All things G1176 - the new "repost" thread.

[spoontex]

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

yes, if my calculations are correct, the two units fit in a 2u rack. The VU it's a little big, but it's okey.

Thanks gyraf!

 

[gswan]

Yes, you can fit 2 in a 2RU 19" rack case. I've built a few.
But these are all 2xmono channels, not stereo. For true stereo (bus) use you need to have both units tracking virtually identically with the compression curves, which is not easy due to component tolerances. With a lot of tweaking and measuring you can get them close. And then you have the gain-reduction amplifier section, which should not be independent-per-channel for stereo bus use or your image will swing about depending on the material and differences between L and R channels.

 

[raoul1983]

I'm worried the ratio's are a bit off, but i'm not sure.
I did some tests.
the first is with the input knob between 9 and 10 o'clock. the second is at 10 o'clock.

 

[raoul1983]

is this right? if not, what can I do?

 

[gswan]

Compression ratios are all really high here, regardless of your ratio setting.
Check your calibration/FET bias. Also check that you have the ratio switch wiring correct.

 

[raoul1983]

I did the FET bias calibration, like as done on this video
The ratio wires make contact and go to the correct places. (did you mean that?)

 

[gswan]

Your compressor is pretty much acting as a limiter at the moment. A 4:1 ratio is looking like 10:1.
Check over the GR amp section, something is sending too much signal bias to the FET when it is switched in and causing a lot more gain reduction than what your front panel says.

 

[spoontex]

Yes, you can fit 2 in a 2RU 19" rack case. I've built a few.
But these are all 2xmono channels, not stereo. For true stereo (bus) use you need to have both units tracking virtually identically with the compression curves, which is not easy due to component tolerances. With a lot of tweaking and measuring you can get them close. And then you have the gain-reduction amplifier section, which should not be independent-per-channel for stereo bus use or your image will swing about depending on the material and differences between L and R channels.

Yes! I know. I have two matched bf245a. Now I need to check hfe of transistors, and match some diodes.

 

[raoul1983]

Your compressor is pretty much acting as a limiter at the moment. A 4:1 ratio is looking like 10:1.
Check over the GR amp section, something is sending too much signal bias to the FET when it is switched in and causing a lot more gain reduction than what your front panel says.

I'll look in to that,
Is it also strange that 20:1 is way les compressing than 4:1 and 12;1? or is this normal?

 

[raoul1983]

I replaced the 5532 IC and changed (and recalibrate) the q bias this is what comes out now.
I have no idea if it's right or not, what would a standard graph look like?
What more could I do if it's not right?

 

[gswan]

Looks better. The 4:1 setting is now approx 6.7:1 and 12:1 setting is compressing at around 10:1.
A lot of things affect the ratios. As you can see in the chart that the knee is quite soft, so we use the last 6dB of input change to work out the compression ratio where the compression curve is more linear (away from the knee). The Vf of the diodes will affect it, and that is temperature sensitive so the compression will be different on different days or temperatures. That's the nature of analogue electronics.

 

[raoul1983]

Looks better. The 4:1 setting is now approx 6.7:1 and 12:1 setting is compressing at around 10:1.
A lot of things affect the ratios. As you can see in the chart that the knee is quite soft, so we use the last 6dB of input change to work out the compression ratio where the compression curve is more linear (away from the knee). The Vf of the diodes will affect it, and that is temperature sensitive so the compression will be different on different days or temperatures. That's the nature of analogue electronics.

Is there something I should do or is this acceptable how it is now?

And btw, thanks for the response! ;-)

 

[gswan]

You can measure the DC conditions to make sure the transistor operating points are where they are expected to be. Components can be tweaked a little to bring them closer to the same values, but the BJT's and diodes will still have temperature-related drift. It all depends on how close you want them to be to the panel values. Are you using close tolerance 1% metal film resistors?

 

[raoul1983]

yes there all 1% resistors, the DC is like it should be.
I don't really care about the drift, that's like it supposes to be I guess ;-)

Would changing the BD517 and BD518 do anything?

 

[gswan]

I doubt it. It's likely to be components in the GR detector/amp section.

 

[spoontex]

Anyone have the layout of this PSU?

http://mnats.net/psu.html
Thanks.

 

[gyraf]

Ask mnats?

 

[macleod69]

maybe you can try this PSU

https://proaudiogc.com/en/34-power-supply-gc76-pcb.html

 

[spoontex]

Anyone knows the power consumption of this device? For a stereo build it's enough 0.6Amp?

https://www.tme.eu/de/details/55113...dS0V0DxtK0nCCP-gZuZBYtHuDcgel5wRoC_x8QAvD_BwE
Thanks.

 

[spoontex]

Hello,

if I change the Q Bias trimmer with a muti turn trimmer, this will improve the adjustment? It's worth it?

Thanks!