Waiting for ZEBRA'S MXL2001 mods beyond Royer

[tubemonkey35]

Zebra, I just completed the MXL2001 Royer mod and it sounds good. However I saw at the omnipressor page where you had made further modifications to the royer mod; at first I thought it was Gusses.

From what I could gather via the pics was that you added a 470uf electrolytic between R1 (750ohm) and ground; not sure what voltage. Why, what was your reasonsing here?

I also noticed that you added another cap that looks as if it is 33uf 160v at pins 5,7 of the 5840 tube; not sure where the other end is going (is it to R5 100k in series with C2 (1uf 250v) or to the tranny itself in parallel with C2? Why again did you add this cap here, what was the reasoning?

What was the biggest thing you were trying to achieve with the additional modifications?

I'm trying to learn from what you have done and why you did it.

Oh FWIW I perfed my mod from the ground up including the PSU so I'm growing into this; no PCB kit.

I first thought the pics I looked at were of Gusses mxl2001, They are not.

Zebra????

 

[okgb]

Hi i did one of the small disphram mics , and i thought it sounded better
than a akg c-60 , i don't know if the transformer i picked was the best
though ,

which royer mod were you referring to ?

regardds Greg

 

[Gus]

I built a different PS.

No better or worse than the Royer one just different a taste issue

Mine is 140VDC so I changed the operating points a little cathode R is a 1K bypassed by a good 100uf at 16V cap and I used a 1 gig grid to ground R.

using a cathode bypass lowers the output R of the circuit. It also increases the gain a little and should drop noise a little. It also operated the tube with as close to no neg feedback as possable(still is some in the tube that we have no control over set by spacing and grid winding and............)

However what Dave Royer did is clever there are some subtle design ideas in his IMO.

other wise the schematic is the same, they don't sound the same.

Remember operating point and B+ can have an effect on tone at under 200Vdc with most tubes IMO.

wow someone studied the picture

 

[tubemonkey35]

oops, the pics I studied are that of Zebras mic.

 

[zebra50]

Hi!

It was an experiment for my own curiosity

Gus pretty much covered the reasoning for it. I added power supply stabilisation/filter caps (to ground) on the heater and B+ in an attempt to lower the noise floor. The advantage is minor. Look at the G7 circuit for inspiration!

Also a cathode bypass for the reasons Gus stated. It sounds different but not necessarily 'better'. You have to listen and decide yourself!

But I must stress that there is nothing wrong with Dave Royer's original circuit - it sounds very good and is very efficient in terms of parts.

Hope that helps - go do some experiments.

Stewart

 

[zebra50]

[quote author="tubemonkey35"]
I also noticed that you added another cap that looks as if it is 33uf 160v at pins 5,7 of the 5840 tube; not sure where the other end is going (is it to R5 100k in series with C2 (1uf 250v) or to the tranny itself in parallel with C2? Why again did you add this cap here, what was the reasoning?
[/quote]

Aha! I see it now. The big mustard cap that looks like 33 uF is actually 1 uF - the label got smeared when I defluxed the board. That's the OUTPUT cap from tube to xformer. The 2.2uF orange cap is a local B+ filter cap. I think this mic lacks a heater filter cap in the mic, but some of my other builds have this.

[quote author="tubemonkey35"]
Oh FWIW I perfed my mod from the ground up including the PSU so I'm growing into this; no PCB kit.
[/quote]
Cool!

[quote author="tubemonkey35"]
What was the biggest thing you were trying to achieve with the additional modifications?
[/quote]

Knowledge - understanding the effect of adding/changing those parts!
:thumb: