[BUILD] New FET/RACK Official Help Thread - Please read first post!

[alex_dempsey]

What about the output between + and -    ?

Mike

Im reading about 8.4VAC between the + and - on the output XLR.

 

[Echo North]

Im reading about 8.4VAC between the + and - on the output XLR.

All sounds great.

Try setting your QBias again. Any luck?

 

[alex_dempsey]

All sounds great.

Try setting your QBias again. Any luck?

Nope. The Q-Bias adjustment still has no effect on the voltage reading across the output test points.

 

[Echo North]

Nope. The Q-Bias adjustment still has no effect on the voltage reading across the output test points.

What is you DC V at the gate of Q1 from one end of the QBias trimmer to the other?

Mike

 

[alex_dempsey]

What is you DC V at the gate of Q1 from one end of the QBias trimmer to the other?

Mike

AHHHHH!! I never put in Q1!!!! I bet that will solve all my problems!!

 

[scott2000]

AHHHHH!! I never put in Q1!!!! I bet that will solve all my problems!!

Where might I find one of these Q1s?

LOL

 

[alex_dempsey]

Where might I find one of these Q1s?

LOL

Well it worked!! Thanks so much for the help. I have everything calibrated and didn't run into any other big issues.

The only issue I have now is that the gain nobs are very very sensitive that I think is definitely unnatural. Any ideas of adjustments or places to check? Sounds like I might have a wrong resistor someone but not sure where it might be. Any ideas?

 

[Echo North]

Well it worked!! Thanks so much for the help. I have everything calibrated and didn't run into any other big issues.

The only issue I have now is that the gain nobs are very very sensitive that I think is definitely unnatural. Any ideas of adjustments or places to check? Sounds like I might have a wrong resistor someone but not sure where it might be. Any ideas?

We've talked about the Rev A being really hot on the last page or two. You can turn down your clip gain, or I posted a 4 resistor mod to fix it.

Mike

 

[alex_dempsey]

We've talked about the Rev A being really hot on the last page or two. You can turn down your clip gain, or I posted a 4 resistor mod to fix it.

Mike

Thanks Mike!

Is the mod just in the forum or is it posted somewhere on the site?

Alex

 

[Echo North]

Thanks Mike!

Is the mod just in the forum or is it posted somewhere on the site?

Alex

https://groupdiy.com/index.php?topic=63600.msg870974#msg870974

I would suggest 10x.

So 47K would become 470K.

 

[cdeboda]

I swapped out those four ac section resistors on the ratio board with 10x the values. Found it to be impossible to get any reasonable amount of gain reduction and very difficult to calibrate. So I swapped them out again with 5x the original values (two resistors each and a bit of creativity to get the values) and it feels MUCH better. No more carefully blowing on the pot at 7o’clock to dial in some GR.

Still having a bit of trouble calibrating the tracking adjust, however. It’s just short of showing -10dB at the end of the trimmers rotation. I’ve ordered a 2.5k trimmer to swap in - hopefully that’ll do it. This of course was much further off with the 10x resistors. Any insight on this?

Measured the compression curves as well - pictures to follow. Found it interesting that the ratio selection (at least on my unit) doesn’t actually change the threshold like in the classic 1176 compression curves we’ve all seen. Any idea why?

 

[cdeboda]

All four ratios begin compression at about the same threshold, unlike the compression curves I’ve seen and heard in these units. Not an issue, just struck me as odd.

 

[cdeboda]

And just for funzies:

Some interesting knees in some of those combinations.

 

[Echo North]

I swapped out those four ac section resistors on the ratio board with 10x the values. Found it to be impossible to get any reasonable amount of gain reduction and very difficult to calibrate. So I swapped them out again with 5x the original values (two resistors each and a bit of creativity to get the values) and it feels MUCH better. No more carefully blowing on the pot at 7o’clock to dial in some GR.

Still having a bit of trouble calibrating the tracking adjust, however. It’s just short of showing -10dB at the end of the trimmers rotation. I’ve ordered a 2.5k trimmer to swap in - hopefully that’ll do it. This of course was much further off with the 10x resistors. Any insight on this?

Measured the compression curves as well - pictures to follow. Found it interesting that the ratio selection (at least on my unit) doesn’t actually change the threshold like in the classic 1176 compression curves we’ve all seen. Any idea why?

Were Q12-Q13 matched well?

I still have to fully test the mod, but it my brief test I didn't experience anything like that and those resistors shouldn't have an effect on that.

I'll try to get some testing in later this week.

Mike

 

[Echo North]

All four ratios begin compression at about the same threshold, unlike the compression curves I’ve seen and heard in these units. Not an issue, just struck me as odd.

I've done a lot of testing on all of that and I think a lot is dependent on the input level and amount of compression.

 

[Echo North]

Here is one I plotted a while back for reference.

 

[alex_dempsey]

https://groupdiy.com/index.php?topic=63600.msg870974#msg870974

I would suggest 10x.

So 47K would become 470K.

Hi Mike,

So I'm actually having a different problem than mentioned before. Its not really that the input is too hot its a little different. On GR mode, the meter is pinned to 0 anytime I go above like 48 on the input gain. On the +4 setting, with the output nob at unity, the input nob needs to be cranked to almost 0 for the meter to get back to unity. And its not a smooth increase in gain it spikes and jumps a bit. I'm not totally sure I did the final step of calibration correct but this doesn't just sound like a calibration issue to me. Any ideas of where to start looking?

I referenced a working black face 1176 to make sure I wasn't crazy lol.

Thanks!

- Alex

 

[Echo North]

Hi Mike,

So I'm actually having a different problem than mentioned before. Its not really that the input is too hot its a little different. On GR mode, the meter is pinned to 0 anytime I go above like 48 on the input gain. On the +4 setting, with the output nob at unity, the input nob needs to be cranked to almost 0 for the meter to get back to unity. And its not a smooth increase in gain it spikes and jumps a bit. I'm not totally sure I did the final step of calibration correct but this doesn't just sound like a calibration issue to me. Any ideas of where to start looking?

I referenced a working black face 1176 to make sure I wasn't crazy lol.

Thanks!

- Alex

Not enough info. No idea what your input level is or if GR is enabled. If GR enabled you'd have to crank your input that high. Eventually the input gain levels off between increasing signal and gain.

The beginning, of the turn on the input pad will spike. It's not a volume pot, it's a 35ish dB variable pad. So it has an on/off point, it's a little different than the originals which used a very unique and hard to replicate input pad, at least that early turn smoothness. However, it happens only at the start around 48, some place you normally wouldn't be, especially with that mod in place or on a stock D/F.

Mike

 

[alex_dempsey]

Not enough info. No idea what your input level is or if GR is enabled. If GR enabled you'd have to crank your input that high. Eventually the input gain levels off between increasing signal and gain.

The beginning, of the turn on the input pad will spike. It's not a volume pot, it's a 35ish dB variable pad. So it has an on/off point, it's a little different than the originals which used a very unique and hard to replicate input pad, at least that early turn smoothness. However, it happens only at the start around 48, some place you normally wouldn't be, especially with that mod in place or on a stock D/F.

Mike

With the meter set to GR, I have to drop my input nob all the way down to 48ish (7 o'clock) to keep the meter from being pinned at zero. So it seems like there is way too much input gain getting into the circuit somewhere. When I have the input and output nobs set to 24, the GR meter is all the way pinned to the left. When the meter is set to +4, the input nob has to be cranked all the way up to almost zero (5 o'clock), with the output nob at 24, to get the meter to read unity gain.

I'm just running the 1k signal through the circuit to run some tests.

Alex

 

[Echo North]

With the meter set to GR, I have to drop my input nob all the way down to 48ish (7 o'clock) to keep the meter from being pinned at zero.

By zero, I assume you mean pinned left? -20?

That's been discussed in this thread in the last few pages. The rev A input is hot, twice as hot as the D or F. In addition, our TPad is hot so that makes it more obvious. The UREI TPad had a real weird hard to replicate taper. You can turn down the amount of signal you send to the unit, or you can do the 4 resistor mod we posted about a few posts ago. That lower the amount of gain hitting the sidechain.

If I understand you correctly, turning down your clip gain, or doing the mod, would make the unit behave like you expect.

Mike