[BUILD] 1176LN Rev D DIY

[audiosway]

Hi guys, I've tried to be in touch with Hairball through the website but didn't get any reply. Anyone with same issue? Thanks!

I've been in touch with Mike from Hairball. He is really busy and normally takes a day or two getting back to you.

 

[Sputnik]

Hello Everyone,
I bulit two FET/RACK 1176 Rev D compressors. The devices work perfectly except for a strange little anomaly. When I change the output signal level I hear a strange hissing sound. Any idea what could be the problem? Thanks!

 

[noiro]

I have a problem with a 1176D
"The output pot is scratchy at the 18 point and is producing a large amount of subsonic information as well as a large increase of noise and output. Seems that there’s a problem with the sweep in the pot and a 6 db stepped increase in level and noise at sweep noise. " Is there something I can do to resolve that, what could be the problem?

 

[gswan]

Sounds like you have DC across the pot. Check the voltages around the pot in question.
Should be no DC voltage relative to ground on any of the pins.

 

[noiro]

Sounds like you have DC across the pot. Check the voltages around the pot in question.
Should be no DC voltage relative to ground on any of the pins.

Thanks all fine now! I had some flux around C17, always time to learn about cleaning up hey!

 

[midiraven]

After I complete the null adjustment and place the jumper back to "normal" the needle just takes a dive and won't go back up to zero unless I remove the shunt, then the needle returns up to normal. Any input, anyone? Thanks.

 

[home-run]

I have recently completed a build of a Rev D 1176 and are having some issues.

First off, I'm very much an amateur when it come to electronics but have built a few things before so am not entirely stupid!

When I started the calibration process, it went reasonably well but I got frustrated with step 3 (can't get the meter to drop 10dB) so thought I’d try some audio through the unit to see what it sounded like. It didn't seem to be compressing at all and after a while (10 mins or so) the input level suddenly dropped to about half of what I had.

I went back to try and re-calibrate but was having issues there now too.

After doing some reading through this forum I got some ideas but I’m still unsure as how to properly diagnose the problem.

At Q1 the resistors around it, R4, R5, R10, are all reading differently to their actual values, 7.3k, 27k, 270R is what I'm getting, so I'm wondering if the Q1 transistor is the problem. This probably means Q11 should be swapped out as well I think.

I have triple checked that they are in fact the correct resistors, 10k, 27k & 270R and they are

I’d love to hear what the community here thinks, if you can understand my post, so I can remedy the situation.

 

[Ricardus]

You're not really going to be able to read the correct resistor values in circuit. You're going to have to take them out to be completely sure.

I always test every component before I install it, so I know that isn't the issue down the road.

Make sure your process is correct. I built the Hairball, and their calibration process worked. That input signal has to be applied correctly and measured correctly.

Try centering the pots and redo the calibration process a few times. That's what I did with mine and eventually everything worked nicely, and I got really good at the process for future builds.

 

[audiosway]

I'm having a problem with my build that is really odd. I fire it up and the R32 is smoking. The only thing I saw searching was from 2008 when they first went to Rev 2 boards. The output transformer wiring markings were wrong for a short time. I checked my board tonight against the Rev 2 schema and everything looked good. I was just about to start checking voltages but I wanted to see if anyone has run into this recently. I literally just got the boards from hairball a few weeks ago so they are new boards.

 

[Echo North]

I'm having a problem with my build that is really odd. I fire it up and the R32 is smoking. The only thing I saw searching was from 2008 when they first went to Rev 2 boards. The output transformer wiring markings were wrong for a short time. I checked my board tonight against the Rev 2 schema and everything looked good. I was just about to start checking voltages but I wanted to see if anyone has run into this recently. I literally just got the boards from hairball a few weeks ago so they are new boards.

I'd check Q6. It may be bad, you could, at the very least diode test it. Also make sure it's not mounted tight to the PCB.

 

[audiosway]

I'd check Q6. It may be bad, you could, at the very least diode test it. Also make sure it's not mounted tight to the PCB.

Thanks. I have Q6 in a mount so I know it's not tight to the PCB. How would I diode test it? I need to make another parts order so I will probably order another one along with R32. Thanks.

 

[Echo North]

Google test a BJT with a diode tester. There are a million youtube videos that can explain it better than I can here.

 

[audiosway]

Google test a BJT with a diode tester. There are a million youtube videos that can explain it better than I can here.

Thanks Mike. I hadn't had my coffee yet or I wouldn't have even asked. lol.

 

[gswan]

Just a heads up for those following along from home...
Site has been changed so old links will soon go away.

1176 project and info page can be found here now:
https://axtsystems.com/axtsystems/proj_1176.php

 

[JW]

Is the ratio circuit the same between the Mnats rev D and rev J boards?

(Also, I'm gathering that there is no problem powering two Rev D boards with the Mnats little psu?)

 

[guitarrock04]

Seeking help to troubleshoot. MNATS Rev D , no version, dated 10.03.08. Using rotary ratio and meter boards.

Attempting Q-bias, but the trimpot changes nothing through full range of travel. I'm attempting the hairball method, referencing 2.75vac at output - but it doesn't change.

Unit passes signal. I've tried with and without pin 22 grounded. And with the trimmer on ratio board set all the way out (output won't reach 2.75vac with it at mid-travel).

Perhaps noteworthy; the meter does not register anything on VU mode. It works. It reads 0 in GR mode, but nothing when rotary is full CW. (or full CCW, for that matter.)

Any help appreciated

 

[gswan]

First, have you verified all voltages on the transistors and power supply?
Measure the voltage on the trimmer centre pin. Does it change as you turn the trimmer?
If your meter does not register anything in VU mode then it is likely missing internal diodes. You may have to add a bridge (either germanium OA91 or schottky diodes) to the meter terminals. A meter with an internal bridge normally has a diode symbol near the class indicator on the decal.

 

[guitarrock04]

First, have you verified all voltages on the transistors and power supply?
Measure the voltage on the trimmer centre pin. Does it change as you turn the trimmer?
If your meter does not register anything in VU mode then it is likely missing internal diodes. You may have to add a bridge (either germanium OA91 or schottky diodes) to the meter terminals. A meter with an internal bridge normally has a diode symbol near the class indicator on the decal.

Thanks

I've verified the power supply: I have 30v at R87.
Voltages do NOT match, namely Q2 and Q3. However, I anticipated that these require some degree of calibration - which has not been executed.
It's a bear to monitor, but I did confirm that the DC voltage on center pin of trimmer moves. It moves from -1.139v noted on one leg, up to 0vdc as measured on the other as the trimmer screw is turned.

My meter is a salvage deal, and does not have any label, though it wouldn't surprise me if it didn't have diodes. Frankly, in situ, I'll leave it in GR mode anyways (which appears to function, as-is) so I'm likely just to leave it be for now

 

[gswan]

Thanks

I've verified the power supply: I have 30v at R87.
Voltages do NOT match, namely Q2 and Q3. However, I anticipated that these require some degree of calibration - which has not been executed.
It's a bear to monitor, but I did confirm that the DC voltage on center pin of trimmer moves. It moves from -1.139v noted on one leg, up to 0vdc as measured on the other as the trimmer screw is turned.

My meter is a salvage deal, and does not have any label, though it wouldn't surprise me if it didn't have diodes. Frankly, in situ, I'll leave it in GR mode anyways (which appears to function, as-is) so I'm likely just to leave it be for now

The power supply has two rails. +30V and -10V. Check both.
The DC steady-state conditions should match irrespective of calibration. If the voltages on the transistors aren't within about 10% then it indicates that you have a problem. It could be incorrectly oriented devices or wrong component values. There's no point starting calibration until you have the basic circuit in an operational condition.
The trimmer voltage should vary from around the voltages you indicate, from 0V down to about -1.2V. It's there to bias the FET slightly into conduction. However you won;t see anything yet since your build is probably defective in some way.
It's an easy fix to add diodes to the meter. You should do this before calibrating as it will affect the DC reading for the gain reduction by the forward voltage of the diodes. The +4dBu setting is as equally important as the GR setting on the meter for gain staging your signal.

 

[guitarrock04]

Progress..
I finally determined that I'd wired pins 18-22 backward on the main board. Apparently I was looking at it upside down, or something. The screw terminals cover the printed numbers.
I like the hairball method of measuring output voltage as surrogate for VU meter, and that worked just fine.
After more troubleshooting, I figured out another issue with calibrating was because 20:1 (nor slam) do not work. All the other ratios work fine, so I used 12:1 for calibration, rather than the specified 20:1. Not sure yet if this is the switch or if there's an open resistor.