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Author Topic: Class A solid state  (Read 11214 times)

Joe

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Re: Class A solid state
« Reply #15 on: September 06, 2009, 12:08:30 AM »
I did something along these lines a few years ago: TIP142 darlington, 70V transformer, and a 220-ohm emitter resistor. Don't remember the details, but I think a darlington might work the best in this situation.

phatt

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Re: Class A solid state
« Reply #16 on: September 07, 2009, 10:15:29 AM »
Hi Phil. Those old transformers *did* have a built-in gap, even if apparently it was not there.
To begin with, the EI lamination was *not* interlaced, as in "regular" transformers, but had all "E"s facing the same side, and all "I"s together closing the magnetic circuit. This already provides a usable gap, simply because of die cutting defects and irregularities. To this some added a single sheet of paper (regular printer paper will do) which becomes invisible after varnish impregnation.
For *mechanical* mounting reasons, the first and last E/I laminations were interlaced, simply to act as clamps enclosing the others.
Thus, on visual inspection the transformer looks exactly as an ungapped one, it can be only seen by dismounting it.

Hi JMF,
          Looks like I owe you a chip point or two :-[
Yes I pulled some OTr's apart today and just as you say the *Lams* are arranged to make the gap.
Though no paper shim in the two OT's I've pulled apart?
Never the less there must be some low power point where this *Gap* is not an issue?

I'm sure you can understand my reason for persuing such an idea.
*If* almost any small Mains Tr can be used as an OT (Cheap and easy to source) and powered from the likes of a computer style SMPS (a lot deliver ~about~ 20VDC).
Then the cost is dramaticaly reduced to the point where anyone could build a small 1/2 watt Amp for very little outlay.
Hey this is a SS forum and a lot of *Chipamps* so I'm just trying to add something a little different.
At the moment it's only a novilty but with the right minds working on it I feel it may have merit.
Thanks for the help :tu:
Joe mentioned Dalington but I've had little success with those.
The circuit I've tried seems to have the highest output due (I think?) to the bootstraping effect but the distortion is huge. sounds Kinda nice going through the transformer but I'd like to have some clean headroom before I post a working unit. Phil

J M Fahey

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Re: Class A solid state
« Reply #17 on: September 07, 2009, 04:21:07 PM »
Hi Phatt. I'm sure that *if* you pull the laminations from a power transformer and re-arrange them with the built-in gap (all E's to one side, all I's to the other) you can use them.
Heavy varnish impregnation will make that difficult, but Chinese manufacturers, trying to help us hobbyists, usually skimp on that ;)

jfetter

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Re: Class A solid state
« Reply #18 on: April 17, 2016, 08:30:04 PM »
I had in mind something like the JLH circuit i.e. single ended with active loading.


printer2

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Re: Class A solid state
« Reply #19 on: April 18, 2016, 09:55:28 PM »
Picked up a few IRFP240's to do a mosfet with constant current source output and a laptop PS.



Need to get a preamp done first, along with my tube/ss amp, guitars....   So many ideas so little time. As far as the inefficiency of the amp it is comparable to a Champ with heaters and tube rectifier sucking up the juice. I don't see the point of running a high voltage and using a transformer to get it back down unless you are going for the sound of the transformer in there. Played around with the 70V transformers in P-P and SE, didn't like them in SE. By the time you gap them enough in order to tame the saturation you kill your limited inductance.

jfetter

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Re: Class A solid state
« Reply #20 on: April 19, 2016, 06:22:57 AM »
i just finished the pre for you.
mounting in a test chassis now.

here is a link on other forum to it.

i like the amp you show. any fft etc available?
 :dbtu:
but i bite the bullet and go to symetrical power.

link:
http://www.diyaudio.com/forums/solid-state/290026-simple-discrete-sziklai-pre.html

Loudthud

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Re: Class A solid state
« Reply #21 on: April 19, 2016, 06:23:40 PM »
An interesting Nelson Pass design called the PLH is worth a close look. It starts with the JLH architecture but is simplified to reduce the amount of feedback and uses MOSFETs. There is a pot that lets you adjust the amount of low order distortion. You can find the article he wrote on one of his websites.

Link: https://www.passdiy.com/project   scroll down to PLH and click the More button.

The PLH uses a 40V rail, so power dissipation is pretty high requiring a huge heat sink and parallel output devices. It will work on lower Voltage, 24V to 30V or even 19V will reduce heat and output power.

The ACA that printer2 posted above is nice because it uses a common 19V laptop power supply. That makes it easy for the novice to get running. In the schematic posted the feedback is eliminated and the amp produces sweet sounding even order distortion.
« Last Edit: April 19, 2016, 06:50:44 PM by Loudthud »

printer2

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Re: Class A solid state
« Reply #22 on: April 19, 2016, 09:05:25 PM »
i just finished the pre for you.
mounting in a test chassis now.

here is a link on other forum to it.

i like the amp you show. any fft etc available?
 :dbtu:
but i bite the bullet and go to symetrical power.

link:
http://www.diyaudio.com/forums/solid-state/290026-simple-discrete-sziklai-pre.html

Have not done anything with this circuit yet, I was after something with limited feedback and in the 5W range when I came across this one. Wanted to make a ss amp to compare with a Champ in response to the threads that pop up comparing tubes to SS.

On another note, don't really know why I am doing it (just to shave a few lb's) but I am dipping my toe in the SMPS pond. Came across a transistor in an electronic florescent ballast, BUL742. 

http://pdf.datasheetcatalog.com/datasheet/stmicroelectronics/7933.pdf

Don't know if it can be useful for tube amps or HV transistor amps if someone wanted to drive a output transformer with it. I haven't even let my mind look at the possibilities as I have enough ideas waiting to be completed.

 

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