Hey all, so this is my first scratch built pre-amp... I've done re-builds, tweaks and some kits but wanted to do a complete scratch build and the BA-2 was the obvious choice. Blindingly simple, and totally rad. I used the chassis of a beat up old RCA WA-44C Audio generator, gutted and repainted it to give it that old school RCA vibe. I highly recommend this to anyone wanting to delve into a scratch built tube pre... the entire experience was really good, I learnt many many lessons (thanks mostly to Doug williams and the other folk on this forum)... and it has given me the confidence to jump straight into my next scratch build (which is now already 90% complete) an OP-6 clone...
I just wanted to share a few things I discovered on building the BA2 that I think would be helpful... a lot of this stuff isn't really new info, it's just stuff I came across and fixed in the troubleshooting stages...
NOISE: This was my biggest headache, considering the tight confines of the chassis I was using... the first time I put it together it was really bad, hum, crackle and hiss, I went through the forums and asked some questions and then completely rebuilt the unit, and nailed ALL the noise, the thing is DEAD quiet now.... here's what I did:
1: Don't drill and screw down the Power tranny until you have built everything. I built the whole unit then powered it up with the power tranny unscrewed, then, with a mic plugged in, gain turned all way up, headphones on with the volume all the way up, I moved the transformer around, rotating it. The hum level would increase dramatically with a mere 1/2 inch rotation, once I found the sweet spot, I marked and screwed the transformer down.
2: Make sure the power transformer is SECURELY grounded, this goes for the shell of the input transformer too, by grounded, I mean making very firm contact with the chassis. I actually soldered the case of the input transformer to the chassis to be ultra sure.
3: Run a star grounded system... I was fanatical, which was easy with this circuit. Every ground connection has it's own wire going to the star ground point.
4: Run shielded cable... now this you'll want to test. I ran shielded cable for ALL audio runs, but then with the unit powered on I listened as I connected and disconnected the shield wires. I found that running shielded from the input Tranny to the grid of the first tube was essential, got rid of a loud hum, running shielded from the gain pot to the second tube did nothing, so i snipped off the shield wire.
5: Shield the grid pins of the 1620 tubes.... again, test this. Without a shield on V1 I had a nasty buzz... with the shield in place... no buzz. V2 didn't need a shield, but I put one on anyway to match them up looks wise.
Anyway, check the photo's!!
Thanks again to the legends on the forum.
FRONT:
FRONT:
FRONT:
BACK:
FRONT PANEL IN PROGRESS:
TUBE SECTION IN PROGRESS:
TONE AND INPUT CIRCUIT IN PROGRESS:
FINAL GUTS:
TUBE SHIELDS:
FINAL BACK VIEW OF INTERNALS:
RESPONSE CURVES:
TILT EQ CURVES:
And how does it sound?..... fckn SICK!!... I'll be doing some sound clips when i do a shootout with my original OP-6, OP-6 Clone and BA-2 Clone... stay tuned.
I just wanted to share a few things I discovered on building the BA2 that I think would be helpful... a lot of this stuff isn't really new info, it's just stuff I came across and fixed in the troubleshooting stages...
NOISE: This was my biggest headache, considering the tight confines of the chassis I was using... the first time I put it together it was really bad, hum, crackle and hiss, I went through the forums and asked some questions and then completely rebuilt the unit, and nailed ALL the noise, the thing is DEAD quiet now.... here's what I did:
1: Don't drill and screw down the Power tranny until you have built everything. I built the whole unit then powered it up with the power tranny unscrewed, then, with a mic plugged in, gain turned all way up, headphones on with the volume all the way up, I moved the transformer around, rotating it. The hum level would increase dramatically with a mere 1/2 inch rotation, once I found the sweet spot, I marked and screwed the transformer down.
2: Make sure the power transformer is SECURELY grounded, this goes for the shell of the input transformer too, by grounded, I mean making very firm contact with the chassis. I actually soldered the case of the input transformer to the chassis to be ultra sure.
3: Run a star grounded system... I was fanatical, which was easy with this circuit. Every ground connection has it's own wire going to the star ground point.
4: Run shielded cable... now this you'll want to test. I ran shielded cable for ALL audio runs, but then with the unit powered on I listened as I connected and disconnected the shield wires. I found that running shielded from the input Tranny to the grid of the first tube was essential, got rid of a loud hum, running shielded from the gain pot to the second tube did nothing, so i snipped off the shield wire.
5: Shield the grid pins of the 1620 tubes.... again, test this. Without a shield on V1 I had a nasty buzz... with the shield in place... no buzz. V2 didn't need a shield, but I put one on anyway to match them up looks wise.
Anyway, check the photo's!!
Thanks again to the legends on the forum.
FRONT:
FRONT:
FRONT:
BACK:
FRONT PANEL IN PROGRESS:
TUBE SECTION IN PROGRESS:
TONE AND INPUT CIRCUIT IN PROGRESS:
FINAL GUTS:
TUBE SHIELDS:
FINAL BACK VIEW OF INTERNALS:
RESPONSE CURVES:
TILT EQ CURVES:
And how does it sound?..... fckn SICK!!... I'll be doing some sound clips when i do a shootout with my original OP-6, OP-6 Clone and BA-2 Clone... stay tuned.
