Hello Hesener,
Having read the remark over your build I'm wondering what an Acoustic Research AR25 line stage is.
As far as I could find in the Internet this is a loudspeaker but not a preamp??
Alex pointed out very well what most likely the problem is.
I don't know if you use your RTP5 phono as a standalone phono preamp and connect it then with an interconnect to your line amp. But you have to know that it was never intended to be used in such a way.
It is namely very important that the line stage used applies a 50 k attenuator with fixed impedance as volume control as shown on the VS website in the RTP3C/5 schematics because otherwise the RIAA might suffer. The phono stage needs to "see" that according to Allen Wright.
So if your line stage for instance makes use of something else it might not be all ok.
Regards,
Günter
Having read the remark over your build I'm wondering what an Acoustic Research AR25 line stage is.
As far as I could find in the Internet this is a loudspeaker but not a preamp??
Alex pointed out very well what most likely the problem is.
I don't know if you use your RTP5 phono as a standalone phono preamp and connect it then with an interconnect to your line amp. But you have to know that it was never intended to be used in such a way.
It is namely very important that the line stage used applies a 50 k attenuator with fixed impedance as volume control as shown on the VS website in the RTP3C/5 schematics because otherwise the RIAA might suffer. The phono stage needs to "see" that according to Allen Wright.
So if your line stage for instance makes use of something else it might not be all ok.
Regards,
Günter
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Frank, thanks for the clarification, thats exactly true. Seems the gain between the RTP5 line stage and LS25 line stage is not the same, obviously.
I am using a Quad 405 power amplifier (yes it is not symmetrical, lets wait another 8 years ;-)) which has a bunch of mods, including reducing the input sensitivity to 3V for full output. Now with the LS25 line stage, I need to turn up the volume about half to get decent listening levels. But with Phono, need to turn up all the way.
Günter, thanks for pointing out, yes it appears that is the problem. The linestage and the phono are both in one case, between them is a shunt attenuator from Khozmo with 50K resistance no matter where the volume tap is. RIAA equalization is just fine, no concern there.
So I just ordered a couple MAT12, will remove the emitter resistors currently in , and increase the gain that way by a few dB. I will also put a couple resistors in series with the input from the CD player, to attenuate, and get the levels a little closer together. And otherwise I will just live with it
It won't be hard, the sound quality and imaging are something really really special.
I am using a Quad 405 power amplifier (yes it is not symmetrical, lets wait another 8 years ;-)) which has a bunch of mods, including reducing the input sensitivity to 3V for full output. Now with the LS25 line stage, I need to turn up the volume about half to get decent listening levels. But with Phono, need to turn up all the way.
Günter, thanks for pointing out, yes it appears that is the problem. The linestage and the phono are both in one case, between them is a shunt attenuator from Khozmo with 50K resistance no matter where the volume tap is. RIAA equalization is just fine, no concern there.
So I just ordered a couple MAT12, will remove the emitter resistors currently in , and increase the gain that way by a few dB. I will also put a couple resistors in series with the input from the CD player, to attenuate, and get the levels a little closer together. And otherwise I will just live with it
It won't be hard, the sound quality and imaging are something really really special.Hi Hesener,
Ok, remains for me only the question why you decided to build the RTP5 and not the RTP3B/C phono amp as this is the more recent one.
Differences I noticed in the schematics on the VS website are a B+ of 200 and not 300 V as in the RTP3B ( typo ?? ) and 13 vs 20mA current. So I consider this significant differences!
And the most recent one ( RTP3D ) I found under the MPP thread under # 470 at the very bottom of that page:
MPP
Regards,
Günter
Ok, remains for me only the question why you decided to build the RTP5 and not the RTP3B/C phono amp as this is the more recent one.
Differences I noticed in the schematics on the VS website are a B+ of 200 and not 300 V as in the RTP3B ( typo ?? ) and 13 vs 20mA current. So I consider this significant differences!
And the most recent one ( RTP3D ) I found under the MPP thread under # 470 at the very bottom of that page:
MPP
Regards,
Günter
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Thanks a lot Günther, exactly the circuit I built, with the changes you mention (B+ is 180V from SuperReg, current 13mA). This schematic does not show B+ though. I think with a higher current a higher B+ would be needed, otherwise the anode voltages of the tubes would be way too low.... major surgery...
From Allen's book, reading it over and over , it just seemed to me the logical choice to build the "5", I was not aware that this 3c is more recent.
Also, I noticed that this schematic shows slightly different values for the RIAA section. So, I ran a simulation with this circuit and a close, using the capacitor and resistor values I have on hand, to adjust especially the resistors until I get a perfect match, and then insert that one - yet another set of values.....
From Allen's book, reading it over and over , it just seemed to me the logical choice to build the "5", I was not aware that this 3c is more recent.
Also, I noticed that this schematic shows slightly different values for the RIAA section. So, I ran a simulation with this circuit and a close, using the capacitor and resistor values I have on hand, to adjust especially the resistors until I get a perfect match, and then insert that one - yet another set of values.....
I just caught up with the thread and congratulations. I know the challenge to build these beasts, having built a number of versions, including some for use as microphone preamps (sans RIAA). Allen also built some that way.
Yours looks amazing, in fact gorgeous.
My hat's off to you. And to the guys that helped you.
Cheers, Joe
Hi Günter, my apologies for the late reply. please find my simulation schematic attached, note you will need the TL431.lib since thats what I use as regulator for the grid voltages, but you could simply put a DC voltage source there.
It is currently set for B+ = 180V and 12.5mA current in the diffamp (R51 has no other purpose than to measure that current). Increasing B+ which allows for higher current increases the gain somewhat. Hope you like it!
I wasn't aware of that configuration (of the RTP3D) - mine is the RTP3C. What is the difference between those two? Are those jfets on the emitters of the transistors acting as current sources (sinks)?
RTP3D
Kenev,
I gave that information on the phono amp already earlier in this thread and yes the Jfets are current sources.
Please go to page 48, #473 in this thread.
Other information w.r.t. differences/changes of the D Version can be found on the VS website. Biggest change is the power supply.
Regards,
Günter
Kenev,
I gave that information on the phono amp already earlier in this thread and yes the Jfets are current sources.
Please go to page 48, #473 in this thread.
Other information w.r.t. differences/changes of the D Version can be found on the VS website. Biggest change is the power supply.
Regards,
Günter
FWIW, I am using bipolars (BC337-40) for the current sinks in the phono stage, with a LED as a reference - exactly the circuit as shown in the simulation circuit - and it works fine. I chose these as I calculated the power dissipation in the transistors, and felt better with the larger margin here.
Apart from the differences in power supply that Gunther mentioned, I noticed a slight change in the RIAA EQ circuit in the RTP3D circuit Allen posted in the other thread. There are 1K21 resistors in series between the anodes and the EQ network where the RTP3 had none, and slightly different component values in the latter. I wonder why Allen added the series resistors? Increased stability, perhaps?
Alex
No, this came from different available values (we switched to a different brand) for the filter Cs.
Thanks for the clarification, Thomas. Can you say which brand and type you use for the filter caps?
In my RTP3 I use standard polystyrenes, paralleled to get the required values - the DC voltage between the anodes is low enough to allow this. In my SVP I had to use polypropylene film caps in the RIAA network, as in the single-ended circuit it is the DC voltage between anode and ground that matters, and this is much higher.
Alex
In my RTP3 I use standard polystyrenes, paralleled to get the required values - the DC voltage between the anodes is low enough to allow this. In my SVP I had to use polypropylene film caps in the RIAA network, as in the single-ended circuit it is the DC voltage between anode and ground that matters, and this is much higher.
Alex