improving the Mcintosh C22

[Craig405]

What do people think of this classic preamp?
and how could it be improved?

I have put in a tube rectifier (5Z4) and a tube regulated supply so far on mine (VR150's and VR105's) and run the heaters from DC, it sounds good.
Although at full output i get 0.3v pk pk supply ripple in the form of my music is this acceptable?!

I dont know much about tube circuits yet but is there any advantages changes in topology can give like SRPP stages, active loads?

Anyway its a really easy preamp to build

Cheers
Craig

[SY]

at full output i get 0.3v pk pk supply ripple in the form of my music is this acceptable?!

Are you saying that you see 0.3V of signal on the rail? Or do you see 0.3V of ripple on the output?

[Frank Berry]

"Anyway its a really easy preamp to build"

I assume that you're saying that it's not a "real" McIntosh C22 but rather a knockoff kit.

If I were building this copy, I would be inclined to find a Service Manual for the C22 and start by building it exactly as McIntosh built it.

[Craig405]

I measured my supply rail with a scope and saw 300mV, i didnt check the output.

[SY]

300mV is not a huge amount of ripple, but I would ideally want it lower. The important thing is how much is appearing on the output.

[Craig405]

Frank

Yea it is not the whole circuit just the one in my diagram, i didnt put in the phono stage and the tone controls etc.

It is not a kit though, i just put one togeather because i needed one and it looked easy.

SY
That sounds very sensible i will get that measured very soon and post what i find.
Im guessing its ok because i saw no interference on the signals from both both channels (they both run from the same regulated supply) when testing a while ago.
I was just disappointed to get any ripple after putting my nice regulators in.

cheers
Craig

[SY]

Whoa! If you've got regulators, 300mV is a LOT of ripple. My preamp B+ regulator, a very simple 2 transistor job, gets me below 0.1mV. I'm not familiar with tube regulator performance, but I'd be astonished if you can't do better than that.

Now that said, what matters is (again) what's at the preamp's output.

[cerrem]

The ONLY 12AX7 I would use for Hi-End audio is a Telefunken....
I don't see the point to using 2 Gain stages before the follower..then using a TON of feedback to bring the gain down...
I would get rid of the two coupling cap that are in series that feed the grid of the follower....I would go DIRECT COUPLED...then hook up the feedback to the output of the follower...
As for the B+...make it CLEAN and FAST as possible...

Chris

[Craig405]

SY
yes i know i was suprised too it is definatly an issue. Ill try swapping the regulators about.
The supply before them is adequate enough i think 22uf then 20H then another 146uf of parallel caps.

Cerrem
Thanks for your input
I currently am using a selection of old triodes (12AX and 12AT as buffer) Consisting of Mullards, Brimar and one Hitachi! all are quite old already and probably arent performing their best.

I will read into direct coupling, this involves letting DC onto the buffers Grid?
I was actually thinking of changing my coupling cap values in order to get a lower frequency response to match my power amp, (-3dB at about 8HZ) but direct coupling might do the job.


Cheers
Craig

[kmtang]

Hi Craig

I just ran the PSU program. With just 22uF-20H-146uF CLC pi filtering, the ripple should only be 3mV. Are you sure that your measurement is correct?

With 300mV ripple, the hum noise would be so high that you would shut the damn thing down immediately.

I believe the MC C22 is a good performer. It is so famous compared to the Marantz M7. However, the Conrad Johnson's PV6 really caught my eye.

Johnny