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?
128x128Ag insider logo xs@2xparsons
It's easy to turn the VPI Classic into a balanced output, just change out the junction box to XLR's.

The Atma-Sphere MP1 preamp will work well with adapters, but it will sound better without them. IMHO.

A friend of mine has the Atma-Sphere MP-1 preamplifier and the MA-1 amplifiers with balanced cables.  When we placed my 300b SET amplifier into his system we used a  rca cable.  The sound was room filling gorgeous with both amplifier and cable configurations.  You'll be very fine with the MP-1 with either cable type based on what I heard. 
I don't think you won't need to use adapters on the amp end, at least.  The Atma amps that I have owned (S-30 and M-60 ) all had RCA/SE inputs.
I'm specifically asking about using them with SET amps that only have RCA/SE connections.
Charles, do you remember how you connected it?  Did he have adapters or did his have SE outs?
First, I would contact Ralph at Atma-Sphere directly. He sometimes has demos/trades available. He sold me my equipment for a reasonable price. I always wanted to try tubes, but thanks to Ralph, I now have a killer system.
Second, I would consider an MP-3, if cost is concern.
I run my Vandy Treo's with the MA-1's and MP-3. I could not be happier.
Be careful before using XLR to RCA adapters on outputs!  Most of them short the signal on XLR pin 3 to ground (XLR pin 1).  Some equipment can tolerate that, but some cannot.  See this thread for an example of a situation in which it could not be tolerated. 

Also, note that RCA outputs on the MP1 are described as "optional."

Also, I would assume that the tape outputs you referred to are "ahead" of the volume control in the signal path, and therefore would not be suitable for connection to a power amplifier.

The suggestions of contacting Ralph and considering the use of a Jensen transformer are good ones.  And perhaps Ralph will respond in this thread when he returns to work tomorrow.

-- Al
Agreed..."tape output" is full signal (no attenuation)...I misspoke there.  Also good advice to contact Ralph...I know he's quite active here as well.
Parsons there's a used, current Novacron on Audioasylum.  Looks like a good deal.
Hi Parsons,  
It was my friend's system so he did the cable connections himself behind his rack.I just assumed that his MP-1 had rca inputs.  As I wrote above the sound quality was excellent with either type of cable. 

The MP-1 mated flawlessly with my SET amplifier. It was a very memorable listening session for all involved. 
The more I think about it I believe that he didn't use a cable adapter,  so his unit probably has SE outputs. 
The Atma-Sphere MP-1 and MP-3 are both available with optional RCA outputs (in addition to the dual balanced outputs). When this option is added there is also a switch installed to switch between single-ended and balanced operation. This is needed as otherwise you can encounter a buzz. When the switch is in the single-ended position the output of the preamp is then single-ended regardless of the connector used.

You can also use and adapter or cable that does the conversion. If so, it is important that pin 1 and pin 3 of the XLR be somehow connected together. This will not harm the preamp in any way and is needed to prevent buzz.

The reason the buzz can occur is that the output of the preamp (pins 2 and 3 of the XLR) is a true balanced circuit, and therefore is 'floating' with respect to ground. If only one side of the output (for example pin 2 of the XLR connection) is used, it will behave like an open input, because that is exactly what it is. To solve this, one side (usually pin 3) is tied to ground (pin 1). 
The problem with XLR-to-RCA adaptors is that they’re made of brass, including the Cardas. But then so are most RCA jacks. Apparently copper is too soft.
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?
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.

@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.
@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).
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.
Sure, but just so you know Cardas and many others make adapters that will do the job. Just make sure no matter who you order from that pin 1 and pin 3 must be tied together.
Hello, just have a quick question to anyone who can answer. Making an adapter cable for an Atmasphere MP-3 XLR output to a tube amp with single ended input.It is clear pin 2 on the XLR goes to the center pin on the RCAIt is also clear pin 1 and 3 should be shorted on the XLR MP-3 output.
My question relates to the cable shield. Would it be recommended:1. Tie shield to pin 3 on the XLR as well and leave it floating on the RCA end?
2. Tie shield to pin 3 on the XLR as well and connect it to the RCA outer shell?3. Do not tie shield at all to pin3 on the XLR connector but to the RCA shell
4. Do not tie shield at any ends?
This might sound simplistic but I believe that to avoid ground loops maybe the ground on the atmasphere should not be connected in any way to the ground of the RCA single ended amp

@luisma31  Tie the shield at both ends, or only at one end. If only at one end traditionally that would be at the preamp end, but you'll find its not of much concern. What is important though is that pins 1 and 3 are tied together, and that connection is then tied to the RCA ground at the other end of the cable, and that there is a shield as well.

I think RCA output to XLR input cable will be safe, but XLR output and RCA input will be careful.

I use the Jensen isolation transformer, and the sound lose a lot of detail.  I think the isolation transformer should have gain volume control and let you get the right gain after the transformer, as the signal will become weak  if no gain increase and that's the reason I give up the way to use Jensen isolation.

So what is final solution for RCA pre to go xlr  only  power amplifier? The answer is passive preamplifier with XLR output.

You put that passive preamplifier in between your  RCA pre and. The power amplifier, that's it.

Get high quality one to match your RCA pre.


I think the isolation transformer should have gain volume control and let you get the right gain after the transformer, as the signal will become weak  if no gain increase and that's the reason I give up the way to use Jensen isolation.

There are a variety of different Jensen transformers. Some have step-up, others step down and still others are 1:1, doing only isolation or conversion from balanced to single-ended (or vice-versa).

The one I got is defective one, when I connect it ,just less than 5 minutes later, strong noise coming from the speakers even I shut down the volume.

I am discussing with Jensen for return.


I have to say that when I dealt with Jensen, they were very easy to work with.

I am sure if you explain the situation, they would be able to find a suitable product.


i had forgotten about this thread.  Sorry I never responded back to my own original post once I got further in my own search.


In the end I tried a number of different solutions.  Adapters seemed to be less than ideal for me on a number of different single-ended amps, including the Atma amps I had that also had single ended inputs.  I tried a few different pairs from some decent brands.  Balanced out and in from the Atma gear were great.  All the adapters, if I recall, seemed to collapse the sound stage and ultimately seemed to be a poor solution for the quality of the rest of the gear, including the MP-1.  There was also a bit of noise that was inconsistent with the amps fed from other (unbalanced) pre-amps I owned.


I sent the MP-1 in for service (for a different reason) and while there I had Ralph install some single-ended outputs which included a switch.  I will admit when I got it back I didn't totally understand what the switch did because in either position there was the same level single-ended output (it also didn't appear to cut off the balanced output).  I didn't have the greatest luck with single-ended connections out of these outputs either, again with a pretty large number of amps I tried, and with the switch in either position.  Similar issues, but maybe even more noise than with the adapters, or at least as much.  I remember being pretty dissatisfied overall.  Impedance issues between the pre and the amps?  I don't know, but that's what my un-educated brain concluded.


Later settling on some fairly high-end SET amps, I got a bit desperate and through research took a long-stretch last chance on an Art Accessories Clean Box Pro.  This was WAY outside of what I was going for but somewhere I had read that they were very effective even in some pretty serious systems, wall wart powered and all.  In an ultimate irony I had $1K balanced cables going to $1K RCA cables with a $79 converter box sandwiched in the middle.  Ironically enough, the whole setup sounded pretty amazing, low noise and much better sounding than I had reached with the MP-1 and these unbalanced amps, and I ran with that configuration for probably 18 months.



In the end I bailed on the Atma- pre-amp once I had found another that worked better for me, knowing I wasn't going back to balanced amps again.


Worth a $79 try if you're in the boat I was in...just return it if it doesn't work.

@parsons Just a FWIW, any SET can be set up (if you see what I did there 😁) to use both phases of a balanced signal. Its easy to do, inexpensive and does not change the character of the amp. By doing it this way there is no buzz or the like. That is how I have used the MP-1 (or MP-3) with SETs in the past and it works a treat.

The hardest part of this mod is finding a spot on the amplifier chassis to install the XLR connector. The rest of it does not require any component changes in the amp. Normally the SET accepts a signal on the grid of its input tube; but it can accept a signal on the cathode of that tube as well. So we just make that input available on the XLR connector.

I got return and refund of the ISO MAX transformer finally.

It has strong noise for my system, I do not know how other's situation.





I'm also a happy SET amplifier owner. I wonder if your issue is specific to your particular SET. I heard my Coincident Frankenstein 300b SET paired with the Atma-sphere MP-1 and it was splendid! This MP-1 had RCA outputs.  No noise, just very open, transparent, full bodied beautiful sound filling the room.

If I did not already own the superb sounding Coincident Statement Line Stage I could very happily live with the MP-1.


I appreciate all the feedback.

I tried it with 3-4 SET amps actually with unfortunately the same results in each...never had the impact that the all Atma- in balanced provided when being driven single-ended from the MP-1.  Perhaps it was just something with mine if others are having better luck.

I sold my Atma gear last year as the amps were more power than I needed and I found a really strong preamp that complimented the SET amps straight away.


I'm sure you are thrilled with your Thoress 845 SET,  an excellent sounding amplifier by all accounts.