Circlotron Amplifier Project

[Johnloudb]

Hi all ... I feel I should lose my HTGuide credentials given my bad behavior ... going AWOL all the time ... can't explain it.

Anyway, got my first senior project presentation out of the way. It went well

So I'm building a cyclotron amp based on this phase splitter

http://www.amplimos.it/phase%20splitter.htm

I like the symmetry of the circuit and that is it capable of low distortion. I'll post my current schematic ... need to get on my computer

[Johnloudb]

Oh, how do I change the name of the thread? It is supposed to be circlotron not cyclotron , my bad


no worries....i fixed it :W

[Johnloudb]

Okay here is where I am at with the amp project -

So, here is my amplifier design so far ... it will be designed for 150 Watts RMS into 8 ohms, 300 Watts in 4 ohms

[Johnloudb]

I've modeled it in spice .... right now Q1 - Q4 is the BF862 JFET part and Q11 and Q13 are the IRFP244 (actually I have two in parallel, so four total). Q9 and Q10 are the zvp3306a part, also I have two in parallel so actually four transistors in that VAS stage. I just wanted to keep the schematic simpler.

[Johnloudb]

The voltage gain is 168v/v open loop , and a bias current of 500mA through the output stage

Just want to get the open loop response as linear as possible and then and some local or global feedback

This purple trace is just the current through the Q13 output transistor

[Johnloudb]

ideas and suggestions for parts good parts? particularly for Q9 and Q10 and output transistors? know any source for getting SIT FETs? Perhaps a driver stage is a good idea ... or just a hefty VAS is good enough to drive the output transistors. I tried with a driver stage but at least with the spice models I used it created a lot of higher order distortion. But I know the output transistors like current to drive the large capacitance.

[BobEllis]

To drive or not to drive? That's a discussion Pass and Thagard had way back when designing the A75. See pages 7-8 http://www.firstwatt.com/pdf/art_a75_1.pdf In the end they settled on a hefty VAS. You could follow their lead and use IRF9510. At around 20 mA there's plenty of drive for a dozen IRF240.

Not an expert, nor do I have significant test gear. I used IRF510/9510 in the input stage of my A75s as well (lower input capacitance than the IRFD110/9110 and since I run higher rails I need more dissipation capability. Probably my favorite amp so far, beating out a couple of Class AB amps, but I have other Pass projects in the works.

Good old IRFP240 or if rails are low enough IRFP140 should do nicely for outputs if you're in the proper Vgs realm. There are those who prefer lateral FETs. I have a lateral FET Hafler DH-500, but it's in need of recapping so it's not a fair comparison at this point.

[Johnloudb]

Thanks Bob. I know Pass has used the IRF610 often. I used the irf510 in a preamp with very good results, but I remember it having a 100 volt breakdown voltage which would be too low. I'll also be raising the rail volate on the input stage a bit. I'll give the irf9610 a try.

I get the spice model for the irfp240 too

Thanks for the link

[Johnloudb]

Oh, how do I change the name of the thread? It is supposed to be circlotron not cyclotron , my bad


no worries....i fixed it :W

Awesome , Thanks Bill !!

[BobEllis]

John, have you seen this article? https://www.passdiy.com/project/ampl...fet-circlotron

[Johnloudb]

John, have you seen this article? https://www.passdiy.com/project/ampl...fet-circlotron

Yeah , I saw it awhile back but I just peaked at it. Nice distortion plots , I'll have a close look at it

I see he used the irfp240 ... I could incorporate thermistors in parallel with R9 and R10 of my circuit for thermal stability.

I need to buy some real parts and start testing.

Thanks!

[wkhanna]

John,

some old info i found in my links.
probably not much help for some one of your knowledge, but thought i would share anyway.

just do a 'cntr f' for circlotron for all John Broskie's stuff HERE

[Hank]

Okay John, it's time for an update - how did the amp pan out? If it's finished, are you going to resume the you-know-what's?