Can Pre Outs Be Added To The Stereomour

[astroimage2002]

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

[Paul Joppa]

Not easily, and/or not without sonic compromise.

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

[astroimage2002]

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

[astroimage2002]

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

[Saturntube]

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.

[Paul Joppa]

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.

[astroimage2002]

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

[Paul Joppa]

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?  :^)

[astroimage2002]

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

[Paul Joppa]

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.

[Paul Joppa]

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?

[astroimage2002]

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.

[Paul Joppa]

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.

[astroimage2002]

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

[InfernoSTi]

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