_manual.pdf



Is there a shunted power regulator as a kit out there? Or a good solution as it’s seems all the regular power regulators from the usual sources mentioned on here Aren’t available. Yes I know the super regulator is available but people keep telling me it’s difficult. And suggestions would be greatly appreciated
 
Is there a shunted power regulator as a kit out there? Or a good solution as it’s seems all the regular power regulators from the usual sources mentioned on here Aren’t available. Yes I know the super regulator is available but people keep telling me it’s difficult. And suggestions would be greatly appreciated

Not a shunt, a hi-end series reg instead. More of a kit with good instructions:

The σ22 regulated power supply
 

6L6

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The AMB sigma22 is a neat PSU, well worth it.

I'd drop the TwistedPear folks an email and see if you can adjust it to 22 or 24v. I bet it's not that hard, and having a good bipolar shunt available for the BA-3 pre would be great!

Also, ZenMod's "Shunty" regulator would work beautifully. Send him a PM, I think he has PCBs
 
The TP Placid uses opamps which is why it's probably voltage limited.

Lot's of shunts on eBay as well. Also, there is the Kubota reg, cap multipliers, etc.

Personally, I think there is nothing wrong with LM-series regulators in this circuit. EVUL, a frequent contributor to Pass projects uses lm317/337 + a cap reg on lot's of low-level designs. I have this reg too, sounds good. Salas new preamp uses a cap reg, not his shunt.

Not every regulator needs to be fancy or a shunt or whatever...depends on the task.