All things G1176 - the new "repost" thread.

[gswan]

It's easier to use the rotary PCB's with rotary switches than to have to wire them up to the pushbutton boards - too much spaghetti and room for mistakes.

Check out the 'Black Market' discussion topic here to find out about the PCB sets that Mako produces.

 

[gary o]

Anyone found  where to buy 5 meg release pots yet ? I can find a 3 meg reverse log .....what does reverse log mean would that matter I no 3 m is under value was gonna add 2 meg fixed resistor for now.

Cheers

 

[diyfanatic]

Gary,

you could find 4m7 at audiomaintenance, the're in Uk!!

http://www.audiomaintenance.com

cheers!
Jr.

 

[gswan]

Anyone found  where to buy 5 meg release pots yet ? I can find a 3 meg reverse log .....what does reverse log mean would that matter I no 3 m is under value was gonna add 2 meg fixed resistor for now.

Cheers

If you can find a dual 2M2 pot you can use it like this:
http://www.axtsystems.com/index.php?view=article&catid=34%3A1176ln&id=47%3A1176lnreleasepot&option=com_content&Itemid=62

And it really does not matter whether it's lin or log type.

 

[casrec]

you can use Log or Lin on the release and both can be found at mouser in a few different brands. Guaranteed to have Alpha. Cheap, super smooth but don't know how they would last over time. here is the alpha Linear.

http://www.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMtxdMMi52izyjSrvJtvLO7BGiFJlIITlB4%3d

Here is one from digikey who also have a few to select from, but quite a bit more.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=381N505-ND

 

[gary o]

Thanks for the 5 meg pot info the Mouser 5 meg one looks best 12 pounds delivery fee to me in UK ouch thats a bummer .............I really wanted the full 5 meg.... unless anyone knows of anywhere here in the UK il have to swallow that delivery fee..but thanks everybody

 

[casrec]

Hello all,
    I noticed that on the Mnats board, he has the output transformer wired in series on both the primary and secondary for a 1:2 ratio and 600ohm on the primary and 2k4 coming out of the secondary. Is this more beneficial then wiring parallel on both ends so 600ohms is coming out of the secondary for a nominal impedance. Sorry for the stupid question, but I'm a newb and trying to figure out how to wire some transformers. I'm slowly learning. Thanks Guys!

Brandon 

Sorry, i am speaking of the OEP transformers. Thanks again!  

 

[casrec]

I used panasonic's as well, but used OEP's on the input and output. I had to reverse the input from 1:1 to 2:1 because there was way to much gain. After that it reacted like the original and with no noise. I don't know how the IC input works, but i would suggest replacing with either lundhal or I thought the OEP sounded quite nice.

Brandon 

 

[bpucekov]

I made two, one with lundahl input and one with elektronic input and bouth are apsolutly noiseless
puc

 

[casrec]

I was very pleased with the OEP xformers  on both input and output. Had a Neve quality without compromising the highs.

 

[JW]

Hey guys I have a problem that completely baffles me w/ my dual G1176.
First of all, both channels were working well. (I was in the calibration process and had finished the Q bias on both channels)

Now 1 channel has a lot less gain than the other (both in bypass mode and GR mode) This channel is also not audibly compressing but the VU meter shows GR, weird.

The drop in level sounded to me at first like there was a short on one side of the balanced signal somewhere. However, testing continuity to ground on either side of the in/out balanced circuits reveals no short.

I've looked and looked for tiny solder shorts all over the board but can't find anything. I've also measured the power rails on this channel and these are fine.

What would be causing?:
1. A drop in level
2. GR not working audibly (but showing up on the VU?)

P.S.
I should mention that after calibrating the Q bias (w/ such high sensitivity trimmers) I looked for some glue to keep them in place. All I could find in the house was Gorilla Glue which I didn't realize would foam up. Anyway, it expanded covering the Q bias trimmer, a capacitor and a resistor nearby. This happened on both channels, but like I mentioned one channel is fine. On the problematic channel I replaced the trimmer and measured the resistance of both the capacitor and resistor and they're the same as the corresponding components on the working channel.

 

[user 37518]

The FET in charge of displaying the GR metering is different from the FET that actually makes the GR, thats why is recommended to match the fets, i guess your problem lies in the FET that does the GR.

 

[gswan]

What would be causing?:
1. A drop in level
2. GR not working audibly (but showing up on the VU?)

It sounds like you may have a FET biased too far into conduction (ie the Qbias point has changed after you trimmed it). There are two FETs, one for metering and one for GR so it's possible that you will see something on the meter.

Try:
1. Measuring the gain of each stage with the GR turned off. This will confirm that you have the amplifier stages operating correctly.
2. Re-calibrating the bias on this stage.

P.S.
I should mention that after calibrating the Q bias (w/ such high sensitivity trimmers) I looked for some glue to keep them in place. All I could find in the house was Gorilla Glue which I didn't realize would foam up. Anyway, it expanded covering the Q bias trimmer, a capacitor and a resistor nearby. This happened on both channels, but like I mentioned one channel is fine. On the problematic channel I replaced the trimmer and measured the resistance of both the capacitor and resistor and they're the same as the corresponding components on the working channel.

This is a bad idea. You don't need anything to 'keep them in place'. These units often need re-calibrating to compensate for temperature and aging. It's best to use a multiturn trimmer (cermet 25 turn is good) so you can get a fine adjustment and better temp stability.

 

[JW]

Hey gswan,

The gain of the working channel is still a lot higher when they're both in bypass mode.

 

[gswan]

What are the gains?
Measure the gain from the input to the top of the output pot and then from the output pot to the output connector. First stage should be about 26dB and seconds stage about 10dB gain.

 

[JW]

Hey gswan,

Thanks. For measuring gain, what reference do I use (.775V 1K sine wave?) and how should I have my input and output pots set? I guess the only way to set them would be maxed out right? They're not stepped or anything.

 

[gswan]

No, use something smaller, maybe 100mV RMS. Wind the pots right up and measure between the stage input (eg wipre of input pot) to the stage output (eg top of output pot).

 

[JW]

Okay,

I wasn't sure if you meant putting the leads across the input pot wiper and the top of the output pot, or measuring both of these points in reference to ground, so I made measurements both ways.

With a 1K .1V tone, both channels in bypass:

with leads across input pot wiper and top of output pot:
ch.1 (bad channel): .005V
ch.2: 5.7V

Voltage measurements in reference to ground:
ch.1 input pot wiper (.1V of course as this is what is coming in)
ch.2 input pot wiper: .1V

ch.1 top of output pot: .1V
ch.2 top of output pot: 2.08V

 

[gswan]

Good.
Channel 2 is showing 26.4dB gain in the input stage (which is what we expect) and you have component problems in Channel 1.
I'd suggest checking your component values (resistors particularly) and transistor type and orientation in channel 1.

 

[JW]

Thanks gswan,
ch.1 was working as well as ch.2 at one point. I'll look over the values again, but I think it would be more the case of a failed component than a wrong component?

Is there a way to test the GR FET without desoldering it from the board?

Thanks for your help