All things G1176 - the new "repost" thread.

[orangerec]

Hi,
I'm building a stereo version of the mnats RevJ including his dual power supply board. I originally was going to just build a single unit and ordered an Amveco TE62065-ND (digikey part #)
http://parts.digikey.com/1/parts/1000042-transfrmr-22v-1-136a-wires-62065.html
My question is can I still use this power x-frmr with the mnats dual power supply board. I believe I can but wanted to check to see if someone else already has or if a DIY pro could check out the specs and confirm I could still use it.

Thanks

 

[Echo North]

22V is pretty low.

There are a few people earlier in this thread that built units with 22V transformers with mix results.

You could always give it a try, but what you really want is something in the area of 25V/30VA.

Mike

 

[gswan]

A 22VAC secondary will end up giving you about 28V on your 30V rail. The regulator won't regulate until you have about 32V or so on the DC input to the rail, so your 30V rail will move around with mains fluctuations. Much better to get a 25V secondary.

 

[orangerec]

...and this is why i asked. Thank you for the answer. I'll play it safe and order a new power x-frmr. Mike, I believe the x-frmr at the Hairball store should work, yes?

 

[adrian]

hello,
so since last time i fixed off a part of my problem,
the TL071 of the vu meter wasn't powered correctly due to a broken track,
now it's powered but :
when i try to adjust it to 0 Vu the indicator can't go more than -4db (-0,51V between 28-29 plots),
and in GR mod the vu meter doesn't react even if i ear the compressor is compressing....
so that's my first problem...

the second is that when i try to do the Qbias, i began (unit bypassed) with the Qbias trim full ccw,
i send a 0dB 1khz signal in the unit and when i adjust input and output pots they seemed doesn't function correctly because i have to much input gain and the output pots doesnt affect the signal so much...
I'm using:
http://fr.farnell.com/jsp/search/productdetail.jsp?sku=1684824    as input
and
http://fr.farnell.com/jsp/search/productdetail.jsp?sku=1684829  as output

for example:
if i put output pot at 12 o'clock i can't adjust input pot to have 1db output level because when i begin turning input pot it immediatly overload every things!

 

[Echo North]

...and this is why i asked. Thank you for the answer. I'll play it safe and order a new power x-frmr. Mike, I believe the x-frmr at the Hairball store should work, yes?

Yes it will work great.

Thanks,

Mike

 

[slowbass]

Hello !
I've just finished one dual 1176 (mnats J version) and surprisingly (for my very limited skills), it works (thanks to mnats' very precise guideline and thanks to this thread) despite beeing really ugly (my compressor) !
Well, in fact, I still have a problem on one of my compressors : the 1:4 mode doesn't work (the others are ok). I've checked everything but couldn't find why. When switching to 1:4, the meter (in GR mode), goes totally on the left. When I press a little on the knob, it goes on the extreme right. Could it be the rotary switch ?

BTW, I tried to use the spots named "VU lamp" on the board to power the Vu leds (Hairball's VU meter ones) but no voltage. I guess it's because I used the external PSU ? The + point isn't connected ?
And I made this silly mistake : the Hairball site says "5V dual leds" so I figured the leds need 2x5V power ! and they blew...

 

[MrShhh]

Hi, I've just finished another 1176 and found that in VU mode, the VU meter is displaying values 6db under what it should. In GR mode the best it will display is below -10dB.

This had me vexed for a long time until I decided to actually think logically while looking at the schematic and measured the output from CR11 while twiddling the meter zero trimmer. There was over 2.5V leaving the diode and making it to the meter and yet the meter showing nothing. To make it more confusing, the meter would show the "best" level of just under -10dB while the voltage across it was negative (the zero trim pot gives a range of slightly negative to 2.5V+ positive)

Next I try putting a 1.5V battery across the VU meter and find it only reacts to negative voltage. Aha! There must be the problem.

I think that half the rectifier network inside the VU meter must be knackered, hence the -6dB readings (only rectifying half the output waveform). Anyone agree?

Before I go hacking the VU meter to pieces looking to see if I can fix it, does anyone know if the diodes inside can be got at? Or fixed?

Thanks ;D

 

[gswan]

Some 'VU' meters don't have diodes inside, which can cause a slightly different problem.
In your case it looks like it is acting as a half-wave rectifier instead of a full-wave. It is possible to get at the diodes inside after removing teh face of the meter usually. Replace all 4 diodes in the bridge with Germanium diodes or small schottky rectifiers.

 

[MrShhh]

Thanks for the quick reply  Germanium or Schottky because of the low voltage drop/fast switching? I guess 1N4148's would not be any use, being silicon. Shame as I have them in abundance.

 

[gswan]

Low Vf for using the meter directly across the signal lines when in +8/+4 metering mode. Of couse this does introduce some distortion, so it's best left in GR metering mode when it's being used.

 

[MrShhh]

Nice one gswan, I took the VU meter apart and found a single dead germanium diode in the positive rectifier leg. The other 3 measure Vf ~ 0.6V with a 4.7ma test signal, which seems quite high for germanium diodes?? A 1N5822 Schottky gives a Vf ~ 0.23V @ 50ma.

 

[Spendor]

Hi there.Have just completed my first 1176. Sounds great! I have 5532 input and OEP output  in 2:1 config. ratios are pretty cool 5:1, 8.7:1, 12.5:1 and 23:1. I will have to do the input mod though as I'm getting compression very early when turning up input. I've half built my second unit and have been given a 95VA 12-0-12 transformer - my understanding is if the outputs are wired in series i get half current and twice voltage - therefore 50VA and 24V. Will this work OK and what do I do regarding the center tap?
Thanks very much!

 

[gswan]

I've half built my second unit and have been given a 95VA 12-0-12 transformer - my understanding is if the outputs are wired in series i get half current and twice voltage - therefore 50VA and 24V. Will this work OK and what do I do regarding the center tap?

Not quite. The VA rating is the product of the voltage and current. So 95VA is 24V @ 3.95A or 12V @ 7.92A.
This transformer is unsuitable for the 1176 since you need 25-0-25 (ie 50V CT) for the power supply.

 

[Spendor]

Thanks there gswan.  Before i go ahead and do the input mod, i wanted to ask which mod would suit me best. According to my plot the knee is much softer on 4:1 ratio, but it starts compressing at just over -15dB input. I need to raise the threshold overall and have much less sensitivity on the input knob. As it stands I only have to move it a millimetre or two and it's making big changes. Will changing output transformer to 1:2 help this predicament or will that just lower output gain?

Thanks again - your advice has been really helpful when reading through previous posts.

 

[gswan]

If you look on the original 1176LN circuit you will see a box labelled T&C across S4B. This part can be a resistor that is selected on test to set the threshold to a particular value.
On my switch board I have this resistor and two test pins so I can attach a trimmer across them and trim to the required threshold, then measure the pot resistance and solder in the appropriate resistor value.

You could also use a reverse log pot for the input rather than a log pot, which will allow more pot travel in the initial half turn for less effect on the level.

 

[Spendor]

thanks again for the info. i can see the box you're talking of. I get what you mean, but as they are in series why not just have a trimpot instead of R26  - is there any need for the 56k resistor in addition to a trimpot if the trimpot is of a suitable value?

 

[gswan]

Look again, they are not really in series. The trimming part is across the first switch.

 

[Spendor]

Gotcha - I tried it with a 100k pot. Ended up soldering a 5K6 resistor from where R26 meets R25 to ground - works a treat. Thanks again!

 

[mac]

Hey all,

I did a search but couldnt find the answer to this question anywhere. I have some old stock TL071CP IC's which I want to use in my Dual 1176 build, (Mnats Rev J Boards). I notice that the BOM calls for TL071.

Can someone please explain what the "CP" stands for on my IC's and if it will be OK to use these TL071CP instead of TLO71?

thanks,
Mac.