Tubed pre

nirodha

Well-Known Member
Aug 11, 2010
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Hi all,
this may sound like blasphemy :p but has any tried a tubed pre to drive a Spectral power amp? In particular Nagra or Audio Research.
Thanks!
 

Maz65

Well-Known Member
Sep 26, 2014
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Italy
Why not ? Fundamental in these cases is, imho:
- following Spectral recommendations about MIT cabling just to avoid the risk of fluctuations that can be damage the power amp
- avoid old equipment
in the past, during a transition phase, my preamplifier was a Mc C2500 - pure plasphemy :D - ...not bad.
 

microstrip

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May 30, 2010
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Hi all,
this may sound like blasphemy :p but has any tried a tubed pre to drive a Spectral power amp? In particular Nagra or Audio Research.
Thanks!

What is the input impedance of the Spectral amplifier you are considering?
 

nirodha

Well-Known Member
Aug 11, 2010
407
30
433
Why not ? Fundamental in these cases is, imho:
- following Spectral recommendations about MIT cabling just to avoid the risk of fluctuations that can be damage the power amp
- avoid old equipment
in the past, during a transition phase, my preamplifier was a Mc C2500 - pure plasphemy :D - ...not bad.

Thanks for your reply! The Nagra Jazz is like new and my cables are the MIT Oracle MA-X2...love them!
 

bonzo75

Member Sponsor
Feb 26, 2014
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Hi Marty uses the VTL 7.5 with his spectral DMA 400. It has a low output impedance
 

marty

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Apr 20, 2010
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United States
I believe all Spectral amps have an input impedance of 10K ohms. Accordingly, only preamps with a low output impedance are potentially suitable for Spectral amps. The Nagra preamp output impedance of 50 ohms should be a good fit as long as you use MIT interconnects and speaker cables .

I discuss the issues of non-Sprectral pre-amp compatibility with Spectral amps in more detail here:

http://www.whatsbestforum.com/showt...rive-in-New-Jersey&highlight=spectrals+arrive

But to save you time, Spectral has gone back and forth on their insistence to use only Spectral pre-amps with the amps. My Spectral 400 manual clearly states only that you should use a preamp of low output impedance, but that was about 2 years ago. I'm now told they will not let dealers sell their amps unless the customer also uses a Spectral pre-amp. If that is indeed the case, you may wish to reconsider using a Spectral amp with the Nagra. I can tell you that the Spectral universe is not unlike the world Ayn Rand abhors, and that you might just find that there is considerable sonic joy and magic if you can free yourself from the Spectral shackles and use a tube preamp of your liking with good compatibility. Yes, there may be some risk, but in my view, it is nominal. What I and others have discovered is that some tube preamps and Spectral amps make wonderful bedfellows.
 
Last edited:

nirodha

Well-Known Member
Aug 11, 2010
407
30
433
I believe all Spectral amps have an input impedance of 10K ohms. Accordingly, only preamps with a low output impedance are potentially suitable for Spectral amps. The Nagra preamp output impedance of 50 ohms should be a good fit as long as you use MIT interconnects and speaker cables .

I discuss the issues of non-Sprectral pre-amp compatibility with Spectral amps in more detail here:

http://www.whatsbestforum.com/showt...rive-in-New-Jersey&highlight=spectrals+arrive

But to save you time, Spectral has gone back and forth on their insistence to use only Spectral pre-amps with the amps. My Spectral 400 manual clearly states only that you should use a preamp of low output impedance, but that was about 2 years ago. I'm now told they will not let dealers sell their amps unless the customer also uses a Spectral pre-amp. If that is indeed the case, you may wish to reconsider using a Spectral amp with the Nagra. I can tell you that the Spectral universe is not unlike the world Ayn Rand abhors, and that you might just find that there is considerable sonic joy and magic if you can free yourself from the Spectral shackles and use a tube preamp of your liking with good compatibility. Yes, there may be some risk, but in my view, it is nominal. What I and others have discovered is that some tube preamps and Spectral amps make wonderful bedfellows.

Thanks Marty! I have been told by my audio dealer that the Nagra Jazz and Spectral power amp would cause no trouble. One final problem for me to fix is an interlink between the CDP- cd-player and the Nagra Jazz. I can buy an older type MIT Oracle 350 but it has a fixed low impedance (meant for spectral). However, the input impedance of the Jazz is > 75 k Ohms...is this a big problem?
 

microstrip

VIP/Donor
May 30, 2010
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Thanks for your reply! The Nagra Jazz is like new and my cables are the MIT Oracle MA-X2...love them!

Although the Nagra Jazz is a tube preamplifier it is transformer output coupled - it should drive the 10kohm Spectral perfectly. Besides, audio output transformers have limited bandwidth that limits the RFs - a good think with Spectral ultra wide bandwidth power amplifiers.
 

dan31

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Jul 22, 2010
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SF Bay
The Nagra preamps (Jazz and PL-L) are only coupled by a transformer if the unit was ordered with them as they are optional. The output impedance for the single ended outputs is actually lower than the XLR transformer balanced outputs. I have a PL-L and the single ended outputs were measured by stereophile. "The unbalanced output impedance was 36 ohms across most of the audioband, this increasing slightly to 125 ohms at 20Hz. The balanced figures, from the optional transformer-coupled XLR output, were 63 ohms at 1kHz, 66 ohms at 20kHz, and 158 ohms at 20kHz." They should work fine especially with the MIT interconnects.
 

ack

VIP/Donor & WBF Founding Member
May 6, 2010
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Thanks Marty! I have been told by my audio dealer that the Nagra Jazz and Spectral power amp would cause no trouble. One final problem for me to fix is an interlink between the CDP- cd-player and the Nagra Jazz. I can buy an older type MIT Oracle 350 but it has a fixed low impedance (meant for spectral). However, the input impedance of the Jazz is > 75 k Ohms...is this a big problem?

Preamp input impedance has no bearing to the discussion; it's the output impedance that has to be low (e.g. 100 ohms).
 

nirodha

Well-Known Member
Aug 11, 2010
407
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Preamp input impedance has no bearing to the discussion; it's the output impedance that has to be low (e.g. 100 ohms).

Are you sure Ack? The proper impedance setting is determined by the input impedance of the component that is at the delivery end of the signal, so I have always been told. But since this is just a temporary solution (until I can buy a used MA-X, my only real concern is if a wrong impedance setting can damage my equipment.
 

bonzo75

Member Sponsor
Feb 26, 2014
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info@audioconcept.se is a dealer in Stockholm who has both spectral and nagra. I think his first advice will, as expected, be to use spectral but if pushed for a non-spectral pre he will probably recommend nagra, but you can check with him
 

nirodha

Well-Known Member
Aug 11, 2010
407
30
433
info@audioconcept.se is a dealer in Stockholm who has both spectral and nagra. I think his first advice will, as expected, be to use spectral but if pushed for a non-spectral pre he will probably recommend nagra, but you can check with him

Thanks! I hope to get the Jazz and CDP next week. The only thing to sort out is the interlink between these two; I am no longer "forced" to stick to MIT (not Spectral components) but I want to use them. MIT top section is still the champ in my book.
 

ack

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Are you sure Ack? The proper impedance setting is determined by the input impedance of the component that is at the delivery end of the signal, so I have always been told. But since this is just a temporary solution (until I can buy a used MA-X, my only real concern is if a wrong impedance setting can damage my equipment.

Preamp input impedance is totally irrelevant to the discussion about driving an amplifier; you are mixing in another interface, that of the source to the preamp, which is entirely different and independent.
 

ack

VIP/Donor & WBF Founding Member
May 6, 2010
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And FWIW, 75K input impedance is too high, so be careful matching sources and preamp...
 

nirodha

Well-Known Member
Aug 11, 2010
407
30
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And FWIW, 75K input impedance is too high, so be careful matching sources and preamp...

Yes,,, the pre amp to amp is no problem: I use MIT MA-X proline set on "low" to feed the Spectral 360. The remaining question: is it safe to use a Oracle 350 with low impedance between the NagraCDP and Nagra Jazz pre (input > 75K)? Or is this a big NO? I have never heard about a wrong impedance choice of an MIT in a NON SPECTRAL SET UP to damage equipment...
 

ack

VIP/Donor & WBF Founding Member
May 6, 2010
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Yes,,, the pre amp to amp is no problem: I use MIT MA-X proline set on "low" to feed the Spectral 360. The remaining question: is it safe to use a Oracle 350 with low impedance between the NagraCDP and Nagra Jazz pre (input > 75K)? Or is this a big NO? I have never heard about a wrong impedance choice of an MIT in a NON SPECTRAL SET UP to damage equipment...

It's not a matter of blowing up equipment, it's about optimal operation. And you would need a high impedance version of the cables for the sources. WRT the amps the impedances may be compatible but also keep in mind they need 100-200mA of current to be driven properly. This has been discussed numerous times before.
 

nirodha

Well-Known Member
Aug 11, 2010
407
30
433
The Nagra preamps (Jazz and PL-L) are only coupled by a transformer if the unit was ordered with them as they are optional. The output impedance for the single ended outputs is actually lower than the XLR transformer balanced outputs. I have a PL-L and the single ended outputs were measured by stereophile. "The unbalanced output impedance was 36 ohms across most of the audioband, this increasing slightly to 125 ohms at 20Hz. The balanced figures, from the optional transformer-coupled XLR output, were 63 ohms at 1kHz, 66 ohms at 20kHz, and 158 ohms at 20kHz." They should work fine especially with the MIT interconnects.

The Jazz output section has the transformers but the input hasn't. Nagra adviced me to use XLR between the pre and the power amp and an RCA between the CDP and the Jazz.
 

nirodha

Well-Known Member
Aug 11, 2010
407
30
433
It's not a matter of blowing up equipment, it's about optimal operation. And you would need a high impedance version of the cables for the sources. WRT the amps the impedances may be compatible but also keep in mind they need 100-200mA of current to be driven properly. This has been discussed numerous times before.

Besides not being a technically inclined audiophile, I have not read every post, sorry for asking.
 

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