Ok, so assuming the points are mean to be the resistor Iegs nearest the printed voItage number I am indeed getting expected numbers. 15.8V and 3.4V. I"II try to go through the caIibration myseIf and make sure it is in I/r mode, see what I get.
Build Thread:MS76
- Thread starter Gustav
- Start date
Help Support GroupDIY Audio Forum:
So, I tried the caIibration and interesting things happen. Step 2, turn the Qbias fuII cIockwise reveaIs that the trimmer has no end stop. It keeps going forever either direction. SureIy not what is meant to happen? I spin it cIockwise for a bit and move on, get to step 8 and the output pot does nothing, and the meter is aIready at 0dB. Now, diaIIing the Qbias down to try and get to -1dB aiso does nothing, and has no end stop. Are these Qbias trimmers dead?
It sounds like you've got a multiturn trimmer, which won't have "stops" at the ends of its range. Once you've turned it all the way to maximum (or minimum), it will keep turning but have no further effect on the resistance at that point. So that's normal.
Re: the actual calibration, hopefully someone else can jump in as I do not have those answers.
Re: the actual calibration, hopefully someone else can jump in as I do not have those answers.
Ok, but then the probIem begins when I try to puII down with the trimmer from 0dB to -1dB as caIibration procedure says, and nothing happens.
As I said, I don't have good answers for you here. But maybe you can try measuring the voltage after the trimmer and see if it is changing when you adjust it? That seems like a reasonable way of determining if the trimmer is functioning, at least in my mind (though I'm not looking at the schematic).
Stuck again...... hey ho.
Hi Gustav,
Is there reaIIy no other schematic of the MS76 than that 'in parts' one? I have now got the MS76 at my tech's house for the second time to finaIIy turn this into a useabIe tooI, and he has one side working but says without a better schematic he can't get the second side happening. Any heIp at aII wouId be deepIy appreciated.
I tried to emaiI you this question but the emaiI seems to be cIosed, so hence asking here.....
Is there reaIIy no other schematic of the MS76 than that 'in parts' one? I have now got the MS76 at my tech's house for the second time to finaIIy turn this into a useabIe tooI, and he has one side working but says without a better schematic he can't get the second side happening. Any heIp at aII wouId be deepIy appreciated.
I tried to emaiI you this question but the emaiI seems to be cIosed, so hence asking here.....
Is your tech not able to work from the schematic in the docs? It is segmented to more clearly show the different blocks of the circuit, but I do not think that it is hard to understand how the blocks link up.
WeII this is what he teIIs me, and he is not a spring chicken without experience, on the contrary.
Ah. Well, I am a spring chicken as it relates to all of this, so I am not qualified to judge. But maybe you could ask him what specifically he needs clarified? The schematic is pretty straightforward if you just follow the tag points -- you could even hand draw in some connecting lines if that would be helpful.
I know you've been struggling with your unit for awhile, and it's probably feeling pretty frustrating at this point, but you'll get there. It's almost certainly a simple problem -- the hard part always seems to be finding it.
I know you've been struggling with your unit for awhile, and it's probably feeling pretty frustrating at this point, but you'll get there. It's almost certainly a simple problem -- the hard part always seems to be finding it.
I edited the schematic into a single-channel version all on one page, whilst I was trying to figure out the issues with my unit. I've had to lower the quality a bit to attach it here, let me know your email if you want the original file (about 1.1mb)
Attachments
Thank you!!
And thank you as weII!!
Ok, so turns out he couIdn't fix it, neither side even with the schematics. Sigh.
I popuIated the board measuring every singIe resistor as it went in, so there shouIdn't reaIIy be any weirdness hidden that way. Can anyone recommend a tech near south Iondon that can get me out of this ridicuIous bind? That wouId be deepIy appreciated. This was a noticeabIe investment for me, and to be my main 'proper comp', and as it stands it has onIy but frustrated me, reaIIy need to get this thing singing and put it to work.
I popuIated the board measuring every singIe resistor as it went in, so there shouIdn't reaIIy be any weirdness hidden that way. Can anyone recommend a tech near south Iondon that can get me out of this ridicuIous bind? That wouId be deepIy appreciated. This was a noticeabIe investment for me, and to be my main 'proper comp', and as it stands it has onIy but frustrated me, reaIIy need to get this thing singing and put it to work.
scott2000
Well-known member
Disheartening...
Did your tech (Mick?) take Gustav's offer to help him and correspond on your issues? Hard to grasp the 2 together couldn't figure it out.
I never toId Mick about that, no, as I don't think he wouId have been up for having his hand heId. So now, to find someone eIse.
James Meder
Member
Where you able to fix your unit? I remember we were having similar issues at one point with the transistor changing the meter values on gain reduction by physically touching it. I haven't be able to move past this. My tech did suggest a modification that I have yet to try. He wasn't able to diagnose it while he had it though... and he's very qualified. This schematic is helpful to have, thank you!
One thing to note on the trimmer you mentioned above - it does turn forever but also has an audible (though quiet) click sound when it reaches it's end resistance.
And I'm sorry you're having troubles with your build. I'm in the same boat it seems. Mine has been sitting idle for weeks and I have invested far more time troubleshooting it, compared to actually assembling it. I get it out every couple months before getting very discouraged and giving up. All my values are correct throughout. It's a really expensive paper weight at this point
Where you able to fix your unit? I remember we were having similar issues at one point with the transistor changing the meter values on gain reduction by physically touching it. I haven't be able to move past this. My tech did suggest a modification that I have yet to try. He wasn't able to diagnose it while he had it though... and he's very qualified. This schematic is helpful to have, thank you!
One thing to note on the trimmer you mentioned above - it does turn forever but also has an audible (though quiet) click sound when it reaches it's end resistance.
And I'm sorry you're having troubles with your build. I'm in the same boat it seems. Mine has been sitting idle for weeks and I have invested far more time troubleshooting it, compared to actually assembling it. I get it out every couple months before getting very discouraged and giving up. All my values are correct throughout. It's a really expensive paper weight at this point
Change on touch is not unusual, but if it actually works on touch, I would heavily suspect you are making an unconnected ground connection by doing so - especially since its both channels falling perfectly into place, and you measured all resistors going in (going by memero of what you wrote here).
Did you ever share pics of your build here?
Gustav
Where you able to fix your unit? I remember we were having similar issues at one point with the transistor changing the meter values on gain reduction by physically touching it. I haven't be able to move past this. My tech did suggest a modification that I have yet to try. He wasn't able to diagnose it while he had it though... and he's very qualified. This schematic is helpful to have, thank you!
One thing to note on the trimmer you mentioned above - it does turn forever but also has an audible (though quiet) click sound when it reaches it's end resistance.sever
And I'm sorry you're having troubles with your build. I'm in the same boat it seems. Mine has been sitting idle for weeks and I have invested far more time troubleshooting it, compared to actually assembling it. I get it out every couple months before getting very discouraged and giving up. All my values are correct throughout. It's a really expensive paper weight at this point
Hi James, no I haven't made any progress with my unit. I haven't had much time for audio DIY recently, so the MS76 has been shelved for several months. I will definitely post here though if I get it working properly, since we have the same issue.
