Build Thread:MS76

[scott2000]

If that 47uf cap negative goes to ground, it'll be fine.It may not though so be sure.
Any components next to it may have a connection to ground as well. Just use your meter to check.

 

[Mugge]

If that 47uf cap negative goes to ground, it'll be fine.It may not though so be sure.
Any components next to it may have a connection to ground as well. Just use your meter to check.

Well, it does actually look like it is connected to ground in the schematics?? (See the attached picture)

 

[scott2000]

Not sure what you're trying to say. The 100uf cap negative you are saying goes to ground? Or the 47pf cap has a ground? You had mentioned a 47uf cap. Too bad the components on the pbc aren't silkscreened. Would make it a bit easier.

 

[Mugge]

Not sure what you're trying to say. The 100uf cap negative you are saying goes to ground? Or the 47pf cap has a ground? You had mentioned a 47uf cap. Too bad the components on the pbc aren't silkscreened. Would make it a bit easier.

The 100uF negative goes to ground. Tried checking with the multimeter, and there was a connection between the two although the pad fell off...

 

[JMan]

Looks like that's a ground connection. If you aren't able to get a good connection to ground because of the damaged pad, you could try connecting the negative side of the capacitor to the bottom leg of that 1k8 resistor right next door (on the schematic). Everything along that horizontal line is connecting to ground, presumably through a ground plane on the board.

EDIT: For some reason, the site only showed me Mugge's first question about this damaged pad until I replied, at which point it suddenly loaded a whole bunch of extra responses lol. Guess this has been answered already.

 

[Mugge]

Looks like that's a ground connection. If you aren't able to get a good connection to ground because of the damaged pad, you could try connecting the negative side of the capacitor to the bottom leg of that 1k8 resistor right next door (on the schematic). Everything along that horizontal line is connecting to ground, presumably through a ground plane on the board.

EDIT: For some reason, the site only showed me Mugge's first question about this damaged pad until I replied, at which point it suddenly loaded a whole bunch of extra responses lol. Guess this has been answered already.

Thank you for the reply anyway! I tried measuring with the multimeter between the cap (where the pad fell off) and the point at the PCB that says GND on the right side of the PCB. And there was a connection, so I'm quite sure that it's okay.

 

[LinusGrane]

Hello, i have finaly put my ms76 together but i guess i have put in VU meters whit the wrong impedance. It was impossible to callibrate. Does anybody know the right specs?

 

[Gustav]

Hello, i have finaly put my ms76 together but i guess i have put in VU meters whit the wrong impedance. It was impossible to callibrate. Does anybody know the right specs?

Hi Linus

Send a 0dBU signal to the unit, then check the meters on "input" setting.

What do you see?

The meters are not wrong spec, unless they are not actually VU meters, but DC meters - inability to be able to calibrate indicates either 1. a problem with the circuit, or 2. some mistunderstanding in the calibration procedure.

Make sure you aren in L/R mode, make sure blend is out.

...and let us know more specifically, what the problem with calibration is.

Gustav

 

[LinusGrane]

Ok, when i send the 0dBU signal the meter cant reach 0, only -10 or -7 (if i boost the signal way too high).

 

[Gustav]

Ok, when i send the 0dBU signal the meter cant reach 0, only -10 or -7 (if i boost the signal way too high).

"way too high" is a little vague.

Does the increase in the meter correspond to the increase in the signal youre sending to the unit "boosting it way too high"?

Check at the output of the 1206, and see if your signal is coming out and responding as expected.

To be clear. I would not proceed with trouble shooting assuming the meter is not showing what is actually going on/blaming the meter, before I had measured directly on the circuit to check if that was the case.

Hope that makes sense.

Gustav

 

[LinusGrane]

sorry "way to high" is not so specific
I made a little video to show how the compressor respond to the 1khz sine wave (0:22 mobile phone in to a preamp whit balanced output in to the input of the MS76)


How do i check the 1206 output?

Best
/Linus

 

[Gustav]

sorry "way to high" is not so specific
I made a little video to show how the compressor respond to the 1khz sine wave (0:22 mobile phone in to a preamp whit balanced output in to the input of the MS76)


How do i check the 1206 output?

Best
/Linus

I dont really have the mindset to do troubleshooting via video, and in my experience, its really a mess for trouble shooting. Maybe someone else reading the thread, who reads video better than me can chime in on that.

If I am to help, it would help me if you wrote wether the increase on the meter corresponds to the increase in amplitude you are sending to the unit. So, if you increase the signal sent to the unit by 1dBU, does the meter go up 1dB (even if the outset it too low).

To check the output of the 1206 (or replacement, if you are using that), you find the output pin of the chip. You can do that by looking for the datasheet.

I have a description here for power-up and start up, which also gives a good hint on how to find the chip set-ups.

https://www.pcbgrinder.com/post/power-up
As it is now, I would say that focusing on the meter is not helpful. There can be various things at play - maybe you reversed the meter selector, or you have a problem in that part of the circuit, or maybe there is a basic circuit problem. Maybe your bias is set really high on the outset!?

For now, its like getting a reading on your 15V supply with a voltmeter of 11V and starting off by chasing after a problem with the voltmeter, instead of the supply in terms of how I think.

I would go about it by first checking how the circuit acts, and if its good, then the next step is making sure the meter shows that behaviour.

Hope that helps you a step, and hope someone more videooriented comes along!

Gustav

 

[LinusGrane]

the 1206 seems to be ok. Checked the input (3) and output (6) whit my old oscilloscope and the sine wave looked the same.
Also checked the voltage test-points on the pcb and they seems to be ok (diffed 0,1-0,2v on some points)

 

[James Meder]

Hey all, I'm gonna chime in with my experiences here. Thanks for reading and for any insight anyone is able to offer.

First, just a little overview of my build experience. I'm an amateur builder but have done many small builds and have recapped/troubleshot a bunch of vintage circuits successfully. I dealt with the headache of sourcing many missing parts in my kit (meter hardware, mounting hardware for the power pcb and voltage regulators, missing resistors, the 6pin molex pinouts/cabling, and the default extra pots that were mentioned in the note). I ended up spending quite a lot of money after shipping costs ...and after 'finishing' the build, my unit is having issues. With all this adding up, I'm pretty frustrated but I'm trying to keep focused so that I get this working. Thanks for all the useful links in this thread so far from other users and Gustav - many have been very helpful.

It seems I'm echoing some of the others who are having difficulties.

I have audio coming through both channels, unity in/out and both channels are showing the same issue. I don't have the 'm/s', 'all' or 'wet/dry' engaged when calibrating.
My voltage coming off the power pcb is all correct (other that the -12v as stated in the note).
I follow the calibration procedure for the Q-bias. I have the Q-bias pot completely right. With roughly a -10db signal from my converters, I'm able to get the meters to read 0db 'VU in'.
Once I switch the meters to 'VU out' and adjust the 'input' pot to 12o'clock and try to adjust the 'output' pot so that it reads 0db, the meter never moves past -20db even fully clockwise. If I have the 'input' and 'output' level fully clockwise, I get 0db but it can't go higher.

If I set the 'input' to 12o'clock and engage the 'wet/dry' pot, I'm able to get 0db and higher - I notice this happens independent of the 'output' pot, because it's all the way down.
That's as far as I can get. I don't get any compression. The relays all seem to engage as far as I can tell. I notice when I switch in the 'link m/s', the level on channel 2(side) is roughly halved and is reflected on the meter (I understand I likely can't properly judge this until after calibration).

I have used my scope to see the signal on the four 'tp' points on the pcb. It seems like 1, 2, and 4 all show the same gain, but 3 looks to be halved.
I have tested the voltage on the resistors wherever I find there's a number on the pcb, and they all test correct.

My kit came with 10k Linear input pots but I emailed Gustav and he said they should be 10k Log - so I have the 10k Log installed on mine. Is this correct? I assume that would change the 12o'clock throw point if it's supposed to be linear.

I've had a tech who was kind enough to go through it with me after I tried my best. He didn't appreciate the layout of the schematic but was able to follow the signal path through quite a lot of it. He has a couple ideas for me (nothing that is a certain/obvious fix) ...so before I do that, I'd like to see if there's any obvious mishaps that someone can identify. Or maybe just a place to start to troubleshoot further.

Thanks for any thoughts!

 

[Gustav]

Hey all, I'm gonna chime in with my experiences here. Thanks for reading and for any insight anyone is able to offer.

First, just a little overview of my build experience. I'm an amateur builder but have done many small builds and have recapped/troubleshot a bunch of vintage circuits successfully. I dealt with the headache of sourcing many missing parts in my kit (meter hardware, mounting hardware for the power pcb and voltage regulators, missing resistors, the 6pin molex pinouts/cabling, and the default extra pots that were mentioned in the note). I ended up spending quite a lot of money after shipping costs ...and after 'finishing' the build, my unit is having issues. With all this adding up, I'm pretty frustrated but I'm trying to keep focused so that I get this working. Thanks for all the useful links in this thread so far from other users and Gustav - many have been very helpful.

Hi James.

If you were not refunded for your missing parts report/acquisitions list, please let me know. Ill search through the mail archives to verify and make sure you are! I offered this to anyone missing parts. I am truly sorry about the missing parts. The lack of consistency in the kits is a big reason why I shut it down to focus on GOLY, even after finding a third party to pack them. Shipping out a missing resistor, just to get a mail about another missing resistor the week after, and a missing cap the week after that, is as frustrating and time consuming on my end as it is for the builder, so I have asked that people send me a final list of parts missing to avoid this part-by-part fulfillment.

Again, I am sorry if I did not make such an offer to you, and you should get in touch, if you were not compensated.

Input pot should be 10K log,
Output pot should be 100K log.

If they are not, it will certaintly throw off calibration using my instructions.

For the reference signal, you state that your signal is set to -10dB to reach 0. I dont know what that is without reference, but FYI, the meter should be set up, so 0VU =+4dBU.

For the schematic, if you are having trouble following it, note that the aux board "overlays" on the main board schematic. That should make it pretty easy to trace out.

I have built many of these, and seen many sucessfull builds, so I have no doubt the basics of it are solid - I have also built it using the 7912 regulator instead of the 7910, since that went obsolete, but - I slightly suspect there may be some ideosyncracy with the difference in voltage on that rail (like where the trimmers start out), that doesnt make me think twice, because I sort of know my way around it, but could cause problems for a beginner.

Maybe try to find a 7910, replace it, start over calibration, and let us know. .

You can also check to see if the ratio switch is stopped correctly, and if you have reversed the connector to the ratio board. If all voltages are correct, as well as the printed ones around the transistors, the most common errors are really cleared.

Also, what if you dial the Q-bias completely left instead of right at the outset? (I cant remember which way its set to be turned. This is something I just adjust and see) (edit:sorry, just checked the write-up for calibration, and if I specified it, it will be correct).

Did you make sure compression is out?

And please double check if you reversed the input and output pots by any chance (not just the auxilary PCB mount, but observing the orientation/mounting is upside down as shown in the build guide, so you dont have out on in, and in on out, or even the connectors to main crossed).

Gustav

 

[Gustav]

the 1206 seems to be ok. Checked the input (3) and output (6) whit my old oscilloscope and the sine wave looked the same.
Also checked the voltage test-points on the pcb and they seems to be ok (diffed 0,1-0,2v on some points)

The meter in "VU in" should show you what you have on the output pin of the 1206.

Does it do that, and does the meter level reflect increases/decrases in level sent to the unit?

Gustav

 

[LinusGrane]

Does it do that, and does the meter level reflect increases/decrases in level sent to the unit?

The needle moves but only to about -10, 0 is impossible. The signal reaches the + on the meter but is weaker when i test it whit the oscilloscope.
This is the type of VU meter i use to the project: 2pcs TN-73 VU Meter Power Verstärker DB Ebene Header Audio Meter Chassis | eBay

Just to be shure, the on-off switches in the blend pots is not connected to the +12v and the pcb, is that a problem?

Thanks
/Linus

 

[Gustav]

The needle moves but only to about -10, 0 is impossible. The signal reaches the + on the meter but is weaker when i test it whit the oscilloscope.
This is the type of VU meter i use to the project: 2pcs TN-73 VU Meter Power Verstärker DB Ebene Header Audio Meter Chassis | eBay

Just to be shure, the on-off switches in the blend pots is not connected to the +12v and the pcb, is that a problem?

Thanks
/Linus

Im sorry for being unclear.

I do not need the absolute or max reference, what I need to know, to take it "step-by-step", is the following.

If you send xdB to the unit, and see ydB on the meter in the VU in setting, and you increase the signal you are sending to xdB+1dB, does the showing on the meter also increase to ydB+1dB?

This is a really simple test at a very early stage of the circuit, to get an idea of how the meter reacts.

If it does give a 1:1 increase, as expected, I would next ask you to measure the actual voltage on the output of the 1206, relative to the actual reading on the meter.

For these steps to "work", the blend does not matter, were checking at a very early stage of the circuit to do basically clear, how your meter is reacting.

Take a look at the schematic, and see if you can spot, how the "VU in meter setting taps the signal at the output of the 1206 right at the input, before anything else happens through the circuit.

If you cant shake the feeling its the actual meter, it could be beneficial if you just get a different one, then proceed with trouble shooting, if it doesnt solve your issue. The model I used for my panel design is TR57,

https://www.google.com/search?q=TR5...hUKEwij7dj49a_yAhWDQvEDHcOCAsIQ4dUDCA4&uact=5
Hope that helps!

Gustav

 

[Gustav]

For reference.

I have tried to make it clear, so when you look at the schematic, you might be able to see, why I ask you to check the meter on the VU in. Nothing really happens, so here we can check for reference. What I am asking you to do is first to check if a 1dB increase in what you send into the unit translates to a 1dB increase on the meter, and on the 1206 output.

If the level of the meter in VU in mode is dependent on any settings on the unit, thats also a clear indicator, there is some error, as you can see,"VU IN"really just monitors, what you are sending to the unit, and not any internal adjustments with the pots.

 

[Harpo]

This is the type of VU meter i use to the project: 2pcs TN-73 VU Meter Power Verstärker DB Ebene Header Audio Meter Chassis | eBay

The TN73 seems to be a 1mA meter, (missing the internal rectifier) , so not a true VU-meter.