The BA-3 as preamp build guide

[ItsAllInMyHead]

^ Since it looks like you are buying from the store, I'd get "Toshiba 2SK170/2SJ74 Quad Idss 8-11mA - $45" and rest easy. One quad for two channels.

 

[Analogico]

I guess that's what I'll do!

 

[DIYHarry]

First version of BA-3
Glassware regulator
Next for testing VRDN in progress
With IRF640N/9640...NEXT Toshiba J313/2013

 

[DIYHarry]

Thanks to all, who Like my pic

sounds warm and smooth
19dB is too much , doupled R13 and reduce to about 13,2dB
20Hz amplification is slightly 0,6dB more...
low end punch is a lot, but additonal with F5 Lateral it is tooooo much in the low end. souinds very fat but controlled

will do the second PCB with Toshiba J313/2013....

 

[DIYHarry]

how high could the bias be, or make it sense to run this 80-100mA??

 

[DIYHarry]

New for me. Second PCB works not ok.
Strange DC parameter and measurement
Funny signals if I go over 200mVrms input or go below 900Hz input

 

[Zen Mod]

setting procedure is - observe voltage across R10 to set your desired Iq, second DVM across R13 to set as close to possible to 0mV

during setup procedure ignore measuring anything else, especially do not look at R11

start with P3 preset in mid position

again, parameters are Iq and DC Offset across R13, not symmetry of voltages across R10 and R11

 

[william2001]

how high could the bias be, or make it sense to run this 80-100mA??

I would want more substantial heatsinks myself if we're talking about doubling the dissipation here. Would it "sound better?" 🤷‍♂️ But obviously get the circuit properly dialed in first with these qty=100 trimpots..

 

[DIYHarry]

But trim pot P2 is wrong designated, P1' traces go to Q3

I set with P3 Vdrop on R3 and R4 equal to 52 mV

 

[DIYHarry]

What forgot..I use 17.70V rails
For measurement is a load of 47k that what you recommend? Thx

 

[DIYHarry]

Still no change to the measurements above. Also when I use 24V rail, so....slightly shift of errors in low frequencies from 900Hz to 500 Hz below. the JFets reduce their Id from 5.1mA till 3.9mA if lowering freq.
I think the JFets are not working correctly.

 

[Zen Mod]

did you tried setting as I explained in my previous post?

 

[DIYHarry]

yes Sir,
with P1,P2 ..... DC offset is 0 to 0,1mV on R13

 

[Zen Mod]

OK then

make proper recapitulation of current state of circuit and problems you have (now)

if you don't inform about changes, that's just sending us to tail-chase

 

[DIYHarry]

Scope shows the same issues

 

[Zen Mod]

origin of your JFets?

 

[DIYHarry]

Quad 8-11mA from store last year, as usual, Sir

 

[Zen Mod]

origin of pcbs?

 

[DIYHarry]

Yes also Store...
Tomorrow i will change the JFets.....
Now it is listening time...😉

 

[Zen Mod]

if you have problem, better not listening to it

power it off, inspect once more do you have all components with right values in right positions

if both channels are behaving same wrong, you made some systematic error

I mean - circuit is very simple per se, what's tricky (somewhat) is setting procedure, if you want to pursue some specific THD Spectra

so, usual drill - confirm proper rails, proper parts positioning, proper soldering job....