Balanced Szekeres amp
Feb 27, 2006 at 4:33 AM Thread Starter Post #1 of 30

a1rocketpilot

500+ Head-Fier
Joined
Apr 19, 2005
Posts
988
Likes
10
Just browsing through the Headwize projects today and just got to thinking about a balanced Szekeres amp. The thought sounds like a good intro to balanced amps for a low price. Has anyone built this before?
 
Feb 27, 2006 at 5:23 AM Post #2 of 30

ECM

100+ Head-Fier
Joined
Jan 9, 2004
Posts
175
Likes
19
i too have thought about building a balanced szekeres amp. i actually have all the parts for one, except i never got around to building it since i would have to mod my headphones for balanced op.

One thing to consider is building a single supply version or dual supply version, which would be more of a TORI amp.

the best version i built of the amp (i built three) is the original single supply with resistor css and output cap. i couldn't control offset with a dual supply version and adding an opamp would have made it a TORI. using a LM317 as a css thinned out the bass with my Grado 125's.

keep us posted on your work.
 
Feb 27, 2006 at 5:56 AM Post #3 of 30

a1rocketpilot

500+ Head-Fier
Joined
Apr 19, 2005
Posts
988
Likes
10
What exactly is the resistor CSS? I don't see that anywhere on the schematic. Also, how would having a single supply vs. a dual supply make a difference? Instead of having +9-15V going to ground, wouldn't you just split it and have +4.5-7.5 V going to -4.5-7.5 V? With regards to powering it as well, would a STEPS board be able to supply enough power for the four circuits needed for a balanced amp?

PS. I am not going to be building this for some time, if I do decide to build it. Since the dorms don't allow open heating elements (ie. soldering irons), I will have to wait till at least May before any progress is made.
 
Feb 27, 2006 at 7:08 AM Post #4 of 30

robzy

500+ Head-Fier
Joined
Sep 17, 2004
Posts
951
Likes
10
Quote:

Originally Posted by ECM
One thing to consider is building a single supply version or dual supply version, which would be more of a TORI amp.


Actually, the main difference between a Tori and a Szekeres is that in the Tori the MOSFET is within the feedback look. There is a dual supply version of the szekeres which you will find in the Addendum.

Rob.
 
Feb 27, 2006 at 12:27 PM Post #5 of 30

Tomo

DIY tube amps can be SHOCKING
Joined
Jun 22, 2001
Posts
1,067
Likes
13
Hey,

What do you mean by Balanced Szekeres? Do you mean by MOSFET mirror? Two pairs of common-source(like) MOSFET amplifiers?

In which case, single PSU or dual PSU do not matter. After all it is BALANCED.

In the usual Szekeres amp (UN-Balanced), operating in dual-PSU can cause problems. This is because there is a voltage drop across Gate and Source. ToriAmp uses feedback to "enforce" DC offset to Zero by pulling the input offset up. (Thus you NEED the input coupling capacitor)

Don't ask me how the balanced sound though. I am not courageous enough to rewire my BRAND NEW HD580.
tongue.gif


Tomo
 
Feb 28, 2006 at 4:48 AM Post #6 of 30

ECM

100+ Head-Fier
Joined
Jan 9, 2004
Posts
175
Likes
19
doh, i mean CCS not css. Constant Current Source. if you take a look at the original schematic, it's R4. It's supposed to be a constant current source for the mosfet, but as the voltage changes, so does the current across the resistor, according to ohms law.

i think it was Tomo who developed a voltage regulator for constant current duties. the regulator acts as a true CCS.

Tomo has a point with the balanced operation and PS. with balanced operation, we are looking at a "difference" so if both inverted and non-inverted amps are at the same voltage, then the headphones will see zero volts. (doesn't the Nelson Pass Firstwatt operate on this principle?)

I have plenty of time on my hands to build something like this, but right now, I'm out of the country and don't have my equipment or parts...
 
Feb 28, 2006 at 7:02 AM Post #7 of 30

a1rocketpilot

500+ Head-Fier
Joined
Apr 19, 2005
Posts
988
Likes
10
Thanks for the clarification. Also, how would one go about phase inverting the signal for the ground? Should this be done with the source or can it be done with the amp (if the source can't output a balanced signal)? Also, what does Tomo mean by MOSFET mirror? And when you say common source, is that opposed to a balanced source?

As you can tell, I'm pretty new to amp building, having only built a CMoy before and planning to build an M3 this summer, so please bear with me.
 
Feb 28, 2006 at 4:51 PM Post #8 of 30

Tomo

DIY tube amps can be SHOCKING
Joined
Jun 22, 2001
Posts
1,067
Likes
13
Hi,

I am sorry. I meant to say MOSFET differential amplifier (forget about current mirror for now).

Anyways, I would like to be some help, but I would like to know more about your problem. So far, I haven't found anything on "balanced Szekeres" amp in this forum or Headwize. So I am confused as to which balanced design you are referring to.

This is an example of balanced MOSFET amp (differential amplifier is its scientific name).

http://www.passdiy.com/pdf/zen-v6.pdf

For the next summer homework check the rest of Mr. Nelson Pass' work.

http://www.passdiy.com/

Good luck!

Tomo
 
Feb 28, 2006 at 6:10 PM Post #9 of 30

a1rocketpilot

500+ Head-Fier
Joined
Apr 19, 2005
Posts
988
Likes
10
Sorry, didn't mean to cause the confusion. The idea of a balanced Szekeres amp just sprang up as I was browsing through Headwize and looking at the Szekeres. I wasn't referring to any other amp design in particular. I know that with a balanced source, one just needs to have four amplifying circuits, since the source has already inverted the ground. Since I don't have a balanced source at the moment, I was wondering how to modify the circuit that amps the ground to phase invert the signal. Is this possible?
 
Feb 28, 2006 at 9:01 PM Post #10 of 30

rickcr42

Are YOU talkin' to me?
Joined
Jun 21, 2001
Posts
13,874
Likes
14
Quote:

Since I don't have a balanced source at the moment, I was wondering how to modify the circuit that amps the ground to phase invert the signal. Is this possible?


Differential input with each leg driving a separate szekeres amp,on for each polarity but my only question is "WHY ?"

boredom ? Just to do it ? There are many already "rolled" balanced designs available and the Szekeres while being good at what it does is maybe the worst candidate for balanced operation all things considered
 
Mar 1, 2006 at 5:20 AM Post #11 of 30

ECM

100+ Head-Fier
Joined
Jan 9, 2004
Posts
175
Likes
19
rickcr42: "Differential input with each leg driving a separate szekeres amp,on for each polarity but my only question is "WHY ?""

a two channel szekeres sounds good to me, so why not try a balanced design? My initial thoughts were to build on my modified sony DVD/CD player. the plan was to install transformers inside the chassis to add balanced outputs, then use a balanced headphone amp and mod my 125's for balanced operation.

might still try it one day.
 
Mar 1, 2006 at 6:04 AM Post #12 of 30

rickcr42

Are YOU talkin' to me?
Joined
Jun 21, 2001
Posts
13,874
Likes
14
Quote:

a two channel szekeres sounds good to me, so why not try a balanced design?


because the Szekeres circuit is not at all suited to a balanced design and by the time you make it so it ceases to be a Szekeres and becomes an entirely new animal.

What makes the Szekeres sound the way it does is because of its pure Class-A single ended nature not in spite of.A single active device recreating the entire postive and negative cycles of the music and closer to a tube cathode follower than any real solid state amp (which is also the secret to making this puppy sound good,treat it as a vacuum tube and not a transistor
wink.gif
)

Many think you can just take any two stereo amps and make a superior sounding balanced amp but the truth is not even close to that and you need to set out with a balanced design from the start or you are making a comprimised amp right out of the gate.Balanced is not a be all end all and every amp topology not only has a reason but is optimised to sound the way it does because of the circuit topology

If you must make such an amp the simple method would be a differential JFET front end as phase splitter to a stereo Szekeres amp for each channel.The results can be bettered by many many other designs (balanced,see Gilmore....) but if you must do it that is how.
 
Mar 1, 2006 at 7:11 AM Post #13 of 30

a1rocketpilot

500+ Head-Fier
Joined
Apr 19, 2005
Posts
988
Likes
10
Thanks all for the clarifications. As I said, it was purely an idea that popped up in my head. I had no idea if it was feasable or practical or anything, just a random musing. Rick, your knowledge of amps/electronics is superb, where do you recommend I start reading to learn this stuff? I don't just want to build the amps, but also understand how they work, with hopes of possibly designing something in the future.
 
Mar 1, 2006 at 1:27 PM Post #14 of 30

rickcr42

Are YOU talkin' to me?
Joined
Jun 21, 2001
Posts
13,874
Likes
14
Quote:

Rick, your knowledge of amps/electronics is superb,


I wish ! Still in the learning stage after 35+ years of "hobby" and the fact that I learn new things almost daily is what keeps it fresh and exciting.
icon10.gif


Quote:

where do you recommend I start reading to learn this stuff?


Build build build and not just audio but useful toys as well.I was very lucky in a way because there were a number of readily available electronic magazines when I was a youngster and I read them all avidly until some actual knowledge broke into my brain
very_evil_smiley.gif


Popular Electronics,Radio Electronics,Audio Magazine for the nuts and bolts of audio plus five or six I can't remeber the name of off hand.Every month something new to build and with the "this is how it works and why" part.All long gone but not forgotten by me and many others in my age group.
It mattered not that the "thing" was only a simple blinking light or a relay attached to a switch for "something" on and off and I would be hard pressed to actually find something useful to do with most of the projects i built back then but it was the build process from reading a schematic ,laying out the circuit using terminal strips and the controls as tie points or making home made heat sinks that counted.The learning and self toubleshooting the circuit was the important part and the "troubleshooting stage not the least of since a "typo" meant you either knew why something did not work or spent a month blowing it up until the next months issue came out with the "oops ! We screwed it up ! Part B should have been postivie and not negative ! sorry !".

Today we have the internet and instant gratification,the ability to build damn near anything and have it work,plans available to build just about anything but the simple nuts and bolts projects that teach good electronics practice,the actual learning by doing is not there.
"Designs by committee" where you may accidently come up with something that works then everyone follows and builds the same .
Plug and play electronics that while WAY more sophisticated than any of my early efforts are no more than "kits" where you plug part A into slot B with very little in the way of the "why does this part do this and if I change it to X what then ?" because everyone is in love with the opamp or monolithic buffer and would be hard pressed to design a simple single transistor amplifying stage and not have it be an oscillator intead of amplifier.
very_evil_smiley.gif


I would start with the past and go straight to some of the early articles that got me going when i was thirteen and waiting for the next issue :

Popular Electronics projects online.Some may seem a bit dated and maybe even goofy in this day of high density SMD microchip but all those "minicircuits" on the substrate have an actual discrete base in their past before being miniaturized and many of the building blocks can be fouind here-
http://www.swtpc.com/mholley/Popular...lectronics.htm

Musical intrument and and hi-fi amps,control circuits,gadgets,color organs,test equipemnt,all broken down into the actual stages where you can actually "see" the why of it unlike the closed black box of the I.C. chip.

If you want to learn how to design an audio amp stage about the best information out there is by Dr.Leach.This article/project actually was in Audio Magazine in 1976 and unlike a simple "here it is,here are the PC boards,buy them and go build it" the text explains in detail the how and why of every single stage of the design.You don't need to build the amp to find the text OR parts of the amp (Hint-the front end makes a dandy nalanced/differential gain stage
wink.gif
) and explanations useful.

http://users.ece.gatech.edu/~mleach/...77articles.pdf

for a different take on power amp design this is a great text :

http://www.passdiy.com/pdf/A75p1.pdf

http://www.passdiy.com/pdf/a75p2.pdf

Or maybe class-A from the undisputed champion of.Not the recent single ended single device amps he designs,also cool but not applicable here, but a fully fleshed out "traditional" Class-A power amplifier suited to driving not only a wider range of loudspeakers than the SE designs but is the one I use to drive my Stax Transformer Interface/Stax Cans.Probably would make a kick a*s K1000 amp even with less parallel output devices and again, full blow by blow of the "why" certain choices are made :

http://www.passdiy.com/pdf/classa_amp.pdf

The reason for inclusion of these power amp designs for audio electronics understanding is because there are actual discrete stages involved.A front end gain stage,a driving stage and an output stage and each can be useful when designing a headphone amp (for instance take it just to before the output and you have a headphone amp,just before the driver a preamp or discrete opamp !)

Actual discrete opamps ? how about the first "audio" opamp design published widely and a fully useable circuit as it is (from 1977 !) :

http://users.ece.gatech.edu/~mleach/...b77article.pdf

then move on to more refined discrete opamp designs but the important part is the WHY,the detailed explanations of each part :

The simple "you finish it to suit your needs,here is the loose outline" type design :

http://www.passdiy.com/pdf/diyopamp.pdf

to the fully finctional with total descriptions as to operational points :

http://www.forsselltech.com/JFET%20Opamp.PDF

and finally everything you ever wanted to know about designing with JFETS (and then some
tongue.gif
) from the intput stage to biasing :

http://www.borbelyaudio.com/adobe/ae599bor.pdf

http://www.borbelyaudio.com/adobe/ae699bor.pdf

if you look at every single product/kit on this page http://www.borbelyaudio.com/special_articles.asp you will see that the "building blocks" are all in the two files above so anything you want is there.


Rather than point you to tecnical texts or advanced electronics pages/content I personally beleive it is far more useful in the long run to do projects that you can actually use that teach the same principals as you build.Screwing up is part of it as is the troubleshooting stage but my opinion is you learn more by building from scratch,from a bare schematic with explanations (and maybe even at first failing) than you do by building a "kit" then looking for a wiring or soldering miscue.
With the above texts once you understand them you can conceivably begin to design your own audio stages to suit your own personal needs.All there man just a matter of implementing the content in real world situations
cool.gif


hope this helps answer the "how can I" question.the rest comes down to listening and keeping the parts that sound good while crap canning the parts that don't.

rickster
 
Mar 1, 2006 at 11:56 PM Post #15 of 30

a1rocketpilot

500+ Head-Fier
Joined
Apr 19, 2005
Posts
988
Likes
10
Wow, thanks for all of the information! Better start reading up (unfortunately, can't build anything in the dorms, some crap about fire safety or something...
biggrin.gif
)
 

Users who are viewing this thread

Top