GREETINGS FROM OTTAWA CANADA : AND A QUESTION

[GEORGE ABRAHAM]

Hi all..my name is George Abraham. I am 68 and have been an audiophile since 1974. I love vintage equipment and my basement is full of records, turntables and various pieces of equipment that I've been collecting since a very long time. My association with Conrad Johnson (CJ) has been years in the making as I always wanted to get a PV10 preamp but never could find one with a phono stage. About 2 weeks ago my stars aligned and instead of purchasing a couple of Lotto tickets I invested $1,100 ($800 USD) in a PV10 advertised in Canuck Audio Mart located in Vancouver which is on the other side of the country. The photos looked good and the owner vouched that everything was fine.

Nuff said...out of the box the PV10 did not work and of the 5 tubes one was blown and the other 4 tested weak plus all 4 tubes were all of different brands. I installed 4 new old stock tubes and kept the 5751 and powered it up. However, I quickly found out that the PV 10 gain was extraordinarily high not only on phono but all other line stages on various solid state power amps that I currently use. By extraordinarily high I mean just a little 1/4 inch crack in volume pushes my amp to clip.

I don't think this is normal...do you? This happens whether I use either the main or tape out jacks to connect to the power amp.

I have heard about impedance mismatching issues when mating tube pre amps to solid sate power amps but I currently have 3 other tube pre amps that don't have excessive gain issues like the PV10. The PV10 is not usable in this condition and it looks like a trip to Dr CJ repair shop is required.

What do you think is the issue? I would love to hear from you.

George

[AnotherJohnson]

Ouch !

No that’s not normal. Well, the gain’s not normal. It is normal for stuff on Audiomart to be misrepresented.

Sadly Dr. CJ is mighty proud of his work … and if the unit has been bastardized by a previous owner, Dr. CJ will kick its sorry butt to the curb without so much as a bandaid.

Will the seller take it back? Credit card company or PayPal may help.

If your stuck with it, it could go back to CJ for evaluation. The low hanging fruit is always the tubes. Are they correct? Are they good? The twin triodes offer a huge range of gains. Is there a 12AX7 in a socket that ought to be a 12AU7, for example.

[AnotherJohnson]

FWIW, there really wasn’t anything special about a PV10, so you could decide to cut your losses and sell it for parts.

If you want vintage and special, maybe a PV11 w/phono. Or, better still, a Premier 14 with a Premier 15 or TEA2 phono preamp. Full disclosure: I’ve got a TEA2 for sale on Audiogon myself.

[GEORGE ABRAHAM]

Ouch !

No that’s not normal. Well, the gain’s not normal. It is normal for stuff on Audiomart to be misrepresented.

Sadly Dr. CJ is mighty proud of his work … and if the unit has been bastardized by a previous owner, Dr. CJ will kick its sorry butt to the curb without so much as a bandaid.

Will the seller take it back? Credit card company or PayPal may help.

If your stuck with it, it could go back to CJ for evaluation. The low hanging fruit is always the tubes. Are they correct? Are they good? The twin triodes offer a huge range of gains. Is there a 12AX7 in a socket that ought to be a 12AU7, for example.

Thanks for the reply...I am in mediation with the seller thru CAM as intermediary. I am requesting some money back to have it repaired.
I don't think the PV10 was bastardized as I did not see any evidence of it with the top off. I had a Tech take a quick look but he just checked the tubes and did not do any measurements. I checked the positioning of the tubes myself and it all seems that they are all correctly positioned.

I read somewhere that substituting the 12 AX7 with 12 AU 7 in the phono stage will tame the gain...would you recommend doing that?

I am anxious to put the preamp to work without having to see Dr CJ.

George

[AnotherJohnson]

I would not personally roll tubes … but that’s just me. I’m a “stock is best” kinda guy. It makes it easier to sell the gear when I’m done with it.

Lots of guys roll tubes. Gain is one of the obvious parameters that is changed.

Another approach to gain taming is Roberto’s suggestion to replace the volume pot with a logarithmic one. He just suggested this, with a link, in an active thread on fixing a PV11.

[AnotherJohnson]

This explains 12AX7, 12AT7, 12AU7 gains.

https://producerhive.com/guitar-tech/12 ... au7-tubes/

100 vs 60 vs 20. 12AX7 is the most gain. 12AU7 is the least gain.

[AnotherJohnson]

Here’s Roberto’s link to the pots.

https://www.ebay.com/sch/i.html?_from=R ... &_osacat=0

Keep in mind that the volume pot does affect the sound of the unit. I’m not up for pot substitution either.

[AnotherJohnson]

Is it the phono gain that’s too high?
Maybe someone modified it to run an LOMC cartridge.

What cartridge are you trying to match to it?

If it’s got a lot of phono gain, maybe a sub 1 mV cartridge would be an enjoyable solution.

I see you say it’s both phono and line stage.

What amps are offending? A PV10 was a pretty compatible preamp.

You should be main out, not tape out, to the amp.

Sources should be fixed out to line in on the preamp.

[AnotherJohnson]

And then there’s the speaker part of the equation. Are you running 95+ dB/W/m or higher efficiency? If yes, try something less efficient (85ish might work).

You say the amps clip. Are you looking at it on a scope with 8 ohm loads?

Maybe they’re not clipping, but just sound lousy.

What preamp most recently gave good sound?

Seriously … what’s the whole chain?

[AnotherJohnson]

FWIW, I ran LP275Ms (.7 V to full power) with ET7s2 (lots of gain). No problems. The LP275Ms are extremely sensitive amps … more sensitive than anything else I’ve heard.

[admin]

Hi George,
Welcome to CJO, great to have you with us.

Sorry to heave about your troubles. I think there is something wrong with the unit. To have so much gain that it's clipping any amp at such a low volume setting is abnormal. Other users have presented appropriate questions on whether you have a system that is extra sensitive to gain which need to be ruled out,... but something doesn't make sense here, unless you are perhaps using a high gain cartridge as that can swing things by 10's of decibels.

Considering all the trouble, including the tubes,... if I were you I would maybe push for a return/refund.

[roberto]

Hola and welcome. Try to use 12AU7 instead the 12AX7...this will lower the volume. The behaviour of the tubes would be about the same, only that the 12AU7 has lesser gain.

[roberto]

Also check the specs. Some PV10 with phono stages are made for .7mV cartridges.