[mgalusha]

Paul/Josh, I wasn't quite sure where to put this. It's definitely a DIY project but move it if you think it should go elsewhere.

I finished up building a Twisted Pear (www.twistedpearaudio.com) TXO-2 amp for a good friend last week and have to say this is one really nice amp. When I first got it up and running it was OK but nothing special but he'd asked me to put Black Gate's in and they tend to take some time to start sounding good.

After about 3 days the amp was sounding very nice and I was really enjoying it. I put it into the system in place of my R.E. Designs LNPA 150's driving the mids/tweeters of my speakers. The system is actively bi-amped so they are running from 275Hz and up.

These amps are fully balanced from input to output and use a TI chip that incorporates the Pass Labs Super Symmetrical technology and are a very interesting design. They actually use the LM3886 amp chip, which is used in many gain clones though in this implementation they are used more as a current pump (at least that's how I read it). I can say this doesn't sound anything like a gain clone. Anyway, since these are fully balanced and my active XO (Marchand XM44) is capable of balanced operation I took the Marchand down to the bench yesterday and added some XLR jacks and wired up the balanced outputs.

Connected everything back up, still in single ended mode between the XO and the amp. Sounded the same, very good but not a major change from the LNPA's. This is good as the LNPA's are IMO very good amplifiers. I then pulled out the single ended IC's and put in the balanced set and adjusted the XO gain accordingly.

Holy shit! I was stunned and shocked. It was literally like someone swapped in a different amp.  It's hard to describe just how much better the system sounded. Literally everything was better. Midrange had more body and a richer tone with supreme clarity. Highs were crystal clear and exceptionally detailed but at the same time very sweet with no grain to be found. The spaciousness and imaging were greatly expanded and even the sense of height was improved. I've switched things from SE to balanced before and sometimes it's better and sometimes not. With the TXO amp the difference was not subtle and I am hearing things I've never heard in any system before. It's really going to be hard to give the amp to it's owner. I will have no choice except to build one for myself. The owner came by yesterday and I switched it back to SE before he arrived and once he was happy with the sound I switched it over to balanced mode. He was as shocked as I was. Fortunately I get to keep it for another week or two so I can add 4 more output modules. This will allow it to drive 4 ohm loads at nearly 300WPC. I almost forgot, the dynamics are really good as is the tone. Strings, piano and woodwinds just sound so right. Acoustic guitar is mesmerizing.

If you're a DIY type and have a balanced source you might consider building one of the Twisted Pear amps. It has an SE to balanced converter in the amp so I didn't expect much change, maybe a little quieter but the change is quite amazing. The cool part is that it only has about 100 hours on it and will likely keep improving. 

Here are some photos of the amp. I used a chassis from DIYEnclosures.com, a pair of 400VA transformers and some heat sinks from an old Carver amp. It's dual mono after the IEC/Fuses and power switch.












Mike

[Turk]

Once again MG picks a winner.  I was looking for something different and Mike came up with the Twisted Pear.  I am the friend Mike built it for and he is extremely accurate in his observations in this active bi-amp role.  With Mike's version of Bolder Cables' superb SB2 and terrific power supply, the amp exhibited many of the best qualities of different power amps.  It had the ultra transparency of the chip amps without noise or glare.  It was dynamic and quick on its feet. 

It had near tubelike dimensionality without any loss of focus.  Piano, guitar and violin sounded lifelike.  While Mike is right about acoustic instruments sounding natural in solo or small group, what caught my attention was the ability of the amp to remain stress free while playing large symphonic works in an effortless manner (yes, I am sure the 400 watts available from the bass amp helped).  Still, it never sounded strained or congested. 

"The Great Gate at Kiev" about blew us out of the room but instruments and instrument sections remained very discernable.  The LNPAs are terrific amps and run full range with many of the same qualities, but this technology as implemented really does sound different than any other amp I have heard.  I guess the bass will remain a mystery until Mike installs the additional power modules so I am going to reserve my comments until its either switched into the bass position or run full range so stay tuned for part two.

Oh, and Mike and his delightful wife Mary prepared delicious beef brisket and babyback ribs. 

We capped off the listening session with a toast of a nice 14 year old single malt. aa

Way to go Mikey!!

[Occam]

Mike,

Fascinating results wrt the differing subjective impression of balanced vs single ended inputs. As the XM44 isn't balanced throughout, the balancing I/O being options, I wouldn't think its the inherent harmonic cancellation of differential balanced circuits.
Barring something as mundane as a circuit layout error or faulty components, the only topological suspect I can come up with is the choice of that 'instrumentation' front end with the opamps which when fed a single ended signal has noise gains that allways differ by 1 and also have different bandwidths.
http://www.analog.com/UploadedFiles/Data_Sheets/AD815.pdf
figures 55 & 56 and associated text. As to why they adopted the 'instrumentation'  topology of 55 rather than the 'twisted' topology of 56, or even if it could account for the difference, dunno 

It might be possible to provide those benefits of balanced interface quite simply from single ended outputs, if you access to the innards to the source. The interface is balanced, its just not differential.
At its simplest -

http://www.dself.dsl.pipex.com/ampins/balanced/balanced.htm#4
or more sophisticated, if appropriate -

http://www.jensen-transformers.com/an/an003.pdf

I'm looking forward to what extent these differences persist when running full range (instead of that girly-man 270Hz highpass) in balanced vs single ended.

Regards,
Paul

[mgalusha]

Paul,

I agree, the subjective improvement from using the balanced outputs of the Marchand were much more than expected. As you say, the Marchand isn't balanced internally, just at the input's/output's using an op-amp.

I will likely try the circuit you posted from Doug Self as I have the needed parts on hand and can do so without hacking up the XO.

Dan has PM'd me that he believes there is a grounding problem and given how much things change he's likely right. I plan on doing a few things with the grounding and see what the results are. In the meantime I'm going to keep listening to it as the sound is delicious with the current configuration.

I think Jerry was ordering the additional output modules today, so I'll let you know how it sounds running full range.

Mike

[brj]

Hi Mike!  Sounds like an interesting project, and very neatly assembled - well done!  (And congrats to Turk!)

Idle question... since the amp design is fully balanced, do you think that the internal addition of a Felix or Felicia would buy you much?

(I'm years away from pursuing it, but I'd eventually like to evolve my own 3-way system into a fully active configuration coupled to a DEQX or TacT, and thus tend to look for likely 3 channel amp solutions that punch above their price point.  I wonder how the TXO-2 might compare to a Hypex based solution in such a scenario...)

Thanks!

[mgalusha]

Brian,

I have a BPT-2.5 balanced power unit and have tried the amp plugged into that and straight into the wall.  With the TXO it sounds better to me  when plugged into the wall. My LNPA amps however sound better when fed balanced power as did the Response Audio 3205 I had on loan last year before RMAF.

I'll have it for at least another week, perhaps two, depending on how long I can fend Jerry off. You're more than welcome to come by for a listen if you like.

Mike

[brj]

You're more than welcome to come by for a listen if you like.

Thanks, Mike - PM sent so as to avoid further derailing the conversation!