Spectral vs. Threshold phono sections: Does one sound better than the other?

DaveSpectral

Well-Known Member
Aug 30, 2010
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0
388
Near Chicago
Hi all.

So I own a Spectral DMC-6. I put some shots of somebody else's up in American Audiophile's great review of it. I LOVE this preamp. They can be had for about $650-$800 on the used market. Anyway, being the owner of a threshold Dac-1E, and three Threshold S-300's, I am also a huge fan of vintage Threshold gear. So here is my question: I am thinking of buying a threshold Fet-9 (complete preamp with phono included) or a Fet-10 phono (the older, slightly taller version with of phono only, and smaller power supply - about two inches tall) or maybe even a Fet-10E which is the slimmer, newer phono which includes the balanced outputs, and a more robust supply, like my Dac-1E has.

So my question is, has anybody compared or owned any of these preamps, and if so, what are your thoughts about comparing their sonics? I pilfered a bunch of Spectral internal shots off of the internet, and it really looks like the DMC-6 is about the same phono as the DMC-10, and DMC-12. They are very close in the way that they look. The DMC-20, which I ache for, is buried in circuitry, so I couldn't tell much. LOL

I noticed that the one advantage that the Threshold gear has, is you can also adjust the capacitance. Here is the rub on that though: I read that capacitance is only good for moving magnet cartridges, while I thought it would benefit MC carts more. Is that true?

The first shot is the Threshold Fet-9 high level with phono. The second shot is the Spectral DMC-6 series 2 which also has high level with phono.

Let me know what your ears have told you!:confused:

Dave
 

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1audio

Well-Known Member
Sep 17, 2010
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SF Bay Area
i know virtually nothing about the threshold stuff, but on the DMC-6 (10, 20) I can comment. The circuits are all very similar. The DMC-20 has higher rail voltages for more dynamic range and some other refinements. The phono section was designed to be an optional component and was removable. The biggest difference between a DMC-10 and the DMC-6 would be the coupling caps on the output of the phono section, the DMC-10 using very large film caps for the time.

The issue of cartridge loading has always been controversial. I never liked the effect of a loading resistor on a moving coil cartridge, others might. For a cap loading to have much effect on a moving coil it would need to be a large cap.
 

ack

VIP/Donor & WBF Founding Member
May 6, 2010
6,774
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Boston, MA
Have you had an itching sensation the last few years (with the revival of analog) to design a new separate phono section, considering how extremely good the Spectral ones were (and probably still are)?
 

DaveSpectral

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Aug 30, 2010
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Near Chicago
Thank you Demian. That's very helpful! Here's another odd question for you: Do you think it would be safe to use my DMC-6 outputs to drive headphones directly off of it? I did this once with a Sumo Athene preamp, and it seemed fine, and it sounded excellent with plenty of gain. The phones would be in the 30-40 Ohm range, typical of today. I think the Sumo actually had a lower output impedance though. Any ideas you have on that would be great.

Dave
 

1audio

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Sep 17, 2010
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I actually had almost finished a matching phono section to the NuForce P-9. its still a ways off. nuForce is doing well with headphones and quite distracted.

The line out would be very well suited for headphones. the 100 Ohm series resistor will limit the performance some. You could change it to a smaller value (10 Ohms) and get better sound. Anything more involved would require a good test bench.
 

DaveSpectral

Well-Known Member
Aug 30, 2010
28
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388
Near Chicago
I actually had almost finished a matching phono section to the NuForce P-9. its still a ways off. nuForce is doing well with headphones and quite distracted.

The line out would be very well suited for headphones. the 100 Ohm series resistor will limit the performance some. You could change it to a smaller value (10 Ohms) and get better sound. Anything more involved would require a good test bench.
Thanks a lot Demian! Now I'll try it for sure. I also have a question on behalf of an Inet friend of mine about the DMC-5. He needs to know just how to set the rocker switches, and gain for phono cartridges. Here is a blurry picture that he sent me, to refresh your memory. I will also send him a link to this forum and thread.

I REALLY appreciate your answers on these two threads regarding Spectral. They are so hard to get a hold of or find info on.
 

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1audio

Well-Known Member
Sep 17, 2010
31
2
353
SF Bay Area
That's beyond my memory and the picture is a little too blurry for me. You might be able to tell by looking at the resistors next to the switch. My guess is that the switch closest to the left in the picture will change the phono gain from 32 db to 40 dB. it will sound better in the high gain position. The rest correspond to the adjcent resistors with all off equal to 47.5K Ohms (My personal recommendation for everything. . .). If i could see it better I might be able to offer more insight.
 

Ubik

New Member
Sep 19, 2010
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0
0
That's beyond my memory and the picture is a little too blurry for me. You might be able to tell by looking at the resistors next to the switch. My guess is that the switch closest to the left in the picture will change the phono gain from 32 db to 40 dB. it will sound better in the high gain position. The rest correspond to the adjcent resistors with all off equal to 47.5K Ohms (My personal recommendation for everything. . .). If i could see it better I might be able to offer more insight.

Hi, I am the guy looking for info and It's a true pleasure to get in touch with you personally. I apoogize for the blurry picture and i give a try with a new one here below. Meanwhile the seller have been able to get in touch with Spectral (easier for him as I live in Italy) and there informed him switch from 1 to 7 are related to load being 7 the 47K value (now in on position in the picture to mate with high output MC), while selector 8 is the gain. Does this makes sense to you as well? I currently use volume at aroun 11am-12am position. So extra gain would not be needed as the cart gives 2,5mV. Based on your post, should I anyway go to high gain and consequently reduce the volume control? Thanx so much and cheers from Italy Daniele
 

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1audio

Well-Known Member
Sep 17, 2010
31
2
353
SF Bay Area
I always found that it sounded better to have the gain at the high position. Enjoy.
 

steve_b_in_az

New Member
Jan 23, 2011
5
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0
Spectral Impedance

Quick question for all you Spectral fans :

I have a DMC-10 delta preamp that I absolutely love. Right now, I am doing most of my listening over headphones. I would like to run the main outs of the Spectral into the primaries of a spare set of output transformers that I have (primary impedance should be about 6,600 on these - they were pulled from an old EL-84 based receiver), and then take the headphone feed off of the low impedance secondaries of the transformers.

Is this advisable ? I don't want to harm the outputs of the Spectral in any way by overdriving them.

Any advice you can offer would be VERY much appreciated !
 

1audio

Well-Known Member
Sep 17, 2010
31
2
353
SF Bay Area
Actually you can drive the headphones directly from the outputs. There is a 100 Ohm resistor in series with the outputs. For better sound I would replace that resistor with a 10 Ohm resistor. You should get a good one since it will have a more significant impact on the sound in this application. The transformer will actually not work well because of the 20-30 dB signal loss plus the effect of the 100 ohm resistor.
 

steve_b_in_az

New Member
Jan 23, 2011
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0
0
Thanks Demian ! That is really interesting ! I guess I am just a bit worried about running the main dc-coupled variable output of this DC-to-light preamp with just 100 ohms (plus the 36 ohm headphone impedance) as the load being driven. I had thought that the input impedance of whatever you are driving from the main outs (not the 'tape out') needs to be higher than the output impedance of the dc-coupled main outs (which I believe have a 2K source impedance).

(I guess I just need a little 'hand-holding' here on this one, since I love the preamp so much and I'm scared to run it with essentially no load other than the series resistor plus headphone impedance.)

Thanks again !!!

--Steve B. (in AZ)
 

1audio

Well-Known Member
Sep 17, 2010
31
2
353
SF Bay Area
The actual source impedance of the output circuit is close to zero. The 100 ohm resistor is for impedance matching to an unterminated twisted pair (audio interconnect) to reduce HF reflections and make it more tolerant of shorted outputs. I don't recommend directly driving the headphone because you could have oscillations that you are not equipped to test for or correct for. The 10 Ohm resistor should prevent anything bad happening. Be aware that the DMC-10 can deliver as much as 10V at the output which with most headphones can be over 130 dB SPL (as much as 150 dB but they would probably break first). Be cautious with the volume control. Enjoy.
 

steve_b_in_az

New Member
Jan 23, 2011
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0
Thanks again Demian. I was not aware that the source impedance of the Spectral was THAT low ! Wow. I'm also assuming that since the Spectral uses single-ended (i.e., not balanced) outputs, that tying the grounds of the two channels together at the output will also be safe for it. (I have thought about rewiring the 'phones for true separate grounds on each channel, but i haven't gotten around to it yet).

Once again, thank you SO very much for your help and advice. I very much appreciate it.
 

1audio

Well-Known Member
Sep 17, 2010
31
2
353
SF Bay Area
No reason to split the grounds in this application. it might help the sound but an optimized output interface (inductor in parallel with the resistor and a suitable Zobel network) would make a bigger difference in the output and less hassle.
 

steve_b_in_az

New Member
Jan 23, 2011
5
0
0
I'm not an audio engineer, but I can look into the design of a Zobel for this interface. However, for the current situation, if I understand the situation correctly, just running the DC-coupled output into the 'phones through either the 100-ohm resistor that's already in the DMC-10 (or swapping it for a high quality 10-ohm resistor), but in either case using a common ground connection, will be completely safe for the preamp (if not necessarily for my hearing viz. the volume possibilities !). Am I correct in my understanding of the current situation ?

p.s. - Congratulations on the great reception of the Nu-Force P-9 ! It looks like a fantastic line stage. Were you also involved in Nu-Force's power amp designs ? (I will soon need a new power amp to use with my DMC-10 !)
 

steve_b_in_az

New Member
Jan 23, 2011
5
0
0
Just wanted to let you know that I'm currently listening to the DMC-10 through its DC outputs direct into my headphones, and WOW !! I simply cannot believe how much unforced detail is produced by this preamp !! How did you do it ??! Entire lines that were unheard before are completely audible through this preamp ... and without any stridency at all. Thank you for designing such an amazing device !
 

codimension.one

Well-Known Member
Nov 21, 2012
3
0
296
Bias setting in Spectral DMC-10

Hi all,

I have a Spectral DMC-10 revision Delta, and I am trying to make sure that the bias is set correctly. According to the manual, each stage must be set to have a 2V voltage drop across the biasing resistor, and have under 100 mV output to ground. However, no test points or testing resistors are indicated on the board or in the manual. Can anyone tell me where on the DMC-10 Delta circuit board should I go to test the bias and the offset values ?

Thanks so much for your help !!


i know virtually nothing about the threshold stuff, but on the DMC-6 (10, 20) I can comment. The circuits are all very similar. The DMC-20 has higher rail voltages for more dynamic range and some other refinements. The phono section was designed to be an optional component and was removable. The biggest difference between a DMC-10 and the DMC-6 would be the coupling caps on the output of the phono section, the DMC-10 using very large film caps for the time.

The issue of cartridge loading has always been controversial. I never liked the effect of a loading resistor on a moving coil cartridge, others might. For a cap loading to have much effect on a moving coil it would need to be a large cap.
 

Kinn

Well-Known Member
Jan 30, 2021
20
20
68
Hi all.

So I own a Spectral DMC-6. I put some shots of somebody else's up in American Audiophile's great review of it. I LOVE this preamp. They can be had for about $650-$800 on the used market. Anyway, being the owner of a threshold Dac-1E, and three Threshold S-300's, I am also a huge fan of vintage Threshold gear. So here is my question: I am thinking of buying a threshold Fet-9 (complete preamp with phono included) or a Fet-10 phono (the older, slightly taller version with of phono only, and smaller power supply - about two inches tall) or maybe even a Fet-10E which is the slimmer, newer phono which includes the balanced outputs, and a more robust supply, like my Dac-1E has.

So my question is, has anybody compared or owned any of these preamps, and if so, what are your thoughts about comparing their sonics? I pilfered a bunch of Spectral internal shots off of the internet, and it really looks like the DMC-6 is about the same phono as the DMC-10, and DMC-12. They are very close in the way that they look. The DMC-20, which I ache for, is buried in circuitry, so I couldn't tell much. LOL

I noticed that the one advantage that the Threshold gear has, is you can also adjust the capacitance. Here is the rub on that though: I read that capacitance is only good for moving magnet cartridges, while I thought it would benefit MC carts more. Is that true?

The first shot is the Threshold Fet-9 high level with phono. The second shot is the Spectral DMC-6 series 2 which also has high level with phono.

Let me know what your ears have told you!:confused:

Dave
Hi Dave,

I’ll try…similarly, I have a Spectral DMC-6 and enjoy its built-in phonostage. Loving the simplicity, not having too many boxes, since I use only 1 tonearm/1 cartridge. Cartridge in use is an Ortofon A95(0.2mv). Apparently, with the gain dialled to the highest, one can tell gain is insufficient. Did a lot of research and eventually I purchased a Dave Slagle SUT, switch the built-in phonostage to MM and bang! Dynamics, tone and speed all in spade.

No further audio purchase since I was loving the music which to me is balanced sounding and enjoyable. A used Threshold Fet Ten/e phonostage appeared for sale locally which I could hardly resist, in which I think happened to many of us here.

Been listening to it for several months(2-3 months), basically, same tonearm, same cartridge and same SUT with Fet Ten/e set to MM. Then I decided to switch back to use Spectral built-in phono.

Spectral DMC-6 built-in phono, has a smaller soundstage. Imaging is slightly diffused. Midrange is slightly more pronounced, highs are clearer. Leading edge is more evident.

Threshold Fet Ten/E, as above, has bigger soundstage and imaging is more precise and layered. Presentation is not as upfront as Spectral built-in phono. Not that Spectral has a very upfront presentation but Threshold has it slightly placed a bit further back.

Both are very good in my opinion, I’ll say, Spectral built-in phono sounds great with rock, heavy metal music. The slightly more upfront presentation and leading edge suits music of this genre.

Both are quiet and detail sounding. Speakers in used is a pair of ATC SCM 19A. Now, I’m toying with the idea of a second tonearm and cartridge(mono).
 

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