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Orsefon C22 (McIntosh C-22 circuit copy)

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Steve Hynes said:
The 8 pin chips are op amps. I am using a Linn LP12, Ekos, Troika, as well as an Oracle Premiere, SME V, Koetsu - also a Grade Signature tonearm with a Denon MC, not mounted to anything to check. Same behaviour with all of it. All works perfectly with a Krell KRS preamp, Audio Research preamp, and Luxman C-05 and some others. The reason I did not mention any of this is that the same thing happens when you short circuit the tonearm leads (or any cable) plugged into the MC input, so it seems like its really a fault in the preamp. The MC input is dead quiet with nothing plugged in. Too quiet in my opinion.

CohibaJoe - have you used the mm/mc inputs on your unit yet?
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I will hookup the pre-amp tomorrow. I have the unit apart as I ordered replacements films (Amtrans AMCO) in place of the WIMA's Films. What is installed in my unit does
not look right to me. I also will be replacing the stock MM/MC Opamps with Burson Opamps.
 
CohibaJoe said:
I will hookup the pre-amp tomorrow. I have the unit apart as I ordered replacements films (Amtrans AMCO) in place of the WIMA's Films. What is installed in my unit does
not look right to me. I also will be replacing the stock MM/MC Opamps with Burson Opamps.
Click to expand...
Looking forward to hearing about your experience!
 
nj pheonix said:
I know the c22 ce has 4 12AX7 and 3 12AT7.
Not sure how that coincides with this. The original used all AX7s.
(Not implying this has anything to do with the hum issue)
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This unit is using 4 12AT7 for MM/MC Phono Amp and 2 12AX7 for Pre-Amp. I will hookup a TT today as I had not tested the internal Phone Section since I use an external Roy Mottram PH-16X Phono Preamp.
 
wonder if the op amps are being used as a head amp for the LOMC section. Bump the signal and feed into the MC stage for the rest of the gain and the EQ stuff. Easier to boost low level signals like that with solid state and not add a bunch of noise than it is with tubes.
 
arts said:
I'm curious; what are all of those 8-pin dip chips used for?
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I suggest, that since the 8 pin OP amp looking chips, being very close to the back panel end jacks that are usually phono inputs on preamps so equipped might very well be the phono preamp stages..

Easier and cheaper to design/copy very low noise high gain circuits with OP amps, than with tubes..
Just a speculative guess, Mr. ArtS, Sir.
 
Steve Hynes said:
Hello! I have one of these as well. The MM and MC inputs were an added cost on mine and it looks identical to the one you have posted. Mine has a problem of very noisy MM and especially MC inputs. The MC input is dead quiet with nothing plugged in, and dead quiet with a turntable connected with no cartridge installed. Pop the cartridge in and radio noise and heavy dark sounds make for a very grim background to any music. The other inputs are dead quiet and the unit sounds very good to me. The seller has not been terribly helpful but I think the issue is mainly language. Any thoughts would be appreciated!
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***
Probably not the advice you’re looking for, but I’d return your preamp to the seller, demand a full refund, and buy a genuine McIntosh C22 (new or used) from Audio Classics. I love mine (C22MKIII). Its phono preamp is lush and dead quiet.
 
Bushikan said:
***
Probably not the advice you’re looking for, but I’d return your preamp to the seller, demand a full refund, and buy a genuine McIntosh C22 (new or used) from Audio Classics. I love mine (C22MKIII). Its phono preamp is lush and dead quiet.
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Great advice, and I am looking for a genuine McIntosh c22, but its quite a waiting list in Vancouver. This copy is in fact excellent as a line level preamp. It makes no claim to being more than it is, with a whacky brand name. It looks Mac like, but at best its an echo in that regard and not a copy. I have other genuine Mac stuff, this was just a purchase of interest and kind of a fill in til I find a c22. My plan now is to fix the thing and see what I can make of it!
 
Bill Ferris said:
I suggest, that since the 8 pin OP amp looking chips, being very close to the back panel end jacks that are usually phono inputs on preamps so equipped might very well be the phono preamp stages..

Easier and cheaper to design/copy very low noise high gain circuits with OP amps, than with tubes..
Just a speculative guess, Mr. ArtS, Sir.
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You are right, they are the preamp stages. The opamps are 2x ne5532n, I assume they are cascaded in each circuit. I have replaced the them with 2x opa2134 in the mc section, which behave differently in the circuit, not drop in compatible although I thought they would be, and still noisy. It was a shot in the dark!
 
CohibaJoe said:
I will hookup the pre-amp tomorrow. I have the unit apart as I ordered replacements films (Amtrans AMCO) in place of the WIMA's Films. What is installed in my unit does
not look right to me. I also will be replacing the stock MM/MC Opamps with Burson Opamps.
Click to expand...
Have you connected a turntable to your "c22" yet? Looking forward to hearing what happens!
 
Upgrade the Caps and Films and a check on the Caps had most at -20%/25% :eek:. Unit has been running 24hrs :music: and WHAT
a big difference at this point. Next checkup at 150hrs.

Films: Amtrans AMCO
Caps: Mundorf M-Lytic AG, EPCOS / TDK B4188C, Panasonic FM, Nichicon PA
OPAMP: Burson V6 VIVID DUAL, Burson V6 Classic DUAL

C22h.png C22i.png
 
Is anyone interested in the schematic for this preamp? I finally got it from the seller. It is interesting but has not helped me find the problem with the mm/mc inputs.
 
Steve Hynes said:
Is anyone interested in the schematic for this preamp? I finally got it from the seller. It is interesting but has not helped me find the problem with the mm/mc inputs.
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WOW....I will send you a PM for the schematics. Does the schematics show adjustment process? No issues with my upgrade but will be go to review.
 
A few upgrades too this unit. I noticed when changing the Balance rotary pot an uneven Left/Right balance. A quick check
on the Multimeter and the Right side was off -35%. Replace with New Bourns Audio and A OK. I also changed on the Tone Control
board Burson V6 Classic DUAL to Burson V6 VIVID DUAL with is more Vivid in the Treble/Bass. The V6 Class was too relaxed.

Next up is to replace the Remote Volume Control with Alps 100K Blue Velvet.

Schaffner AC Power EMI/RFI Filter
Balance Switch: Bourns Audio Pot 100k

C22j.png C22k.pngView attachment 2712048
 
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CohibaJoe said:
A few upgrades too this unit. I noticed when changing the Balance rotary pot an uneven Left/Right balance. A quick check
on the Multimeter and the Right side was off -35%. Replace with New Bourns Audio and A OK. I also changed on the Tone Control
board Burson V6 Classic DUAL to Burson V6 VIVID DUAL with is more Vivid in the Treble/Bass. The V6 Class was too relaxed.

Next up is to replace the Remote Volume Control with Alps 100K Blue Velvet.

Schaffner AC Power EMI/RFI Filter
Balance Switch: Bourns Audio Pot 100k

View attachment 2712041 View attachment 2712042View attachment 2712048
Click to expand...
You are really going to town on this preamp! I hope the schematics are useful. I was surprised that the mm/mc branches are identical. And if you don’t use a phono input, 4 of 6 tubes are always powered and unused. I have not figured out the noise in my unit yet!
 
Steve Hynes said:
You are really going to town on this preamp! I hope the schematics are useful. I was surprised that the mm/mc branches are identical. And if you don’t use a phono input, 4 of 6 tubes are always powered and unused. I have not figured out the noise in my unit yet!
Click to expand...
Thank You for the schematics. I need to contact my seller and asked on steps for settings the BIAS for the tubes.
I just installed the New ALPS volume control and will test later today.
 
Alps 100K Blue Velvet RK27 is installed and without the remote. Compared to the Alps RK168, the RK27 is very musical, clean and deeper.
At this time, we are done with the upgrades and looking to put sometime on the Pre-Amp (125hrs currently). I will be switching out
the stock Orsefon Tubes at 200hrs and will update to what brands.

C22m.png
 
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