[SET Man]

Hey!

   Well, I can't take it anymore!  My pre-amp of which is a Audio Note M1 Phono of which I have been using since 1998 I think.

    Lately I've been having a little problem with the phono stage. It is much louder than my CD. And since I have step attenuators in my pre the step become too coarse when I play LPs but fine when I play my CD.

    This problem started after I changed my cart from Blue Point Special EVOIII to my current Benz Micro "ACE" HO. Strangely according to the spec both carts have output of 2.5mv. But somehow the new Benz sound louder! 

     Yes, I've tried making L-pad before the attenuator but every resistors I've tried didn't sound right to me.

    Now I wonder if I could lower the gain of the phono stage that use four 12AX7s (2 per channel) and leave everything else alone as is?

   Any help or suggestion is appreciated 

Take care,
Buddy

[lonewolfny42]

I don't know Buddy....but send a PM to Bill Baker/Response Audio....he sells and mods Audio Note...

[silverfi]

Setman,

You can  use 4X5751 (preferably GE 5 Star's which are the best) which is equivalent and offers better balance and lower output. (If I am not wrong appr. 30% lower).

Sincerely.

[SET Man]

Setman,

You can  use 4X5751 (preferably GE 5 Star's which are the best) which is equivalent and offers better balance and lower output. (If I am not wrong appr. 30% lower).

Sincerely.

Hey!

     Yes, I know about the 5751 tube But the other problem is that I already have a stash of 12AX7 tube that I like. So, I would prefer to use them.

     The other thing about this pre. It seem to run those tubes quite hard at 280V. Hmm... will lower it a bit to let's say 260V help a bit?

    But if nothing works than I guess I have to move to plan B of which is 5751 tube.

I don't know Buddy....but send a PM to Bill Baker/Response Audio....he sells and mods Audio Note...

       Yes, Chris I might do that. But from what I know it look like those kit now use difference tube and layout now. So, I don't know if he is familiar with older M1 pre. And he seems pretty busy too 

Take care,
Buddy

[BobM]

You may want to try some 5751's before you do anything more costly. They don't work in every situation because of their lower gain, but they may be perfect for you. They are also reported to be quieter and better sounding than 12AX7's if they work in your circuit, so you could have a double benefit from them.

The other option may be to put a toggle switch on your preamp with a different grounding resistor to half the volume attenuators. This would give you a broader range of adjustability.

Just a few thoughts.

Bob

[SET Man]

You may want to try some 5751's before you do anything more costly. They don't work in every situation because of their lower gain, but they may be perfect for you. They are also reported to be quieter and better sounding than 12AX7's if they work in your circuit, so you could have a double benefit from them.

The other option may be to put a toggle switch on your preamp with a different grounding resistor to half the volume attenuators. This would give you a broader range of adjustability.

Just a few thoughts.

Bob

Hey!

   Thanks Bob. Yeah, I guess I might have to move to plan B of which is to get a set of 5751 tubes . The problem is that those 12AX7s in side the pre still good and I also have two more new set in my stash 

    I did considered toggle switch but I don't have room on my pre and I don't want to drill the front of my pre. But maybe 

   Also, right now I absolutely love the sound of my pre and any change in the signal path like one more resistor before the attenuator will change the sound. I know this for sure because I've tried L-pad pre-attenuator and even the best Vishay nude 102 I could still hear the change and I didn't like it at all.

   BTW... what you do think is the ideal high voltage HT operation point for 12AX7 and 12AU7? 260V or?

Take care,
Buddy

[GBB]

    Now I wonder if I could lower the gain of the phono stage that use four 12AX7s (2 per channel) and leave everything else alone as is?

Buddy,
It would be easier to give some advice with a copy of the phono stage schematic.  Do you have one?

---Gary

[SET Man]

    Now I wonder if I could lower the gain of the phono stage that use four 12AX7s (2 per channel) and leave everything else alone as is?

Buddy,
It would be easier to give some advice with a copy of the phono stage schematic.  Do you have one?

---Gary

Hey!

    Gary, that is another problem. I don't have and I can't find it anywhere on the net. You are right about the schematic. This is going no where, without it will be impossible for you guys to help me.

   Oh! Well... back to the drawing board for me.

Take care,
Buddy

[GBB]

    Gary, that is another problem. I don't have and I can't find it anywhere on the net. You are right about the schematic. This is going no where, without it will be impossible for you guys to help me.

Buddy,
Well in that case, your phono preamp probably uses the same circuit as the one I've attached except the values will be changed for use with 12AX7 tubes.  The easiest way to reduce the gain is to remove capacitor C5.  This will reduce the gain of the output stage without changing the characteristics of the phono stage in any other way.

---Gary

[SET Man]

Hey!

   Gary, thanks.... I think I could take it from there.

  BTW... don't know if you could guess from this picture of my phono stage of what can be change...



    This came from my tiny point and shot digi-cam. If better picture needed I could take it with my DSLR.

   Hope this will give you better idea of what type of circuitry my phono stage use.

Take care,
Buddy

[GBB]

   Gary, thanks.... I think I could take it from there.

  BTW... don't know if you could guess from this picture of my phono stage of what can be change...

Buddy,
I'm pretty sure it's the same type of circuit, so my advice still holds.  The cap labeled C10 looks like it might be the right one but there should be another one just like it for the other channel that I don't see.  Maybe it's hidden in this picture by the wires on the bottom of the photo.  Can you take another shot that shows what's going on underneath those wires?

What you really want to do, is look at the other side of the board and trace back and see what is wired to pin 8 of V3 and V4.  It should be a resistor/capacitor combination like what's shown on the schematic I posted earlier on pin 8 of the output tube.  In case you don't know which one is pin 8, I've posted a diagram showing the numbering of the pins when looking from the bottom.

---Gary

[JoshK]

You'd need to be able to trace the traces to reverse engineer the schematic.  Usually I find it easiest to start with the power, since + and ground are easiest to determine and then you will see the PSU filter and then out comes B+.  Then you can tell by the way it attaches to the tube and how the rest is figured.

[JoshK]

Gary,  the schem you show looks like a cascode to me, do you agree?  Why would AN call it an SRPP?  Still I think you are probably right about the C10 and presumably C5. 

[GBB]

Gary,  the schem you show looks like a cascode to me, do you agree?  Why would AN call it an SRPP?  Still I think you are probably right about the C10 and presumably C5. 

Josh,
You're right - the schematic I included is from the current Audio Note UK phono stages and uses a cascode 1st gain stage, not an SRPP.  But I think the last gain stage is still the same so the point about how to reduce the gain should still hold.  For reference, I've attached a schematic for a generic SRPP gain stage, which is probably closer to what is used for V1 and V2 of Buddy's phono stage.
Thanks for catching this.

---Gary

[SET Man]

Buddy,
....The cap labeled C10 looks like it might be the right one but there should be another one just like it for the other channel that I don't see....

Hey!

     Yes, there is another cap just like the one labeled C10 on the other side of the PCB.

What you really want to do, is look at the other side of the board and trace back and see what is wired to pin 8 of V3 and V4.  It should be a resistor/capacitor combination like what's shown on the schematic I posted earlier on pin 8 of the output tube....
---Gary

     I see... I will open my pre up tomorrow and see if C10 and the other on the other side connected to pin 8 of those tube.

     If so, I just have to remove them out right? Any idea of how much gain will this reduce?

    Gary, thanks again for your help so far. Greatly apreciated. I will let you know how things turn out.

Take care,
Buddy

[GBB]

     I see... I will open my pre up tomorrow and see if C10 and the other on the other side connected to pin 8 of those tube.

     If so, I just have to remove them out right? Any idea of how much gain will this reduce?

Buddy,
Yes - you just remove the caps from the circuit without any other change.  You should remove them carefully so that you can reuse them in the case that you don't like the change.

Regarding how much the gain is reduced - it's hard to say.  It depends strongly on values of the resistors used in the circuit and the load presented by the next stage.  I would guess that it's at least a factor of 2 = 6db reduction but it could be more depending on the details of the circuit.

---Gary

[SET Man]

Hey!

   Eureka! It works! 

   Gary, I opened up my pre last night. Traced those caps and yes they traced back to pin 8 If I remembered correctly the cap was 100uf and the resistor was 2.2K or so.

    Anyway, I took them out of the circuit last night and finally have time to listen to my system tonight. Yes, the gain is definitely lower now. And from that I think about 6dB lower is about right. Not much but enough to make the steps of my attenuators a bit finer

   As for the sound... you are right on this. I think it still sound the same. But if there is any change in sound, I don't hear it!

   Well, my pre's gain is a bit high overall. I didn't this problem back than with less efficient speaker than what I have now (86dB vs 94dB)

   Anyway, this kind of thing is beyond my capability. I'm so glad that this annoying problem that I've been having for months is now better. Now I can pretty much listen to music at the level I like and not one click way too loud or one click a bit too low.

    Gary, thank you so much for helping, greatly appreciated. 

Take care,
Buddy

[GBB]

Hey!  . . . It works!  . . .
   
   As for the sound... you are right on this. I think it still sound the same. But if there is any change in sound, I don't hear it!

   
    Gary, thank you so much for helping, greatly appreciated.

Buddy,
That's great - I'm glad I was able to help.  Regarding the sound, if anything, I'd expect the sound to be slightly better since you're getting one electrolytic out of the signal path.  But it would be a subtle change.

---Gary

[SET Man]

Hey!  . . . It works!  . . .
   
   As for the sound... you are right on this. I think it still sound the same. But if there is any change in sound, I don't hear it!

   
    Gary, thank you so much for helping, greatly appreciated.

Buddy,
That's great - I'm glad I was able to help.  Regarding the sound, if anything, I'd expect the sound to be slightly better since you're getting one electrolytic out of the signal path.  But it would be a subtle change.

---Gary

Hey!

    Gary, as for the sound.

     It is likely to be very subtle as you said. That's why I didn't notice any change when I first listen to it without the caps for the first time tonight.

     But maybe I should give it a more careful listening again tomorrow evening with my more usual LPs this time

    Anyway, one less cap is definitely better than having one more resistor before the attenuator for sure

    Thanks again Gary for your help.

Take care,
Buddy