Build Thread:MS76

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Gustav

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Jun 4, 2004
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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...

These were only sold as kits, and when I stopped those sales, I offered the spare boards. There were about 10, and I found a pile of another 20 when I cleared out the PCB storage. I dont think there is a huge need for a shared BOM based on that.

To try and help you.

1. 2 x 10K lin will do.
2. You are correct, it sets the SC HP. Its rather high "stock", but you can change as you wish.
3. They are just neutrik PCB mount XLRs.
4. Yes - 4003 is fine throughout.
5.You can use both.
6. No idea - youd have to try, but again, we dont really need a public BOM, so just find the 2n5457 for your build, and dont worry about universal availability.
7.Up the trimmer values a little - next step in line will be fine.
8. As long as the minimum voltage and amperage rating are fine, you will be fine. Your mentioned part is rated 800V, 1.5a, which is more than enough.
9.Lay board on bottom of case, punch markers, and drill, if you want to add support studs.

Gustav
 

James Meder

Member
Joined
Aug 19, 2012
Messages
8
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

I'm checking back here after having to take some time away from the build due to work.

I have tried backing off the level of what I send and it doesn't change how the ratios react. It just does little to no gain reduction on all ratio settings after following the calibration setup. The level drops when I engage the 'comp in' and the threshold gets way low on the lower ratios - even when giving it no signal.

I did measure the resistors when I put them in but I could have mixed something up so I'll go through those.
I have the pcb diaphragm for the main board from an earlier post, but could I get the one for the aux pcb's please?
 

Gustav

Well-known member
Joined
Jun 4, 2004
Messages
2,211
Location
DK
I'm checking back here after having to take some time away from the build due to work.

I have tried backing off the level of what I send and it doesn't change how the ratios react. It just does little to no gain reduction on all ratio settings after following the calibration setup. The level drops when I engage the 'comp in' and the threshold gets way low on the lower ratios - even when giving it no signal.

I did measure the resistors when I put them in but I could have mixed something up so I'll go through those.
I have the pcb diaphragm for the main board from an earlier post, but could I get the one for the aux pcb's please?


Ok!


Documents folder/MS76.

AUX board overlays (I "cut" it out of the main schematic to separate the board layout, but kept the placements for overlay reference).

Gustav
 
Last edited:

c1184701

Member
Joined
Jul 7, 2016
Messages
9
I'm checking back here after having to take some time away from the build due to work.

I have tried backing off the level of what I send and it doesn't change how the ratios react. It just does little to no gain reduction on all ratio settings after following the calibration setup. The level drops when I engage the 'comp in' and the threshold gets way low on the lower ratios - even when giving it no signal.

I did measure the resistors when I put them in but I could have mixed something up so I'll go through those.
I have the pcb diaphragm for the main board from an earlier post, but could I get the one for the aux pcb's please?

Hi James, I'm still certain we have the same issue. Apologies for not posting more, I have also been busy with work.

I have made some progress with my unit, and I can now get it operating correctly, although the fix is a bit unusual... I'm hoping you would be up for seeing if you get the same results with your unit.

With my unit in 2:1, the meter is buried to the left, and there is very little output. If I physically touch the top of the BC107 next to the 6-pin connector (I've highlighted it on the attached image) the meter springs back to zero where it should be. I can send drums through, and now the unit is compressing properly at all ratios, provided I keep my finger on the top of that transistor.

I know it seems unwise poking around with your fingers, but this component only has 15V DC on it, it won't cause you any harm.
 

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Gustav

Well-known member
Joined
Jun 4, 2004
Messages
2,211
Location
DK
Hi James, I'm still certain we have the same issue. Apologies for not posting more, I have also been busy with work.

I have made some progress with my unit, and I can now get it operating correctly, although the fix is a bit unusual... I'm hoping you would be up for seeing if you get the same results with your unit.

With my unit in 2:1, the meter is buried to the left, and there is very little output. If I physically touch the top of the BC107 next to the 6-pin connector (I've highlighted it on the attached image) the meter springs back to zero where it should be. I can send drums through, and now the unit is compressing properly at all ratios, provided I keep my finger on the top of that transistor.

I know it seems unwise poking around with your fingers, but this component only has 15V DC on it, it won't cause you any harm.

Please measure from pin 1 on your XLR to chassis.

Do you have continuity/very low (a couple of ohms) resistance on the meter?

Gustav
 

James Meder

Member
Joined
Aug 19, 2012
Messages
8
Hi James, I'm still certain we have the same issue. Apologies for not posting more, I have also been busy with work.

I have made some progress with my unit, and I can now get it operating correctly, although the fix is a bit unusual... I'm hoping you would be up for seeing if you get the same results with your unit.

With my unit in 2:1, the meter is buried to the left, and there is very little output. If I physically touch the top of the BC107 next to the 6-pin connector (I've highlighted it on the attached image) the meter springs back to zero where it should be. I can send drums through, and now the unit is compressing properly at all ratios, provided I keep my finger on the top of that transistor.

I know it seems unwise poking around with your fingers, but this component only has 15V DC on it, it won't cause you any harm.

I'm really surprised but mine does seem to start working correctly as you mention when I place my finger on that transistor.

Please measure from pin 1 on your XLR to chassis.

Do you have continuity/very low (a couple of ohms) resistance on the meter?

Gustav

Yes - I have a reading of 11ohms. What does this mean?

Thanks for the pdf, that's perfect. I'm going to go through and see if I misplaced any resistor values.
 

Gustav

Well-known member
Joined
Jun 4, 2004
Messages
2,211
Location
DK
I'm really surprised but mine does seem to start working correctly as you mention when I place my finger on that transistor.



Yes - I have a reading of 11ohms. What does this mean?

Thanks for the pdf, that's perfect. I'm going to go through and see if I misplaced any resistor values.

It could be you are making the connection for a missing reference, so wanted to see if you have chassis connection on the GND

It could also be that you are skewing a reference, and thereby getting it into range, but messing up the reference, and just by chance being "spot on", relative to some build error, seems very unlikely.

Not sure here - one of those things where it could poke me in the eye, if I was sitting with it, or did 2-3 measurements to check, but Im not seeing it right now.

Gustav
 

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