Avalon VT 737 sp

[TheseGoToEleven]

1k hz sinewave at 0db +4dBU out
i measured in ACV, maybe thats the problem?
i will try again with a 100hz sinewave

4,5 and 0,05 for the 100hz sinewave

The audio signal (100 Hz sine wave) should always be measured as AC volts. Assuming this last set of measurements is accurate, it would seem to indicate that the signal is getting lost somewhere in the first stage of tube amplification, which for line input is tube V2. There could be a problem with the tube, tube socket, solder joints, or some other component on the tube card. That stage of amplification doesn't involve electrolytic capacitors, just one of the big white ones (C2) on the tube card.

And of course power supply, if that isn't working consistently.

Edit: Correct big white cap on the tube board for tube V2 is C2. C8 is used by tube V3.

 

[TheseGoToEleven]

Ok i changed all the caps on the 7374, plugged everything back in, forgotto put in the tubes and srarted the avalon
as soon as i turned on the power switch sparks came out the device, r19 on 7372 died, gonna replace the different caps and order a new resistor

Ok wow, there was no need to do anything to those cards until the original problem was found. The 7374 is the compressor so it wasn't even in the signal path. And the 7372 was providing signal to the gain knob so seemed to be working. But I guess now you have a new problem to solve.

 

[punkt]

Ok wow, there was no need to do anything to those cards until the original problem was found. The 7374 is the compressor so it wasn't even in the signal path. And the 7372 was providing signal to the gain knob so seemed to be working. But I guess now you have a new problem to solve.

Puncho mentioned to change the caps on the 7372, thought if i am already onto it, i can change all of them on every card.

am thinking the short ahppend, because i didnt placed the 7373 in correctly, i hope thats the problem

 

[punkt]

Ok wow, there was no need to do anything to those cards until the original problem was found. The 7374 is the compressor so it wasn't even in the signal path. And the 7372 was providing signal to the gain knob so seemed to be working. But I guess now you have a new problem to solve.

yea r19 blew, because i didnt fitted the cards exactly in the right slot

 

[punkt]

The audio signal (100 Hz sine wave) should always be measured as AC volts. Assuming this last set of measurements is accurate, it would seem to indicate that the signal is getting lost somewhere in the first stage of tube amplification, which for line input is tube V2. There could be a problem with the tube, tube socket, solder joints, or some other component on the tube card. That stage of amplification doesn't involve electrolytic capacitors, just one of the big white ones (C8) on the tube card.

And of course power supply, if that isn't working consistently.

I attached a picture of my tubecard in a post before, u sure the problem is within tubev2,because the same issue appears for mic input
eitherways whats to test on the tubecard, resistors seemedto be fine crossreferncing the colorcodes with each other

 

[pucho812]

yea r19 blew, because i didnt fitted the cards exactly in the right slot

careful with that ax Eugene. One thing I always hated was removing and putting back on modules. Luckily the Avalon stuff has such high tolerances, it's hard to do that. If the screw holes do not line up, the module is in wrong. We never powered modules without the screws firmly in place on any daughter card.

I will make the offer again, If you get the unit to me, I will get it working for you and even do a write up of what went on so we all can learn some stuff. I did suggest a recap as I do that with any 737 that comes it. Most of them are due just from age.

 

[punkt]

careful with that ax Eugene. One thing I always hated was removing and putting back on modules. Luckily the Avalon stuff has such high tolerances, it's hard to do that. If the screw holes do not line up, the module is in wrong. We never powered modules without the screws firmly in place on any daughter card.

I will make the offer again, If you get the unit to me, I will get it working for you and even do a write up of what went on so we all can learn some stuff. I did suggest a recap as I do that with any 737 that comes it. Most of them are due just from age.

Haha, yea the new resistor and desolderpump arrive tommorow, i will replace all the other caps and will give an update

yea i didnt lined up the holes, that was my bad, just was excited to see if recapping helped

i really appreciate it, but unfortunately shipping to the us is hella expensive 150€ one way

any other suggestions what tocheck, if recapping doesnt fix the problem? studied all the other threads, seems i got a older unit, cause r19and r18 are at 10ohms, didnt find any infos what to check on the tube card tho, resistors seem to be fine, since this problem re-occured a couple times and dissappeard after a while, i am starting to think it might be a bad connection somewhere

 

[TheseGoToEleven]

yea i didnt lined up the holes, that was my bad, just was excited to see if recapping helped

Yeah I get that. You were going to have to recap anyway. While you're waiting for parts, unplug the power supply harness that has the 7 colored wires and check those power supply voltages again. When sparks fly you can get power supply damage so make sure the voltages are all correct.

I would also suggest testing the motherboard for shorts before plugging the harness back in.

resistors seem to be fine, since this problem re-occured a couple times and dissappeard after a while, i am starting to think it might be a bad connection somewhere

My next question was going to be trying a sine wave into the mic input or instrument input to see whether tube V1 amplification failed. (Only mic or instrument input uses tube V1.) If the signal gets lost there too then the fault may not be in the individual tube stages but a power supply issue.

Solder point T9 is the input signal to the tube V1 amplification stage.
Solder point T8 is the output signal from the tube V1 amplification stage.

 

[punkt]

Yeah I get that. You were going to have to recap anyway. While you're waiting for parts, unplug the power supply harness that has the 7 colored wires and check those power supply voltages again. When sparks fly you can get power supply damage so make sure the voltages are all correct.

I would also suggest testing the motherboard for shorts before plugging the harness back in.


My next question was going to be trying a sine wave into the mic input or instrument input to see whether tube V1 amplification failed. (Only mic or instrument input uses tube V1.) If the signal gets lost there too then the fault may not be in the individual tube stages but a power supply issue.

Solder point T9 is the input signal to the tube V1 amplification stage.
Solder point T8 is the output signal from the tube V1 amplification stage.

ehh how do ido that, like do i have just to plug in my line cable into the mic slot and send a sine from my daw?

psu voltages seem to be fine tho

 

[pucho812]

ehh how do ido that, like do i have just to plug in my line cable into the mic slot and send a sine from my daw?

psu voltages seem to be fine tho

Seem fine and measure fine are two different things. I have seen many things that were ok until measured. Best to be sure

 

[punkt]

Seem fine and measure fine are two different things. I have seen many things that were ok until measured. Best to be sure

i measured them ^^

 

[punkt]

n

Yeah I get that. You were going to have to recap anyway. While you're waiting for parts, unplug the power supply harness that has the 7 colored wires and check those power supply voltages again. When sparks fly you can get power supply damage so make sure the voltages are all correct.

I would also suggest testing the motherboard for shorts before plugging the harness back in.


My next question was going to be trying a sine wave into the mic input or instrument input to see whether tube V1 amplification failed. (Only mic or instrument input uses tube V1.) If the signal gets lost there too then the fault may not be in the individual tube stages but a power supply issue.

Solder point T9 is the input signal to the tube V1 amplification stage.
Solder point T8 is the output signal from the tube V1 amplification stage.

recapped couple more caps, will do the rest tommorow when the desolderpump arrives, couldnt got any hole clean, soldered the caps on top of the pcb, not the prettiest job, but will do its job ,
no readings on t8 or t9, but full volume now on mic channel * Great Success, Very Nice!*


still quiet output on line and dunno if that was always the case, but the signal is panned to the left coming out, but that might be because on the send track

discovered new strange behaviour, when turning on the phase, the meter maxes out and there is a low rumble sound, almost like a lowpassed kick

 

[TheseGoToEleven]

ehh how do ido that, like do i have just to plug in my line cable into the mic slot and send a sine from my daw?

Don't do that because if you accidentally turn on phantom power you might damage something. If nothing else, you could play the sine wave on a speaker and place the mic next to it. If there are no readings at T8 or T9, make sure you are measuring AC not DC.

 

[punkt]

Don't do that because if you accidentally turn on phantom power you might damage something. If nothing else, you could play the sine wave on a speaker and place the mic next to it. If there are no readings at T8 or T9, make sure you are measuring AC not DC.

did that, didnt turn phantom power on, that much i know

yea no readings with ac, but as i already stated, mic channel works again after recapping couple more caps

 

[pucho812]

I didn't realize you used euro's as your currency. Then yes do not ship it to me as I am in the U.S.A. But all good.

Sounds like a recap is putting you on the correct path.

 

[TheseGoToEleven]

did that, didnt turn phantom power on, that much i know

yea no readings with ac, but as i already stated, mic channel works again after recapping couple more caps

If mic channel is working then there has to be a signal at T8 and T9. You are measuring T8 and T9 near the gain knob, right? Not 8 and 9 near the XLR?

I hope you are not sending +4 dBu to the mic input, or for sure it would distort. Probably should be more like -50 dBu.

Also, I just looked up your multimeter. When measuring AC with the 200V range setting, it is only accurate to 100mV which is not very helpful. It might say no signal when there is actually 25mV present, for example.

Also the multimeter's frequency response is only to 40 to 400 Hz so it's good that you are now using 100 Hz not 1000 Hz.

 

[pucho812]

Avalon test procedure would be between -30dBu and -20dBu at 1K sinewave for mic input. It would always be followed with an actual condenser mic.

 

[TheseGoToEleven]

Avalon test procedure would be between -30dBu and -20dBu at 1K sinewave for mic input. It would always be followed with an actual condenser mic.

That sounds even better. I have to wonder about the measurements being made since it doesn’t make sense that mic input makes it through the Avalon but no signal is present at the output of the V1 tube amplification stage (solder point T8).

 

[pucho812]

That sounds even better. I have to wonder about the measurements being made since it doesn’t make sense that mic input makes it through the Avalon but no signal is present at the output of the V1 tube amplification stage (solder point T8).

I concur

 

[punkt]

I concur

Eureka, my avalon works again, line and mic, rumble noise when pressing in phase also disappeard

issue lied within in the 7372, must been one of the caps on the left