Roger Mayer RM57 build?

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RuudNL

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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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dasnevestheo

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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.
 

RuudNL

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Recently I made another version of the 'modernized' design, this time as a 'plugin'. ;D
Works perfectly. Also good stereo tracking.

plugin-module.JPG
 

soapfoot

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Dec 27, 2010
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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.
 

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Rob Flinn

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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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