The BA-3 as preamp build guide

[MEPER]

I got matched JFETs from a trusted ebay dealer and I went for the Fairchild output transistors and because of that I went for 1k pots to adjust bias etc.
For JFETs maybe you can use the LS variants sold at DIY Store.....they sell matched pairs now. Only one set pr. order…….other may advise if you can use those…..

 

[MEPER]

Those JFETs from the store you may be able to use…….but has to be confirmed by some experts! but it is my guess that you can use them…..grade B should have the right Idss:
Linear Systems Matched LSJ74/LSK170 JFET pairs (Grade B) – diyAudio Store


The Fairchild output trans should be easy to get……..

 

[MEPER]

And if you email:
contact@diyaudiostore.com


….you may ask for a mathed pair with Idss that is optimum for BA-3 pre build.

 

[anhton82]

And if you email:
contact@diyaudiostore.com


….you may ask for a mathed pair with Idss that is optimum for BA-3 pre build.

Many thanks for your quick reply. I hope I can find it and build a preamp by myself.

 

[kpsthakur]

Dear all, what is the ideal Voltage for BA-3. I am runnin this off +18 0 -18 and sounds good. I am using 317/337 based PSU and reg it up to 24V (+ -), will there be any change to sound quality, sorry don't have analysers to measure quality and distortion

 

[6L6]

If you don't need an incredible amount of voltage swing to run a buffer amplifier (F4, MoFo, etc...) then +/-18v is fine.

 

[6L6]

And if you email:
contact@diyaudiostore.com


….you may ask for a mathed pair with Idss that is optimum for BA-3 pre build.

No, you can't, aside from ordering "B" grade, any matched set of which will work great.

 

[MEPER]

Ok.....if they all works great matched with Idss from 6-12 mA then there are no issues!

 

[kpsthakur]

If you don't need an incredible amount of voltage swing to run a buffer amplifier (F4, MoFo, etc...) then +/-18v is fine.

Only F6, so I am not changing anything in this case

 

[anhton82]

Can you compare the SQ of K170/J74 V serries and BL serries (same B grade or not?)??? Which is better ones?
Thank you !

 

[McQuaide]

Any issue putting this in an F5 case and running off the PS?

 

[Hikari1]

Any issue putting this in an F5 case and running off the PS?

No, other than it would probably sound better with a regulated supply instead of the F5's unregulated supply.

You could add a regulator off the F5's PSU but since the f5 PSU is 24V it would drop your BA-3 front end to 21V or so after regulation.

 

[6L6]

Can you compare the SQ of K170/J74 V serries and BL serries (same B grade or not?)??? Which is better ones?

There is no difference in sound quality, one series in not "better" than the other. The suffix G, BL, V have to with the Idss range of the device.

V series has an Idss range of 10-20mA, BL has an Idss range of 6-12mA

The BA-3 should use BL Jfets for proper operation in the circuit.

 

[anhton82]

There is no difference in sound quality, one series in not "better" than the other. The suffix G, BL, V have to with the Idss range of the device.

V series has an Idss range of 10-20mA, BL has an Idss range of 6-12mA

The BA-3 should use BL Jfets for proper operation in the circuit.

Many thanks !!! I will choose BL Jfets.

 

[McQuaide]

No, other than it would probably sound better with a regulated supply instead of the F5's unregulated supply.

You could add a regulator off the F5's PSU but since the f5 PSU is 24V it would drop your BA-3 front end to 21V or so after regulation.

How about this as a temporary supply? It's currently powering my Pearl 2.

 

[McQuaide]

No, other than it would probably sound better with a regulated supply instead of the F5's unregulated supply.

You could add a regulator off the F5's PSU but since the f5 PSU is 24V it would drop your BA-3 front end to 21V or so after regulation.

Well, I have a regulated supply on the way, along with a lot of other parts to build one of these. I plan to add it to the F5 case and see how that works. I originally had a DCB1 Mezmerize in there, so it has all the holes already.


Question - are these trimmers appropriate for the BA-3?


RJR26FW102M Bourns | Mouser

PV12T101A01B00 Bourns | Mouser


Also what's a good heatsink for the JFETs from the DIYaudio store?

 

[WalterW]

Search for Bourns 3296Y series

 

[McQuaide]

Search for Bourns 3296Y series

Thanks! They weren't coming up in my search for some reason.

 

[McQuaide]

Also, I'm having trouble finding Vishay RN55s in the needed values on Mouser/Digikey.

 

[WalterW]

you can also type CMF55 in the search function, same resistors.