[jlafrenz]

I recently bought a tubed phono stage and ideally wanted to use it with a passive pre, but figured it wouldn't work because the output voltage is only .5V. I figured I would need a preamp with some gain to use it with an amp requiring 1.25V input. I just happen to have a volume pot (100K) that I wired to some RCA cables to test out if gear would work with a passive pre in my other setup. Tonight I decided to hook it up to the phono stage just to see what the results would be. To my surprise it worked and played fairly loud. Louder than I listen in fact. This has me thinking I may actually go with a passive now. My question is by doing so, do I put any extra stress on the tubes or the unit power supply that may cause damage? What other concerns should I have when looking to go this route?

[deicide67]

What is the output impedance of your phono stage? Your Emotiva has an input impedance of around 25K, so you should try to get at least down to 5K or so on the output of your Phono Stage. They "Rule of thuimb" is 10:1, so ideally, it should be around 2.5K. I've had no issues going down to 3-5:1 using various tubes with their different output impedances.

You will not hurt anything by driving your amps with less signal, but you will never get your full output potential on the Emotiva. Since your phono stage has a "set" output level of 200mV, it should be a clean signal and never clip really.

Blair

[Quiet Earth]

jlafrenz,

I don't know which phono pre you have, but most capacitively coupled tube gain stages have an output impedance between 1000 and 2000 ohms. Let's say that yours is 1.2K ohms, which would be typical.

You won't hurt your phono stage at all by hooking it up to a 100K pot because the phono stage will always see a fixed 100k ohm resistive load provided by the 100k pot. The phono stage will dump its entire output voltage across this very easy load. (This is a simplified explanation, but its close enough.) The amplifier, on the other hand, will see a variation of resistance in the potentiometer which will be the value that you have dialed in to achieve your preferred volume. The more you turn up the volume, the higher the resistance that the amplifier sees. If you turn the volume all the way down, the amp will see 0 ohms.

This is the typical situation that you have when choosing which value to use for a passive volume control. A very high value pot is good for the source because it doesn't load it down. A very low value pot is good for the amp because it looks like a low impedance source. (Simplified again, but good enough.) It's a balancing act of sorts. FWIW, this impedance matching issue does not magically go away when you use an active pre amp. You still have to have a potentiometer value that best matches the source's output impedance and the input impedance of the next active gain stage (in the pre).

Long story short, if it seems to be working well for you, then let it work for you. You are not damaging anything. The only other concerns that you might have are that you might be able to improve the sense of drive and dynamics by choosing a different resistance value for your pot, and you might get improvements by shortening your cables.

[Steve]

I recently bought a tubed phono stage and ideally wanted to use it with a passive pre, but figured it wouldn't work because the output voltage is only .5V. I figured I would need a preamp with some gain to use it with an amp requiring 1.25V input. I just happen to have a volume pot (100K) that I wired to some RCA cables to test out if gear would work with a passive pre in my other setup. Tonight I decided to hook it up to the phono stage just to see what the results would be. To my surprise it worked and played fairly loud. Louder than I listen in fact. This has me thinking I may actually go with a passive now. My question is by doing so, do I put any extra stress on the tubes or the unit power supply that may cause damage? What other concerns should I have when looking to go this route?

I would use less than 100k as the high frequency response with ICs will be quite low. Minimum high frequency response will occur at mid resistance, or around 2pm mechanically.

50k will double the high frequency response, but must be careful of losing bass response. Typical outputs use low value caps which likes very high output impedances. So it becomes a balancing act where both frequency extremes are compromised.

Cheers.

[jlafrenz]

Thanks guys. I did a quick search and could not find the actual output impedance of the phono stage. I was using a 100K pot to test this out with, but my thought was to pick up one that was 25K or 10K. It sounds like I may need to go even lower. The 100K works, but the top end is very recessed. My thought is to get some tubes that have a more open top end and reduce the resistance of the pot. This should open up the highs and create the sound I am looking for. As long as I am not going to damage my gear, I can do some more research on various pots and wiring schematics. If you guys have some advice on what pots to look at, I'm all ears (or eyes).

[Quiet Earth]

I don't think I would go any lower than 20k for the value of the pot in your case jlafrenz. The only exception would be if your phono stage was transformer coupled to the rca jacks, instead of capacitor coupled.

Also, I wouldn't spend too much time tube rolling until you get the value of the pot nailed down. This, plus the length and capacitance of the cables will probably have more of an effect than the brand of tube in the phono stage. I feel like this is generally good advice, but without knowing the specifics of your system its a best guess.

Also, If you tell us your budget for building (or buying) your passive pre, you will get a better list of suggestions for your next step.

[jlafrenz]

I don't think I would go any lower than 20k for the value of the pot in your case jlafrenz. The only exception would be if your phono stage was transformer coupled to the rca jacks, instead of capacitor coupled.

Also, I wouldn't spend too much time tube rolling until you get the value of the pot nailed down. This, plus the length and capacitance of the cables will probably have more of an effect than the brand of tube in the phono stage. I feel like this is generally good advice, but without knowing the specifics of your system its a best guess.

Also, If you tell us your budget for building (or buying) your passive pre, you will get a better list of suggestions for your next step.

The phono stage I am using is the Yaqin MS-22b. It has stock Chinese tubes, which I have not been fond of in any gear I have owned. I do see your point about focusing on the pot first though. All the cables I will be using in the system will be 1M in length as everything in an AV rack. I haven't really come up with a budget for the passive unit as I figured I could build it rather inexpensively. I am looking to be able to connect 2 sources so I will need a switch before the pot and a few RCA jacks. I figured I would just pick up a project box at Radio Shack and if I have some spare wood in the garage, dress up the face plate a bit. I want to make sure I get a quality pot and switch, but don't see myself going with a DACT or Goldpoint. Something a more like the Alps should be suitable. I will also need to pick up some wire for the unit. I haven't looked, but am hoping Teflon coated wire is carries at local home stores.   

[doug s.]

eva-2 is a killer sounding pre.  its input impedance is 50k ohms; not sure what the output impedance is.  ldr attenuators are excellent!

http://diyparadise.com/shop/index.php?main_page=product_info&cPath=18&products_id=113

doug s.

[sharpsuxx]

So no a big fan of the MS-22b, I have read a lot of good things but only good for budget.  I was thinking about running it with some nicer ax7s with the Pro-ject debut 3 I just ordered.  What didn't you like about the MS-22b, was there anything good about it or was it jsut a big downgrade after hearing those Aurum Cantuses on the little Jolida amp?

Care to send it over so I can get a test listen, if you have a spare phono lieing around to tide you over, I could cover shipping of course or just make the trek out there with the N2xs for a day trip this weekend? 

[jlafrenz]

Tonight I tried the Yaqin with my Goldpoint passive pre which is 25k. It seemed to work better than the 100K pot I was using, but that isn't surprising. It still wasn't quite as open on the top end as I expected. Things were a bit 2 dimensional as well. As far as the passive goes, I have very little attenuation on the signal until I turned the gain on the actual amp up a bit to help compensate. This did work a bit better and I was able to increase the amount of attenuation on the signal to have more volume control. I am thinking that there still needs to be some tubes rolled into the phono stage. I also connected it to my DAC. This was really a huge disappointment. Same flat boring sound. I really did not expect this. It seems as though all the components work with a passive, it may not be my best bet in this situation. I am rethinking this and some of the components I am using.

[doug s.]

Tonight I tried the Yaqin with my Goldpoint passive pre which is 25k. It seemed to work better than the 100K pot I was using, but that isn't surprising. It still wasn't quite as open on the top end as I expected. Things were a bit 2 dimensional as well. As far as the passive goes, I have very little attenuation on the signal until I turned the gain on the actual amp up a bit to help compensate. This did work a bit better and I was able to increase the amount of attenuation on the signal to have more volume control. I am thinking that there still needs to be some tubes rolled into the phono stage. I also connected it to my DAC. This was really a huge disappointment. Same flat boring sound. I really did not expect this. It seems as though all the components work with a passive, it may not be my best bet in this situation. I am rethinking this and some of the components I am using.

you said:

 "As far as the passive goes, I have very little attenuation on the signal until I turned the gain on the actual amp up a bit to help compensate."

are you referring to the yaqin?  i would suggest turning the gain all the way up, on the yaqin, (and on the amp itself, if that's what you are referring to) - and use the the goldpoint to adjust gain from there.  unless doing this means you are getting blasting spl's w/only a tiny amount of opening up on the goldpoint pot.  then, back down the gain of your yaqin and/or amp only as much as necessary to get adequate range from the goldpoint.

doug s.

[jlafrenz]

you said:

 "As far as the passive goes, I have very little attenuation on the signal until I turned the gain on the actual amp up a bit to help compensate."

are you referring to the yaqin?  i would suggest turning the gain all the way up, on the yaqin, (and on the amp itself, if that's what you are referring to) - and use the the goldpoint to adjust gain from there.  unless doing this means you are getting blasting spl's w/only a tiny amount of opening up on the goldpoint pot.  then, back down the gain of your yaqin and/or amp only as much as necessary to get adequate range from the goldpoint.

doug s.

There is not gain on the Yaqin. I am referring to the gain on the power amp.

[doug s.]

There is not gain on the Yaqin. I am referring to the gain on the power amp.

sorry, i yust assumed you meant the ms-12b.     in any case, i would still set your amp on max gain, and go from there...

but, an active tube pre is still nice.  even tho i use an eva-2, it is between my tubed pre and my amps...  the pre's gain is set almost max'd out...

doug s.

[Quiet Earth]

I'm a little confused. It sounds like there are a couple of things going on here.

When you first tried the 100K pot, the loudness and dynamics were dialed in but the high end was a little rolled off. You said :

I just happen to have a volume pot (100K) that I wired to some RCA cables to test out if gear would work with a passive pre in my other setup. Tonight I decided to hook it up to the phono stage just to see what the results would be. To my surprise it worked and played fairly loud. Louder than I listen in fact.

Then you tried the Goldpoint, which is 25K and the high end opened up a bit but now the sound is soft and two dimensional. Wimpy. Is that right?

Tonight I tried the Yaqin with my Goldpoint passive pre which is 25k. It seemed to work better than the 100K pot I was using, but that isn't surprising. It still wasn't quite as open on the top end as I expected. Things were a bit 2 dimensional as well.

So, it sounds like you are either loading down the source with the 25k goldpoint, or suffering with high end roll off with the 100k pot. Is this correct?

But then you threw this into the mix :

  I turned the gain on the actual amp up a bit to help compensate

Are you saying that your power amp already has a volume control on it, the way that an integrated amp does?    If that's the case, I would not use a passive volume control in front of it. If you do, then you will have two resistive attenuators in series which will give you the wimpy sound that you are describing. Or am I missing something else?

Sorry if I did not get it right the first time. 

[doug s.]

quieearth, yes, he's saying his amp has a wolume pot.  assuming the goldpoint has to be more transparent than the pot in the amp, i would run it w/the amp's pot wide open, or consider bypassing the amp's pot altogether...

doug s.

[jlafrenz]

Hopefully I can clear up some confusion. Quiet Earth, you have it pretty well nailed as far as what I am trying to say. The 100K pot holds back the top end and vocals. The Goldpoint is more transparent, but shows the true sound of the source components which is quite flat and "whimpy" as you put it. That is a good way to put it, just no life to the music. The amp I am using is the Emotiva UPA-2 which has a gain control on the back of the unit, not a volume pot.

http://www.emotiva.com/upa2.shtm

[doug s.]

Hopefully I can clear up some confusion. Quiet Earth, you have it pretty well nailed as far as what I am trying to say. The 100K pot holds back the top end and vocals. The Goldpoint is more transparent, but shows the true sound of the source components which is quite flat and "whimpy" as you put it. That is a good way to put it, just no life to the music. The amp I am using is the Emotiva UPA-2 which has a gain control on the back of the unit, not a volume pot.

http://www.emotiva.com/upa2.shtm

it seems emotiva assumes this amp may be used in a bi-amp configuration, where one may want to level-match this amp w/another amp.  in any ewent, a gain control is still a wolume pot - in this case i suspect is is not a wery good one.  before you give up and go w/a tube preamp, as you are not trying to level match this amp w/another amp, i would still recommend setting the emotiva's "gain control" at max and then try the goldpoint.  almost all wolume pots have the least degradation when at max level.

doug s.

[Quiet Earth]

Yep. That's what I would do too Doug. You nailed it.

jlafrenz,

Since you already have the Goldpoint, and since you mostly prefer it over the 100k pot, turn the "level" control on the amp all the way up so you can utilize its entire 32dB of gain. When you use a passive pre, you usually need all of the amplifier gain that you can get. I would leave that "level" matching pot turned all the way up even if I decided to use the 100K pot. You don't need a second attenuator in the way. Think of it as a feature that you don't need.

The only other issue is if the 25K Goldpoint is too small of a load for the output of your sources. I would think that 25K is plenty large enough, but you never know.

[jlafrenz]

During my listening, I did adjust the gain on the back of the amp. I guess I could give it one more try with the gain maxed. This may give me output, but not certain that it is going to give me the dynamics and 3D sound that I am looking for. This is my assumption and I will trying before any final decisions.

[sharpsuxx]

You should just go back to the Jolida with the magical sound it gave that room Judd... ...What pre were you using before with the Jolida, was it the Music Hall pre?

PS other than the quick jab, I am with everybody else here open the pot on the EMO taking the resistance out of that path so you can just here the attenuation of the passive pot, knowing how much those EMOs have on tap you will probably be just barely squeaking you passive past 0.