All things G1176 - the new "repost" thread.

[SequenzenOhneGrenzen]

Hi,
I'm building a G1176. I was thinking I could use the normal input path as well as the Lundahl transformer and put a fancy "modern/vintage" switch on the front panel... Will it work if I just put a switch right at the input or should I work with seperate inputs?
Thanks!

 

[gswan]

You could do either, however the 'modern/vintage' switches seen on compressors generally have nothing to do with transformers. It's usually either feed-forward or feed-back gain reduction configuration.

Feed-forward gain reduction samples the input signal, to determine the amount of gain-reduction to apply, before the gain reduction element (in this case the FET). This is the 'modern' mode.
Feed-back gain reduction samples the signal after the gain-reduction element to determine the amount of gain reduction. The 1176 does this, sampling the signal just before the pot feeding the output amplifier, after gain-reduction has been applied. This is the 'vintage' mode.

 

[SequenzenOhneGrenzen]

Hi and thanks for your reply!
Do you think a DPDT On-On switch on my audio cable will do? I'm afraid it might cause noise.

You could do either, however the 'modern/vintage' switches seen on compressors generally have nothing to do with transformers.

Ah yes. I was confused as I think the Slate Pro Audio Fox pre-amp does work with transformers for it's "vintage" setting.
In any case I think it's interesting to have both options. I might get it another arbitrary term, something not so confusing.

 

[gswan]

It may cause a click if there are any small DC offsets present on one of the inputs. A good quality switch should work fine though. The number of poles required will depend on whether you switch the balanced signal or the single-ended signal after it is unbalanced in the circuit.

 

[orpheusmaximo]

I want to swap my Hairball 1176 blue stripe trafo to an UTC A-20.
Any pointers?
Attached some details of the schematic.

I'm worried that I will mess it up.
Is it: De-solder original, solder extension wires to A-20?

My questions:
Is there a maximum length for these wires?
Connect A-20 pins 1-6 in to 1176 1-5 and A-20 pins 7-12 out to 1176 6-8 right?

P.S: Going more"out there" with the idea, could I connect a pot to the internal
A-20 connectors and "dial-in" an impedance? Is that even necessary, if all I'm
looking for is sounding ( so to speak ) "fat & vintage"? Isn't going the full 600
the way to go, then?

Sorry for asking here, if not allowed I will take down, thanks.

 

[Whoops]

I want to swap my Hairball 1176 blue stripe trafo to an UTC A-20.

This thread is not dedicated to that model, it's a Gyraf 1176 thread, a different circuit.

I guess by Blue Stripe it means it's Revision A.
There's a thread in the forum somewhere for the Mnats Rev A 1176, you will have better luck there for sure

 

[orpheusmaximo]

This thread is not dedicated to that model, it's a Gyraf 1176 thread, a different circuit.

I guess by Blue Stripe it means it's Revision A.
There's a thread in the forum somewhere for the Mnats Rev A 1176, you will have better luck there for sure

Thanks, sorry about that.

 

[SequenzenOhneGrenzen]

Hi! My PCB's populated (Gyraf Rev#7) and my case is almost finished so I'm really excited to get the wiring done and start testing, adjusting & compressing... Seems pretty straightforward. I wanted to leave the option open so I could switch between the Lundahl input transformer and the balanced input. I have a switch right after the input. I was thinking to connect 1 and *1 both to the same terminal of the input gain pot. Does anyone predict I might fry some parts by doing this? Has anyone done this before? I've read about someone with the same plan but he never really came back to it.
Thanks! and cheers! Will share some pics when I'm finished!

 

[Whoops]

Does anyone predict I might fry some parts by doing this? Has anyone done this before? I've read about someone with the same plan but he never really came back to it.

I have no idea if that feasible or not,
but post that part of the schematic here so we have a look at it (not the full schematic, just the input part of the circuit).
You're a new member so my recommendation if you want to have more help around here is always provide as much information as possible in your post, that can be photos, schematics, video files, audio files, whatever is needed or related to the specific question asked. I guarantee you that you will have much more help.
No one knows all the schematics and cicuits by heart...

I'll have a look at it and try to help, but be aware that the Lundahl transformer is pretty clean and transparent so what you want to do is a bit irrelevant operation wise and not that useful as you will not have a big difference in the final sound because of that

 

[SequenzenOhneGrenzen]

Hey thanks for the advise!
I've read about difference in focus and low/hi-end response. It's more of an experiment, I love to have the option when I'm tracking.
So basically it's this section, going to the "input gain pot".
Connection 2 and 3 remain. If you work with the Gyraf rev#7 board, connection 1 becomes *1 (I uploaded that part of the PCB for reference).
I was thinking to connect 1 and *1 to the same terminal of the "input gain pot" and have a switch after the input XLR to switch the input path from the IC path to the Lundahl path. I'm afraid I might fry the C33 cap.
Thanks for putting in the time, really appreciate it.
Cheers!

 

[Whoops]

I think you should try it.

Why do you think it could fry the C33 cap?
I'm not seeing why at the moment

 

[BGroen]

Hi all,
In order to check my build I decided to measure all the DC voltages. To make it a little more easy I added the DC voltages onto the PCB layout.

Maybe it is usefull for more people!

 

[BGroen]

Hi all,

My unit seems to work very nicely.

Two things seem weird:

1). At start-up the GR meter slams all the way to the right. Only in GR mode. After 10 - 15 seconds or so the meter stabalises and works perfectly. Is this usually or should I check for a faulty capacitor(connection) or shield the power transformer?

2). I got some hum (50Hz and 100Hz) at full gain. I got it with input to zero and output to full. I will try if shielding the power transformer works and I will take a look at the wires from the output pot. Anyone else encountered this or something similar? I read the cutting traces solution maybe a thousand times and still forgot it. Totally clean now!!

 

[raoul1983]

That's really strange.
Whats the voltage you have before the 7824 regulator?

Measure and test all the rectifier diodes (CR7,CR8,CR9,CR10)

Very important also, measure and test the Zener Diode (CR6) in the -10V rail

Measure resistors R85, R86, R87

After that you should do a video showing how you taking the voltage measurments and also some photos of that part of the PCB

I Finally got to replace the zener and rectifier diodes. This did the trick!
I got a normal Voltage read on both points now ;-)
I'm going to replace the bias trimmer to get more precision.

 

[gyraf]

The gr meter jumping is a known thing, I think even one of our originals did it. If it works otherwise, I wouldnt care.

/Jakob E.

 

[spoontex]

At last I found good BF245A!

Here are the results. I need to match two of them for a stereo build. What would be good candidates? This 10 devices are enough? I have more of them...

 

[gswan]

There's 4 devices with virtually the same transfer curve that would be good candidates to start with. The FETs are not the only components that should be matched for identical performance. You will find the Hfe of the transistors in the GR amp and the Vf of the diodes will also contribute to differences. Once built, measure the ratio curves and see if they compress with the same curves. This will be the important test.

 

[spoontex]

There's 4 devices with virtually the same transfer curve that would be good candidates to start with. The FETs are not the only components that should be matched for identical performance. You will find the Hfe of the transistors in the GR amp and the Vf of the diodes will also contribute to differences. Once built, measure the ratio curves and see if they compress with the same curves. This will be the important test.

Device 4 and 6
Device 7 and 9

No?

Thanks for the advice about hfe and Vf. I'll keep it in mind

 

[spoontex]

1176 Stereo Build process. What do you think about this front panel that I made?

 

[gyraf]

Looks really good - LA4'is in some way.. Do you have room for two units in 19"2u? (or is it 3u?)