[BUILD] 1176 Rev A - Back to the beginning...

[junkface]

back again for a little troubleshooting help. power supply checks out. q bias and meter calibration went fine. the problem I'm having is in the tracking adjust step. When I push the input put up to +10 db with no GR, it pushes the signal up considerably with GR engaged. And conversely, when I then reduce the output with GR engaged, it then considerably lowers the signal I see with GR off.
As such, I'm unable to get back to 0db with GR while still showing +10 without. Feel like I've made a wiring mistake, but I've double and triple checked everything so...? Here's the GR pads you usually ask for
Pad 22 ( w/ .775vac signal)
20:1 = .221 vac
12:1 = .130 vac
8:1 = .085 vac
4:1 = .043 vac
Pad 21
20:1 = -5.7 vdc
12:1 = -3.09 vdc
8:1 =  -2.25 vdc
4:1 = -1.44 vdc

 

[Spencerleehorton]

Hi,

Still getting all my bits together for this build but nearly there, just wondering if a 3 gang 1k pot will be ok?
I have spoken to a few people but I'm slightly in the dark about the input pot. What attenuation is it trying to achieve? From what I've been let to believe a 1k 3 gang would be 0db to infinity?
Could anyone explain please?

Regards

Spence.

 

[Echo North]

Hi,

Still getting all my bits together for this build but nearly there, just wondering if a 3 gang 1k pot will be ok?
I have spoken to a few people but I'm slightly in the dark about the input pot. What attenuation is it trying to achieve? From what I've been let to believe a 1k 3 gang would be 0db to infinity?
Could anyone explain please?

Regards

Spence.

You want about 40dB of attenuation while maintaining a 400-600Ω impedance on the input tx secondary.  If you search around this forum you should fine some different options for the t-pad.

 

[Echo North]

back again for a little troubleshooting help. power supply checks out. q bias and meter calibration went fine. the problem I'm having is in the tracking adjust step. When I push the input put up to +10 db with no GR, it pushes the signal up considerably with GR engaged. And conversely, when I then reduce the output with GR engaged, it then considerably lowers the signal I see with GR off.
As such, I'm unable to get back to 0db with GR while still showing +10 without. Feel like I've made a wiring mistake, but I've double and triple checked everything so...? Here's the GR pads you usually ask for
Pad 22 ( w/ .775vac signal)
20:1 = .221 vac
12:1 = .130 vac
8:1 = .085 vac
4:1 = .043 vac
Pad 21
20:1 = -5.7 vdc
12:1 = -3.09 vdc
8:1 =  -2.25 vdc
4:1 = -1.44 vdc

Nothing too weird there. What is your AC V same conditions at 20, 12,  8, and 4 at the anode (+/non striped) of CR2?

Mike

 

[junkface]

@ +CR2:
20:1 = 3.45 vac
12:1 = 1.6 vac
8:1 = 1.02 vac
4:1 = .45 vac

Nothing too weird there. What is your AC V same conditions at 20, 12,  8, and 4 at the anode (+/non striped) of CR2?

Mike

 

[Echo North]

@ +CR2:
20:1 = 3.45 vac
12:1 = 1.6 vac
8:1 = 1.02 vac
4:1 = .45 vac

Nothing too weird there. What is your AC V same conditions at 20, 12,  8, and 4 at the anode (+/non striped) of CR2?

Mike

Seems ok. Hmmm.

Are you sure that you have your attack switch wired correctly. When in "off" do you have continuity between Black (ground) and pad 22?

 

[junkface]

there is continuity when GR is switched off.  and none when switched on

 

[Echo North]

there is continuity when GR is switched off.

When you switch GR ON/OFF  with in and out at 12 oclock and a 0dBu signal, do you see the -VDC at pad 7 fluctuate at all?

Mike

 

[junkface]

nope

 

[junkface]

switch seems to be wired correctly. got continuity from the common to pad 22, and it switches correctly between the ground at pad 2 and the green at pad 4. resat pad 7 (and it's ground shield) JIC but that's fine continuity wise too.

 

[junkface]

should I be seeing fluctuation there?

When you switch GR ON/OFF  with in and out at 12 oclock and a 0dBu signal, do you see the -VDC at pad 7 fluctuate at all?

Mike

 

[Echo North]

should I be seeing fluctuation there?

When you switch GR ON/OFF  with in and out at 12 oclock and a 0dBu signal, do you see the -VDC at pad 7 fluctuate at all?

Mike

Should be. Have you double check all the ratio/attack/release wiring?

 

[junkface]

just double checked this test and there is a small variation. on is -1.1, off is -1.2 FWIW I've checked the ratio, attack and release wiring a number of times, confirming all the appropriate continuities.

When you switch GR ON/OFF  with in and out at 12 oclock and a 0dBu signal, do you see the -VDC at pad 7 fluctuate at all?

Mike

 

[Spencerleehorton]

I found one of these on my travels!!!

http://www.ebay.co.uk/itm/331753333921?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

not bad for £6 i thought.

regards

Spence.

 

[junkface]

man this one really has me stumped. :-[ triple checked all wiring, reflowed attack and release knobs just in case and tested continuity. went through the schematic with voltages on both units today and everything is within 5% (with the exception of one of the Q4 j309s, which has a drain around 11 vdc as opposed to 13.7, still pretty close)
the -vdc variation at pad 7 you had me look at is pretty small, about +/- 0.05 vdc between gr off and on. -1.22 vdc gr off and -1.17 vdc gr on. all the other GR specs I've tested for you seem fine though.
they're definitely reducing gain, and without calibrating it at all the meters seem within range to reflect the actual gain reduction, it's just not dumping more than about 5db max. the q bias is definitely dailed. ug.
I've built what, 2 dozen + of these now? never had such a problem with a build or a diagnosis. i'm close to just sending you fellas these two to look at cuz I'm at a loss, about ready to throw in the towel.

 

[Chrome Heart]

So, I went to calibrate my 1176A and when I put a .775 1K tone on the input the meter oscillates. Looks like Im sending a vibrato to the input but its a sine wave. Any clues?

 

[Echo North]

man this one really has me stumped. :-[ triple checked all wiring, reflowed attack and release knobs just in case and tested continuity. went through the schematic with voltages on both units today and everything is within 5% (with the exception of one of the Q4 j309s, which has a drain around 11 vdc as opposed to 13.7, still pretty close)
the -vdc variation at pad 7 you had me look at is pretty small, about +/- 0.05 vdc between gr off and on. -1.22 vdc gr off and -1.17 vdc gr on. all the other GR specs I've tested for you seem fine though.
they're definitely reducing gain, and without calibrating it at all the meters seem within range to reflect the actual gain reduction, it's just not dumping more than about 5db max. the q bias is definitely dailed. ug.
I've built what, 2 dozen + of these now? never had such a problem with a build or a diagnosis. i'm close to just sending you fellas these two to look at cuz I'm at a loss, about ready to throw in the towel.

Let me back up a bit. I've been helping a lot of people so sometimes I get confused with who is having what symptoms. So the issue is that you can not get a 10dB drop at the output correct?

Is your max gain ok? Like in bypass if you feed it a -40dBu signal and crank the in/out can you get like 9dBu on the output? (for +49 gain)

Mike

 

[junkface]

Let me back up a bit. I've been helping a lot of people so sometimes I get confused with who is having what symptoms. So the issue is that you can not get a 10dB drop at the output correct?

Is your max gain ok? Like in bypass if you feed it a -40dBu signal and crank the in/out can you get like 9dBu on the output? (for +49 gain)

Mike

with a -40dBu (.0077vac) and in/out cranked I'm reading 69 vac and 52 vac on the respective units.

 

[Echo North]

Let me back up a bit. I've been helping a lot of people so sometimes I get confused with who is having what symptoms. So the issue is that you can not get a 10dB drop at the output correct?

Is your max gain ok? Like in bypass if you feed it a -40dBu signal and crank the in/out can you get like 9dBu on the output? (for +49 gain)

Mike

with a -40dBu (.0077vac) and in/out cranked I'm reading 69 vac and 52 vac on the respective units.

Wow not sure what that is, but that is insane. Maybe oscillation. If you pack off the output a little does it drop down to like 2VAC?

May be moot if you don't have a proper audio analyzer.

So it's just not compressing enough?

 

[junkface]

i thought that was cray.  so ya after dropping the output a bit they both max out around 2 vac before they jump into crazy land.