All things G1176 - the new "repost" thread.

[gyraf]

Synth,

Great voltage plot, that one!!!

The input pot forms a simple voltage divider to ground. Shouldn't be hard to trace signal through.

Make sure that you have ground at one end (ccw), signal in at the other (cw), and take out signal to the compressor section from the centre thingy, the viper...

Jakob E.

 

[synthetic]

It took me a minute to figure out that viper=wiper. I'm not making a joke about your excellent English, it just took me a while to figure out. :grin:

OK, the input pot problem is solved, it was a broken pad on pin 3 of the input. I had another broken pad on the board: there was no contact between the pad and the trace next to it, so I had to scrape off a little bit of plastic and make a solder bridge. Just a note for people troubleshooting the otherwise excellent mnats board. :guinness: :guinness:

Now I have it mostly functional, but there are two problems. First, I can't get the GR meter to reach 0dB. It hovers around -14dB at the max, and none of the adjustments make much of a difference. The VU meter is working fine, although I had to add a rectifier circuit to the meter to get a good signal level. The gain reduction meter is low with or without this rectifier in the circuit.

The second problem is that there's a fair bit of distortion as I increase the compression. I can't align the Q Bias either, so I'm assuming this is all related. I've been trying to find answers in the repost, but it's tough to search for this type of problem.

Thanks again for your help.

 

[spacecho]

Hi all,

i have finished my board and i have a few questions?

i noticed that there is a voltage difference of 46! volts between the hot and earth connectors of the audio output. this cant be right?

has anybody had this occur?? is it normal???

it is there regardless of the volume settings.

i searched the forum and found the wonderful voltage diagram but there is no measurement reading of the audio in or out.

Apart from this, the unit sounds and works fine???

also, the meter dosen't work in VU mode - it is a cheap meter without rectification - maybe a ge diode bridge will fix this??

i guess i should find the cause of the 46v before i use it again - or unless this is normal???


thanks all!

 

[gyraf]

Synth,

Seems likely that you have the wrong FET's? BF245 Atype?

spacecho,

Output is transformer-balanced, so there's nothing between 0 and hot/cold. The other questions have been answered before.

Jakob E.

 

[spacecho]

Yeah, im using the bf425A as listed on the mnats site.

i knew that the voltage thing was bad, will start checking for problems, it's funny that it works fine though.

i have begun re-reaqing the thread to find out about the meter, i have some true vu / ppm dual meters in a high end tape deck that i could connect to compare as well.

will post pics when it is all good.

thanks Jakob.

 

[synthetic]

No, I have BF-245A. Mouser part# 512-BF245A.

 

[EEMO1]

hey,


i got my baby done. still need the light for the meter. damn this compressor sounds sweet. the volume is pretty LOUD, the characteristics is awesome!

i used oep output transformer and ic thing on the input. i fried a couple of regulators in the process but i managed to get it working. the calibration was a bit over my head but i guess i pulled it off, because this thing works great!

thought i'd share. thanks groupdiy.

-eero

 

[synthetic]

So, should I be replacing my BF245A? Does it sound like my FETs have given up the ghost?

 

[gyraf]

Yes, try with different ones - the ones you have may be fine, but just out of specs.

 

[synthetic]

I replaced both BF245As and the trimpot, but no luck. Any other ideas?

 

[synthetic]

I measured voltages against the plot again, and the TL071 is only getting -8.3V, not -10V as the schematic says I should be seeing. Is this a symptom or a side-effect? All of the other voltages are within 0.5V as far as I can tell.

To review, the VU meter mode works, but not the GR meter mode. When I switch the unit on in GR mode, the meter starts at around -15, drops to 0, pegs, then rests around -15. I can adjust the meter track trim (R54) to change this +/-3 dB or so. When I try to set the Q bias, turning that control has no effect. The VU zero trim doesn't seem to do much, either. The compressed audio seems distorted, probably because I can't set the bias.

Thanks in advance for any ideas you might have.

 

[spacecho]

hi everybody,

just finished my 2nd 1176, glad that they both work! 1st time

i noticed that my voltages are all identical to the checkplot except that my voltage reading on the voltage regulator leg reads 30v instead of 35v - could this be because i used a 1.1k resistor for r87 as in the schematic - i have heard of many using a 1k or 1k2 resistor instead as these are readily available. (i just put 1k + 100r in series)

excuse my ignorance but i noticed that both inputs have 14v on the hot and cold signal points. Is this normal?

(as for my unit reading 45v on the output - last post - that has suddenly vanished? i might have imagined this - 6 hours of inhailing solder!

truly great project!

i might change direction and build some guitar effects now - mutron 3 and univibe anyone? - check out this link? www.generalguitargadgets.com

thanks again Jakob and Mako.

 

[synthetic]

Bump.

Help me, Gyraf Kenobi. You're my only hope.

 

[gyraf]

:grin:

Sorry, Synthethic - I'm out of ideas...

Try checking again for component values, orientation, soldering, wireing, and shorts - it's nearly always these problems when it comes to it. And then try tracing the signal through the sidechain - it could look like you have excess DC leaking through to the fet's (hopefully you did NOT replace the FD333 ultra-low-leakage diodes with something else)

spacecho,

I think there's something wrong with the way you measure - or maybe your voltmeter. Check it's batteries :razz: this is a known problem..


Jakob E.

 

[Esset]

Hello guys!

I?m building a dual G1176 on mnats rev H-boards and one is completely dead (going to switch the transistors and FET?s on that on because I?ve think I?ve burnt them all in a little shortage-story).

The other one, passes audio, all pots, the meter and switches work, but the audio is heavily distorted and no bass-frequencies.

My PSU voltages are: +30.1 and ?7.8 on the following points (these are the same on the burnt board):
http://www.geocities.com/m_natsume/images/1176_-10_small.jpg
http://www.geocities.com/m_natsume/images/1176_30V_small.jpg

Checked the voltages over the transistors, and some are a bit off but not much though.

E | B | C
Q2- 0,52 | 0,85 | 1,77
Q3- 1,16 | 1,77 | 12,14
Q4- 11,74 | 12,15 | 30,1
Q5- 4,4 | 4,22 | 28,2
Q6- 29,0 | 28,2 | 14,35
Q7- 29,6 | 29,0 | 14,4
Q8- 13,8 | 14,4 | 30,1
Q9- 13,7 | 13,3 | 0,004
Q12- 5,05 | 5,64 | 17,98
Q13- 17,73 | 18,08 | 30,1
Q14- 2,4 | 2,4 | 26,5
Q15- 26,5 | 27,1 | 30,1

Could it be that the audio-signal into the board is to hot? That would explain the distortion but not the lack of bass-frequencies. But I doubt that since the meter doesn?t overload.

Any idea´s? And if any please put them in ?stupied-mans-terms? though this is my first project with not much electrical-skills to start with, I?m learning as I go.

Regards
Stefan

EDIT: Using Lundahl output transformer and IC-based input

 

[spacecho]

hi stefan,

my unit definently distorts if the input gain is set to high - this unit seems to have heaps of gain so i usually have it set at 3-5 for a signal around 0db

as for the lack of bass response - is it possible that you have wired the input or output out of phase? - the connectors for these on the board are mirrored (ie. opposite) -/+ and +/- ?

hi jakob - i dunno - maybe i am doing something fundamentally wrong but i checked the input voltage by putting the black lead to the earth point and the red lead to either the hot or cold - it gave me a reading of 14v when the meter was set to DC <20v range.

the thing works and sounds good - hasn't blown up yet, i might get to the bottom of it when i pull the unit out to finish calibrating it - borrowing a scope.

 

[Esset]

[quote author="spacecho"]as for the lack of bass response - is it possible that you have wired the input or output out of phase? - the connectors for these on the board are mirrored (ie. opposite) -/+ and +/- ?[/quote]

I'll take a closer look at that this weekend when I have some time over.

The distortion however is there the whole time, even with input and output gain as low as possible (pots fully CCW)

Wrong resistorvalue somewhere in the inputstage maybe?

 

[FotisGR]

ATTENTION please.
Yesterday i finished a 1176 for a friend of mine but it didn't worked at once. All was OK but no gain reduction at all at 4:1 and 8:1 potition. On 12:1 and 20:1 switch potition it has enough gain reduction . I spent a couple of hours doublechecking the circuit and i found this problem.
Impossible for me , but real.
The ratio switch (like Lorlin type 2 contacts 6 potitions) it has WRONG contacts. Turning it full ccw for 4:1 the contacts are A,5 and C,11 instead A,1 and C,7.
I don't know if there are different switch types. I have 6 pieces like this, but this is the only exception.

Cheers
Fotis

 

[gyraf]

Have you tried taking the locking nut out, turning the switch completely countercloclwize, and reinserting the pin?

If the switch is set to a position higher than the programming - at the time of programming - then the switch gets caught on the "wrong" side of the end-stop, with unpredictable results..

Jakob E.

 

[FotisGR]

You are right Jakob. :thumb:
The swithc was looking like 2 cont. 8 potitions. I fixed it 100%..
for a couple of minutes i was thinking that it is a bad dream... :grin:

Cheers
fotis