CJ tube preamp experts

[kward]

Some tracks could be recorded with inverted polarity, so it can be hard to distinguish if you're trying different program tracks. You might need to double blind test with known polarity on the recording to distinguish.

 

[Pio1980]

I'm not a huge fan of dbt, but it is applicable if not final here, depending.

 

[kirk57]

Some recordings could be recorded out of phase, so it can be doubly hard to distinguish if you're trying different program tracks. And then to do it "really right" you would need to double blind test it with known polarity on the recording.

Adding to the fun is the fact that certain tracks in a multitrack recording may be out of (absolute) phase with other tracks in the same recording.

 

[David Bright]

I

I purchased a Conrad Johnson PV-8 a few years back that I really like, but never tried reversing phase of the speakers like the manual says. I'm a bit confused with the reverse phase thing that they state about the preamp and why they wouldn't design it with regular phase. Below is what is stated in the manual, just curious how many have experimented with this. Never reversed phase with my JBL 4435's.

THE PV8 IS PHASE INVERTING. If your system has an odd number of inversions, then you must add one phase inversion. This will be the case if the PV8 is the only unit in the chain that inverts phase. THIS IS CONVENIENTLY DONE BY REVERSING THE POSITIVE AND NEGATIVE CONNECTIONS TO YOUR SPEAKERS (be sure to reverse both channels). If you are not sure about the phase of every piece in your system, you can establish correct absolute phase by careful listening. When the system is in correct phase, transients will be noticeably cleaner and more sharply defined. The effect is especially apparent on plucked string sounds. A final warning-not all recordings are phase correct (including some "audiophile" recordings), so listen to several before concluding your investigation of absolute phase.

Just picked up a CJ PV8. I switched speaker wires. I get a tone sound after amp turns on...not sure what's going on

 

[David Bright]

CJ tube gear of that era was minimalist in design. They used the minimum number of stages to achieve the gain needed with the tubes types chosen. In the case of the PV8 that meant phase inverted outputs.

It would easily be possible to create a preamp with phase correct outputs but it either adds a stage or adds complexity or puts transistors in the signal path. One simple way to achieve this would be to use an "inverting" OP amp based buffer on the input. But then they'd have to call their preamp hybrid. Or they could have used a single differential stage but then output impedance would be higher. They could have addressed high output impedance by using constant current sinks, but then complexity rises. Or they could have used a lower gain tube so adding an extra stage to obtain phase correct outputs would be possible without having too much forward gain, but that adds another stage for the signal to travel through. Or the could have ... (you get the idea).

I had a PV12 for many years. It was dead simple in the line stage--one common cathode gain stage direct coupled to an output stage buffer (with no loop or global feedback), which created phase inverted outputs, and I expect the PV8 had a similar line stage topology.

For the PV8 can I add a 2nd turntable?

 

[kward]

I’ve never had a pv8 so I don’t know for sure. The pv12 had only one turntable input. But you could add an extra outboard phono preamp and connect it to the pv12 via its aux input and therefore run two turntables

 

[mcgjohn]

I purchased a Conrad Johnson PV-8 a few years back that I really like, but never tried reversing phase of the speakers like the manual says. I'm a bit confused with the reverse phase thing that they state about the preamp and why they wouldn't design it with regular phase. Below is what is stated in the manual, just curious how many have experimented with this. Never reversed phase with my JBL 4435's.

THE PV8 IS PHASE INVERTING. If your system has an odd number of inversions, then you must add one phase inversion. This will be the case if the PV8 is the only unit in the chain that inverts phase. THIS IS CONVENIENTLY DONE BY REVERSING THE POSITIVE AND NEGATIVE CONNECTIONS TO YOUR SPEAKERS (be sure to reverse both channels). If you are not sure about the phase of every piece in your system, you can establish correct absolute phase by careful listening. When the system is in correct phase, transients will be noticeably cleaner and more sharply defined. The effect is especially apparent on plucked string sounds. A final warning-not all recordings are phase correct (including some "audiophile" recordings), so listen to several before concluding your investigation of absolute phase.

I have had several CJ preamps including the 8. Yes you need to swap your speaker pos and neg to keep phase correct when listening. The PV-8 was also from an era where tubes were mostly NOS. Most of the tubes are run in a current starved condition. the PV8 will sound better if you get a bit more current flowing to the tubes.

 

[zackthedog]

I have had several CJ preamps including the 8. Yes you need to swap your speaker pos and neg to keep phase correct when listening. The PV-8 was also from an era where tubes were mostly NOS. Most of the tubes are run in a current starved condition. the PV8 will sound better if you get a bit more current flowing to the tubes.

No offense to David, but if getting the phase correct is a challenge, then modifying the preamp probably isn't in the cards. ;-)

 

[David Bright]

I am looking at the preamp (CJ PV8) to ensure of tubes and any cap issues

 

[David Bright]

I have had several CJ preamps including the 8. Yes you need to swap your speaker pos and neg to keep phase correct when listening. The PV-8 was also from an era where tubes were mostly NOS. Most of the tubes are run in a current starved condition. the PV8 will sound better if you get a bit more current flowing to the tubes.

'

get a bit more current flowing to the tubes.' please elaborate on this statement....

 

[Pio1980]

No offense to David, but if getting the phase correct is a challenge, then modifying the preamp probably isn't in the cards. ;-)

It's about acoustic polarity, not phase angle which can be problematic in itself.

 

[zackthedog]

It's about acoustic polarity, not phase angle which can be problematic in itself.

Thanks, I know that. People use "phase" and "polarity" interchangeably. The CJ manual itself refers to "phase."

 

[Pio1980]

Thanks, I know that. People use "phase" and "polarity" interchangeably. The CJ manual itself refers to "phase."

Nonetheless, phase relationships can vary by degrees, polarity is either positive or negative, an absolute phase reversal.

 

[Pio1980]

Nonetheless, phase relationships can vary by degrees, polarity is either positive or negative, an absolute phase reversal.

As to whether acoustic polarity reversal is audible, it seems to depend on an individual's perception.
Some conditioned audiophiles as well as other folks say they hear no difference, others hear a definite affect on SQ naturalness, I am one such. I hear a marked dynamic dullness and reduced transparent aliveness when polarity is inverted, notably male vocals, percussion, brass, in-polarity recorded piano (upper for grand, backside for upright).

 

[mcgjohn]

'

If you calculate out the current flow the plate and load resistors are a high enough value the current flow is way under 1 ma. Its been a long time since I last looked at a PV preamp but decreasing the values will provide greater current flow through the tube. I do not recall what the newer values were.

 

[mcgjohn]

No offense to David, but if getting the phase correct is a challenge, then modifying the preamp probably isn't in the cards. ;-)

would agree unless a tech can do the change.