Conrad Johnson PV-5, my next project, some simple questions

[Razorblade]

Hello,

since i finished my pass F5 Monos, i need something to drive them properly, i decided to go with the Conrad Johnsons PV-5, since it has enough gain and a phono stage. It will be my first tube project, but i have an oldtimer at hand who will support me, he is building tube amps for over twenty years so i guess I can try a Preamp with Phono Stage.

I have some minor questions on this circuit:

1. What are the transformer secondary voltages / Ampere Ratings?
2. Which of the powersupply transistors (Q1, Q2, Q3) should be heatsinked?
3. What voltage should the regulated power supply have?
4. Where to get 1% Caps for the RIAA Network? Digikey seems to have none left and my Fluke 29 isnt the most accurate in measuring capacity.

I have attached the schematic at the end.

Thanks for your help

[Eli Duttman]

Which of the powersupply transistors (Q1, Q2, Q3) should be heatsinked?

Q3 needs a heatsink, as it's the pass element. If airflow is good, I'm guessing Q1 and Q2 are OK, without heatsinking.

Where to get 1% Caps for the RIAA Network?

Try Nebraska Surplus. A mix of NOS mica and 'styrene parts should serve you well.

[Razorblade]

Try Nebraska Surplus. A mix of NOS mica and 'styrene parts should serve you well.

0.5% micas, this is a DIY heaven ! Thank you so much for the info.

2 problems solved, two remain : The Transformer voltages, I guess one secondary is 12.6V and the current needed can be calculated quick and easy by summing up the heater currents, but i am searching for 3 days now to get the other secondary and voltage for the plate. I even searched old triad transformer catalogues since the part number is given in the parts list but with no success.

Can anyone else help me out?

Thanks for your help

[Razorblade]

Well i tried to model the power supply in Microcap to see whats the output voltage of the PSU but i failed, i dont know how to connect the sinus voltage source to the rectifier diodes, and implementing a trafo instead of a sinus source ... no way that i get this done right

I also simulated the phono section of the PV-5 just to see that its like 1db off minimun. Either the tube models are not right or the whole parts list for the preamp is screwed up.
Its nearly 2 o clock in the morning, i spent the last 3 days and nights simulating and researching on this circuit and things just get worse and worse.

I think i reached the point where DIY is not fun anymore

But i came up with a better schematic for the phono section, since the original copy is nearly unreadable.

[Eli Duttman]

I think i reached the point where DIY is not fun anymore

RB,

IMO, CJ's design is overly complicated. Also, it uses the out of favor active equalization method. For overload handling and other good reasons, passive EQ is in vogue. I've uploaded a schematic for a tweaked version of the "classic" RCA design that works very well with many MM level cartridges.

An important point you have yet to cover is the sensitivity of your power amps. What sort of drive voltage at the I/P causes full power O/P to be produced? It's quite possible that you don't need any gain whatsoever in the line stage.

[Razorblade]

Thanks for cheering me up

The F5s need about 6V-7V input for full output swing, so i need a total gain of roughly 65dB from the preamp including , 40dB from the phono stage, another 25db from the line stage, I just listen to vinyl so the line stage is only needed to amplify the phono section, no high level sources here.

I know passive EQ is hip at the moment... but ... well there are many good sounding active EQ circuits out there too.

I just obtained the schematics of the premier 3, including all node voltages, might give it a try, but it think ill have to get some sleep first and think this over again.

I might just get a pearl two and use a single opamp as linestage... naaah, i dont want that, i'd really like to give tubes a chance for my next project, choices choices choices and i just dont know which way to go.

I need : 65db-70db gain, MM compatibility, Riaa Accuracy +/- 0.2dB, proven design with easy to source parts, pre and linestage using the same power supply and a knob to control the volume and low distorsion (below 0.1 or better) since my speakers are not really effective (89dB) and output should be phase correct and contain absolutely no DC since F5s are direct coupled.

But for now, its bedtime

[Eli Duttman]

RB,

The tweaked RCA circuit yields approx. 45 dB. of gain. You can easily get the remaining 20 dB. from a resistively loaded common cathode ECC99 section. What's the I/P impedance of a F5?

[Razorblade]

The tweaked RCA circuit yields approx. 45 dB. of gain. You can easily get the remaining 20 dB. from a resistively loaded common cathode ECC99 section

That sounds interesting, tell me more. The Circuit looks really nice, what about RIAA accuracy
Do you have a link to some example schematics for the ECC99, this could mean i can get a fully functional preamp with just 3-4 tubes, if the output phase is correct and not inverted, i am in.

BTW, is it neccesary to keep the Phono tubes shielded or can they be put on top of the case to shine in all their beauty (PS will be in an external shielded case)?

Sorry for all these simple questions, i am still learning a lot and am happy that i finally understood the basic principles of amplification and just recently got my first scope and function generator.

What's the I/P impedance of a F5?

Its 101K

P.S: Just found this simple linestage with the ECC99, but no gain is mentioned

[Eli Duttman]

The Circuit looks really nice, what about RIAA accuracy

RIAA accuracy is good. If you are fanatic, use plastic film, adjustable caps., as shown here, in the EQ network, to achieve "perfection".

Do you have a link to some example schematics for the ECC99, this could mean i can get a fully functional preamp with just 3-4 tubes, if the output phase is correct and not inverted, i am in.

Common cathode cathode topology inverts absolute polarity. So, constant current source (CCS) load each ECC99 section and cap. couple the plates to transformers, which allows you to make the line section non-inverting, end to end. The MagneQuest model B7-10K:10K seems suitable. The step down B7 models are also interesting. You may be able to get something suitable from Sowter in England, which is closer to home.

[Razorblade]

But isnt the Mosfet of the MM Pre a source follower and inverts the signal, this is fed to the first half of the ECC99 which is non inverting and the last ECC99 is a cathode follower which inverts the already inverted signal and in the end i have a nice noninverted signal.
I dont mind to have inverting and noninverting stages mixed as long as its noninverted in the end.

Thanks for your help Eli. Things are slowly clearing up.