My REF PHONO 2 needs service !

[Jerome W]

Hello folks,

Just a few words to inform you that since a few weeks, my REF PHONO 2 started to hum / buzz at volume 60 on my C1000 mostly in high gain mode. At 100 on the C1000, the buzz is huge and the C1000 needles "dance " around -40 dB.
At 50 on the C1000, the buzz starts and is a bit bigger on the right channel, as shown by the C1000 vu meters.
It does not really bother me because I don't listen on it at more than 40 on the C1000 and at this level, the REF 2 is dead quiet. But this hum was not here when I got it so I'm a bit frustrated.
My dealer sent to me 2 new 6H30 and I tried them in all the possible positions including V6 but it did not change anything.
The big power tube has not been tested. Jeff Dorgay told me that when this one fails, the stereo image collapses. So it should not be concerned with this hum.
It seems that this problem is not tube related....
Opinions ?

My C220 phonostage was making a hum at 70 so I thought it could be normal for the REF 2 too but both Howie and Jeff Dorgay told me that their unit is dead quiet even at full volume.
Could be the gain of the C1000 too high compared to the REF 2 ?
This could be a reason because at 40 on the C1000, the music already plays very loud ! At 50, the hum is very small with no signal and the sound pressure gets very high when a record is played : did not measure but maybe around 100dB.
Maybe that I dreamed when I say that no hum was there at max volume at the beginning...This was in july so my memory could simply be faulty....

[Jerome W]

I'm experiencing further now.
I tried to use my Talismann cart with the low gain of the REF 2. And with a load of 47k, it sounds very good ! Even with the "ideal" load of 100K actually, I get a decent sound at volume 50 on the C1000....
Probably that the high gain setting of the REF2 is off and the gain may be too high or if the REF 2 is ok, then the gain of the balanced line inputs of the C1000 could be too high.
The Talismann is a DL103 modified by Clearaudio. If I remember correctly, its output is not so big at around 0.7 mV.
Normally, I should not be able to hear anything with the REF 2 set at "low gain" for this cart.
In low gain mode, the REF2 hum / buzz is totally acceptable.

Opinions ?

[Jerome W]

I gained some more informations this morning.

REF 2 :
Output impedance : ( BAL ) 400 ohm
Recommended load : 50k to 100k ohms / max 100pF
Minimum load : 10kohms / max 2000pF
Gain: 74 dB


C1000P :
Max input signal : 10V
Input Sensitivity : 450mV for 2.5 V.
Input impedance : 22k ohms
Gain : 15 dB

It is clear that the C1000P has an input impedance lower than the one recommended by ARC, although it stays between acceptable limits.
What do you think ?

I would also be interested to read the maximum output signal of the REF 2 with gain set on High (with my Talismann cart ) on my voltmeter since this info is not given by ARC...but I doubt that this could cause this problem.
The high gain output of the REF2 may just be too high for the input C1000 sensitivity, if the impedances are not ideal....

[Jerome W]

Some other interesting datas :

The REF 40 preamp has an input impedance of 600k ohms and the REF 5 has an input impedance of 300k ohms.

These are much higher than the 22k ohms of the C1000P.

Moreover, the Gain of the C1000P is clearly superior at 15dB, while the gain of the REF40 and the REF5 are both of 12 dB.

All this could explain easily why the low gain setting of my REF2 at 51 dB could be enough for the C1000. The C1000 internal MC phonostage has a gain of 60dB; The 74dB of the REF2 could just be too much gain for the C1000 with the 0.7mV output of the Talismann cart....

I may have found the solution alone on this....
The time difference gives me work indeed, while my american friends are sleeping.... !

[Jerome W]

Funny how this thread is turning in a monologue....

[jdandy]

Jérôme.......Without a signal both of my MCD1100's are dead quiet at all volume levels.

[Jerome W]

Originally Posted by jdandy

Jérôme.......My MCD1100 is dead quiet at all volume levels without a signal.

Thanks a lot Dan !! I appreciate your help !
Seriously, I'm sure that you may have an opinion about all those technical data ?

[jdandy]

Jérôme.......I don't believe you are having an impedance matching problem between the C1000P and the Ref 2 phono stage preamplifier, nor do I think it is a gain issue with the C1000P. Something has changed in the Ref 2. Your memory hasn't failed you. I am certain that the Ref 2 did not have this noise issue when you first received it, or you would have made note of it, and perhaps thought it was defective. Something is not right with the Ref 2, either tubes, and a hard part on the circuit board.

[Jerome W]

Originally Posted by jdandy

Jérôme.......I don't believe you are having an impedance matching problem between the C1000P and the Ref 2 phono stage preamplifier, nor do I think it is a gain issue with the C1000P. Something has changed in the Ref 2. Your memory hasn't failed you. I am certain that the Ref 2 did not have this noise issue when you first received it, or you would have made note of it, and perhaps thought it was defective. Something is not right with the Ref 2, either tubes, and a hard part on the circuit board.

Thank you Dan !

[Removed]

Originally Posted by C220MC275

Some other interesting datas :

The REF 40 preamp has an input impedance of 600k ohms and the REF 5 has an input impedance of 300k ohms.

These are much higher than the 22k ohms of the C1000P.

Moreover, the Gain of the C1000P is clearly superior at 15dB, while the gain of the REF40 and the REF5 are both of 12 dB.

All this could explain easily why the low gain setting of my REF2 at 51 dB could be enough for the C1000. The C1000 internal MC phonostage has a gain of 60dB; The 74dB of the REF2 could just be too much gain for the C1000 with the 0.7mV output of the Talismann cart....

I may have found the solution alone on this....
The time difference gives me work indeed, while my american friends are sleeping.... !

.7mV is knocking on the door of a medium output and 74db of gain may be over driving the cart a bit......I own several Clearaudio cart and find gain settings in the 57-60db is about perfect and that is with a half dozen different phono stages....