TL Audio VI1 Schematics anyone have them!?

[faelucho]

Hi!
I just got a Vl1-8 used to setup with my desk as inserts for summing. All seems to be working properly, but I do notice a slight imbalance between left and right channels if using as stereo pairs. For example, channels 7 and 8, while sending a stereo vocal track panned dead center seems to sound a little tilted to a side, and this changes in all 4 paris.

Anyone have experience with this? I noticed inside it has eight small white flat knobs that seem to be adjustable. In my case all of them appear to be at different positions, anyone know about this?

I'm guessing it could be the BIAS for the tubes, but wanted to ask before trying to change anything. I've read the manual but can't seem to find any info about this.

What I don't get is that as it has 4 tubes, divided into two channels, how it level can differ from one side to the next.

well anyways, thanks very much for your help!

 

[scott2000]

How much imbalance are you getting?

 

[faelucho]

Are the +4/-10dB jumpers on the pcb all set the same?

Yes, all of them are set to +4. The difference between channels seems ot be about a couple of dBs, testing with a 1Khz tone generator in protools and reading it back with a meter

 

[scott2000]

Yes I caught the "little off" and revised the question. Have you tried swapping tubes around to see if the issue follows them?
Those trimmers are for balancing the output Hot and cold I believe. Like you want the positive and negative waveforms to be the same... Maybe that's the wrong terminology...

 

[faelucho]

Swapped tubes but seems to be the same. I'm hearing a little noise sporadic like air on one of the channels though, moving the tube a bit makes super loud noises and then fixes itself, I'm guessing the tube is not seated properly or the base is damaged?

But the difference between changing tubes in the stereo field is the same between channels 5-6 and 7-8. Are the trimmers supposed to be the same position?

 

[scott2000]

Swapped tubes but seems to be the same. I'm hearing a little noise sporadic like air on one of the channels though, moving the tube a bit makes super loud noises and then fixes itself, I'm guessing the tube is not seated properly or the base is damaged?

But the difference between changing tubes in the stereo field is the same between channels 5-6 and 7-8. Are the trimmers supposed to be the same position?

Could be goofy solder joints under the tube sockets or dirty pins... Obviously moving them enough to cause things to disconnect will cause noises but it's unclear how much movement you are talking about.
The trimmers are usually safe set in the middle of their rotation but that's not as accurate as measuring your hot and cold output pins and adjusting to same voltages if I have this right.

Also, if you have those baby blue rubycon electrolytics in there, they for sure can get tired from my experience and sometimes will even bulge for you.

So the channels stay with the same behavior even when swapping tubes? For example channel one is 2dB quieter than channel 2 and channel 3 is 4db quieter than channel 4, but when you swap channel 1/2 tube with channel 3/4 tube, channel 1 stays 2dB quieter than channel 2, not 4dB quieter?

 

[scott2000]

The output trims really should not be needed. There are many dodgy "electronic balanced outputs" where loading is critical. Center "should" be an excellent trim. Some rainy day you could run a 400Hz tone through at some convenient level and put a voltmeter to the outputs. The ACV pin 1 to pin 2, and pin 1 to pin 3, should be very similar. Within 10%. Don't see how it could need 1% trim.

From when PRR responded to my similar question about the trims in the Indigo mic pre. I knew it was here somewhere...

 

[faelucho]

From when PRR responded to my similar question about the trims in the Indigo mic pre. I knew it was here somewhere...

Thanks, makes since, as I~ tried moving them a bit and noticed no clear changes, so I will set them all the same in the middle then.

So the channels stay with the same behavior even when swapping tubes? For example channel one is 2dB quieter than channel 2 and channel 3 is 4db quieter than channel 4, but when you swap channel 1/2 tube with channel 3/4 tube, channel 1 stays 2dB quieter than channel 2, not 4dB quieter?

Exactly! I just tried balancing the stereo image in protools using a trim plugin and an analyzer, and all pairs of channels have different discrepancies.

1_ +4 dB. 2_ -0.2 dB
3_ -0.5 dB. 4_+0.3 dB
5_ -0.1 dB. 6_+0.5 dB
7_ +0.4 dB. 8_ -1 dB

This gets all the pairs sounding the same and the mono signal dead center. So I´m guessing maybe is the tube response or some component somewhere, but its definitely not the same difference between all of them. I have to say, this unit I bought has different tubes in all 4 pairs, so I´m guessing its normal that some pairs run hotter than others, but if I swap them the difference stays the same. This makes me think that it has to do with the unit itself and not the tubes

 

[scott2000]

but if I swap them the difference stays the same. This makes me think that it has to do with the unit itself and not the tubes

Have you verified your chain outside of the unit just to rule that possibility out?

 

[faelucho]

Have you verified your chain outside of the unit just to rule that possibility out?

Hi! Sorry I never got back with news, it has been working fine until now, I just measured the imbalances and set a trim plugin before the summing output of the DAW. It’s all working properly and I set the trims to the same position.

I’m having a different problem now, channel 2 suddenly stops passing signal after a while, and as I know channels 1 uses the same tube In guessing it was the base of the tube.

So I’ve swapped in a new tube just in case and cleaned te pins, that seems to do the job but after a while it goes out again.

I’m not sure if it could be the tube base itself? Should I clean it directly? I just cleaned the tubes pins before.

Or is there a component I should be checking for?

Thanks again.

 

[scott2000]

Maybe use a chopstick or something and poke around inside to see if you can duplicate the issue.
Outside of that, you can trace the signal to see where you're losing it. Maybe check the ribbon cable as well. They can get goofy sometimes

 

[cyrano]

In case you're still looking for the schematics, I've uploaded them here:

https://groupdiy.com/threads/tl-audio-vl1-schematics.84934/

 

[faelucho]

Maybe use a chopstick or something and poke around inside to see if you can duplicate the issue.
Outside of that, you can trace the signal to see where you're losing it. Maybe check the ribbon cable as well. They can get goofy sometimes

Thanks, good ideas!

 

[faelucho]

In case you're still looking for the schematics, I've uploaded them here:

https://groupdiy.com/threads/tl-audio-vl1-schematics.84934/

Thanks a lot, will have a look at them

 

[scott2000]

If something happens, they are also in the TL Audio folder.. 2nd page
https://groupdiy.com/threads/tl-audio.44989/page-2