The Kuartlotron - keantoken's simple error-correction superbuffer

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keantoken

keantoken

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Joined 2006
#1
September 2020: PCBs are still available, PM me. Build info/BOM: The Kuartlotron - keantoken's simple error-correction superbuffer

This is the official thread to announce my Kuartlotron buffer. It's based on a 4-transistor Tringlotron-like error correction scheme. If I did my job right, I shouldn't need to describe it here because I've already made a webpage for it:

The Kuartlotron

I started discussion in the Mpp thread originally, which included measurements, theory, discussion and even reviews from Joachim and one of his friends. Note: the schematics in the Mpp thread are pretty but few of them have been built and tested, and they are old versions - see the Kuartlotron webpage instead.

Beginning of Kuartlotron discussion:

MPP - diyAudio
 
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#3
I build the circuit very close to the schematic on the new page.
I do not have the offset trim but my build did not have much problems with DC.
The sound i get is wounderful and no exotic Fets are needed.
Earlier versions of the buffer sounded very good too but i missed a little focus and " height " information. That was with BC327-40 and BC337-40 that i usually prefer over BC550/560. In this buffer though the BC550/60 give a more snappy sound.
This little wounder can be build on a weekend more or less from parts in the waistbin.
Highly recommended.
 
#6
Thanks Joachim!

Here is a review by Martina Schoener, if I remember right using the old version Joachim mentioned:

Martina Schoener said:
Kean, I had the chance to listen to the construction on the Tangram speakers
and with the brandnew rauschfrei for two full days before one channel went on "a momentary leave of absence"....

there is somthing very impressive and winning about the sound of your
buffer at Joachims place and at the time Joachim
and I agree its more than worth it to follow up this aproach and inquire further to where your design will lead us to sonically.

We have often at Joachims place very precise setups, so it helps to pinpoint and
identify acoustic ( sorry for my english here - not native language) phenomenas

So far I do agree with the way Joachim tried to describe the music reproduction
quality. It is undoubtably " ausgeformt" in all criterias has a profound tonality and I loved the information, speed, naturalness, big punch, small punch, energy everywhere - and it did like my amplifiers also, so even more pleasure
on my side..
We had more precission in the criteria Joachim called "Focus"
with one of the other buffers then..

Joachims system has a really precise and big soundstage
wide and deep and dynamically homogenous, meaning :

Big dynamics and still open to all acoustic information at any level in that monent ...
when dynamic information should be tiniest they shouldn't be attificially thrown in your face but still precisely audible and distinguished from all other
musical contributors - Joachims system allows to audition including these
criterias in most of the setups these days.
eg : dynamic informations when far away are also very clear and " formed " well belonging to the instrument even at pianissimo.

So with this reproduction environment , we spend hours with listening
and I enjoyed especially the buffer comparison and the rauschfrei ( for a long time Joachim and i didn't have a rauschfrei in our hands, so it really was
an evening that was very enjoyable , no stress but joy in listening!)

Thanks Kean for the sharing and a heartfelt WOW! regarding the result

Good Night ( as if Audio People ever sleep..)🙂

Martina

PS forgot to name the complete system Joachim used when I had the chance to listen to
Keans buffer
Lyra Titan i MC with Centroid Tonarm, Immedia spiral groove turntable
Also we tried with the Kean a little Rega with AKG P8 ES retipped which was fun

cable were Mundorf (silver/gold) , Wireworld, a cable Alan Perkins supplied, Nordost
and Matthias Kurz cables - so when we would doubt any oscillation is induced
by interaction with a given cable design , Joachim inquires quite quickly and we
have enouhj stuff that collected itself at Joachims place to swap

Phonostages - you name it! - any MPP stage
we started with the valve phono, then the Rauschfrei ( three cheers!)
and two MM versions from this MPP thread with the little Rega deck

Buffers where Kean and two others, Joachim could give the name if wanted , because
I simply cannot remember what the design was - one was an upgraded double
mono design, that we gave the best verdict for that moment of testing

Power Amp an LA Audio version ( Modified by Joachim and friends)
As well as another prototype Amp

Speaker were a new development Joachim names Tangram
on other occassins we have some other speakers of Joachims fundus at hand
many with very good chassis to listen to.
I would consider his system to be of great monitor quality, so it helps to identify
what halpens sonically, but also test ones temptation to just " like or dislike" something
without proof - Joachims system allowed me quite often to find, identify
and correct built errors -
Click to expand...
 
#7
RCruz said:
Any recommendations on what to use for the coils L1 2uH ?
Click to expand...

I just use an air wound coil. Here is a build photo showing what I did:

363555d1375326530-mpp-kuartlotron_7-31-13.jpg


I'm not sure whether it actually sounds better with a toroidal coil, but any 2u inductor will do really. I haven't experimented with many different coils.
 
#10
RCruz said:
Can it be modified to be powered by a 0 to +20V PSU ?

I know I would need to use a cap in the output but I would like to use it in a circuit that has not simetric psu 🙂
Click to expand...

For single-rail use, do this. This version has 110k input impedance. Use 22k instead of 220k for R8/R12 for 11k input impedance, but you'll probably want a larger input cap.

EDIT: Better schematic.
 

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#14
Guys, I'm suddenly having some interesting ideas, so the Kuartlotron is still very much an evolving circuit. Anyone who would be interested in testing out different versions should speak up. I have one idea to increase PSRR and another to make trimming simpler, but at the moment I can't test all these ideas and don't like to post untested circuits.
 
#16
Well then, try a 560R resistor in series with C1. This causes the error correction to compensate for PSRR. Simulation shows a 27db improvement in PSRR (20 times), to 102db for the positive half. The simulator is usually accurate for the BC5xx/BC3x7 transistors, so I really think this is worth a try.

So is there a way you could test PSRR before and after?
 
#19
With Joachim and Marina's approval of the early design coupled with the improvements you have in mind - it does appear that you have a very viable design. Congratulations.

I may well try a PtP build as a switching + volume control. In the meanwhile I would like to see the initial PS design provided you feel like sharing.

Good luck.
 
#20
@ keantoken

Re - The Kuartlotron

Hi, i've only had a little time to play with it, but so far in Sim 🙂

I found that with R1 = 60R - R5 = 2k THD was less than 0.001% @ 1kHz & 20kHz. Output load was tried @ 1k & 2k, so driving most next stages should be no problem !

Is R9 supposed to be 2700k = 2.7M or 270k ? Anyway i tried both & didn't see a difference !

Great work
 

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