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Tube pre, SS amp incompatibility, which amp 2 use?

I wanted to see how a tubed pre-amp would sound in my system so I purchased a Jolida Music Envoy pre-amp to mate with my McCormack DNA-1 amplifier. When I put the pre-amp in the system it would not work. After talking to Jolida, where Jerred helped me try various things, we came to the conclusion that they were just not compatible, since the Jolida works just fine with an old Marantz I have. The Jolida has in output impedance of 600 ohms. The McCormack has an input impedance of 100K ohms.

Next I emailed Steve McCormack asking his opinion, and he also gave various reasons for the failure, but after letting him know what was done in an attempt at making them work together, he also stated it may just be a compatibility issue.

Now I would like to get a different amp to try with the Jolida, but am a little weary of purchasing another just to find out that for one reason or another it will not work.

Since this is just to see if I would like what I hear, I don't want to put a lot of money into it. My speakers are 6 ohm Gershman Acoustics Sonograms and are 89db efficient, so I'm looking at an SS amp with good power for less than $1K.
Does anyone know of any amps I can look into that DO work with the Jolida, knowing for sure, that they will be compatible?
128x128abucktwoeighty
unsound
7,335 posts
 
The McCormack amps input impedance shouldn't be an issue. When Stereophile originally measured the McCormack its input sensitivity was greater than specified, which could be problematic with some tube pres typically high output, but this should typically only reduce the usability range of the volume control.
Just to rule out possible problems I'd try different interconnects (not for flavor, but for integrity). Just a hunch, but I'd hazard a guess that the Jolida is misbehaving.
johnsonwu
469 posts
 
Output caps are leaking DC if they pop when connected to SS amp.
Change them out with high voltage rated ones like mundorf and you will have no problem.
almarg's avatar
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almarg
9,670 posts
 
Another possibility, which would be consistent with the fact that there is no problem when the preamp is used with the Marantz amp, is the scenario described by Atmasphere in his two posts dated 8-3-12 in this thread.

Basically, the very high input impedance of the DNA-1 may be bringing out a design issue in the preamp. The Marantz presumably has a much lower input impedance, perhaps 47K or less, which does not bring out the issue. The very extended low frequency bandwidth of the DNA-1 (specified as 0.5 Hz) is presumably also a factor that contributes to bringing out the issue, as explained in Ralph's (Atmasphere's) posts.

If that is what is occurring, and I suspect that it is, a readily practicable solution would be to insert a pair of 10 db Rothwell attenuators at the inputs of the DNA-1. That would result in the preamp seeing a load impedance of something like 33K.

Doing that would cause you to operate your volume control at settings that are 10 db higher than those you would otherwise be using. But given the relatively high gain and sensitivity of the DNA-1, as noted in the Stereophile measurements that Unsound referred to, I doubt that would be a problem. It might even be beneficial.

Best regards,
-- Al
abucktwoeighty's avatar
abucktwoeighty OP
1,079 posts
 
I thank everybody for your input.

Almarg, I do have a CI Audio VPC-1 that I can insert between the units. I'll give that a try to see what happens. I don't believe the output caps are leaking as suggested by Johnsonwu since the pre-amp was just given a going over by Jolida.

I'll post results shortly.
almarg's avatar
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almarg
9,670 posts
 
It appears that the VPC-1 has a total resistance of 10K. I suspect that the problem will not occur with that in place, which would help to confirm the diagnosis I proposed.

However I suspect that 10K is too low a value to be a permanent solution. Interaction of the 10K load with the rise in the preamp's output impedance that most likely occurs at deep bass frequencies, as a result of the coupling capacitor it probably uses at its output, will probably result in perceptible rolloff of the deep bass.

I don't think that would occur with the approximately 33K input impedance of the 10 db Rothwell attenuator (as measured by me, using a not particularly accurate analog multimeter).

Also, since the Rothwells would be inserted directly into the input jacks of the power amp, with no intervening cable, the possibility of sonic effects resulting from interaction of the VPC-1's output impedance with the capacitance of the cable connecting it to the amp would be eliminated.

Best regards,
-- Al
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