[BUILD] 1176 Rev A - Back to the beginning...

[Echo North]

Hi, I finish the build, there is my voltage, cant you help with some tip, for calibrated the unit. Actually, it is not possible to calibrate the Zero ajust for 0.0 Volts across R74.
Thanks
JB

The Rev A you measure across TP10 and TP 11, not R74.  See the guide:

http://www.hairballaudio.com/blog/resources/post/calibration

Mike

Sorry, yes across TP10 and TP11. It is not possible to have a 0,00v?
You cant see the attachement, they have all my voltage. In the Gr meter drvier section everything good. But, in the Gr control amp I have significat difference. Cant you help

Did you match the HFE for Q12/13?

If their HFE is way off that can be the issue.

Mike

 

[Spencerleehorton]

Hi,

Well it seems this build has been going on months now and so many problems!
Have finally wound a same spec transformer and have good signal up to the output pot middle leg.
Testing signal on pin 2 of output XLR I don't seem to have very good sinewave.
If I go easy on the input and output controls I can get a nice wave but there seems to be way too much output!
Plugging in the unit and putting a bass guitar in I don't get very much level out and I don't seem to be able to get it too compress?
Putting the bass into a preamp then into the 1176 gives loads of level and compression, but quite distorted sound, but sound is workable for a nice lemme sound!
Can't seem to get the GR meter onto 0db with the trimmer?
This unit is definetly the most frustrating unit I've built so far!!!!

Spence.

 

[Spencerleehorton]

Hi,

I have changed around the feedback winding and get slightly better wave form now but GR I can't seem to adjust where it needs to be?
I've put a 10k pot on the 8.2k resistor to adjust +4 but this doesn't seem to help get the GR trim any better?
I am getting a pretty good sound out of the unit now and I think also putting in the 10k on the source leg of Q1 will help improve distortion.
Just need to sort the meter, I think the meter is the wrong meter and I might need to implement an amp for it which will also help reduce distortion.

Spence.

 

[Spencerleehorton]

Hi,

I have been told that putting a 10k on the source let of Q1 down to gnd will result in much less compression?
Could someone explain this please?

Regards

Spence.

 

[Echo North]

Hi,

I have been told that putting a 10k on the source let of Q1 down to gnd will result in much less compression?
Could someone explain this please?

Regards

Spence.

Have a look at the Rev D schematic or later and the Rev A schematic.  You'll see the Rev A is missing the 10K resistor.  The resistor will help prevent early saturation of the Q1 FET.

 

[Spencerleehorton]

I think in rev A which ive got the 10k will reduce the compression down to 3:1 being the max you can get out of it as there is the 27k R5.
There are quite a few other things going on in the rev d, i dont think just putting in a 10k will do anything but just reduce the compression.
Im going to try a few other things which hopefully should be better.

Spence.

 

[Echo North]

Compression is a ratio not an absolute  value.  It's controlled by the ratio resistor ladders DC threshold vs AC sidchain amplification.

 

[Spencerleehorton]

I was  meaning about r5 27k then putting in 10k would be a potential divider of 3:1 less, which would end up with 3 times less compression right?

 

[Echo North]

I was  meaning about r5 27k then putting in 10k would be a potential divider of 3:1 less, which would end up with 3 times less compression right?

Nope.  That's not how it works.

I'm out now.  I can post a link later.

 

[Echo North]

Total gain reduction at a single given point is not ratio.  Ratio is the change between to levels vs the original uncompressed signal.

Some fantastic reading:
http://prorecordingworkshop.lefora.com/topic/3841871/All-Buttons-In-1176

Mike

 

[Spencerleehorton]

Hi,

I think there is some difference in what your talking about and what I'm saying.

The compression ratio is dependent on the side chain gain and DC conditions and the push buttons on the front select the ratio by changing the gain and DC off-set of the side chain..

All I am saying is that, with the 10k in, in the limit, with the FET saturated, the max compression ratio that you can get is 3:1. Now that applies to this version of the 1176 (Rev A). The link you sent refers to the other version of the 1176 (Rev D) where there is a 10k resistor in the FET source BUT it is by-passed (AC-wise) by a 180ohm, and that is an entirely different matter.

Do we have an understanding now?

Regards

Spence.

 

[Echo North]

Then try a lower value like 180, pop a pot in there, or don't do anything at all.  There is a whole discussion, started by Gus IIRC, related to adjusting the source resistor. That's why it was added as an OPT resistor on the FET/500 Rev A.  Unfortunately, I don't have the time to dig for it, you might be able to find it with a search.

Mike

 

[Spencerleehorton]

I'm sorry if you feel I have been awkward this wasn't my intention, I am really in my DIY, and love the process of learning. From not knowing anything to then light bulb moments I find enthralling.
I haven't followed the normal route for this unit I know but I have now arrived at a place where I have a great sounding unit which I have wound my own output txf and used some other modifications to get around some funky things within the Rev A design.
Hopefully if anyone else goes down the same route as me I can help them.

Regards

Spence.

 

[Spencerleehorton]

Spoke to soon! I'm getting ultrasonic  frequency from somewhere? Is there other areas in the circuit that need screening that aren't documented?
Shortened the txf wires and changed the phase of one, all fine, sounds great!!!! Finally.

Spence.

 

[Spencerleehorton]

my final points about the rev A version:
R74 in rev A version should be left out and link put in and 2.7M across TP10 to TP11 then setup as per Mnats videos.
mine finally sounds very nice indeed!!!

regards

Spence.

 

[blackartmixing]

so after my last post and many attempts to fix myself i finally took my unit to a "pro" guy and the next day it was fixed due to the output pot being faulty.  in a way i'm glad it wasn't my fault as i couldn't find anything wrong when i went back numerous times to check the wiring etc.  So today i've calibrated and all seems to be working great.....except one thing.  maybe its just cosmetic but the needle doesn't return to 0 even with the fastest release setting and not much compression.  its just really slow .  when i turn the release to slow its even slower.  Is this normal with these builds?

 

[blackartmixing]

Hi, anyone any idea about the release issue i have?  can i assume its another faulty pot do you think? 

 

[mnats]

maybe its just cosmetic but the needle doesn't return to 0 even with the fastest release setting and not much compression.

Is it just cosmetic or can you hear it?

Hi, anyone any idea about the release issue i have?  can i assume its another faulty pot do you think?

When troubleshooting you should assume nothing.

 

[blackartmixing]

maybe its just cosmetic but the needle doesn't return to 0 even with the fastest release setting and not much compression.

Is it just cosmetic or can you hear it?

Hi, anyone any idea about the release issue i have?  can i assume its another faulty pot do you think?

When troubleshooting you should assume nothing.

ok so i tested a bit and really i can't hear the release  doing anything to the signal.  Any suggestions or things to test?

 

[mnats]

ok so i tested a bit and really i can't hear the release  doing anything to the signal.  Any suggestions or things to test?

The meter circuit only reports what the GR Control Amp is doing to the gain. The attack and release circuit along with C22 sets the time constant. So if the limiter itself is working but the meter isn't correctly reporting what the sidechain is actually doing then there must be something wrong with the GR Meter Driver circuit. But it's hard to tell from your description if the limiter itself is working correctly. It seems impossible that the meter would show a slow release but the audio level recovers at a different rate.

If the problem is simply that the release time itself is too slow (audio is affected) then there must be a wiring or component issue with the release pot because this part of the circuit is the only way C22 can discharge at a varying rate.