New development on old project: Roger Mayer RM58

[ashdot]

Could you tell me some of the things you did intuitively?

 

[soapfoot]

It's been a couple of years, and I don't really remember! I remember I looked at the original documents, which had some sort of calibration procedure, and tried to replicate that.

 

[soapfoot]

Page 6 here.

Frustratingly, 3 of the trimmers give no information and are just listed as "do not adjust, factory set."

I don't remember what I did for those, unfortunately

 

[ashdot]

Thanks @soapfoot !
I’ll try to experiment with that.

 

[JMan]

@ashdot Please let us know if you gain any insight into what those 3 mystery trimmers do during your experiments!

 

[grid_stopper]

wish i had taken notes when i calibrated mine because i could offer some real insight, but if you hook up your osciliscope and multimeter, it will start to make sense with a bit of trial and error

 

[ashdot]

wish i had taken notes when i calibrated mine because i could offer some real insight, but if you hook up your osciliscope and multimeter, it will start to make sense with a bit of trial and error

What would you test with the scope?

 

[richiyobs]

Hi folks...
I believe one of the important part is get proper symmetry at 2 npn going to timing net... They re the full wave rectifier.... Also the trimmer at Sidechain input will set the fixed threshold.... Put 0dm at 1k or 500Hz and 3k... The set that trimmer to have no compression, to get 0 in and 0 at out.... Set thr pot quite 9 o clock.... After that point the thr pot should work.... If you got compression after 9 o clock I believe everything is fine....
The meter calibration is important too... Cause when moving sidechain trimmer you have to stop after you see the first needle movement... Always thr pot at 9 o clock or whatever position is for you a 0dB position between input and output....
Actually i m focused on the modern version redraw.... More easy to understand and calibrate... If you check the schematic you ll better understand each part of the unit....
This is what I did remembering my first build.... But not so expert to say it is true!
Hope it helps
Best
Richi

 

[richiyobs]

this is the simulation i did for the modern redraw.... i believe is a good starting point... never had time to simulate the original design
i built different units based on this , running different jfet, and 2n5461 is the best one.... according to distortion and sound.... i m still focused on j175 cause it s cheap and easy to find, but distortion come close 60% of compression
hope everything is well done and helps
best
richi

 

[Sorr]

What 20db output amplifier are you using? I don't seem to be able to find it in the manual?

 

[richiyobs]

Hi Sorr
You re right in that pdf is not showed...
There s another copy that should contain each part...
I ll post if I find in my hd

 

[richiyobs]

here at pag 4 you can see the drive Amp...
the main difference with the other pdf is that it s more referred to RM57
in the attach at pag 7 a resistor at jfet IN, pag 6 the block diagram shows different values for Att and Rel....
so if you re running RM57 you have 22k for Att and 2.2Mohm for Rel. and 220k to ground at input stage

hope it helps
best
richi

 

[AudioPro]

Fellows, can you please help me with the wiring? I am not sure if the Rotary switch for release control should go to point V from the 470k...I am attaching drawing of my understanding of the expected wiring.Any ideas will help me a lot.Excuse my bad drawing.If this is the proper wiring then I will search for the problem of not passing any signal somewhere else(check for soldering errors although the board is fairly simple)

 

[Rob Flinn]

Fellows, can you please help me with the wiring? I am not sure if the Rotary switch for release control should go to point V from the 470k...I am attaching drawing of my understanding of the expected wiring.Any ideas will help me a lot.Excuse my bad drawing.If this is the proper wiring then I will search for the problem of not passing any signal somewhere else(check for soldering errors although the board is fairly simple)View attachment 95867

The release switch should have no bearing on whether the unit passes a signal if it wired up correctly. If you look at the attached diagram it will probably help you figure out how it's connected.

 

[AudioPro]

The release switch should have no bearing on whether the unit passes a signal if it wired up correctly. If you look at the attached diagram it will probably help you figure out how it's connected.

Thanks a lot Rob! I"ve found my error and managed to make it work!

 

[dshepp806]

wow nice chaps around here indeed!
just found an early 70's Era RM58 ..untouched. thinking about which direction to head down, if any. it's completely original. no serial numbers. first we see if she's working eh? will be checking in here in the future. you guys are an amazing resource. thanks in advance!!!

 

[ashdot]

wow nice chaps around here indeed!
just found an early 70's Era RM58 ..untouched. thinking about which direction to head down, if any. it's completely original. no serial numbers. first we see if she's working eh? will be checking in here in the future. you guys are an amazing resource. thanks in advance!!!

Wow! Can we see some photos of what it looks like inside?

 

[ashdot]

This is a test of my RM58 build, still uncalibrated, but sounding very interesting on some drum tracks.

 

[groselicain]

Before I commit, I just wanted to get opinions. I'm working with a Collective Cases enclosure so I'm not able to center the power supply and power transformer, nor hang the transformers off the back in any constructive way. Has anyone who used UTCs or the like experienced any real noise issue with placement inside the case?

I say before I commit, but as you can see I've already drilled for my PCB standoffs—if someone sees a smarter way to place things, be my guest!

 

[soapfoot]

I feel pretty certain you can make it quiet, you'll just have to leave yourself the freedom to rotate the power transformer in all three dimensions. There will be one orientation that's quietest, and then you figure out how you need to mount it.