All things G1176 - the new "repost" thread.

[fum]

Ok, found the problem and fixed it. was a short between two pins of Q3.

Even tho it didn't look shorted, it was =). I found it by measuring resistance across the resistors, and in this case, the 560K resistor near Q3 was reading 2K. I started removing components that connected via trace to this resistor, and I'd removed all but Q3. Once I continuity checked the pins of Q3, I found the short. Nothin an exacto knife can't fix.

Trackin drums with a pair of 1176's tomorrow :!: :green: Thanks for the project Jakob :!: :!: :thumb:

 

[gyraf]

Ju,

That is good news. Let us know how it turns oyt..

Orson,

Remember to recalibrate the "Q-Bias", now that you fixed the rest of the circuit..

Jakob E.

 

[orson whitfield]

I did that already, Jakob. Whats happening is that I can't get the GR meter tracking calibrated because the output is always 1/3rd the voltage of the input no matter what I do. Something's up but what?

 

[deanp920]

Hey Orson,

Put a known signal level, like 50mV 200Hz on the input XLR(measure across pins 2&3 and ground pin 3 with a clip lead if you signal generator is unbalanced).

Crank the input and output knobs(unit in bypass).

Measure signal level from the input wiper to ground.

" " output wiper to ground

" " across pins 2&3 of the output XLR(no need to ground pin 3)

Let's start there.

Dean

 

[orson whitfield]

[quote author="deanp920"]Put a known signal level, like 50mV 200Hz on the input XLR(measure across pins 2&3 and ground pin 3 with a clip lead if you signal generator is unbalanced).[/quote] Done. 49.9mV @200hZ from SG and 49.9mV measures across pins 2&3. Pin 3 grounded to pin 1.

[quote author="deanp920"]Crank the input and output knobs(unit in bypass).[/quote]

[quote author="deanp920"]Measure signal level from the input wiper to ground.[/quote]it measures 49.7mV.

[quote author="deanp920"]" " output wiper to ground[/quote]it measures 227.4 mV.

[quote author="deanp920"]" " across pins 2&3 of the output XLR(no need to ground pin 3)Dean[/quote] It measures 1.402 V.

 

[deanp920]

Orson,

Only the input XLR and input wiper look right.

Bear with me and pull Q1 BF245A and repeat the measurements.

Also measure from ground to the transformer side of C15. Is the output transformer stock or modded? If so, what mod(mine or Chef's)?

Gain is way low in both the signal pre amp and signal line amp.

Let's try to find the cause.

I'm going to put mine under the same test conditions tomorrow evening so we can compare directly.

Dean

 

[orson whitfield]

ok here we go again.

Removed Q1 BF245.

50mV input from signal generator @ 200 hZ.
input XLR pin 2 and 3 with one tied to three is 50.mV.

I crank full CW input and output knobs and place unit in bypass mode.

Signal input from input wiper to ground is 50 mV.


output wiper to ground measures 1.073 V.

output XLR across pins 2 and 3 (no grounding on pin 3) measures 6.73V.

So there is a difference with the BF245 removed. I have done the CHEF mod on mine. I believe it's Chef's - where I had to cut traces and wire places together.

 

[deanp920]

Orson,

Also measure from ground to the transformer side of C15.

We still need that measurement. That helps take the OPT out of the equation.

Signal preamp gain looks correct now. Signal line amp is probably alright, if you did the 1:1 mod by Swedish Chef. Go back and find out what you did for certain. If you did my 1:2 mod you have an error.

Sounds like something is wrong with your Qbias supply and/or compressor side chain circuit.

I need to think about this some more.

We're getting closer.

Dean

 

[orson whitfield]

[quote author="deanp920"]Also measure from ground to the transformer side of C15. Is the output transformer stock or modded? If so, what mod(mine or Chef's)?
Dean[/quote]

3.783 V from ground to the transformer side of C15. Sorry I left that one out before. I know your mod was changing a resistor but I cut traces on the pcb so it must have been Chefs mod.

 

[Zee1usa]

Hello,

I have 2 torroid transformers I have purchased from AVEL LINDBERG
p/n Y236106 they are :

30VA Load rated

25+25 secondary voltage


I hooked up the primary with 122VAC and I am getting

30+30vac output :shock:


Their p/n Y236107 is a 30VA 30+30 unit.
I am thinking that they mis labeled these?
How would it affect the 1176 unit if I were
to use these with 30vac rather than 24vac?

any comments/suggestions welcome
I emailed the company that makes these a week
ago and they have not yet responded. :roll:


Thanks!

 

[Rob Flinn]

Are you just connecting only your meter to the secondaries ?

If so you would expect the reading to be high. If the transformers secondaries are loaded. i.e they are supplying the circuit these readings would drop.

 

[Zee1usa]

Thanks rob.. I had this on my mind when I posted.

Yes..just the "Fluke" meter unloaded.

I was wondering how much the voltage would drop when loaded?

I guess I could break out the old calculator and try to do some math
to figure what it might be under load. I don't think the 1176 draws much?

Hopfully when loaded down it will drop to approx 24 vac

thanks again :wink:

 

[Rob Flinn]

Even if the output voltage was a bit higher than 25v it shouldn`t be a problem since the 7824 regulator & zener for the -10v are "fairly" flexible to input volatge changes

 

[deanp920]

Orson,

I know your mod was changing a resistor but I cut traces on the pcb so it must have been Chefs mod.

We need to straighten this out.

I did a mod that involved changing a resistor. It works fine, but instead I implemented a transformer mod suggested by Jakob that involved cutting traces on the PCB and adding jumpers to get a ~1:2 step-up ratio. This is the mod I currently am using and also the one I'm pretty sure you are using also. I posted earlier that I thought you had either the Chef 1:1 mod an error with my 1:2 mod, but I see now that I was wrong.
The instructions are a page or two back on this thread reposted by mnats.

The Chef mod involves trace cutting and jumpering as well, but creates an ~1:1 output ratio. Instructions for this mod were posted by Swedish Chef on the More Gain for G1176 thread from the old forum.


OK, I set my G1176 up just like yours with the Q1 pulled and a 50mV, 200Hz input signal. Input and Output cranked. Unit set to bypass.

Input wiper: 50mV

Output wiper: 1V

C15 transformer side: 3.8V

Output XLR: 6.8V

Now I put the FET back in and I get...

Input wiper: 50mV

Output wiper: .96V

C15 transformer side: 3.4V

Output XLR: 6.13V

So, with Q1 pulled we have nearly the same gain figures; roughly 43db overall. :grin:

But with Q1 reinstalled my gain only falls to 42db, where yours falls to 29db. :?

Furthermore, you are losing it all in the signal preamp stage. This confirms that Q1 is either damaged or starved for negative bias voltage.

With no signal applied, I/O max, Attack and Release max, Ratio 20:1, Bypass mode, I get about -2.2Vdc from ground to any pin on the release pot. The reading is the same whether Q1 is in or out of it's socket.

Check this voltage and let us know the results.

Hang in there, Orson!

Dean

 

[gyraf]

Good work here Dean!

:thumb:

It should be noted that the voltage at the release pot is adjusted with the "Q-Bias" trimmer. So it would make sense to know what the voltages at the release pot is for both end adjustments of the Q-Bias-trimmer..

Jakob E.

 

[deanp920]

It should be noted that the voltage at the release pot is adjusted with the "Q-Bias" trimmer. So it would make sense to know what the voltages at the release pot is for both end adjustments of the Q-Bias-trimmer..

Jakob E.

Right! :grin:

A good, specific reference seems to be putting the release pot at minimum and measuring from the wiper to ground. This is electrically the same point as the Qbias trimpot's wiper, but easier to get at, at least for me.

So, with the release pot at minimum and measuring from its' wiper to ground, I get -2.88Vdc at one extreme of the Qbias trimmer's rotation. At the other extreme of the Qbias trimmer's rotation I get 0Vdc.

What do you measure, Orson?

Dean

 

[orson whitfield]

Okay. Here below is the mod I found back a few pages. After i double checked what I did I found a discouraging thing. I did everything as this mod said to do but I soldered a jumper from 4 to the solder pad for point X instead of Y and from 1 to the pad of Y instead of X. :roll: Now I am in a rush to gig tonite so i don't have time to look for the more gain thread that lists the other Mod. So we have done the same mod Dean? I thought I remembered we didn't - oh well I don't trust my memory anway. :? Well if the other mod is not simply reversing the Y and X jumpers then this is the mod I did with error. Abit Omen! I remember triple checking this before I did it. I can't believe I made this mistake. I'll measure the voltages you said to do Dean and I 'll post them tomorrow. Thank you for the continued help. Oh and by the way, while measuring voltages my DMM lead moved the Q1 BF245 a little in the socket. Perhaps that fried it? You mentioned it might be so i thought I'd throw that in.[quote author="mnats"]found it...

[quote author="deanp920"]If you want to try it 1:2, in and out connections should be reversed - by cutting tracks and soldering on some wires..
On the primary, pin 4 should be isolated from the ground plane by cutting the wide ground trace with a dremel tool or utility knife.

The trace connecting C15 to pin 1 must be cut.

On the secondary, pins 6 and 9 need to be isolated by cutting the traces near the pins.

Solder a jumper wire from pin 4 to the solder pad for point Y.

Solder a jumper wire from pin 1 to the solder pad for point X.

Solder a jumper wire from pin 9 to the solder pad for the negative side (output) of C15.

Solder a jumper wire from pin 6 to pin 3.

That should leave the transformer running 1:2, and increase in the signal line amp's gain by 12db.

For what its' worth, I measured the transformer's output impedance, wired stock (2:1), at about 30 ohms. This is encouraging, since, when wired 1:2, the output impedance should still be well under 600 ohms.

EDIT 4-12-04 Instructions above no longer cause phase reversal.

Dean
[/quote][/quote]

 

[deanp920]

Hi Orson,

After i double checked what I did I found a discouraging thing. I did everything as this mod said to do but I soldered a jumper from 4 to the solder pad for point X instead of Y and from 1 to the pad of Y instead of X.

No worries whatsoever. That just causes phase reversal of the output signal; make the correction and all should be well.

So we have done the same mod Dean?

Yes, we have. Once you fix the little x/y error, you're fine; leave it be.

Make sure you read my posts one page back on this thread that outline the fact that our gain blocks sans Q1 match up perfectly. We just need to figure out why your Q1 is clamping down so hard at idle.

Now I am in a rush to gig tonite so i don't have time to look for the more gain thread that lists the other Mod.

Don't bother right now. What you have done already is probably about as good as it gets and also puts us both on the same page.

Oh and by the way, while measuring voltages my DMM lead moved the Q1 BF245 a little in the socket. Perhaps that fried it?

I doubt it, but we'll soon find out I hope.

I'll measure the voltages you said to do Dean and I 'll post them tomorrow.

Yeah, let's pick up there and see if we can chase down the problem.

Dean

 

[orson whitfield]

[quote author="deanp920"]OK, I set my G1176 up just like yours with the Q1 pulled and a 50mV, 200Hz input signal. Input and Output cranked. Unit set to bypass.[/quote]
Ok I have this exact setup now.
[quote author="deanp920"]Input wiper: 50mV[/quote]I have 50mV.
[quote author="deanp920"]Output wiper: 1V[/quote] I have 1V.
[quote author="deanp920"]C15 transformer side: 3.8V[/quote] I have 3.73V
[quote author="deanp920"]Output XLR: 6.8V[/quote] I have 3.248V :!:
[quote author="deanp920"]Now I put the FET back in and I get...
Input wiper: 50mV[/quote] I get 50mV
[quote author="deanp920"]Output wiper: .96V[/quote]I measure 1V.
[quote author="deanp920"]C15 transformer side: 3.4V[/quote] I have 3.72V.
[quote author="deanp920"]Output XLR: 6.13V[/quote] I have 3.248 :!:
[quote author="deanp920"]So, with Q1 pulled we have nearly the same gain figures; roughly 43db overall. :grin:
But with Q1 reinstalled my gain only falls to 42db, where yours falls to 29db. :? Furthermore, you are losing it all in the signal preamp stage. This confirms that Q1 is either damaged or starved for negative bias voltage.
With no signal applied, I/O max, Attack and Release max, Ratio 20:1, Bypass mode, I get about -2.2Vdc from ground to any pin on the release pot. The reading is the same whether Q1 is in or out of it's socket.
[/quote] I get 2.4Vdc with it in and 2.8Vdc withit out. :!:
I hope I haven't left anything out for testing.

 

[orson whitfield]

Dean, please read my post right before this one incase you missed it.[quote author="deanp920"]

It should be noted that the voltage at the release pot is adjusted with the "Q-Bias" trimmer. So it would make sense to know what the voltages at the release pot is for both end adjustments of the Q-Bias-trimmer..

Jakob E.

Right! :grin:

A good, specific reference seems to be putting the release pot at minimum and measuring from the wiper to ground. This is electrically the same point as the Qbias trimpot's wiper, but easier to get at, at least for me.

So, with the release pot at minimum and measuring from its' wiper to ground, I get -2.88Vdc at one extreme of the Qbias trimmer's rotation. At the other extreme of the Qbias trimmer's rotation I get 0Vdc.

What do you measure, Orson?

Dean[/quote]
I forgot to rotate the trimmer for the "Q-bias" the other way around to see the differnece. So, here is the result of that test:

OK I get -1.5 dc mV with the trimmer all the way cw and the release knob set to full CW. I assumed that this is the "minimum" setting you meant? Well, anyway, thats what I did. And now the result with the Q-bias trimmer all the way CCW and the release knob still set full cw: -2.504 dc V