Singlepower SDS as a preamp?

[mulveling]

Would there any electrical issues with using my old-chassis SDS as a preamp in my speaker rig? As I splurged on the speakers and power amp, I'm not immediately going to have the funds for a high quality dedicated preamp. The SDS doesn't have RCA outputs, so I've been using a 1/4" -> RCA Y cable from the headphone output. My current SS monoblocks have an input impedance of 33K, the new tube monos I have on the way will be 100K.

Would the output impedance of the SDS be a concern for preamp duties? I've got the 5687 output tubes in my SDS; can I assume those will be better than the 6sn7 for preamp use as well? I have briefly tried this (lesson learned - keep volume at 0 while starting the system up), and sonically it's definitely a bit sweeter than the Sugden Headmaster - the best thing about the Sugden is the remote. Before I continue I wanted to make sure this was safe for the tubes, amp, especially speakers, and also that it's technically kosher. Is it still ok for use with for interconnects 2m in length? Thanks!

BTW I did have a Singlepower Square Wave on loan for a while, and it did a SUPER job as a preamp! Unfortunately it's gone now Heh, I need to write some impressions on that amp soon.

[TheSloth]

Remember that preamps are designed to drive much nicer, easier loads than headphone amps, so your SDS should do marvellously. 33k is nothing compared to even 600ohm headphones.

[mulveling]

Remember that preamps are designed to drive much nicer, easier loads than headphone amps, so your SDS should do marvellously. 33k is nothing compared to even 600ohm headphones.

Yeah, that was basically what I thought. Then I saw KG list the measured output impedance of certain RSA tube amps; in these cases the output impedance rose drastically with input impedance of the power amp! I don't know much about electronics but I know that is a really bad thing. Just wanted to make sure I was in the clear with my 5687'd SDS

i had used my former PPX3 Slam a couple times as a preamp and, other than having a lot of gain, it did a very nice job and sounded very good.

I also noticed the SDS has way more gain than the typical preamp (especially with 5687s); too much for the typical digital source, but it works out quite nicely with my analog rig. Subjectively, I agree that the sound is excellent.

I was also wondering whether Mikhail adds any special circuity or parts when he adds RCA preamp outputs to his headphone amps. Anyone know?

[philodox]

Maybe he skips one of the stages on the RCA outputs?

[Guest sacd lover]

Yeah, that was basically what I thought. Then I saw KG list the measured output impedance of certain RSA tube amps; in these cases the output impedance rose drastically with input impedance of the power amp! I don't know much about electronics but I know that is a really bad thing. Just wanted to make sure I was in the clear with my 5687'd SDS

I also noticed the SDS has way more gain than the typical preamp (especially with 5687s); too much for the typical digital source, but it works out quite nicely with my analog rig. Subjectively, I agree that the sound is excellent.

I was also wondering whether Mikhail adds any special circuity or parts when he adds RCA preamp outputs to his headphone amps. Anyone know?

The Singlepower amps are just excellent preamps as long as they dont supply to much gain. I believe he generally sets up preamp outputs so when a headphone is plugged in the preamp outputs are muted. So, he drives both off the output stage .... but not simultaneously.

[mulveling]

The Singlepower amps are just excellent preamps as long as they dont supply to much gain. I believe he generally sets up preamp outputs so when a headphone is plugged in the preamp outputs are muted. So, he drives both off the output stage .... but not simultaneously.

Cool, thanks Earl! Sounds reasonable, I was hoping that was the case. I just didn't want to be missing out on some super secret Singlepower cryo'd military spec preamp-gain-cell box (with red paint, of course)

[tkam]

I believe he generally sets up preamp outputs so when a headphone is plugged in the preamp outputs are muted. So, he drives both off the output stage .... but not simultaneously.

Thats exactly how Mikhail has the preamp out on my amp working.

[Salt Peanuts]

I believe he generally sets up preamp outputs so when a headphone is plugged in the preamp outputs are muted. So, he drives both off the output stage .... but not simultaneously.

That's how my old MPX3 was setup for preamp out.

[purk]

Mike,

Why not just sent your SDS to get a preamp output? It should not take more than a month and the preamp option is relatively cheap. Mikhail only charged me around $130 installed.

[Dusty Chalk]

Possibly. I had issues when I did this. I was using a Singlepower Supra++ (old school chassis as well) -> Musical Fidelity A300 power amp (whose gain is insanely high) -> Dynaudio Special 25's (full-range speakers), and I got this bass clicking -- had something to do with being full range drivers; sounded like tubes expanding when warming up. It wouldn't do it on Hirsch's bookshelves, but it did do it when we tried to use it on a subwoofer of his. Hirsch contacted Mikhail about this, and determined the "problem", part of which was that it wasn't intended to be used as a preamp. Mine is an early model, as is yours, so yours could have the same problem. There is a fix for it. It has something to do with the power supply. I would contact Mikhail about it -- he should know if yours was before or after this or not. It's not a fault of the amp's, I should emphasize -- I believe the ones with a preamp out do not have this problem at all. It might just be a DC filter on the output, but I honestly don't remember. I never "fixed" it on mine, as I got rid of the amp (money crunch) before I had a chance to investigate it.

[JBLoudG20]

Mike,

Why not just sent your SDS to get a preamp output? It should not take more than a month and the preamp option is relatively cheap. Mikhail only charged me around $130 installed.

Have you ordered form Mikhail lately?

[hungrych]

Mike,

Why not just sent your SDS to get a preamp output? It should not take more than a month and the preamp option is relatively cheap. Mikhail only charged me around $130 installed.

Keyword should.

[mulveling]

Keyword should.

Yeah, if I were to send it in, I'd also get the higher voltage mod for the 6BL7GTA/6BXGT/etc tubes. However, the thought of being without it for 2+ months, plus the shipping costs, plus the risk of shipping - has kept me from doing so. That's why I wanted to know if there was any special thing to the preamp outputs; otherwise a simple adapter will do fine by me.

Now the clicking mentioned by Dusty Chalk is more troubling. I haven't experienced that noise myself, but I have noticed that the DC offset from the SDS can be rather high (via ratshack meter) - with the current tubes it can get as high as +/-50 mV, though it usually cycles around and spends most of its time at lower levels. Certain "bad" tube sets will get it as high as 100mV though The Sugden Headmaster stays within +/-5 mV DC, but of course it sounds leagues below the SDS

With my new speaker rig being fairly spendy, I'd rather be safe than sorry, hence the motivation for this thread.

[purk]

Yeah, if I were to send it in, I'd also get the higher voltage mod for the 6BL7GTA/6BXGT/etc tubes. However, the thought of being without it for 2+ months, plus the shipping costs, plus the risk of shipping - has kept me from doing so. That's why I wanted to know if there was any special thing to the preamp outputs; otherwise a simple adapter will do fine by me.

Now the clicking mentioned by Dusty Chalk is more troubling. I haven't experienced that noise myself, but I have noticed that the DC offset from the SDS can be rather high (via ratshack meter) - with the current tubes it can get as high as +/-50 mV, though it usually cycles around and spends most of its time at lower levels. Certain "bad" tube sets will get it as high as 100mV though The Sugden Headmaster stays within +/-5 mV DC, but of course it sounds leagues below the SDS

With my new speaker rig being fairly spendy, I'd rather be safe than sorry, hence the motivation for this thread.

The thing is...you can keep pushing it off and you will never get anything done. Remember, the upgrade I got really maxed out my SDS. The only option I didn't do is the audionote caps. Although, it took awhile to get the work perfomred but I'm much more happy in the end. Your SDS and my SDS are almost identical, therefore one listen should tell you everything you want to know about SDS as a preamp. I have sent my SDS to Mikhail twice in the last 6 months, one for repair an another is for the upgrade....so bite the bullet and send it in. If you really curious, why don't just drop by and borrow my SDS for 2 or 3 days and check it out for yourself.

[darkless]

I believe he generally sets up preamp outputs so when a headphone is plugged in the preamp outputs are muted. So, he drives both off the output stage .... but not simultaneously.

That's the norm, yes. The amp he's building for me will feed the preamp outs all the time. This won't affect the performance at all, Mikhail assured me, since the preamp out will only handle very easy loads.

It's more of a novelty than anything, but it would allow me to drive a pair of open headphones combined with a low-crossover sub for the deep rumbling if watching a movie or listening to organs (I like to feel the deep rumbling in my guts).

Yeah, you heard me. Some people want the option to add a woofer to their headphone system.

[darkless]

And of course having a constantly powered preamp out could double as another balanced headphone connection.

[tom_hankins]

Take Purk up on the offer and try his SDS as a preamp for a couple days.

Or you could do like I did and have him build you a tricked out Maestro-XLR with big outbaord power supply and still have the balanced headphone outputs for the times you may want to use them. Lots of balanced and SE inputs and outputs.

[Icarium]

I think its interesting that SDS/Maestro (And SDS-XLR/Maestro-XLR) are two different circuits entirely. I still can't get that out of my mind!

If I go the XLR route with one of his tube amps I'd probably do the two stage dealio like tkam's or go maestro. SDS is nice, but meh. Or all 3! In one uber amp!

[Marconisalad]

The 2c51 adapter with 6bl7's sounded by far the best for me as a preamp in my MPX3. (no power mods for 6bl7's) Huge soundstage and detail compared to 12au7s.