Any PV7 Experts Out There?

[Elrick]

Hi, this is my first post. I picked up a PV7 last month and I really like it. It's step up from what I've has before. It drives a pair of new Dynakit Mark III's that I build last year using an updated driver board that has two 6SN7's. I do have to turn the volume up a bit when playing the phono however. Not sure if this in normal or not. I was told all the PP caps in the signal path had been replaced, and the PS electrolytics were replaced and and increased a bit. This work was not done at the conrad-johnson shop. After looking at the work, and comparing it to original PV7's, mine seems to be be missing at least three caps. I would appreciate any comments on what's going on here. Thanks

The first few pictures are my unit. I count 8 replaced caps, not counting the e-caps.






This is what I believe a stock one should look like. I count 11 yellow caps.

[admin]

First, welcome to the site, it's nice to have you!

As for your question. The differences in the caps is certainly easily seen by the comparison picture. Unfortunately, we do not have the PV7 schematics in our database here on CJO as my suggestion would have been to simply compare your unit to the schematics. I don't know if the caps were consolidated when it was upgraded or something else was done.

As for the phono volume. That certainly may be a simple issue of your cartridge output and the default phono gain on the PV7. The PV7 is rated as having a gain of 40 dB, so that's not that high to begin with (you didn't tell us what cartridge your using). If you think there is something wrong with the phono gain, you would probably have to find another phono preamp with a gain listed as 40 dB and see what the volume is with that compared to the phono stage of the PV7.

Hope that helps a bit.

[admin]

Look like one of our gracious users saw your post and was nice enough to send me the PV7 schematics and parts list files. I would try to trace the circuit diagram to see what changes were made.

Here is the link to our schematic database:
viewtopic.php?f=17&t=128&p=1288#p1288

[Elrick]

Thanks for responding. Mystery solved, turns out the tech simply soldered the remaining caps to the under side of the board. I'm good to go. My current cartridge is Audio Technica ATP-2XN, spec sheet indicates the output is 5.3mV. Not sure what that tells me but it's a start. I do notice that the recommended tracking weight is 3-5 grams which seems a but heavy, but I see now the box was labeled "disco model" so probably explains the weight. With all those sweaty dancers banging around.

[antaresbluespirit]

hello

In wiewing the previous situation of the unit fitted with PP yellow cap and the new one, two caps are missing in the phono unit (3 tubes on the left site)

Coud you please read the capacity value of the news ones to understand the difference in tracing the schematic....to see if it is an upgrade or not

the new PP caps are very good anyway ,they come from Mundorf (made in germany), I have implemented the same in my Beard amp combo..

Who has donne the upgrade ,a CJ specialist?

Regards

Raymond

[Elrick]

bluesspirit: I found the replacement Mundoff caps on the top of the board to be the same or in some cases slightly larger than those on the schematic. There are also three Mundorf caps on the underside of the board whick I couldn't read but I assume they are suitable.

On the top I have the following caps:
5 ea 2.2uF 400V (originally 2 of these were 0.15uF and 2 were 2.0 uF)
1 ea 4.7uF 630V (originally 4.0uF 400V)
1 ea 4.7uF 400V ( originally 2.0uF 400V)
1 ea 0.15uF 630V (originally 400V)

This work was not done at the c-j shop. I'm using it now, so I can't get in to look right now, but going from memory and looking at the schematic/parts list I think I have all that correct. Those caps, plus the three on the bottom make 11 just like the original design.

[Elrick]

I had to share this example of not taking anything for granted. I just noticed that I've been running the wrong set of tubes in this thing. The previous owner had three 12AU7's in place of 12AX7's, at least he had the 12AT7's in there right. Now the phono level came way up and the other sources are more punchy, noticeable brighter all the way around. I couldn't be happier.

[Joe Appierto]

The misplaced tubes explains it. 12AX7's have an amplification factor of 100 while 12AU7's are 70. A cartridge output of 5.3mV is quite hefty. Glad to hear that it was a relatively straight forward fix because sometimes they aren't. Enjoy the preamp.

[amplifiersurgery]

We restored this particular unit.
The caps on the underside were installed there to further avoid the heat from the tubes. You can see a video of the unit running here:
https://www.youtube.com/watch?v=PUQ7pVuUPPg