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

[StudioSQ]

does anyone have a schematic with voltages? I have the second of two units and the transistors in the gain reduction section seem to not be drawing enough current. I am using bc107 transistors, the same as the other unit. I have changed then 3 times and the voltages are always way to high. the 30v and -10v are fine. the 4.7k resistor in series with the 30v supply is only dropping 1.7v and the base of Q8 is putting out 22v any ideas?

 

[Greg Dixon]

Hi guys, I'm having trouble with the tone of my Rev A. It is very dark and bottom heavy. It doesn't change when in bypass, so I'm assuming it's the amp. Everything calibrated properly and works as expected, it's just that the tone completely changes when you patch it in.

I've just finished a stereo pair of Rev Ds and have previously built 4 of the Rev Js, so I have some idea what I'm doing, but this is my first time with the push buttons. I don't think that's the issue, as the calibration worked well.

I'm using the transformers from Hairball. There's plenty of level, so I'm assuming they're fine.

Apart from being very careful when stuffing the boards, I've double checked all the cap values, as that's what it sounds like the problem is. The sound is similar to what happens when you turn the passive tone control of a guitar all the way down, although with a bass boost as well.

Any suggestions would be appreciated.

Thanks,
Greg

 

[StudioSQ]

figured it out. the bc107 didnt work in the gain reduction area, but works great in the meter area. I used the 2n5088 in the gain reduction and it works great.

 

[Greg Dixon]

OK finally worked out why mine sounded so bad. A faulty output transformer. I swapped it for one from my Rev Ds and it works perfectly. Sounds fantastic. Mike from Hairball is sending a replacement of course. Great guy. Very happy with his service and products. Pretty rare to get a faulty transformer.

I thought this would be my last 1176, but man these Rev Ds and As sound awesome. Might need to find some buyers for my old Rev Fs.  :

 

[Pieter001]

Found a little problem in my rev a whem im calibrate the unit.
When i try to set the Q bias i want to set the meter to read +1, when i bypass the unit the meter drops. The unit don't let any audio pass when in bypass. This only happens when i use ratio 20. When i use ratio 4, 8 or 12 the unit bypassed fine and let the audio pass.
I can't calibrate the unit in ratio 20 this way.

Someone had this problem before?

 

[Pieter001]

Anyone? ;D

 

[tmuikku]

Anyone? ;D

Already checked Ratio board wiring?

 

[Pieter001]

Yes, nothing wrong in the wiring of the ratio pcb. Also checked the resistors on the ratio pcb. They are the same value as in the .pdf file from hairball audio.
i have a jumper on R10, is this right?

 

[Rob Flinn]

Yes, nothing wrong in the wiring of the ratio pcb. Also checked the resistors on the ratio pcb. They are the same value as in the .pdf file from hairball audio.
i have a jumper on R10, is this right?

A link is correct in that position R10.   

I think you should recheck your wiring on the switch pcb, & possibly check for damaged pcb tracks & wiring continuity with a meter.    If you think logically if it works ojk apart from one postion of the ratio switch it is quite likely that the fault is in this area !!!

I always find it easy to assume I have done everything right, but in reality if a unit is not working properly then something is damaged or one has done something wrong !

 

[Pieter001]

Thanks for your reply. Gonna check the pcb traces with a continuity meter and recheck the wiring.
All the other ratio's work perfect so its realy weird i think.

 

[Rob Flinn]

Thanks for your reply. Gonna check the pcb traces with a continuity meter and recheck the wiring.
All the other ratio's work perfect so its realy weird i think.

I always find when somethings not working you have to logically conclude that something you have done is either wrong or you have a bad component.  It's very easy when you have done something yourself to to think that everything is perfect.  After all nobody likes to think they are at fault

 

[Stagefright13]

Greg Dixon the most common things regarding your bad sound thing is: You didn't link the tap in the output transformer. (Orange and Yellow? It's in the JBL schematic)

Number 2 is using it unbalanced. Such as a mixer send with unbalanced sends. (Channel patch) Test it straight from a real balanced pre to 1176 to recording media. But this normally will drop low end. And only on certain recording systems.

Number 3 is having the thing set up out of polarity at some point in the circuit and have phase cancellation in a mix.

There are a few more. But does it function normally? And calibrate properly?

If it is dark and bottom heavy something is wrong. It should sound FULL and Clean. With a slightly smoothed over top end. And only slightly. And in a really good way.

John

 

[Greg Dixon]

Thanks John. You obviously missed my second post. It was a faulty output transformer.

 

[baadc0de]

I'll be wiring a rev. a with rotary switches and am using the mnats meter and ratio PCBs that came with the main mnats rev a PCB. Do I need a dual switch like this:

http://mnats.net/1176_slam_mode_rotary.html

or is a simple switch like this enough:

http://www.banzaimusic.com/Rotary-Switch-2x6-Pins.html

Thanks

 

[Rob Flinn]

you only need the first typw id you want to add the "all in" or slam ratio mode

 

[baadc0de]

Out of curiosity, if you take the second (simple) type and set it to the position of all in mode, you'll get what? 20:1?

 

[Rob Flinn]

Out of curiosity, if you take the second (simple) type and set it to the position of all in mode, you'll get what? 20:1?

Withe the 2nd more simple type of switch you don't have the option for all in mode.  That is why they tell you to use the other type !

 

[California Road]

Found a little problem in my rev a whem im calibrate the unit.
When i try to set the Q bias i want to set the meter to read +1, when i bypass the unit the meter drops. The unit don't let any audio pass when in bypass. This only happens when i use ratio 20. When i use ratio 4, 8 or 12 the unit bypassed fine and let the audio pass.
I can't calibrate the unit in ratio 20 this way.

Someone had this problem before?

I had this issue while putting my unit together.  I am very new to this, and the rev a was my first build.  My issue was caused by having the wiring backwards on the spdt bypass on the attack pot.  I had it wired so when the switch was in the off position (GR bypass) 22 was connected to GRN, not ground.  I am not sure if this helps you, but it caused me to not be able to pass audio in the 20:1 ratio, and thus unable to complete any other cal.

Best of luck.

Josh

 

[Pieter001]

I found the problem. Miswired the bypass switch. 
Have checked all the other connections with the wire picture and a meter. Now i have an other problem.
I try to calibrate the unit using the rev D movies on mnats site. The first 2 steps are no problem.
But at the 3th step i cant get my vu meter to show a 10db drop. Even with the input controll all the way up it show a little less than 10 db's

Did the first staps couple of times but it didn't chance. How can i get my vu to read a 10 db drop in bypass mode?

Thanks for all the help!

Pieter

 

[baadc0de]

Hi.

I've made some progress with my rev a, though I have found new problems as well..

This is an oscilloscope capture of a 1k sine after the input transformer, on the INPUT pad of the main PCB:

This is after the preamp circuit at the output pot pads (15, 17). Both pads have the same signal, as the output pot is fully open.

Now this is on the grey pad of the output transformer.. fail

Do you have any pointers as to where I should check for signal next? Something in between is killing it.

EDIT: this happens on all ratio and meter setting permutations. I have a rotary switch version. Q-bias has not been adjusted properly yet because I can't read anything at the meter yet, but I have listened to the signal coming back and have adjusted the q-bias for least audible distortion.

EDIT2: the problem persists when shorting 22 to gnd. Also, if I have been unclear - I can't calibrate the q-bias adjustment because I can't even hit -20dB on the meter!

Thanks in advance!