Build Thread:MS76

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LinusGrane

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Ok fine :)
If i have approximately 1.2v ac on the meter output on the board the VU meter should show 0?
If it still shows to less, what can i do then?
 

Gustav

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Ok fine :)
If i have approximately 1.2v ac on the meter output on the board the VU meter should show 0?
If it still shows to less, what can i do then?

Put a 20K trimmer in series with the two resistors highlighted, and adjust for meter 0 in VU out mode.

Gustavmtr.png
 

recokim

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20K로 변경하면 VU 동작을 시작합니다. 플레이판에는 10K라고 되어 있습니다. 10K가 설치하면 됩니다.
 

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Mugge

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The good news is, you can compare the bad channel to the good one for trouble shooting/voltages etc.

Find the discrepancy = find the problem, and try swapping ICs! (one at a time).

You only mention the meter and lack of compression. Are you hearing signal through channel 2, and you can change the gain with the pots?

If so, its definitely the SC youre looking at.

Gustav
Still not working. Tried swapping all the ICs one at a time. As mentioned, I'm hearing signal through both channels, and in/out knobs work on both channels as well. But still only a tiny tiny bit or no compression happening on channel 2/right channel, even at extreme settings. Tried comparing the two channels and all of the components, and they're all placed the right way and at the right spots on the PCB.
Could it have something to do with the 100uF electrolytic capacitor, where one of the pads fell off? As mentioned in my earlier post on page 5 in this thread.
There is a connection between the minus leg (the one where the pad fell off) and GND when I measure with the multimeter, but I'm still not sure whether it could be the problem. It's the only thing that's different from the left channel...
 

Gustav

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20K로 변경하면 VU 동작을 시작합니다. 플레이판에는 10K라고 되어 있습니다. 10K가 설치하면 됩니다.


He wrote 5dB - replacing with 20K would move it 6dB.Since his circumstance is special, using the bridge for the DC meter, adding the trimmer in series and adjusting makes more sense.

Gustav
 

Gustav

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Still not working. Tried swapping all the ICs one at a time. As mentioned, I'm hearing signal through both channels, and in/out knobs work on both channels as well. But still only a tiny tiny bit or no compression happening on channel 2/right channel, even at extreme settings. Tried comparing the two channels and all of the components, and they're all placed the right way and at the right spots on the PCB.
Could it have something to do with the 100uF electrolytic capacitor, where one of the pads fell off? As mentioned in my earlier post on page 5 in this thread.
There is a connection between the minus leg (the one where the pad fell off) and GND when I measure with the multimeter, but I'm still not sure whether it could be the problem. It's the only thing that's different from the left channel...

re:your questions about the 100uF - you can check this comparing to the other channel, simply by checking continuity with your meter, unless I am failing to understand some part of the question!?

For overall trouble shooting, you have the oppertunity to send an identical signal to the two units, and seeing where the signal path voltages differ - you can also go at one channel, and we can take that approach, but the ability to compare to a good channel is usually almost like cheating.

Gustav
 
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James Meder

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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

In regards to the refund, I did receive a refund for 33 euros but the pots plus the two missing resistors ended up being 47,94 euros after shipping to the US. Then I found many missing parts as I went along but I remember reading something about only '1 refund' so I thought I was outta luck. I could be mistaken.

Here's an update to my build (video attached). The output from my converters is roughly -10dBFS (setup as +4dBu), my bad for not mentioning that before. I ordered and replaced the 4 tantalum caps to the correct higher voltage version. Now I can get through the calibration procedure all the way through number 18 when I engage the 'comp in' (whereas before I couldn't even get through the Q-bias part). So I think I'm close. I may in fact have the ratio pot installed incorrect because that's were I seem to get hung up during the calibration - though I thought I had double checked that cuz it was confusing when I put it together and wanted to get it right...hmmm Both channels react the same.

<iframe width="560" height="315" src="
" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

Here's a photo of the inside if it's helpful:

Thanks for any insight!
 

Gustav

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In regards to the refund, I did receive a refund for 33 euros but the pots plus the two missing resistors ended up being 47,94 euros after shipping to the US. Then I found many missing parts as I went along but I remember reading something about only '1 refund' so I thought I was outta luck. I could be mistaken.

Here's an update to my build (video attached). The output from my converters is roughly -10dBFS (setup as +4dBu), my bad for not mentioning that before. I ordered and replaced the 4 tantalum caps to the correct higher voltage version. Now I can get through the calibration procedure all the way through number 18 when I engage the 'comp in' (whereas before I couldn't even get through the Q-bias part). So I think I'm close. I may in fact have the ratio pot installed incorrect because that's were I seem to get hung up during the calibration - though I thought I had double checked that cuz it was confusing when I put it together and wanted to get it right...hmmm Both channels react the same.

<iframe width="560" height="315" src="
" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

Here's a photo of the inside if it's helpful:

Thanks for any insight!
You are correct, I only do one replacement,wether its a shipment of spares or a refund. (I just wrote out the rationale behind that in the post you quoted, re:reading it somewhere))

If theres something about the parts and refund you want sorted, and dont feel was handled on my end, my mail is open at [email protected]. I dont think the MS76 help thread is the most productive place to sort that out, and prior to your post here, I considered it closed, based on sending you a partial refund.

As far as trouble shooting goes, I am not good with video. I just see "something is off", and from the video itself, I would guess there is a set-up/calibration issue, but that is wildly speculative.

Going on/off on trouble shooting with a long time apart, I have no recollection of the steps you have been through - it can be good idea to make a decision to "go at it", rather than go to and from, which makes it easier for me to focus and keep everything fresh in mind, if I am the one helping. Right now, I would start by asking you, if your main voltages are ok, and the voltage points around the transistors are ok, and we may have covered that a month ago!?

You mention the ratio switch, and as long as 1 goes to 1, 2 goes to 2 etc on the connector, wiring should be correct (never go by the pictures and colours, connectors can differ).

Also, be aware, that the ratio moves the threshold.

Gustav
 
Last edited:

James Meder

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I'm able to do the calibration procedure correctly through number 18 but when I engage the 'comp in' on the threshold on the lower ratios (2, 4) the needle moves all the way to the bottom of the meter. If I move the ratio to 20, it behaves how I believe it should and shows gain reduction starting form 0VU on the meter - that is what I was trying to describe on my video.

I can understand that the ratio moves the threshold but it doesn't make sense that it moves so low where it's unusable for the meter to show the gain reduction.

Should the 'TRK' trimmer be adjusted maybe? I'm a little confused how that trimmer is involved.

I've checked the voltages from the power supply section and at the resistors where the voltage is written and they are all correct. I will double check this though. I don't see voltages around the transistors on my board, it seems like the voltages only refer to the resistors.

Sorry for the delay in my response. There was another member with the same issue as mine - the tantalum caps supplied were the wrong voltage - so I had to order those and I've been able to get a lot closer to having it work correctly after finding that out. I also don't have a dedicated workspace... I sometimes have clients I work with in the same space so there are moments where I have to set the compressor aside for a while.
 

c1184701

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I'm able to do the calibration procedure correctly through number 18 but when I engage the 'comp in' on the threshold on the lower ratios (2, 4) the needle moves all the way to the bottom of the meter. If I move the ratio to 20, it behaves how I believe it should and shows gain reduction starting form 0VU on the meter - that is what I was trying to describe on my video.

I can understand that the ratio moves the threshold but it doesn't make sense that it moves so low where it's unusable for the meter to show the gain reduction.

Should the 'TRK' trimmer be adjusted maybe? I'm a little confused how that trimmer is involved.

I've checked the voltages from the power supply section and at the resistors where the voltage is written and they are all correct. I will double check this though. I don't see voltages around the transistors on my board, it seems like the voltages only refer to the resistors.

Sorry for the delay in my response. There was another member with the same issue as mine - the tantalum caps supplied were the wrong voltage - so I had to order those and I've been able to get a lot closer to having it work correctly after finding that out. I also don't have a dedicated workspace... I sometimes have clients I work with in the same space so there are moments where I have to set the compressor aside for a while.

This is the same problem I'm having!

I've been absent from his thread for a few weeks whilst I wait for parts to arrive. I've replaced my Tantalums with the correct voltage versions, as well as the FDH333 diodes. Still waiting for some 2N5457s from Banzai Music which I ordered a month ago.

I don't have much else to add at the moment, I have spent many hours troubleshooting this compressor but it has defeated me, I'm hoping someone else has some ideas about what we can try.
 

Gustav

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Should the 'TRK' trimmer be adjusted maybe? I'm a little confused how that trimmer is involved.

I thought you finished the calibration, then had a problem.

Just to be clear. Are you moving around the ratio, and drawing conclusions from the internal metering, before having finished the calibration?

The Trk/tracking adjust the reaction on the meter, so -3dB actually corresponds to 3dB gain reduction. Due to the spillover, you will need to do the 0 and trk adjustment a few times. This is described in the calibration guide.

I see I omitted the reference in step 22, which I have to admit is too "implied", unless you "know". What you do there is match with the trk trimmer, The previous steps ensures that what we are seeing in VU out will be identical to our GR, we then go in GR mode, and match that needle position with the trk trimmer, so GR mode shows actual amount of Gain Reduction.

Gustav
 
Last edited:

James Meder

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Just to be clear. Are you moving around the ratio, and drawing conclusions from the internal metering, before having finished the calibration?

The Trk/tracking adjust the reaction on the meter, so -3dB actually corresponds to 3dB gain reduction. Due to the spillover, you will need to do the 0 and trk adjustment a few times. This is described in the calibration guide.

I'm unable to finish calibration correctly. I was just sharing the ratio switching because it acts strange, more below. I've done multiple checks throughout the circuit and still haven't been able to discover a problem.

I double checked the voltages at the PSU and everywhere on the board where the voltages are printed and it's all correct. All the 12v sends are working correctly. I've checked the connector molex from the main board to the ratio board and it's correct.

Just for reference - during the calibration on #17 & #18, with the input pot at 9oclock, I have to set the output pot to roughly 3oclock to reach 0VU (I imagine this is fine and correct).

When I switch COMP IN (#19) and have the VU OUT selected, the meter falls all the way to the left (with ratio 2 is selected).
When I switch to GR the VU goes to roughly -6VU, and this is only after I put the TRK trimmer all the way counterclockwise - I can't get it any closer to 0VU.
Toggling back to VU OUT, I can only get the needle to reach 0VU when moving the INPUT pot to almost fully clockwise.

With the meter in VU OUT and I have the COMP IN, the odd thing is when I move the switch to ratio 8, the meter moves to -6VU. Then ratio 12, the meter moves to 0VU. Then ratio 20, the meter meter moves to +3.

Ratios 2 and 4 leave the meter all the way to the left. This is reflected similarly with the VU OUT on the meter.

With the compression out, it seems to hold unity as expected from the input, through to the output so I'm sure they're something wrong within the compression circuit.

Does anyone have ideas where I can troubleshoot further?

I've been absent from his thread for a few weeks whilst I wait for parts to arrive. I've replaced my Tantalums with the correct voltage versions, as well as the FDH333 diodes. Still waiting for some 2N5457s from Banzai Music which I ordered a month ago.
Are you having trouble with those components? I went through and checked all those parts in my circuit and they're good.
 

Gustav

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I'm unable to finish calibration correctly. I was just sharing the ratio switching because it acts strange, more below. I've done multiple checks throughout the circuit and still haven't been able to discover a problem.

I double checked the voltages at the PSU and everywhere on the board where the voltages are printed and it's all correct. All the 12v sends are working correctly. I've checked the connector molex from the main board to the ratio board and it's correct.

Just for reference - during the calibration on #17 & #18, with the input pot at 9oclock, I have to set the output pot to roughly 3oclock to reach 0VU (I imagine this is fine and correct).

When I switch COMP IN (#19) and have the VU OUT selected, the meter falls all the way to the left (with ratio 2 is selected).
When I switch to GR the VU goes to roughly -6VU, and this is only after I put the TRK trimmer all the way counterclockwise - I can't get it any closer to 0VU.
Toggling back to VU OUT, I can only get the needle to reach 0VU when moving the INPUT pot to almost fully clockwise.

With the meter in VU OUT and I have the COMP IN, the odd thing is when I move the switch to ratio 8, the meter moves to -6VU. Then ratio 12, the meter moves to 0VU. Then ratio 20, the meter meter moves to +3.

Ratios 2 and 4 leave the meter all the way to the left. This is reflected similarly with the VU OUT on the meter.

With the compression out, it seems to hold unity as expected from the input, through to the output so I'm sure they're something wrong within the compression circuit.

Does anyone have ideas where I can troubleshoot further?


Are you having trouble with those components? I went through and checked all those parts in my circuit and they're good.

On step 22, you should adjust the trk, so GR sits identically to VU out - if you are compressing too much, restart the calibration procedure with the input pot backed off 2 clicks, and try again, or try the trk (step 22 and on, with the repeat of the steps) in one of the ratio modes where you land inside the plate and check from there. Meter can be wildly off until calibrated/nudged into place, due to the spill between the 0VU and TRK adjustments.

Right now, it sounds like you are trying to adjust theTRK in GR mode to read 0 - I dont know if I am misreading this, but if so, that is incorrect. You should adjust it, so it mirrors what you are seeing in VU out. I understand that it slams the needle at some ratios, but refer to what I wrote above for an answer to that.

If this fails, it would be good to check if this is just the meter calibration, or the actual processing. Since you are using the meter to monitor behaviour, and meter behaviour is not verified to be correct, there is a danger we are fencing a bit blind here, which means, seeing what actually happens by reading the output of the unit/compression couold be a good idea.

Hope that helps get you further!

Gustav
 

James Meder

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On step 22, you should adjust the trk, so GR sits identically to VU out - if you are compressing too much, restart the calibration procedure with the input pot backed off 2 clicks, and try again, or try the trk (step 22 and on, with the repeat of the steps) in one of the ratio modes where you land inside the plate and check from there. Meter can be wildly off until calibrated/nudged into place, due to the spill between the 0VU and TRK adjustments.

Right now, it sounds like you are trying to adjust theTRK in GR mode to read 0 - I dont know if I am misreading this, but if so, that is incorrect. You should adjust it, so it mirrors what you are seeing in VU out. I understand that it slams the needle at some ratios, but refer to what I wrote above for an answer to that.

If this fails, it would be good to check if this is just the meter calibration, or the actual processing. Since you are using the meter to monitor behaviour, and meter behaviour is not verified to be correct, there is a danger we are fencing a bit blind here, which means, seeing what actually happens by reading the output of the unit/compression couold be a good idea.

Hope that helps get you further!

Gustav

With COMP IN, I have adjusted the TRK in GR mode to match VU OUT. For ratio 2 it's all the way to the left of the meter. So I move the TRK to match on VU OUT all the way to the left.

When switching COMP IN, the level drops significantly on ratio 2. When I change ratios, the meter moves to the right as I go up in ratios (this is reflected the same on my DAW return monitoring as well).

***I am able to calibrate it correctly at ratio 20. I'm doing little, to no compression when I do this. When I'm on ratio 20, I can move the INPUT pot and start to see the meter move downward on GR so that's correct.

With COMP OUT, the GR on the meter rests at 0VU.

The return monitoring on my DAW matches everything that I see on the VU.
 

Gustav

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With COMP IN, I have adjusted the TRK in GR mode to match VU OUT. For ratio 2 it's all the way to the left of the meter. So I move the TRK to match on VU OUT all the way to the left.

When switching COMP IN, the level drops significantly on ratio 2. When I change ratios, the meter moves to the right as I go up in ratios (this is reflected the same on my DAW return monitoring as well).

***I am able to calibrate it correctly at ratio 20. I'm doing little, to no compression when I do this. When I'm on ratio 20, I can move the INPUT pot and start to see the meter move downward on GR so that's correct.

With COMP OUT, the GR on the meter rests at 0VU.

The return monitoring on my DAW matches everything that I see on the VU.
so ratios and compression move correctly, but the reference is off.

And all voltages work out.

So, at this point, I would look for an incorrect resistor value, either causing your input gain to be way too hot, or to the SC/in the ratio, causing the SC reference to be way too hot.

Did you measure resistors as you put them in? You mention some missing, so if you were missing a value, start by checking if that/those values went into the board somewhere incorrectly, possibly the same basic value, but incorrect multiplier (100R instead of 100K i.e.).

If the 20:1 ratio is within normal range, just bites a little, it could be a 560R/560K swap on the ratio board, for example.

You could also check, if the ratios are moving correctly by backing off what you send, if thats the case, its in the threshold compensation portion of the ratio switch.

Hope that helps move you forward trouble shooting.

Gustav
 
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fragletrollet

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A few q's regarding parts:

BC107: any suffix (A/B/C) ok?

FD333: any suitable alternatives? I know FDH333 is available from Mouser and some other big distributors, but am trying to limit my sources as shipping and taxes for such small orders are substantial.

6.8uF film caps: all the caps I can find at my favorite retailers are huge, either axial high voltage caps, or huge high voltage MKT style box caps. Is this wima MK2 from Mouser suitable?

2n5457: is matching (what?) parameters of these of any importance? Aka, any reason to get more than the amount used in the project?

Also going to sub the obsolete 7910 for a 7912, as mentioned earlier in the thread.

best,
Magnus
 

JMan

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Hey everyone (and particularly Gustav),

I'm putting together a BOM for this project using the schematic and the board itself. I'll be happy to share it with the group once I've got it completed, as I believe (and hope) that it will be helpful for those of us that only have the boards (no full kit), since a published BOM does not exist.

To that end, I have a few questions that would really help me finish it up. Apologies that there are so many, but I hope you can help!

1. What is the value/taper/etc of the blend pot? I don't actually see it anywhere on the schematic, but I might just be blind.
2. The 10nF cap marked "(HP)" has an asterisk associated with it. Presumably this value can be adjusted to affect the frequency of the HPF (I'm just guessing). Is there any reason to include other options or perhaps clarifying information in my BOM, since an asterisk that leads nowhere tends to cause confusion?
3. The XLRS -- is there a product number for the male and female ones that will fit this footprint?
4. Is it alright to use 1n4004 diodes for all 1n400x designations in this design? Seems easier than ordering multiple varieties if a builder doesn't have any of these on hand.
5. Is there a meaningful difference between the FD333 and the more readily-available FDH333? Looking briefly at datasheets, they appear to be interchangeable, but I'd hate to assume and then be wrong.
6. The 2N5457 transistors seem to be a bit tricky to find (I grabbed some from Reverb, but who knows if other builders will have luck). I read that the PF5102 is a reasonable substitute, at least in guitar pedals, and I also found it easier to locate sellers for that one. Would that (or a different one) be acceptable in this design?
7. If substituting the 7912 for the 7910 as recommended in this thread, are any changes required for other components on the board?
8. For the two diode bridges in the PSU, are there any considerations when it comes to choosing one? The ones in the pictures in the build guide seem to be obsolete or otherwise unavailable. Will a W08G work? (I have a bunch lying around, so I'm hoping yes!)

9. Slightly off the topic of the BOM, but since the board is clearly meant to be supported in the rear by the XLR connections and there are no holes for stand-offs on that side, is it possible to get an fpd file or mechanical drawing of the rear panel so that we can have them made accordingly? This seems preferable to drilling new holes in the board lol.

Again, sorry for the numerous questions, and I hope that I'm not asking for redundant information that has already been covered in this thread (I did look, I promise!). Hopefully it is worth the trouble so that we can have a thorough and accurate BOM for these boards...
 

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