If you can get away with a 10K attenuator, I’ve been happy with this one in my BA-3 build. Very beginner friendly to get hooked up. Chicago Electronc Distributors typically has U.S. based stock.
Stepped Attenuator for passive preamp or amps
Stepped Attenuator for passive preamp or amps
Mark,
Using a multimeter or preferably 2 you should be able to compare the resistance readings between each channel as you step through the series ladder arrangement, write down the values as you go.
This should highlight where the fault will be on the affected channel.
If you only have 1 meter then do this for the working channel then repeat the procedure for the other channel. At some point you will get a different or open or closed circuit reading. Keep one meter lead at the GND point and the other lead at what you think is the output (wiper) and turn the shaft one detent at a time and record the resistance value for each step.
Using a multimeter or preferably 2 you should be able to compare the resistance readings between each channel as you step through the series ladder arrangement, write down the values as you go.
This should highlight where the fault will be on the affected channel.
If you only have 1 meter then do this for the working channel then repeat the procedure for the other channel. At some point you will get a different or open or closed circuit reading. Keep one meter lead at the GND point and the other lead at what you think is the output (wiper) and turn the shaft one detent at a time and record the resistance value for each step.
There doesn't seem to be a fault in the attenuator, I thought there was but it checks out. I just did this test and both sides progress from .1 ohms to 16.4K ohms as I turn clockwise, and values match.
I'm feeding it with a Pearl 2 and from there it goes to a crossover in a sub. I've been using another preamp in this spot without a problem. Hooking a source directly to the BA-3 sounds fine.
Could this be ground related? Everything is isolated from the case, same with the Pearl 2.
Edit - I also fed it from different sources and same issue.
Well this has been a lesson in "step away from the soldering iron" when getting frustrated and trying to get a build done by the end of the day (I hate to quit when things aren't working, and my previous builds have gone well).
This morning (I'm off work) I methodically hooked a source to the attenuator and it worked, had both channels, no hum, volume control worked.
Then hooked the attenuator to the stereo-mono switch, put the source into that, worked again. Now I'm putting the source selector switch in line, if that works the build is complete.
This morning (I'm off work) I methodically hooked a source to the attenuator and it worked, had both channels, no hum, volume control worked.
Then hooked the attenuator to the stereo-mono switch, put the source into that, worked again. Now I'm putting the source selector switch in line, if that works the build is complete.
Finally it's working, here it is on its first run next to its cousin F5. First impressions is a very "direct" as opposed to soft or mellow sound, like the F5, and lots of gain. I was a bit over half way on the attenuator and that was plenty. The source is a Pearl 2 that also has quite a bit of gain.
Thanks everyone!
Thanks everyone!
Yes. First, not knowing how a stepped attenuator is wired, and second, getting tired and frustrated and not stepping away and approaching later with fresh eyes. Once I did that, it worked.
cheer up
with mileage , I'm not smarter .... I'm just better in recognizing when short circuit between headphones is too dangerous to proceed
The problem was being off work and having too much time!
Signal chain is now all PassDIY (except when I swap the F5 with the Fisher 400). Having such simple circuits with so few caps in the chain makes for exceptional attack, dynamics, and clarity. I find I don't need as much volume to get a satisfying sound level.
I have just adjusted bias on BA3-pre. Voltage is +-26.5 V. The temperature on heatsink of output transistors is 65 C. Is this considered OK or is it a bit on the high side? ….I assume that junction is well inside the limit. I could reduce voltage to 24V then I would probably get below 60 C on heatsinks.
I think 65 is too high. Is that with lid on or off?
What is the bias you are running at?
nash
What is lid?
Upps…….I just se my error now looking at the schematic again. I have adjusted bias by having 2V over the 22 ohm resistors (R10, R11) so I have double bias current. Backing off to 1V will solve all problems...…...or even 1.5 V.
Are there any advantages running higher bias that specified?
Now I know where the limit is using the small heatsinks……..by accident..
Upps…….I just se my error now looking at the schematic again. I have adjusted bias by having 2V over the 22 ohm resistors (R10, R11) so I have double bias current. Backing off to 1V will solve all problems...…...or even 1.5 V.
Are there any advantages running higher bias that specified?
Now I know where the limit is using the small heatsinks……..by accident..
Not really. Any advantage there might be in decreased distortion can be tuned much more easily and effectively with P3.
I noticed using these Galaxy chassis that there is no galvanic connection from the bottom to the side panels so signal and safety ground is only the bottom. Is that a problem? …..I am more concerned about noise than the safety.
The way the bottom and top is connected to the side panels via the nuts in the rails does not make a galvanic connection when the small screws are in place. At least not in my Galaxy chassis. Something more "violent" has to be done to penetrate the black layer and aluminum oxide layer.
The way the bottom and top is connected to the side panels via the nuts in the rails does not make a galvanic connection when the small screws are in place. At least not in my Galaxy chassis. Something more "violent" has to be done to penetrate the black layer and aluminum oxide layer.
My apologies for such a neophyte question. Is the volume control simply shunted across R1. I have not found a schematic for the build guide. If the volume control was implemented for the full blown BA3 push/pull, would the result simply be an integrated amplifier? Is there a DIY project for building BA3 push/pull as a integrated amplifier. Thank you for commenting.
Last edited: