Can Pre Outs Be Added To The Stereomour

A

astroimage2002

New member
Hi All,

...I am thinking again, dangerous ;)

Is it possible to add pre outs to the Stereomour, easily? I am a newbie so adding them would require "Bottlehead" level of instruction... If it is easy and cheap enough I'd like to try to drive a pair of QuckSilver Mid Monos.

Thanks!

Brian

 
Not easily, and/or not without sonic compromise.

The best (IMHO) practical option would be to take such an output from the speaker terminals.
 
Hi Paul,

Ummm... are you saying that the OUTPUT from the speaker terminals of the Stereomour should be wired to the RCA INPUT on the power amps? Won't that "overdrive" the amp? If it won't overdrive the amp then all that I need to do is build a cable that is male RCA on one end and hook the other end to the speaker terminals on the Stereomour?

Brian
 
Sorry, I gave some more thought to your reply and have another question; would the same hold true if I want to drive a pair of Paramount's?

Brian
 
You could put a passive preamp, say a 15k ohm pot not instead but in the same "hole" of the 100k pot,  Put a 100k resistor on the input of the amp to substitute the 100k pot , from the 15k pot you can add an extra output for your subamps.

Depending on the output impedance of your source you can lower the 15k pot down to 10k, 5k or even 1k.

My DAC has an output impedance of 50 ohms, no problem with 1k pot,  but the Eros Tape has an output impedance of 4k.  then a 15k pot will be barely ok.

As a rule of thumb you need 10 time higher impedance on the recieving end.
 
I just thought of this one:

Put a small resistor, between say 1K and 4K, between the grid resistor and ground. The grid resistor goes from T4 to ground at T6, and T12 to ground at T10. You'll have to use an "air terminal". Take the output across this new resistor. It will be a fraction of the 2A3 grid drive, which is an amplified version of the driver input, so you should get a line level output with a 1K to 4K source impedance. The smaller the new resistor, the lower the output voltage, but also the lower the source impedance.

It will be tricky to find a good place for additional RCA jacks, but if you have only one or two  inputs you can re-purpose one of the existing pairs.
 
Well buggers... I am out of my league on both of theses replies. I thank both of you though. ...Will keep re reading maybe a light will turn on for me on the topic.

Brian
 
Saturntube's idea is the simplest. However, it requires that your sources be able to drive a lower impedance (in the range of 10K ohms). So, what are your sources? CD? Vinyl? Tuner? Aetheric recepticon?  :^)
 
Hi Paul,

Thank you for your reply! My sources are a Logitech Touch Network Player (digital output control) a Direct Connected Presonus Firebox DAC (analogue output control); Vinyl playback is through a Hagerman Cornett II. I do not have a CD Player or tuner.

Aetheric recepticon? This one has me puzzled. Do you mean Aetheric reception or maybe Aetheric transmission maybe Aetheric Mechanics or perhaps
 
The Cornett II is the only component that will have a problem driving low-impedance loads, and the output stage of the Cornett II is similar enough to the Foreplay that I can guess it will work with a 10K load. You might contact the manufacturer to make sure - the specs do not include a minimum load impedance.

In that case, simply replace the Stereomour level control (dual 100K audio taper potentiometer) with a dual 10K audio taper potentiometer. Run a coax or STP from the output and ground connections of each channel to an RCA jack, and you are done.
 
It occurs to me that the application will have an effect too. Is the second amp going to be full range, maybe to drive another set of speakers somewhere else? Will the second amp be located close to the Stereomour? Driving a bass amp would not be as difficult as driving a full range amp, and driving short cables will be easier than long ones.

The Stereomour has three inputs. Are you planning to use all of them, or can one set of the RCA jacks be converted to outputs?
 
Hi Paul,

I only "need" 2 inputs on the Stereomour so one of the three inputs can be used as an output. The power amps can be placed within 1 meter so "standard" interconnects can be used. The "goal" that I had was to drive the amp full range basically making the Stereomour a preamp.

Having said that I should just build a Foreplay to drive the amps full range and be done with it.



 
Naturally I'm happy to encourage purchase of a Foreplay - I get a cut!

But if you want to proceed with this Stereomour mod, the first step is to replace the Stereomour volume control with a 20K dual potentiometer. (That's my guess of the best option - 10K would be better if you needed to drive cables longer than 1 meter.) I'd consider the dual PEC pot because it has a good reputation at a relatively modest price. It's main flaw is poor tracking at low settings, but with no separate preamp you will not usually be using very low settings. The new pot will look almost the same as the existing 100K pot, so replacement will be easy.

Listen to the new pot with both sources, to assure yourself that the lower input impedance does not harm the sound of the system. If that is too low an impedance, you'll hear the change, and would probably want to go back to the stock pot. If the difference is insignificant, then we can go on to connecting the second output.
 
Hi Paul,

I do not need to drive long cables. Do you have a link for the PEC pot so that I can order the right one?

Will be able to use 2 of the inputs just like I currently am? This change will have no effect on them?

Brian
 
I have ordered PEC dual audio pots from Dig-iKey before after having had trouble finding them elsewhere.  Here are a couple of options at ~$33 each.  By the way, I am only posting this because folks seem to be having trouble sourcing PEC dual logarithmic potentiometers.  I'm not saying this is what you want for this application: that is for folks like Paul Joppa who know what they are doing.

10K Dual Pot:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=KKA1031S28-ND

25K Dual Pot:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=KKA2531S28-ND

Antique Electronic Supply (AKA tubesandmore) has mono PEC pots and they are about $10 each but you would need two since they are not dual.

Good luck!
John
 
Hi All,

A follow up. I have ordered and received the new pot. There are a couple of marked differences between the stock one and the new one. First, the new pot is much bigger than the stock one both in diameter and height. Not a show stopper because there is room on the top plate for it and nothing underneath it. The second, and more concerning, is that the anti-rotate lug does not engage the hole in the top plate.

Now I realize that this is a "test" so I do not think that I will modify the top plate until I am sure that "it" will work.Do you see any harm in just letting the lug rest against the top plate and tightening the nut? I know that it isn't perfect, the knob will not sit parallel to the plate and so on but that really does not concern me to much at this point. I will clean up the esthetics if the pot works out.

Lastly, all that I need to do to wire up the new pot is to "move" the wires from the old pot to the new pot, correct? As described in the manual. No voodoo? ...I ain't ready to let the magic smoke out yet ;0)   

Brian


 
 
I'm pretty sure that just moving the wires will work fine, and very confident that even if it doesn't, it won't hurt anything.

Offsetting the anti-rotate lug does not strike me as a good idea, mechanically. Perhaps you can find an extra nut to put on the pot before you install it, which would increase the clearance? It should be a fairly standard nut, easy to find.
 
Hi Paul and All,

I have finally installed the new caps, the new volume control and everything else that I have ordered. The results are very good. The vocals seem to be much more to the forefront. Not a deal breaker...

So I am ready for the next step to add the pre outs. What do I do next?

Brian


 
"Run a coax or STP from the output and ground connections of each channel to an RCA jack, and you are done." That's from my earlier post, referring to the output and ground of the new pot. You already have a STP from one of the RCA jack pairs to the switch, just transfer it to the pot. If it's long enough, that is ...
 
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