New development on old project: Roger Mayer RM58

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soapfoot

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Dec 27, 2010
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Starting a new thread here for a few reasons:

1) The previous RM57 thread had evolved more into a discussion of the RM58

2) That thread had turned into quite a journey, and this seemed tidier.

Using Spencerleehorton's great work in that thread as a starting point, I decided I'd like to make a version of this circuit that incorporated Roy Cicala's modifications to include UTC transformers on the input and output.

Using Spencer's schematic (which is accurate) combined with original documentation and some old photos, I laid out the circuit on three separate PCBs, separating the booster and the limiter into separate cards as the original had done, as well as a small board for a very simple +18v regulated DC supply.

I've got Gerber files of each that I'll attach below (sorry; format not supported by forum software); JLCPCB did a great job on them and turned them around quickly. Pleased to say that everything worked more-or-less properly the first time, with only a few kinks to iron out.

The one change I made to the circuit: I lowered R31 to 6k8, which, combined with connecting the VU meters in reverse, allowed me to set the zero point at 0VU and have it swing to the left under gain reduction, which is more conventional and more to my liking (the original showed gain reduction starting from far left and swinging toward the right under GR).

Finally, I also designed an enclosure in Protocase Designer which I had them make up for me, and it turned out quite well!

I'll upload the Protocase Designer file as well as the Gerber files below in case anyone else wants to have a go. The PCBs are laid out for the specific components I chose... I never put together a full BOM with part numbers, but if there's interest I'd be happy to take the time to do so.

I've gotten a lot of help on this forum on other projects, so I'm happy to share this if it's useful to someone.
 

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soapfoot

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Well, I made a .zip archive with Gerber files of the PCBs and a Protocase Designer file for the chassis, but neither .zip archives nor the associated file types are acceptable attachment types for this forum. I don't always check PMs super-regularly, but feel free to try me with an e-mail address and I'll send to you if needed!

I'll get to work on at least a partial BOM to include in the folder as well.

Happy to share photos of my completed build if anyone is interested. One thing I did was to include the resistors for the stepped release time control on the limiter PCB itself (instead of hanging them off the rotary switch like the original)

Whereas the Record Plant RM57/58 had UTC A21s on input and output, I used A21s on input and A20s on output.
 

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soapfoot

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Rocinante said:
Looks great man. I might consider giving it s whirl

If you do, send me a PM with your e-mail address and I'll forward all files and documents I have.

I kept all of the Gerber files and the Protocase Designer file current and revised as I made tweaks, so everything should be quite ready to go.

One thing I did--instead of hanging the release time resistors off of the rotary switch like in the original, I added them in their own section of the Limiter Board PCB. I labeled it up and color-coded it so it's easy to connect (the pole of the rotary switch connects to point "B" as in the originals).
 

soapfoot

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Brought this by the studio today. Didn't have much time to play around, but did have time to do this:

"All faders at unity" super-rough drum submix, attack and release both at maximum-fast (both of which are still pretty slow!), and a healthy amount of input level, quite a bit of squish happening.

I just recorded the output of the compressor, but it's really nice in parallel.

I find it to be impressively smooth considering how much compression is happening, and really nice and thick, too.

 
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MidnightArrakis

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Sep 25, 2015
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Soapfoot: GREETINGS!!! I would like to take a look at your GERBER and Protocase files. Your project sounds interesting!!! You can send me your files at this e-mail address: midnight_blue_studios (at) yahoo (dot) com

By the way, since you are having difficulty in sharing your files with others on this forum, I would recommend that you create an account on one of the many FREE web-storage sites (i.e. -- box.com -- and -- mega.nz -- are two that I use quite a bit) and upload your files there to share. Once you upload either a single ZIP file or a folder full of GERBER files, you can then easily obtain a link to your files or folder and then paste it into this text box. HOW??? Do you see that symbol that looks like a "chain" right in the middle of the toolbox up above, right there next to what looks like a "picture" symbol? (The rectangle with a "triangular pyramid" shape in it). When you place your mouse cursor over it, a piece of dialog will pop-up saying "Insert Link" and then when you click on it, you'll get a pop-up window asking for you to paste your link there and add a short piece of descriptive text.....kind of like this:

Some Of My Rack-Mount Chassis Designs

Now, should you click on the text that says, "Some Of My Rack-Mount Chassis Designs", you will be taken to an online web-storage site that I have and you will be presented with this huge PDF file that would be way too large to upload onto this forum. And, once you are viewing my PDF file, you will see in the upper-right hand corner a "Download" button, should you wish to do that. But, I'm talking about you here and anyone on this forum would be able to obtain your shared files and download them for themselves. SEE??? Wasn't that easy??? By the way, this PDF file of mine above is on the " box.com " website.

HAPPY SHARING!!!

JBW

/
 

vitopower

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Jul 23, 2009
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St. Louis, MO
Thx, Soapfoot, Spencer, Ruud and all involved. I ordered parts a while back and was going to etch, now this will be even better.
 

Rob Flinn

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Hi Soapfoot. I had some of your boards made & I'm just getting them populated. What value is R33 ? I can't see it on the BOM.
 

Spencerleehorton

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May 12, 2012
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Felixstowe, Suffolk, UK
my findings so far are to :
1. use 50k trimmer for R27 to dial in symmetrical waveform (normally around 15-20k),
2. Screened leads for input/output and use input/ouput txts
3. Use 0.47uf tantalum for C10
4. Match both FETs (quad FETs if doing stereo unit)
5. Use 2.2Meg pot for release 22k pot for attack, 100k for input, 10k for output
6. if you want to bypass compression use a bypass switch, between VR5 and C7, GND one leg
7. Use BC550c throughout along with BC560c for the PNP.
 

soapfoot

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Dec 27, 2010
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For whatever it’s worth, I didn’t need to use shielded wire anywhere in my unit, and it’s dead quiet… but power transformer orientation was important!

I have some PMs, I promise I’ll get to them… it’s been a crazy month
 

groselicain

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Feb 9, 2009
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169
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Tennessee
Brought this by the studio today. Didn't have much time to play around, but did have time to do this:

"All faders at unity" super-rough drum submix, attack and release both at maximum-fast (both of which are still pretty slow!), and a healthy amount of input level, quite a bit of squish happening.

I just recorded the output of the compressor, but it's really nice in parallel.

I find it to be impressively smooth considering how much compression is happening, and really nice and thick, too.

My goodness, that's gorgeous sounding—both the recording and the compression.
 

RuudNL

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Apr 26, 2009
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Location
Haule / The Netherlands
The one change I made to the circuit: I lowered R31 to 6k8, which, combined with connecting the VU meters in reverse, allowed me to set the zero point at 0VU and have it swing to the left under gain reduction, which is more conventional and more to my liking (the original showed gain reduction starting from far left and swinging toward the right under GR).

I have experimented a lot to get a reliable reading of the gain reduction with the meter needle moving 'backwards', but without much success.
How is the tracking between actual gain reduction and the meter indication?
It is no problem to get the meter moving in the right direction, but I experienced that it is difficult to get a true indication of the gain reduction at low amounts (1 dB) AND at much higher amounts of gain reduction (say: 15 dB).
Of course I used matched (quad) FETs.
 

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