Phono Circuit Difference Between Spectral Preamps?

Dave

This is an ancient post. I know I have spoken with you privately. I have a DMC-10 that I have modified as you are aware. You can adjust the bias current in the output stages to deal with "heat". More importantly, you have to be careful you do not use too high a bias current in the output stages or you will create secondary breakdown issues in the output stage. The user's manual (and a few posts in forums) have recommended current levels that are safe and still sound good.

As to the mystic "wide bandwidth" stability issues, these are dealt with by using modern, upgraded power supply coupling caps. The best 105C electrolytics you can buy bypassed with a large number of high frequency NPO ceramics. These must be used both before and after the solid state voltage regulators. It also helps to put in some series output resistors and these will prevent oscillation with longer capacitive cables. Since I modified my DMC-10 I have never had an oscillation problem, and I had the unit connected to a 500 MHz digital OsCope for over a week trying to capture the nasties. Before the mods, I did see some low level oscillation at 10 MHz. Much over that will not be passed by the series coupling polypropylene caps in any event. 

I was a (20) yr Spectral owner. DMC 12 Never a problem,(outboard power supply) A pair of DMA 360s, Goodwins original demo pair. Again, never a problem! Waited 5 1/2 months for a Spectral 30SV! For (1) week it was "Magical" Then decided that it did not want to play well with others! First with Manley Steelhead; Then it decided that it did not like my Pass Xono either!
So I recently divorced from Spectral ( was not going to wait for the Mythical Spectral Phono Stage! ) Bought a pair of Pass 160.8s driven directly w/ Manley Steelhead (rolled NOS Telefukens) last night. Wife noticed as soon as she came in the front door ; that the sound was even better!! 
I would have to say: Vinyl, Manley Steelhead (w/ Telefukens) , Pass 160.8s, Avalons. I am one happy guy now! Everything that I have searched for in the last 20+\- yrs has all come together.
The Spectral DMC 12 and power supply both ran Cool. The Spectral 30SV runs warm; just as it states in the manual. Don't know if this will affect its performance/ longevity. Happy that I decided to not put up with its Wide bandwidth circuits! Old tubes and Class A SS is even better.

Fan

It is the heavy bias and regulation that runs through most of Spectral preamps. A few ventilation slots in the main unit's top plate and things would've been almost solved. However, the factory feels that any chassis open field would be grounds for stray interference and therefore oscillation.
Old time Spectral and owner here.

@Ack question, I currently own the DMC 20 and soon will be upgrading to the 30ss s.2. Want to use the dmc 20 as my phone preamp. How is that done? Specifically do I use the volume controls on the dmc 20? Thanks in advance.

I have always contacted Spectral via fax and got same-day response. Yes, it's because all circuits, including the phono is class A and the volume is very limited in the unit with no ventilation. Same problem exists with SDR-2000s, where eventually all caps need to be replaced (in the PS and main unit).

Because I owned both the DAC and the DMC-20, I now run my 30SL with a slow speed fan on top of the top plate.

Oh I never heard that one, and I appreciate it. I guess because it sits there drawing 85 watts? (!) That's a heck of a lot for a preamp. They are HARD to get a hold of though. You have to have a dealer contact them. Is that the way we would run a business? Market share was never a big concern of theirs. LOL

Thanks Ack

You need to be VERY careful buying a DMC-20 with phono (and probably a similar DMC-12). Reason being, the significant heat build-up in the main unit tends to render the phono section useless in about 10-15 years, or so I've heard from dealers. Which means, you may need repairs and getting a new phono card probably isn't going to be an option. I would strongly urge you to contact Spectral about the life expectancy of the phono stage in the 20 and your options in case you need to repair one.

Oh! Thanks you two! I never thought anybody answered this post.
Yeah the 20...... I LOVE that piece. I think it's gorgeous. Somebody had one on EBay, LOADED, and it went for $1,500. I passed on it because it had a switch replaced with a look alike. I't wasn't a Spectral repair, and I just got cold feet, and I'm kicking myself ever since. Kind of like a Rolex with a Timex second hand! LOL I think in the last months the price of Spectral, and my other fave Threshold gear, has risen on EBay, and here. (Trust me.....I would prefer to buy one from here.) It's kind of like the stock market. Before a good price on the 20 might have been $1,800-$2,000 and now I've seen them go for more toward $3,000.

So, Sydsrig, I guess the phono circuitry is more sophisticated with the 20? Probably a silly question.

> Spectral is eventually supposed to come out with a SOTA dedicated phono

Oh you mean the DMC-25 they demoed 7-8 years ago? I wouldn't hold my breath any longer.

I am using a spectral DMC 12 as a dedicated outboard phono preamp. It used to be my full function preamp until I got a DMC30 SL. The phono section of the DMC 12 sounds pretty good, but not as good as the phono section in the DMC 20. If you're going to do the updgrade, I would go right to the DMC 20 and skip the DMC 12. Spectral is eventually supposed to come out with a SOTA dedicated phono stage which might be worth waiting for. I'm kind of hanging out for that myself.

Just my 2 cents worth... Hope it helps with your decision.

Does anybody have any ideas about this?