Roger Mayer RM57 build?

[mikeyB]

Do the FETs have to be matched? That is the audio FET and the meter FET.
Great sounding unit by the way

 

[RuudNL]

Yes, to obtain good stereo tracking, you should match the Fets. (Since there is no way to adjust the tracking.)
In my case, tracking is better than 0.5 dB over 20 dB gain reduction.
I found two pairs out of 20 Fets.
The meter tracking circuit should use Fets that have the same characterictic as the attenuator Fets.
So in an ideal case a 'matched quad'.  (Although a small difference isn't that critical in the meter circuit, but try to match them as good as you can.)

 

[mikeyB]

Thanks RuudNL

 

[RuudNL]

If there is a small tracking error, you can cheat a little and vary the value of R1 (18K) a little.
This way you can optimize small tracking errors!

 

[mikeyB]

Thankyou,
Probably my next project - I've got an albums worth of drums to squash!

 

[dmp]

Pcb print attached, happy new year yall!!!

Hi Spencer
Can you post the final schematic you used that corresponds to this layout?
I'd like a build an RM57... heard about it in a song exploder this morning with Butch Vig.

Any thought of making this into a 500 series version?

 

[Spencerleehorton]

Hi DMP,

yeah this could easily be worked into a 500 series, I think RuulNL's version would be better as its a smaller footprint on the PCB.
I haven't printed out Ruul's version yet but will do it next week, just need to design the meter for it.
The schematic is per the original and I think I shared all info?
Let me know any help you need.

 

[dmp]

Yeah, but you posted several schematics so I wasn't sure which one was the final. the layout says V5 but I never saw a schematic with that in the name. If the last one was the final? "Schematic_RM58-Clone.sch_Sheet-1_20181123115959.pdf"

Not sure I followed everything but RuulNL's was a different "inspired from" design using opamps instead of discrete transistors

 

[iampoor1]

Yeah, but you posted several schematics so I wasn't sure which one was the final. the layout says V5 but I never saw a schematic with that in the name. If the last one was the final? "Schematic_RM58-Clone.sch_Sheet-1_20181123115959.pdf"

Not sure I followed everything but RuulNL's was a different "inspired from" design using opamps instead of discrete transistors

+1

Im having a hrd time finding the verified working schematic. Can someone repost it, or link to the post its in? My brain is just not cooperating today.  ;D

 

[Spencerleehorton]

I’ll sort this Monday for you.

 

[iampoor1]

I’ll sort this Monday for you.

Thanks! Super excited to buy one of these for 20$.....sure beats 8500$  ;D 8)

 

[Spencerleehorton]

That’s exactly why I built it!!!
Easy enough to make the pcb, the design I’ve done could easily be made better, I was just in a rush so drew it out quickly, and at the time we weren’t sure it was correct.
I’ll put up all details of Psu as well.

 

[iampoor1]

That’s exactly why I built it!!!
Easy enough to make the pcb, the design I’ve done could easily be made better, I was just in a rush so drew it out quickly, and at the time we weren’t sure it was correct.
I’ll put up all details of Psu as well.

Great!

 

[Spencerleehorton]

This is the schematic I did and used, transistor wise it didn't matter what i used i got the same result, BC550C, BC550B, 2N3391 or 2N5088.

For Q1 use PNP BC560c and for the FET's use the 2N3820, match them if you can.

The 4.7uf I used 6.8uf didn't seem to matter, everything else was as per original schematic.

Hope this helps and clears up any confusion, happy building.

 

[dmp]

Cool - thanks Spencer

 

[Hummingwire]

I would be very interested in building a 500 version (either RM57 or RM58) as well!

 

[Spencerleehorton]

Go for it and show us your build!!

 

[diggy fresh]

Hi Spencer,  thanks alot for the redrawn schematic. I want to try a layout but i'm a bit confused about how it goes together because nothing is labeled on your schematic.

Can you update it or tell us what the connection points are? That would be very appreciated. thanks

 

[Fuzz Face]

Hi Spencer,  thanks alot for the redrawn schematic. I want to try a layout but i'm a bit confused about how it goes together because nothing is labeled on your schematic.

Can you update it or tell us what the connection points are? That would be very appreciated. thanks

I was trying to use that schem as well and all of the pots are shown wired as (fixed) resistors. I guess the wipers are supposed to tie to one of the outer lugs?

 

[Spencerleehorton]

had a quick look, this should help, if it doesnt just look at the docs on the first few pages, you should be able to work it all out, I did!!