Roger Mayer RM57 build?

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Some time ago, I published my version of the 'modernized' Roger Mayer limiter:
https://groupdiy.com/index.php?topic=13287.msg907132#msg907132

I designed the PCB very quick, and didn't bother to place the component values on the layout.
Well, here they are!  (Some forum members asked for it.)
Take care of the orientation of the electrolytic capacitors! It might be that they are shown reversed on the PCB layout, because I didn't pay much attention to this when I designed the PCB. (After all: a capacitor is a capacitor...  :D )
Components are seen from the copper side of the PCB!!!
 

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he already did a few posts above :

The VU meter I used is a pretty standard one (I think it was a Monacor), for the measurement of the output level it is simply connected through a 3.6K resistor to the output. (Driving impedance is low here, so no extra distortion from the rectifier in the VU meter.)
For the gain reduction measurement I am using an experimental circuit.
Without signal, the VU meter indicates 0 VU and moves back when gain reduction occurs.
At the moment I am still optimizing this circuit, because there are a few (small) problems:
- The '0 VU' drifts a little with temperature (You can see the small holes between the meters for '0 VU' calibration.)
- Indication isn't really exact. (At 5 dB a bit too much, at 10 dB a bitt too little.) Not a real problem, error is in the 1 dB range, but I would like to see the exact amount of gain reduction.
 
Recently I made another version of the 'modernized' design, this time as a 'plugin'. ;D
Works perfectly. Also good stereo tracking.

plugin-module.JPG
 
So!

I've got what's shaping up to be a pretty nice build going. I made gerber files of the PCBs which I will happily share once I get my unit tested and verified. In the meantime, I wonder if anyone can help me try to figure out a good calibration procedure?

I'll re-attach Spencer's most recent schematic (which I'm working from), along with some notes:

  • VR1, the original documentation says: "Do not adjust, factory set"
  • VR2, original docs say: "Adjust so meter reads zero when output has reached threshold of limiting." Seems easy enough, though determining when that threshold has been reached will require a method of some sort
  • VR3 again says: "Do not adjust, factory set"
  • VR4 in the original is a supply voltage trim, and is made obsolete by a good regulated 18V supply; not included on my unit
  • VR5, docs say: "Adjust to give 0dbm at pin L with 0dbm being applied to
    pin H." This might be a stupid question, but... dB milliwatts? How would I measure this?
  • VR6 is another "do not adjust, factory set

VR1, I'm rather clueless what to do.

VR2, I'm pretty sure I can handle.

For VR3, the old hand drawn schematic appears to say "VR ADJ BIAS (at slo release)" and then another notation in proximity that says "4.4-5.4 V". I assume I adjust adjust this until I read something like 5v... somewhere? This VR eventually connects (through attack and release controls, etc) to the gate of Q10, so maybe gate-source voltage there?

VR5 my only question is... what test equipment do I need to read "dBm," (dB milliwatts, or could they mean dB VU?) and when they say "0dbM applied to pin H" do they mean... signal from a function generator? I'm just a bit confused.

VR6, on the hand drawn and annotated schematic, there's a note in red that says "Waveshape adj. (symmetry)(2f in) (at slo attack)" Off to the side, in black, there's a note that says "5.9k total" with an arrow pointing to the red annotation.

I lack the knowledge to truly understand every aspect of what's going on here in the design, so I'd appreciate if anyone could help me make heads-or-tails of this.
 

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So!

I've got what's shaping up to be a pretty nice build going. I made gerber files of the PCBs which I will happily share once I get my unit tested and verified. In the meantime, I wonder if anyone can help me try to figure out a good calibration procedure?

I'll re-attach Spencer's most recent schematic (which I'm working from), along with some notes:

  • VR1, the original documentation says: "Do not adjust, factory set"
  • VR2, original docs say: "Adjust so meter reads zero when output has reached threshold of limiting." Seems easy enough, though determining when that threshold has been reached will require a method of some sort
  • VR3 again says: "Do not adjust, factory set"
  • VR4 in the original is a supply voltage trim, and is made obsolete by a good regulated 18V supply; not included on my unit
  • VR5, docs say: "Adjust to give 0dbm at pin L with 0dbm being applied to
    pin H." This might be a stupid question, but... dB milliwatts? How would I measure this?
  • VR6 is another "do not adjust, factory set

VR1, I'm rather clueless what to do.

VR2, I'm pretty sure I can handle.

For VR3, the old hand drawn schematic appears to say "VR ADJ BIAS (at slo release)" and then another notation in proximity that says "4.4-5.4 V". I assume I adjust adjust this until I read something like 5v... somewhere? This VR eventually connects (through attack and release controls, etc) to the gate of Q10, so maybe gate-source voltage there?

VR5 my only question is... what test equipment do I need to read "dBm," (dB milliwatts, or could they mean dB VU?) and when they say "0dbM applied to pin H" do they mean... signal from a function generator? I'm just a bit confused.

VR6, on the hand drawn and annotated schematic, there's a note in red that says "Waveshape adj. (symmetry)(2f in) (at slo attack)" Off to the side, in black, there's a note that says "5.9k total" with an arrow pointing to the red annotation.

I lack the knowledge to truly understand every aspect of what's going on here in the design, so I'd appreciate if anyone could help me make heads-or-tails of this.
OdBm is 0.775v from function generator. If you only have a meter to measure this with them make the freq quite low. Maybe 200Hz because not all meters have a great freq resp when measuring a.c.
 
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I would like to build a stereo pair of RuudNL's RM58 version and wonder if matching a pair of 2N3820 jfets using the method in the photo is good enough?
 

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Thanx to Ruuds work with the "2018 version" of the RM58 I'll try to make one mono to use in a guitar pedal. No metering on this one but I'll probably try to come up with some kind of led indicator showing when the signal enters limiter threshold.

I will also make a stereo version that has one GR meter and only one set of controls controlling both channels, and also put that one in a box.

In the smaller guitar pedal version, I'll put in some kind of buffer to make it more guitarpedalfriendly, probably use the Cornish buffer design for that.

When looking at the circuit trying to understand it, I notice that it is a "feedback" design. ... it's always fun to do some experimentation when building stuff so I thought I try to implement a circuit and a switch to be able to chose if I want to put the input of the sidechain in a feed-forward position, or in the original feedback position, just to see what kind of effect a feed-forward sidechain has on the sound in this circuit.

Thanx Ruud for making this project happen, this will be fun!!!

And,,,, this one will be build on vero... wish me luck! :)
 

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A question to those of you that have tested to build Ruuds 2018 version of RM58, what P-channel jfet did you use or Q1?

Asking because I can not get the pinout of my Fairchild 2N3820 to match the markings on Ruuds PCB layout above...

If Ruud reads this, did you use 2N3820 or some other P-channel Jfet?

Thanx!
 
What a mess... But at least it seems to be a working mess! Only thing left to do is boxing and learn how to tweak the circuit and trimmers to personal preference and taste. Great stuff!
 

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Boxed. Drums sound HUGE through this... even though it's mono... Stereo version next. Same size box but with one meter and no footswitch.
 

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Hmmm... I start to question if I really got legitmite fairchild 2n3820 jfets, or fakes... ?

The 2n3820 I got does not behave well when the signal reaches threshold, there is no smorh trasistion, instead there is a short increase in output then the signal gets backed down and after that it is "brick limited"! the behaviour does not seem to be dependent on attack time, and even if I very, very, slooowly adjust the treshold limit to react on incomming signal, then, just as threshold is reached, the signal jumps up a little and then backs down... Its hard to describe, but I start to question if I really have legitit NOS fairchilds or something rebranded and sold as 2n3820... or, there may be somthing wrong with my build... I dont know!

... How could I now if I got genuine 2n3820? Is there a way to test them or something?

Edit:

I tried to adjust the bias and if i set it as low as just over one volt, the missbehaviour disapears and the transistion into limiting is super smooth and virtualy "klickless" even at the fastest attack time. Hmmm I dont know what to think...
 
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I fell into a rabbit hole tonight regarding musician/singer/songwriter Eric Carmen (recently RIP) and his various hits. The first one was in 1972 with The Raspberries "Go All the Way". One search thing led to another, and onto the Steve Hoffman forum where I found a mention that a Roger Mayer limiter was the Magic Mojo to the sound on the record. So, I did more googling, and found and read every post in THIS thread on GDIY!

I distinctly recall noticing that song on the radio and at age 18 was intrigued by the sound of it. Listening to it again you can really hear that Mayer breathing and pumping away and it still sounds really cool to my aging ears. It ain't hifi though....lol!

Found these dubs of a 45 single on Youtube:





Youtube had this as well:



What a crazy compressed sound! I like it 52 years later. <g>

Bri
 

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