anyone in NY area have a p2p la2a build?
- Thread starter sr1200
- Start date
Help Support GroupDIY Audio Forum:
sr1200 said:
Skimming the thread, sounds like you had some or all B-/ground floating, so there'd be no current path, thus high voltages to ground, no current means no tube damage.
Seems I see the only problem now is a lack of compression. I don't see a related high voltage mechanism that could affect the T4 in any way, other than C11 shorting and sending voltage through. I'd suspect the T4 (swap sub to see after confirming lack of DC potential from C11, looks like pin 3) or something in the side chain amp.
CJ posted a voltage chart somewhere, I don't see any reference to that in the thread.
My voltages are till totally out of whack and there is current flowing now (and still really high voltages across things). I think im going to swap out the R34 and R36 resistors to try and get the voltage a little lower as well. New tubes should be here soon, and ill use those to test from here on out unless i find something really "DUHHHH!" lol.
Regarding the resistor thats in the schematic but not on the layout, I haven't been able to find anything out about that and if its a T4A ONLY thing or if its needed for both an A and a B.
Regarding the resistor thats in the schematic but not on the layout, I haven't been able to find anything out about that and if its a T4A ONLY thing or if its needed for both an A and a B.
pucho812
Well-known member
am I missing something based on the photos or is r34 not connected to pin 5 of the 6aq5 tube
Yes, theres a purple wire heading down to the top of it.
pucho812
Well-known member
any updates on this?
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Had to go out of town for a few days. But should have replacement tubes in on monday to continue testing.
pucho812
Well-known member
o.k. was wondering if the tubes came in? answers my question. lets see what happens.
K new tubes came in, i notice the new 6AQ5 has almost no heater light, the old one was almost like a light bulb.
Voltages:
at diodes: 357
@R24 (B+) 315
V1
1 - 120.5
2 - 0
3 - 1.07
4 - 6.56vac
5 -
6 - 136.1
7 - 0
8 - 1.3
9 - AC
V2
1 - 64
2 - 5.5
3 - 6.85
4 - 6.56vac
5 -
6 - 240.6
7 - 53.6
8 - 71.5
9 - AC
V3
1 - 308.1
2 - 0
3 - 5.75
4 - 6.56vac
5 -
6 - 307.9
7 - 0
8 - 5.75
9 - AC
V4
1 - 5.25
2 - 5.75
3 - AC
4 - 6.56vac
5 - 315.2
6 - 308.5
7 - 5.25
I did not replace the R34 and 36 to the new ones i got in. Some voltages are looking better others are still ridiculous V3 and 4 are the worst offenders. Im a little concerned with the 5v on pin 1 and 7... shouldn't i have nothing or next to nothing?
Voltages:
at diodes: 357
@R24 (B+) 315
V1
1 - 120.5
2 - 0
3 - 1.07
4 - 6.56vac
5 -
6 - 136.1
7 - 0
8 - 1.3
9 - AC
V2
1 - 64
2 - 5.5
3 - 6.85
4 - 6.56vac
5 -
6 - 240.6
7 - 53.6
8 - 71.5
9 - AC
V3
1 - 308.1
2 - 0
3 - 5.75
4 - 6.56vac
5 -
6 - 307.9
7 - 0
8 - 5.75
9 - AC
V4
1 - 5.25
2 - 5.75
3 - AC
4 - 6.56vac
5 - 315.2
6 - 308.5
7 - 5.25
I did not replace the R34 and 36 to the new ones i got in. Some voltages are looking better others are still ridiculous V3 and 4 are the worst offenders. Im a little concerned with the 5v on pin 1 and 7... shouldn't i have nothing or next to nothing?
replaced 34 and 36 and things didnt get better...
350 after diodes and 304 at B+
v1
1 - 113.6
2 - 0
3 - .96
4 -
5 - (AC)
6 - 133
7 - 0
8 - 1.23
v2
1 - 39.2
2 - 9.02
3 - 8.0
4 -
5 -
6 - 226
7 - 34.5
8 - 47
9 -
v3
1 - 298.6
2 - 0
3 - 275
4 -
5 -
6 - 298
7 - 0
8 - 277
9 -
v4
1 - 165
2 - 278
3 -
4 -
5 - 293
6 - 288
7 - 163
I am completely stumped now, BTW, the 6AQ is now lighting up like a bulb like the old one did... am I just frying these things?
350 after diodes and 304 at B+
v1
1 - 113.6
2 - 0
3 - .96
4 -
5 - (AC)
6 - 133
7 - 0
8 - 1.23
v2
1 - 39.2
2 - 9.02
3 - 8.0
4 -
5 -
6 - 226
7 - 34.5
8 - 47
9 -
v3
1 - 298.6
2 - 0
3 - 275
4 -
5 -
6 - 298
7 - 0
8 - 277
9 -
v4
1 - 165
2 - 278
3 -
4 -
5 - 293
6 - 288
7 - 163
I am completely stumped now, BTW, the 6AQ is now lighting up like a bulb like the old one did... am I just frying these things?
After some more poking and prodding i found another mistake.
::duh::
Voltages are now: 356v after diodes 280 at B+!!! (im ball parking now)
V1
1) 116
2) 0
3) 1.07
4-5) vac
6)121.3
7) 0
8) 1.16
V2
1)104.6
2) 0
3)4.2
4-5) vac
6)228.3
7) 79
8) 109
V3
1) 94.6
2) 0
3) 0.85
4-5)vac
6) 94.6
7) 0
8) .84
V4 (which im excited about)
1) 0
2) 9
3-4)vac
5)96.1
6)117.1
7)0
Gonna pop that t4 in and see what happens no more 300+ volts showing up on tubes!!
::duh::
Voltages are now: 356v after diodes 280 at B+!!! (im ball parking now)
V1
1) 116
2) 0
3) 1.07
4-5) vac
6)121.3
7) 0
8) 1.16
V2
1)104.6
2) 0
3)4.2
4-5) vac
6)228.3
7) 79
8) 109
V3
1) 94.6
2) 0
3) 0.85
4-5)vac
6) 94.6
7) 0
8) .84
V4 (which im excited about)
1) 0
2) 9
3-4)vac
5)96.1
6)117.1
7)0
Gonna pop that t4 in and see what happens no more 300+ volts showing up on tubes!!
ITS ALIIIIVE!!!!!!! ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D
Where am i sending the beers out to?
Where am i sending the beers out to?
You know what is funny... is you have done what I have done many, many times working on broken gear... I ask all over the place... get lots of ideas... and then find the problem myself.
Not to say these guys aren't great help, cause the really are!!!
The beer you owe me, I insist you drink Yourself!
Not to say these guys aren't great help, cause the really are!!!
The beer you owe me, I insist you drink Yourself!
I think I drank to many working on this thing lol. I sincerely thank everyone that had input on this. Feels good to know i didn't waste about a grand putting this thing together. I notice that i cant really crank it like i cranked the original LA2A. Seems when i get to like 40 on the dial im already clipping my converters. Gotta be conservative with this one. (the old one you could crank to almost 70 or 80 if you were burying the needle before you'd get into danger land. Guess thats what you get when components get tired. Do any of the voltages look wonky still? And whenever you guys want that sent to ya, just tell me what you like and where to send it! Cheers!!! (hope im this happy when the baby is born!) hahahaa (wife would kill me if she read this!)
pucho812
Well-known member
congrads on getting the unit in order. you just tackled one of the more harder things to do, making a unit without a circuit board. It always looks right at first until you really get down on it and notice one or two little things and boom now it works. Good job man. You know with my la2a's I swapped the pots for stepped attenuators. Not sure why other then it seemed like a good idea At the time. out of curosity what was the other mistake you found after more poking and prodding?
Pucho, Im actually thinking of doing that as well, now that I see how these pots react. (either that or changing their value...) I can only use about 1/4 of the dial before the level gets so high its distorting or clipping the converter inputs. (unless im really hammering down the compression knob)
To answer your question, when i wired the unit up the first time, I had different grounding points in the case. (similar to the last problem where i put an insulated post where a ground post should be) in this case, the top pin of R3 was no longer making it to ground, which is connected to R36... Insert wire=working unit. I popped in the other tubes i was using and they all work, (and actually sound better) as did the t4b. I'm still trying to figure out if I should put that resistor across pin 3 and 1 on the t4b (2.2Meg) Even in the reissue la2a from UA, i dont see a resistor placed there, and all the pics I've seen of everyones builds, I don't see i there either.
To answer your question, when i wired the unit up the first time, I had different grounding points in the case. (similar to the last problem where i put an insulated post where a ground post should be) in this case, the top pin of R3 was no longer making it to ground, which is connected to R36... Insert wire=working unit. I popped in the other tubes i was using and they all work, (and actually sound better) as did the t4b. I'm still trying to figure out if I should put that resistor across pin 3 and 1 on the t4b (2.2Meg) Even in the reissue la2a from UA, i dont see a resistor placed there, and all the pics I've seen of everyones builds, I don't see i there either.
pucho812
Well-known member
well give it a try and see what's what's. It's a resistor which is what 10 cents at most. so what harm could it really do. try and listen then go from there.
3nity
Well-known member
Im very happy to read this thread im pretty sure it would help me more and more on my la2a build... (to come)
However im a bit scared about the gain on this beast...SR1200 is not the first one i heard talking about how fast it clipps the converters.
Congrats SR1200, btw my wife is expecting very soon too!
However im a bit scared about the gain on this beast...SR1200 is not the first one i heard talking about how fast it clipps the converters.
Congrats SR1200, btw my wife is expecting very soon too!
Hey Congrats!!! 
I should mention that it didn't help that i used a different ratio transformer than the original which added another 3dB of gain onto this thing. But in all honesty, its not a bad thing. My plugins I have to go to like 60GR and 30gain to get the SAME result as the hardware at 30GR and 12gain. Im a little annoyed that the hardware and UAD plugin sound almost identical. lol I still like to twiddle the knobs for real, so I'm still happy.
My suggestions: Keep a print out of either the schematic and or layout (was linked earlier). Cross off each point as you wire it and make sure all your grounds are grounds and all your insulated standoffs are insulated standoffs lol.
I should mention that it didn't help that i used a different ratio transformer than the original which added another 3dB of gain onto this thing. But in all honesty, its not a bad thing. My plugins I have to go to like 60GR and 30gain to get the SAME result as the hardware at 30GR and 12gain. Im a little annoyed that the hardware and UAD plugin sound almost identical. lol I still like to twiddle the knobs for real, so I'm still happy.
My suggestions: Keep a print out of either the schematic and or layout (was linked earlier). Cross off each point as you wire it and make sure all your grounds are grounds and all your insulated standoffs are insulated standoffs lol.
