Hi, I want to know what you think about making a Conrad Johnson PV12 preamplifier???
I am plannig to make only the line stage, not the phono, so the schematic is a lot more simple...
But I have a couple of question for you, maybe you can answer me:
Here is the schematic:
http://www.drtube.com/schematics/cj/pv12.gif
1-What is the voltage output my transformer need to have, and how much current ??
12AU7 need 12v for the heater, but how much for the power supply ????
2-What transistor car I choose to replace the MPSU10 and the MPSU60 ???
3-What mean (pp) and (ps) near the capacitor on the schematic... pp=electrolytic and ps=poly????
4-It is writing (VTR52) and (2N65) on some resistor, what that mean ???
Thank you!!
I am plannig to make only the line stage, not the phono, so the schematic is a lot more simple...
But I have a couple of question for you, maybe you can answer me:
Here is the schematic:
http://www.drtube.com/schematics/cj/pv12.gif
1-What is the voltage output my transformer need to have, and how much current ??
12AU7 need 12v for the heater, but how much for the power supply ????
2-What transistor car I choose to replace the MPSU10 and the MPSU60 ???
3-What mean (pp) and (ps) near the capacitor on the schematic... pp=electrolytic and ps=poly????
4-It is writing (VTR52) and (2N65) on some resistor, what that mean ???
Thank you!!
Have you heard this circuit ?
I personally think you could easily better it with a better design.
Shoog
I personally think you could easily better it with a better design.
Shoog
arold19 said:
1. Reg voltage is 330v so raw dc should be at around 380- 400v.
AC 280v/100mA should be enough.
2. Anything that can take 600v/50mA
3. Polypropylene and polystyrene
4. RN65, VTA52 - Dale
Why on earth would you want to build it?
I know it is a very good sounding preamp.....
Shoog: you have an other good sounding preamplifier design for me???
thank you for your answer!
Shoog: you have an other good sounding preamplifier design for me???
thank you for your answer!
Arold19,
Sounds like pouring cold water over enthusiasm (and I respect the Conrad Johnson name), but this is really an overdesigned effort if ever I have seen one, in the power supply department.
You are justified in asking for an alternative, which I cannot post right now - apology. If Shoog does not come up with one, I will try to post something (must draw, scan). My main concern is that there is nothing to justify the power supply complexity of the C-J design. An ordinary well-designed circuit (twin triode or triode-pentode) without any power supply regulation should be adequate for a line stage.
Regards
Sounds like pouring cold water over enthusiasm (and I respect the Conrad Johnson name), but this is really an overdesigned effort if ever I have seen one, in the power supply department.
You are justified in asking for an alternative, which I cannot post right now - apology. If Shoog does not come up with one, I will try to post something (must draw, scan). My main concern is that there is nothing to justify the power supply complexity of the C-J design. An ordinary well-designed circuit (twin triode or triode-pentode) without any power supply regulation should be adequate for a line stage.
Regards
Ok.... Thank you very much... I'am waiting for an other design... I found that the power supply was complex but I think that it is a sign of quality...
I appreciate if you can post a good design !!! An if the part are easier to found than the PV12, it will be perfect for me.
I appreciate if you can post a good design !!! An if the part are easier to found than the PV12, it will be perfect for me.
one of best and also simplest preamps here .........
http://www.diyaudio.com/forums/showthread.php?s=&threadid=68267&highlight=
or
http://www.diyaudio.com/forums/sear...63195313&sortby=lastpost&sortorder=descending
http://www.diyaudio.com/forums/showthread.php?s=&threadid=68267&highlight=
or
http://www.diyaudio.com/forums/sear...63195313&sortby=lastpost&sortorder=descending
Ok, this 12B4 preamp will sound better than a 2K$ stock preamp ???
If you are sure, can you give me a good, or very good power supply schematic, and I will begin the preamp right away!!!
The schematic on the 1st page of the 70 page tread is the good one ??
Thank you... It is very cool !
If you are sure, can you give me a good, or very good power supply schematic, and I will begin the preamp right away!!!
The schematic on the 1st page of the 70 page tread is the good one ??
Thank you... It is very cool !
arold19 said:
look for my posts in that thread ;
in fact- re-read entire thread and ask what (if ) you don't get .
regarding 2K preamp .........
show me 3 good junkyards ( to find few parts) and I'll make for nothing preamp better than stock 2K preamp ;
it's matter of knowledge and DIY,not shiny knobs and parts made of preputium
edit:
click on my www button and look for WOT preamp page ;
too lazy to took present state pictures ( just from prototype era) , but there you can see pics of preamp which made me pretty comfortable regarding price competitions
I took my FVP5 clone to a local DIY meet last week and it was the best one there. Could easily be built from salvaged parts for less than a $100.00
If you are really interested then send me an email and I will send you the schematic.
I feel certain that you are right about this amp sounding good - but it seems to have one or two fundamental errors of design which would be holding it back. The choice of a cathode follower final stage is a huge no-no for me. If you search this forum on this subject you will find that this approach is almost universally disliked around here. Make your choices but know why you are making them, a bit of basic research will pay huge dividents in the end.
Shoog
If you are really interested then send me an email and I will send you the schematic.
I feel certain that you are right about this amp sounding good - but it seems to have one or two fundamental errors of design which would be holding it back. The choice of a cathode follower final stage is a huge no-no for me. If you search this forum on this subject you will find that this approach is almost universally disliked around here. Make your choices but know why you are making them, a bit of basic research will pay huge dividents in the end.
Shoog
Johan Potgieter said:
Johan
You may be missing the point behind the PS. In their quest to use high quality caps CJ have really gone below any reasonable capacitance value. And there is a phono stage to feed as well...
Hi Analog_sa,
No, quite aware of that. But to my mind this persuance of "high quality" components in general can go overboard. Define high quality. Audible? Limiting my response to electrolytics, however I look, I cannot see that the general better type of modern capacitor is not more than adequate for a pre-amp filter.
I have not tested the CJ power supply, but know that one can also increase e.g. noise introduced through the HT line by regulators. I am not saying that their's does; simply a general observation. Any half-decent pre-amp circuit is normally well within class A operation i.e. constant current, and I have constructed enough models to really feel that advantage gained by, let us say exotic components/design, is inaudible. And Arold 19 is only looking for a line stage.
Rather than saying the CJ circuit is poor, I feel that it is unnecessarily complex. My own experience includes RIAA circuits with 2 mV input sensitivity, and also a (bass) tone control stage. I have nerver used more than a well-filtered and decoupled supply line.
Regards
No, quite aware of that. But to my mind this persuance of "high quality" components in general can go overboard. Define high quality. Audible? Limiting my response to electrolytics, however I look, I cannot see that the general better type of modern capacitor is not more than adequate for a pre-amp filter.
I have not tested the CJ power supply, but know that one can also increase e.g. noise introduced through the HT line by regulators. I am not saying that their's does; simply a general observation. Any half-decent pre-amp circuit is normally well within class A operation i.e. constant current, and I have constructed enough models to really feel that advantage gained by, let us say exotic components/design, is inaudible. And Arold 19 is only looking for a line stage.
Rather than saying the CJ circuit is poor, I feel that it is unnecessarily complex. My own experience includes RIAA circuits with 2 mV input sensitivity, and also a (bass) tone control stage. I have nerver used more than a well-filtered and decoupled supply line.
Regards
It is also well worth noting that not all regulators are equal and some will have a noticably negative impact on the final result. I say this from my experience with using simple capacitance multipliers. I never ever got them to sound right.
The thing to bare in mind is that the pass element (be it transistor, fet or valve) has its own frequency response which is superimposed over the sound of the preamp. This means that transistors are almost guaranteed to have a negative impact, fet's less so and valves the least.
I personally like to include at least one inductor to guarantee that high frequency hash has little chance of bleeding through - but even here you have to be careful as it is very easy to introduce a resonance (usually right in the hum band). Diode snubbers are almost essential to prevent radio frequency hash been picked up by later stages. Also power transformer ringing needs to be watched for and I tend to include a secondary snubber for this.
When these issues are accounted for I think a multi stage inductor/resistor capacitor network is the safest way to go. Thorsten and others would tend to agree.
Shoog
The thing to bare in mind is that the pass element (be it transistor, fet or valve) has its own frequency response which is superimposed over the sound of the preamp. This means that transistors are almost guaranteed to have a negative impact, fet's less so and valves the least.
I personally like to include at least one inductor to guarantee that high frequency hash has little chance of bleeding through - but even here you have to be careful as it is very easy to introduce a resonance (usually right in the hum band). Diode snubbers are almost essential to prevent radio frequency hash been picked up by later stages. Also power transformer ringing needs to be watched for and I tend to include a secondary snubber for this.
When these issues are accounted for I think a multi stage inductor/resistor capacitor network is the safest way to go. Thorsten and others would tend to agree.
Shoog
Exactly backward. The impact of the regulator's frequency response is proportional to output impedance.
Isn't frequency response at least part of the issue ? A lot of transistor based regulators seems to use feedback to correct for this.
Shoog
Shoog
Hi Shoog,
More importantly, designing without a regulator stage is very silly. It is here where you can keep the outside world nasties from the AC line out of your preamp. I consider rectification and filtering as part of this, a regulator finishes the job for you.
-Chris
Yes, at frequencies where the power supply output impedance becomes high compared to the active circuits it supplies. This can be a very high frequency if the regulator is designed properly. Don't forget that a good regulator often has capacitance across it's output to maintain a low frequency response and transient response. Then your can R-C decouple the circuits from there.
The main use of feedback is to lower the output resistance so that the output voltage does not sag under load. At line stage current levels, this is really not much of a problem. Keep in mind that your average tube preamp is operating in class A all the time.
More importantly, designing without a regulator stage is very silly. It is here where you can keep the outside world nasties from the AC line out of your preamp. I consider rectification and filtering as part of this, a regulator finishes the job for you.
-Chris
About CJ PV12
Hello everybody,
About linear stage, I think PV12 would sound better than 12B4. Using big capacitor on cathode (360uF) and direct output with high impedance on the anode were not good solutions (tight and poor sound). Low output impedance like cathode follower is better. For the same reason, take off PV12, last serial resistor (425 ohm?) and ground relay.
Conrad Johnson use only 2 x 20uF filtering ! With good components (Polypropylen) it's a very good approach. For vacuum tube or transistors, this solution sound better than using good electrolytics capacitors, I use it in my designs.
About tension, I have the same PV12 schematic diagram with mesured tensions, if you are interested in. (I don't remember where I find theses values !!!)
About regulator
I don't thing using two serial regulators sound very good. As say Shoog, introducing an inductor and snubbers would be fine.
Take care with power supply quality, it is as important as a good linear stage.
Eric
Hello everybody,
About linear stage, I think PV12 would sound better than 12B4. Using big capacitor on cathode (360uF) and direct output with high impedance on the anode were not good solutions (tight and poor sound). Low output impedance like cathode follower is better. For the same reason, take off PV12, last serial resistor (425 ohm?) and ground relay.
Conrad Johnson use only 2 x 20uF filtering ! With good components (Polypropylen) it's a very good approach. For vacuum tube or transistors, this solution sound better than using good electrolytics capacitors, I use it in my designs.
About tension, I have the same PV12 schematic diagram with mesured tensions, if you are interested in. (I don't remember where I find theses values !!!)
About regulator
I don't thing using two serial regulators sound very good. As say Shoog, introducing an inductor and snubbers would be fine.
Take care with power supply quality, it is as important as a good linear stage.
Eric
current is not necessary constant in class a operation
Hi Anatech,
In class A, yes, but not with constant current !
Eric
Hi Anatech,
anatech said:
In class A, yes, but not with constant current !
Eric
Hi Eric,
This is a point many designers miss completely! By using high quality, low value filter caps you reduce the amount of hash or spikes coming from your rectifiers. The 120 Hz component is very easy to get rid of, the high frequency components are not.
What is your current draw for your circuit? Less than 100 mA I bet. So how much in the way of capacitance do you need? Keep in mind that increasing capacitance introduces the problems inherent with large capacitors. Increased inductance and resistance at high frequencies being the major issues here. Once you have not created the high frequency spikes on your raw DC, it's easy to clean it up.
-Chris
Edit: Eric, output filtering with capacitors will filter out the minuscule current variations caused by a signal. I've designed both ways and found this to be the better way. Also, watch your grounding!
Exactly!
This is a point many designers miss completely! By using high quality, low value filter caps you reduce the amount of hash or spikes coming from your rectifiers. The 120 Hz component is very easy to get rid of, the high frequency components are not.
What is your current draw for your circuit? Less than 100 mA I bet. So how much in the way of capacitance do you need? Keep in mind that increasing capacitance introduces the problems inherent with large capacitors. Increased inductance and resistance at high frequencies being the major issues here. Once you have not created the high frequency spikes on your raw DC, it's easy to clean it up.
-Chris
Edit: Eric, output filtering with capacitors will filter out the minuscule current variations caused by a signal. I've designed both ways and found this to be the better way. Also, watch your grounding!
- Status
- Not open for further replies.