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Spectral DMC-10 Gamma Preamp & Threshold SL10 Preamp

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Jun 9, 2023
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Hi, I posted a similar inquiry in another thread requesting helpful experience on the Threshold SL10 preamp compared with another preamp and received some very helpful information from forum members. Thank you.

I might now have an opportunity to invest in a Spectral DMC-10 Gamma preamp and am comparing it to our Threshold SL10. After listening to the Spectral DMC-10 Gamma at a store's audio system setup it sounded excellent though i noticed that piano action and decay is not as fleshed out as with the Threshold SL10 and some notes had a sense of edginess -- akin to some digital recordings -- that is not present with the Threshold; had the same impression with bass notes in jazz music, where the Spectral sound was not as fleshed out. Both units are equally fast in terms of relaying the recorded information from vinyl to the speakers; both are very silent, though there was a very noticeable hum from the Spectral-based system (it was hooked up to a turntable with a moving magnet cartridge).

I listen primarily to vinyl using a low output moving coil (0.24mV). I don't have the opportunity to listen to the Spectral in our own system context but just wondering if my overall impression on the Spectral DMC-10 is accurate and inline with others' experiences. My interpretation of the Spectral sound could be inaccurate and it might in fact be a unit worth investing in to substitute for the SL10.

Please help with your experiences on whether transitioning from the Threshold SL10 to the Spectral DMC-10 would be a lateral move or a suboptimal choice give my initial listening impressions and once again, thanks for your input.

The Spectral DMC-10 is in stock but very good condition. Here are upgrades to the Threshold SL10:
  • All electrolytic capacitors in the preamp module were changed for Elna Silmic II capacitors
  • The resistors in the phono input section were changed to Vishay Dale metal film
  • All RCA input jacks were replaced with gold plated copper units
  • The volume potentiometer was replaced with an Alps BLUE
  • All input/output wiring replaced with foamed teflon insulated Single Crystal continuous cast oxygen free copper wire
  • The balance control was taken out of the circuit.
  • Electrolytics in the power supply were replaced with high quality units of higher capacitance (this went up from 13,800 mF to 24,000 mF)
  • The diodes in the power supply were replaced with ultra fast soft recovery hex fred
  • The connecting cable between power supply and preamp was upgraded with higher AWG teflon insulated pure copper wire.
  • The IEC connector was replaced with a gold plated copper unit.
 
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I've had a Spectral like that for a time. Best preamp I've had back in the day. No weaknesses in my opinion. I knew someone with that Threshold. I really doubt you would hear a difference between them if both are operating properly and it was a carefully done level matched comparison. Both are rather old units though I'd expect they hold up well. The phono was especially good on the Spectral. So was the Threshold for that matter.

The Spectral had dead flat response from DC to 1 megahertz. There isn't any emphasis or issue with tonality from that preamp. I forget on the Threshold I think it was flat to 200 khz and it too isn't going to alter response.

I know you can think you hear such subtle differences. I'd almost guarantee if you had a blind level-matched comparison you'd hear absolutely zero difference. I used to believe such things myself. One thing I did with some friends back then was using some CDs with low enough levels I could plug them directly into the power amp. So without telling which was which my friends listened to the Spectral set for zero gain or a piece of interconnect. No one could tell which was which.

So if you have to spend money I don't think you gain anything. OTOH, there is no bad choice with either preamp.
 
In line with your observation on the listening scenario, it was a bit difficult -- perhaps even futile -- attempting to listen beyond the extraneous components(amplifier, turntable, speakers) and focus just on the Spectral signature in context of another system.

There were moments during listening where the Spectral was captivating -- true to live -- with barely if any perceptible difference between it and the Threshold and then I had to keep replaying an excerpt from a Miles Davis track to extract the differentiating essence and just at that time staff fatigue was setting in (hospitable and accommodating people nevertheless), where things reached a threshold to let the listening rest; so, ultimately departed with an intuitive decision on the Threshold derived from simplicity of overall design and engineering, a little more than a decade re-visiting Spectral equipment fully decked with MIT cabling at audio stores, two or three piano action and decays from Edward Auer's RCA Direct-to-Disc Chopin Piano Sonata No.3 in B Minor, Op. 58, and a couple of bass notes from Miles Davis Tutu, "Backyard Ritual," Warner Bros. Records Inc.

Again, perhaps futile given the many variables but the scenario was all that was available and accessible.

Thanks for the detailed helpfulness and especially the information based on first-hand experience. It helps with digesting the technical numbers and figures.

Here's data from the SL10 manual for the forum community's reference:

Active Circuit Data​

  • Frequency response: dc through greater than 10 MHz​

  • Propagation delay: Input to out transit time: < .02 microseconds​

Through-the-System-Data​

  • Frequency response: DC through 200 kHz into 1,000 pf, 10,000 ohm load​

Transistor Bandwidth: 200 MHz​


Once again, much appreciated.
 
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