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Vacuum State RTP3C
Vacuum State RTP3C
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Old 13th January 2021, 09:52 PM   #701
dot is offline dot  Canada
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My RTPC3 also has this 'feature'! The DAC I use is set at 75% volume to even things out with the phono stage. This limits the surprises.
;Glenn
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Old Yesterday, 05:32 PM   #702
airtangent is offline airtangent  Germany
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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,
GŁnter

Last edited by airtangent; Yesterday at 05:41 PM. Reason: typo
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Old Yesterday, 07:58 PM   #703
fdegrove is offline fdegrove  Europe
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Hi,

Quote:
Acoustic Research AR25 line stage
I think what was meant is Audio Research LS25.

Cheers,
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Old Today, 09:20 AM   #704
hesener is offline hesener  Germany
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Vacuum State RTP3C
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.

GŁnter, 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.
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Old Today, 11:40 AM   #705
airtangent is offline airtangent  Germany
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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,
GŁnter

Last edited by airtangent; Today at 11:43 AM.
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Old Today, 12:41 PM   #706
hesener is offline hesener  Germany
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Vacuum State RTP3C
Thanks a lot GŁnther, 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.....
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Old Today, 12:55 PM   #707
airtangent is offline airtangent  Germany
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Hi Hesener

To give you the information for the schematic shown in the link ( RTP3D ), ist works with
300 V coming from the SuperReg and 9mA from each of the two current sources ( 18 mA in
total ).

PS: I would be keen to hear from you what the simulation says!

Regards,
GŁnter

Last edited by airtangent; Today at 12:59 PM.
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