New development on old project: Roger Mayer RM58

[soapfoot]

Hi,

I'm basically done populating my boards.

One question...

How critical are C10, C11, C12? I couldn't find the MKS2 Wimas listed in the BOM. The next shipment is going to be in late April! I can't wait nearly 5 months for caps to come in! First world problems! LOL.

FWIW, I used Vishay/Roederstein MKT1813 polyester axials on their sides. Specifically, MKT1813447065: https://www.mouser.com/ProductDetail/75-MKT1813447065

OK to use?

Thanks,
Chris

Definitely no problem at all.

The only thing that's really critical in these units is the matching of Q10 and Q14... those have to be very tightly matched with each other, and if building a stereo unit, all four have to be very closely matched.

 

[fazeka]

The only thing that's really critical in these units is the matching of Q10 and Q14... those have to be very tightly matched with each other, and if building a stereo unit, all four have to be very closely matched.

Thanks for your reply.

I haven't matched transistors before and I found the process kind of challenging due to the Idss values dropping over a few seconds and changing when reinitiating the tests. What would be something to look out for (in a completed unit, sound-wise) if Q10 and Q14 are not very closely matched?

Thanks!

 

[soapfoot]

One of them is in the meter circuit, so the matching is with the aim of getting the meter to display gain reduction accurately, as far as I know.

In my estimation, the metering isnt the most precise or useful in these units, anyway. Side-to-side balance is most important to me, but I still was pretty careful about matching all four in my unit.

Please be advised that most people on this forum have forgotten more about electronics than I’ve ever known… this was just a pandemic project for me as kind of a learning experience. All of my training and experience is in music, not electronics… so I may not be right about everything.

 

[Alyss]

I've been hunting for 2N3820 and I got an offer for what seems to be a fair price. Those are from Central Semi - I want to know if anyone else is interested - the price is $0.165/pcs

 

[grid_stopper]

I've been hunting for 2N3820 and I got an offer for what seems to be a fair price. Those are from Central Semi - I want to know if anyone else is interested - the price is $0.165/pcs

I would likely be interested. what kind of quantity?

 

[Alyss]

2000

 

[grid_stopper]

2000

If you can wait until monday, I would be happy to take about 200 of them!

 

[Alyss]

Sure, I think that I'll buy it on my own at the moment, if anyone is interested just PM
Cheers

 

[mig27]

Hey there, I'd be interested in buying 200 of your 2N3820 transistors of shipping isn't getting to expensive. I'm located in Germany.

Cheers

Michael

 

[richiyobs]

hi builders,
this is my last approach to a meter driver.... it s for 100uA meter, i own this kind at the moment for my brand new build .... tracking boht verse, on the right side from 0 to -20
i only builded different mono units, so i will go for a stereo one this time
the response on simulation looks fine, but not so expert to confirm it.... have to build one to check...
what do you think?
thanks for your attention
best
richi

 

[richiyobs]

this one is for 1mA vu meter like Tn73 clone...tested on a mono unit
looking for cheap ones found that most of nissei replica are 1mA 50ohm, as per TN42 both version , standard scale and black one like ssl
the bias trim in the SC is very important to get the proper amount both compression and meter scale! It sets the - 20 position....
the other one close to mirror 5461 set max movement, the one to Bc547 adjust the needle if it s out of range....max compression is at 0dB, touching 80% of scale , signal is close to distortion
this was the better tracking response i had.....it was also usefull for new calibration and understand that the trim at SC input set what can be defined Ratio, or fixed THR level
best
richi

 

[soapfoot]

Thank you for this! Great work

 

[paulj12]

I've been hunting for 2N3820 and I got an offer for what seems to be a fair price. Those are from Central Semi - I want to know if anyone else is interested - the price is $0.165/pcs

Hello from New Zealand. Do you have any of your 2N3820 fets left for sale?
Thanks!

 

[ashdot]

Hi,
I’ve just finished building my first RM58 and it’s starting to sound good.
Would anyone of you experts be willing to give a calibration guide?
I’d also love to understand the effect of each of the trimmers.
Many thanks
Izhar

 

[ashdot]

Another question regarding my build.
I like the ‘warm’ sound I’m getting, but I’m losing a lot of high end.
Is there a way to control this?
Thanks!

 

[soapfoot]

Hm! I haven’t noticed that with my unit. Are you using transformers or no?

 

[ashdot]

No, I’m not using transformers. Input and output are unbalanced.

 

[soapfoot]

Could there be a disadvantageous impedance relationship with the gear either before or after, I wonder? I'm only speculating. I'm not sure of input or output Z of this device in stock form (with no transformers)

 

[ashdot]

Possibly. I’ll try adding transformers.
I’m still uncertain about the calibration of the unit.

 

[soapfoot]

I wish I had a good procedure for calibration. Mine required a lot of guesswork.