2. amps-preamps
  3. 130831-71878

Atma-Sphere MP1 with single-ended inputs and outputs? Adapters OK?

I had the opportunity to hear an end-game system (for me) that was fronted by an Atma-Sphere MP1 preamp and their Novacrons.  I was blown away by the overall sound, and am highly considering starting purchases toward that system for myself, but had the following questions I'm hoping someone could answer.

In short, the purchase path for me is likely going to last 18-36 months, given the costs of the various components and speakers, so I'm going to have to be living with "hybrid" systems for that time period while I spread the purchases out.

My current weakest link is my pre-amp (although it's not weak, but...).  If I start with the MP1, both my source material (VPI Classic turntable) and amps (Thoress 845 SET monos) are single-ended.  I'm sure I could get an appropriate balanced output for the VPI (I think?) and my DAC already has balanced out (which is my only other source), but what loss in sound quality will I experience adapting for singled ended RCA connections out from the MP-1 to my SET monos?  My current set-up has short (1.5M) runs, so the length of cable won't be an issue for me in single-ended.  But will using something like adapters or the tape outs on the MP1 negate any sonic benefits of the MP1 I might otherwise be getting for the time period I'll be using single-ended amps?  BTW, I LOVE the Thoress 845 amps, so they will likely be the last part of the chain I will consider replacing, and I may choose to keep them in the end-game system depending on the synergy.

Thoughts or experience with the MP1 and single-ended output?
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dbphd
1,631 posts
 
clio, almarg, et al.

I'm using Parasound JC 2 BP and JC 1 monoblocks to drive KEF Reference 107/2s.  The amps sit next to the speakers, about 15' from the preamp.  The RCA connections of a KEF KUBE prevent me from using balanced lines between the preamp and amps, but I have Jenson Isomax transformers and wonder if using them on either side of the KUBE would be a good idea.  The Isomax units would be close to the preamp with a long run to the amps.

db
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atmasphere
11,936 posts
 
@dbphd  that sounds like that should work.

The Jensen Isomax transformer works very well converting balanced to SE. But, correct me if I’m wrong @atmasphere , doesn’t connecting a stand alone transformer inline w/ an OTL affect the sonics?
Of course, and OTL has nothing to do with it. I prefer to use adapters myself (the ones we make have the correct connections).

Now another way of dealing with this when using an amplifier which has a single-ended input (in particular tube amps) is to modify the amp so that it can process the inverting signal from the preamp (in addition to the non-inverting signal). This is a lot easier than it sounds and the character of the amp is not changed at all. All amplifiers have the ability to do this but the 2nd input (the cathode of the input tube) is usually just grounded.

Essentially you make a connection from the cathode to pin 3 of the XLR input connector via a coupling cap. If the amp is equipped with a cathode bypass capacitor on the input tube that is the cap that is used, if not, you add one. The hardest part is mounting the XLR input connector on the chassis. If any of this sounds even slightly mysterious have a technician do it for you. The cathode input connection is very low impedance, but our preamps have no problem driving that. I've been using this type of connection for years on several different amplifiers.
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dbphd
1,631 posts
 
OTL?
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atmasphere
11,936 posts
 
@dbphd , yes- an OTL is a tube amplifier without an output transformer. In our case, the output of the amp is direct-coupled (so our our preamps).
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parsons OP
149 posts
 
Ralph, may I order your adapters directly from you?  I couldn't see how to order on your site directly.  I'd like to try the adapters first, then I'll consider sending you the pre for modifications.

Thank you very much for your help.
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