Roger Mayer RM57 build?

[Spencerleehorton]

Q13 is not PNP it NPN!! pretty sure i blew it by putting the switch of cutting of the GR in the wrong place so i'm gonna change a few bits and power up again.

 

[Spencerleehorton]

nice one Robb, you called it!!, it was a BC560C!!! a rogue transistor in a 550C bag!!!

both sorted now, looking and working great, next phase is boxing them up and putting some sounds through them.

I need to wait until i get the new screened cable then i'll put them in a nice 2U and transfer into the studio for testing.

stage 3 will probably be making them balanced, I have a few OEP transformers i'll try but could wind my own which i may do as ive got to wind a 5002 transformer for this other 1176 rev i've done.

 

[Spencerleehorton]

This seems the right way to go for balancing:

https://www.diyrecordingequipment.com/pages/balanced-input-output-assembly-guide

 

[Vac11]

Great news!!! Let us now how the comp works.

Can you tell us on which spots did you use tantals and on which electrolytics? where to use styroflex? On 2n2F and 33pF? Where ceramics?

Thanks!!

Milan

 

[Spencerleehorton]

Sure, I’ll report back later, bear in mind this is just the first stage, I would like to improve S/N to this unit.
I know it’s never going to be a hifi compressor but I do want to get it as good as I can.
Mainly I will be using it in parallel and blending sounds with it, rather than in series, but who knows there might be some nice dirty drum sounds with a single room mic that it can fuzzy up!!

 

[Spencerleehorton]

Let’s see how it sounds first, I’ll post a video of it to let you all hear.

 

[Spencerleehorton]

Ok so here is some info on my build, this may change but might be good to emulate to see if it’s different in a wrong way!!!
Attack pot - 22k
Output pot - 10k (has 27k on one leg, other has 330R on other outside leg, middle is output.
Release pot - I found 10meg was way too much, you can get away with a 1meg or 2meg pot here and the release range is much more useable
Threshold pot - 100k

Capacitors
All 0.47uf are tantalum
33pf is ceramic but could have styrene here
2.2nf is film/wima
0.1uf is film
All others are electrolytic the 4.7uf I used a 6.8uf
And the 100uf you can use 150uf

Hope that’s helps you guys.

 

[Rob Flinn]

This seems the right way to go for balancing:

https://www.diyrecordingequipment.com/pages/balanced-input-output-assembly-guide

Personally I would probably just whack a transformer on the in & out.    If you use the That's chips then you need a  +& - 16v bipolar power supply on top of the +24v you need for the RM58.

 

[Spencerleehorton]

That was my first idea, 10k on secondary for output, do I put the same but in reverse for input txf?

 

[Spencerleehorton]

Also I put the bypass switch between the output of the preamp (Q13 emitter, 1) to C7, so just disconnects the control section.

 

[Rob Flinn]

You probably want something like a 10k:10k on input & maybe 600:600 on output but I'm no expert on this  It probably depends a bit on the output stage & what its drive capability & impedance are.


I don't have the diagram in front of me but when you disconnect the side chain for bypass what is happening tothe control point where sidechain is connected ? Are you grounding it or is it flapping in the wind ?    You may be able to look at the 1176 bypass switch for inspiration. Or use a 4 pole 2 throw switch for a hard bypass.

 

[Spencerleehorton]

When I grounded it first as per 1176 it blew q13 as emitter is attached, so that’s a bad way.
Disconnecting the feed to the control circuit works fine.

 

[dirty1_1garry]

When I grounded it first as per 1176 it blew q13 as emitter is attached, so that’s a bad way.
Disconnecting the feed to the control circuit works fine.

your Q13 is a preamp output VT (regards to your V3 schem). If yes, check that you ground detector AFTER capacitor C7. if you will ground it before cap you will connect Q13 emitter directly to the ground and it will blow.
Check attached sch.

 

[Spencerleehorton]

yeah i tried connecting it to gnd after the cap and it didn't work, thats why i ended up floating it.

need to make lorlin 2.2meg Lin stepped pot with 11 steps, anyone have a calculator or able to let me know values please?

 

[Spencerleehorton]

could i go with:
1 - 0
2 - 100k
3 - 220k
4 - 520k
5 -750k
6 - 1M
7 - 1.2M
8 - 1.5M
9 - 1.8M
10 - 2M
11 - 2.2M

 

[dirty1_1garry]

could i go with:
1 - 0
2 - 100k
3 - 220k
4 - 520k
5 -750k
6 - 1M
7 - 1.2M
8 - 1.5M
9 - 1.8M
10 - 2M
11 - 2.2M

its necessary linear pot for release so your steps are Ok.

 

[Spencerleehorton]

I got the weekend off so I’ll try and finish this, also I’ll move that cap and put the switch after down to gnd.

 

[Spencerleehorton]

Also just to remember I used 50k trim pot for R27 and adjusted waveform for symmetry.

 

[RuudNL]

Just for fun, I experimented today with a 2018 version of the circuit.
I replaced all transistor amplifier circuits with OpAmps. (A single quad-OpAmp can be used.)
Also I modified the circuit around the FET a little, in order to reduce the distortion.
Another modification reduced the noise significantly.
The redesign sounds pretty good...
If there is any interest in this, I will publish the circuit here in the near future.

 

[ilfungo]

Interested!!!
THANKS!!!