I am still having issues with my build. With my multimeter on the input of C3 and ground, I’m and still getting 0V DC offset and unable to get bias over 300mv. Below are the measurements I took at the JFETS:
-Q1 at D is 24V and at S is 44mv
-Q2 at D is 24V and at S is 34mv
Both sides are the same reading.
Is there a possibility I fried my Mosfets or JFETs. When I first turned it on I had installed my Transformer incorrectly.
Any help is appreciated. Thanks.
-Q1 at D is 24V and at S is 44mv
-Q2 at D is 24V and at S is 34mv
Both sides are the same reading.
Is there a possibility I fried my Mosfets or JFETs. When I first turned it on I had installed my Transformer incorrectly.
Any help is appreciated. Thanks.
I miss connected my first BA3 FE to the power supply and killed the mosfets. It's possible. I also remember turning the pots a lot before numbers started to register.
Russellc
Russellc
Just installed new mosfets and upon turn on I’m still not getting any Dc offset. I did test the old vs new mosfets and it seems they tested fine compared to the new ones. Could my problem be blown JFETs? I included pics of my build.
Attachments
Last edited:
Hello Dneu2011,
Are your voltages correct on the input of your BA-3 - board?
Measure both channels from +V to ground and -V to ground.
Did you use TOSHIBA or LS-JFETs? Check pinout of JFETs and orientation on the pcb?
Did you use IRF MOSFETS 610/9610 or FAIRCHILDS?
As MEPER mentioned to bias the FAIRCHILDs up you need 1 kOhm trimpots in P1 / P2 position.
And set P3 to midposition.
Only some thoughts..
Greets
Dirk
Are your voltages correct on the input of your BA-3 - board?
Measure both channels from +V to ground and -V to ground.
Did you use TOSHIBA or LS-JFETs? Check pinout of JFETs and orientation on the pcb?
Did you use IRF MOSFETS 610/9610 or FAIRCHILDS?
As MEPER mentioned to bias the FAIRCHILDs up you need 1 kOhm trimpots in P1 / P2 position.
And set P3 to midposition.
Only some thoughts..
Greets
Dirk
This might help you:
Your F5 blew up, now what do you do?
Ba-3 front end is basically an F5 with no feedback.
Your F5 blew up, now what do you do?
Ba-3 front end is basically an F5 with no feedback.
I checked my voltages from the Power Board into the BA3FE and all check out at +-24V.
The Mosfets I purchased are: 512-FQP3N30 and 512-FQP3P20
I am using 1K Ohm Trimmer Pots @ P1/P2
I used Toshiba JFets. Orientation looks correct @ DGS
P3 was set to the middle position
Can you check the bias of the mosfets at first?
if there is no, there won't be any offset. if they are balance 100%, there won't any offset either.
bias voltage should be measured between two lead of the 22 ohms resistor, which is the one behind the heat sink.
if there is no, there won't be any offset. if they are balance 100%, there won't any offset either.
bias voltage should be measured between two lead of the 22 ohms resistor, which is the one behind the heat sink.
Make sure your checking on the correct side of cap for offsets. Cap will block DC so no offset will show. Also, as mentioned above, check across R10 & R11 for any bias as you adjust P1/P2.
1> Check proper values of parts and try to reflow all solder joints.
2> Test P1 & P2: Power on, measure from cap side of R6 & R7 to GND. Make sure voltage changes as you adjust pots. No change, replace pot(s).
3> Test P3: power off - check across R3 & R4, DVM to ohms, turn P3, make sure resistance changes on each. No change, replace P3. Return to center.
4> Test JFETs: power on - check across R3 & R4, DVM to millivolts, turn respective P1/P2. If no voltage change, replace Q1/Q2.
TJ
1> Check proper values of parts and try to reflow all solder joints.
2> Test P1 & P2: Power on, measure from cap side of R6 & R7 to GND. Make sure voltage changes as you adjust pots. No change, replace pot(s).
3> Test P3: power off - check across R3 & R4, DVM to ohms, turn P3, make sure resistance changes on each. No change, replace P3. Return to center.
4> Test JFETs: power on - check across R3 & R4, DVM to millivolts, turn respective P1/P2. If no voltage change, replace Q1/Q2.
TJ
Last edited:
Good news. I replaced the JFETs (and mosfets) and was able to bias and set one side of the preamp.
I’m out to watch some football but will setting the other side tonight!
Thanks for all the help. Hopefully I’m rocking tonight.
I’m out to watch some football but will setting the other side tonight!
Thanks for all the help. Hopefully I’m rocking tonight.
Need BOM for BA-3 pre
Having difficulty with my Office program and hating Excel anyway. Is there some way I could get a PDF of the BOM list? This looks like the preamp project I need to put in front of a pair of tube mono amps, plus it looks way more cost effective than almost any tube pre project. Thanks in advance.
Having difficulty with my Office program and hating Excel anyway. Is there some way I could get a PDF of the BOM list? This looks like the preamp project I need to put in front of a pair of tube mono amps, plus it looks way more cost effective than almost any tube pre project. Thanks in advance.
I'm tryin......
I'm trying to open the BOM listed with the board over on diyAudioStore. Downloaded but won't let me attach here...keep getting message that it's an invalid file....😕
BA-3 FE as a headphone preamp?
Is there any reason this unit wouldn't make a good headphone pre? I was thinking of adding a jack to the front panel, the same one that's on my O2 desktop version.
Is there any reason this unit wouldn't make a good headphone pre? I was thinking of adding a jack to the front panel, the same one that's on my O2 desktop version.
Very high output impedance for a hp amp. Probably not a good area unless your headphones are 600+ ohm.
The higher the output impedance the greater the voltage drop into low ohm loads. The frequency response will not be flat and it will unpredictable. There will be strange or weak bass.
Generally, we are looking for a 1/10 (or less) ration of output impedance to headphone impedance. With the BA-3 as a hp amp your ratio will 10/1.
The BA-3, with it's 300 ohm-is output impedance is really not designed to drive low ohm loads like headphones. It's designed to drive loads in the 10k-100k range like power amps, etc. Typically solid state headphone amps have output impedances in the single digits.
But you can try it. There will be no harm to your headphones. But it like won't sound good or have enough volume.