Here are some pics of the bad channel. My next step is to recheck all of the resistors to make sure none are faulty and then check the traces for continuity to rule out a board defect. I reflowed the board again, checked the output coupling cap and it tested fine. Continuity on both the inputs and the outputs from the bad side to the test set up were also good. If all goes well on the resistor recheck and board trace check, I'll retry it again and if she she still refuses to sing I'll try replacing Q3 and Q4 since I have spares. I didn't see any gross screwups on the installation just a lot of dust from sitting in the garage for 2 years. If you see anything I screwed up please let me know.
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to PJN #2041
Hello PJN,
the values over the bias resistors of your 'bad channel' let me assume, that on the
board is everything o.k..
I would search for bad contacts/solderjoints at the volume pot, RCAs,....
before I would desolder the JFets or Mosfets. Measure resistance from RCA (hot / mid contact to the board input for low resistance - if volume pot is at full vol).
I would check the same for the output.
But I can be wrong
Greets
Dirk
Hello PJN,
the values over the bias resistors of your 'bad channel' let me assume, that on the
board is everything o.k..
I would search for bad contacts/solderjoints at the volume pot, RCAs,....
before I would desolder the JFets or Mosfets. Measure resistance from RCA (hot / mid contact to the board input for low resistance - if volume pot is at full vol).
I would check the same for the output.
But I can be wrong
Greets
Dirk
Success, I must have had a bad mosfet, replaced them on the bad channel with spares that I had and presto, music plays. I just bought a transistor tester to hopefully avoid this situation in future builds. Have it playing through an Aleph J in my garage and I'm impressed. It does have lots of gain which is what I wanted so it will be good with my M2 and F4. Now it's time tp put it in a proper case and off of the plywood test platform.
Has anyone used a balance pot with your preamp build, it is something that would be handy for me with some room setups. If you did what did you use and where did you get it, all I can find is guitar blend pots that don't look very high quality.
Has anyone used a balance pot with your preamp build, it is something that would be handy for me with some room setups. If you did what did you use and where did you get it, all I can find is guitar blend pots that don't look very high quality.
I am going to use one. It’s a very cool „design“ from australia: ESP - A Better Volume Control
Ah, this I haven‘t decided yet.
I‘ll start top to bottom: since I have a elma relay attenuator—as attenuator—I want to see if I can populate another one to become linear (by asking the seller and his source)...
If this doesn‘t work, I‘ll prototype with a Piher 25K (already have it, and right now I haven’t found anything else...
I also was considering to build myself a ladder specifically for the balance, but then I won‘t need the aforementioned network ... and that’s lotsa work...)
Or I couls sink my frontplate-design and go with a slider (which would have to be found)
I‘ll start top to bottom: since I have a elma relay attenuator—as attenuator—I want to see if I can populate another one to become linear (by asking the seller and his source)...
If this doesn‘t work, I‘ll prototype with a Piher 25K (already have it, and right now I haven’t found anything else...
I also was considering to build myself a ladder specifically for the balance, but then I won‘t need the aforementioned network ... and that’s lotsa work...)
Or I couls sink my frontplate-design and go with a slider (which would have to be found)
I used two 10K stepped attenuators like these. One on each chanel.
10KAX2 DALE 4*24 Step Attenuator Volume Potentiometer Dual-10K Ladder Type | eBay
(Other types and suppliers avaliable.)
I’m about to embark on building this preamp and have a couple of questions that I hope someone can answer.
1. I have matched Toshiba 2SK170/2SJ74 with an Idss 10.85. I know the when I asked about using these in my M2C it was recommended that I use 15ohm resistors in place of the 10ohm in the schematic. Should I do the same with the BA-3 and use 15ohm resistors in R3/4?
2. All I have are 100k ohm pots and attenuators. Is 100k ohm okay to use?
1. I have matched Toshiba 2SK170/2SJ74 with an Idss 10.85. I know the when I asked about using these in my M2C it was recommended that I use 15ohm resistors in place of the 10ohm in the schematic. Should I do the same with the BA-3 and use 15ohm resistors in R3/4?
2. All I have are 100k ohm pots and attenuators. Is 100k ohm okay to use?