OK, it´s not a PASS project but...

Fuling · 10th November 2005, 05:26 PM

...I guess SE mosfet amps belongs here anyway.

A while ago I bough some 112mH 2A chokes (with airgaps, before anyone comments that).
Seems like a perfect source/drain load for a smallish SE amp.

The easiest thing to build would be a source follower with a separate gain stage, but that feels a little...boring

What do you guys think about this one:

Nelson Pass · 10th November 2005, 06:02 PM

Excellent. How does it sound?

Fuling · 10th November 2005, 06:14 PM

Quote:

Excellent. How does it sound?

Thanks!

Er, I don´t know yet.
I came up with this circuit just hours ago, inspired by an amp designed by my my fellow countryman Circlomanen.
I basically chopped his circlotron circuit in half and replaced the missing half with the choke.

I´ll start building a prototype as soon as I can, I expect my power fets to arrive withing a couple of days.

Zen Mod · 10th November 2005, 10:04 PM

mebbe I'm just grumpie,but- only 4mA in first stage looks insufficient for proper driving of second stage......

but-when you hear it ,you will tell us.....in any case-there are more than few commerciall amps with wimpy driver stages ,and not all of them are cheap

Fuling · 10th November 2005, 10:13 PM

Yes, the low driver current concerns me a bit but it´s a compromise.
Higher current would lead to very low resistor values in the feedback network (and thus a seriously big capacitor)

At least it´s only a single mosfet that is to be driven, not 2 or 4 or...

Circlomanen · 11th November 2005, 03:35 PM

You can replace the choke with an (Aleph) CCS or a powerresistor and ad a negative powersupply to build a CFB two stage DC coupled amp.

Cheers, Johannes.

Fuling · 11th November 2005, 03:50 PM

Tjenare Circlo!

I´ve thought about the CCS (Aleph type or not) and a negative rail, but I have a strange fetish for chokes.
BTW: Didn´t you post a circuit similar to that at hififorum some time ago?

Fuling · 16th July 2006, 06:49 PM

Today I finally decided to build a prototype of this circuit.
Took me about an hour.
Results? Probably a great midrange amp, cuz´it has neither bass or treble

EDIT: Forget what I wrote about the frequency respone, I had made a wiring mistake in the feedback loop which messed things up quite a bit.
Now it works muuuch better!!
I´m listening to a mono channel right now, and it´s definitely not bad!

Jeb-D. · 16th July 2006, 07:11 PM

Perhaps there is something I'm not noticing.

The way you have your feedback applied is actually giving you positive feedback. It seems that it would be negative feedback because the output signal is out of phase with the source of the first stage. But that will actually increase the gain of the amp in this circumstance, which is positive feedback, not negative. I only noticed because I designed a tube amp that had the feedback the same way, only to find out later what was really going on.

Fuling · 16th July 2006, 07:35 PM

I must disagree on both points.
If the feedback was positive the amp would probably suffer from extremly high gain, very high output impedance and most likely severe oscillations.
This amp has a voltage gain of ~8, "tight" bass response and no oscillations that can be detected on my ´scope.

Regarding the choke, yes it would be nice with 10x the inductance but it would be practically impossible.
Some guy here made a fullrange amp with a pair of 85mH chokes some years ago, so I can´t see why it wouldn´t work.
But as you say, higher inductance would of course be a good thing.

10th November 2005, 10:04 PM	#4
Zen Mod Official Court Jester diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	mebbe I'm just grumpie,but- only 4mA in first stage looks insufficient for proper driving of second stage...... but-when you hear it ,you will tell us.....in any case-there are more than few commerciall amps with wimpy driver stages ,and not all of them are cheap __________________ my Papa is smarter than your Nelson ! clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM

11th November 2005, 03:35 PM	#6
Circlomanen diyAudio Member Join Date: Sep 2004 Location: Göteborg	You can replace the choke with an (Aleph) CCS or a powerresistor and ad a negative powersupply to build a CFB two stage DC coupled amp. Cheers, Johannes. __________________ We live in a horizontal world, why use vertical topologies???

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10th November 2005, 06:02 PM	#2
Nelson Pass The one and only Join Date: Mar 2001	Excellent. How does it sound?

10th November 2005, 10:13 PM	#5
Fuling diyAudio Member Join Date: Aug 2001 Location: Sweden (Mora)	Yes, the low driver current concerns me a bit but it´s a compromise. Higher current would lead to very low resistor values in the feedback network (and thus a seriously big capacitor) At least it´s only a single mosfet that is to be driven, not 2 or 4 or...

11th November 2005, 03:50 PM	#7
Fuling diyAudio Member Join Date: Aug 2001 Location: Sweden (Mora)	Tjenare Circlo! I´ve thought about the CCS (Aleph type or not) and a negative rail, but I have a strange fetish for chokes. BTW: Didn´t you post a circuit similar to that at hififorum some time ago?

16th July 2006, 06:49 PM	#8
Fuling diyAudio Member Join Date: Aug 2001 Location: Sweden (Mora)	Today I finally decided to build a prototype of this circuit. Took me about an hour. Results? Probably a great midrange amp, cuz´it has neither bass or treble EDIT: Forget what I wrote about the frequency respone, I had made a wiring mistake in the feedback loop which messed things up quite a bit. Now it works muuuch better!! I´m listening to a mono channel right now, and it´s definitely not bad!

16th July 2006, 07:11 PM	#9
Jeb-D. diyAudio Member Join Date: Nov 2005 Location: SoCal	Perhaps there is something I'm not noticing. The way you have your feedback applied is actually giving you positive feedback. It seems that it would be negative feedback because the output signal is out of phase with the source of the first stage. But that will actually increase the gain of the amp in this circumstance, which is positive feedback, not negative. I only noticed because I designed a tube amp that had the feedback the same way, only to find out later what was really going on.

16th July 2006, 07:35 PM	#10
Fuling diyAudio Member Join Date: Aug 2001 Location: Sweden (Mora)	I must disagree on both points. If the feedback was positive the amp would probably suffer from extremly high gain, very high output impedance and most likely severe oscillations. This amp has a voltage gain of ~8, "tight" bass response and no oscillations that can be detected on my ´scope. Regarding the choke, yes it would be nice with 10x the inductance but it would be practically impossible. Some guy here made a fullrange amp with a pair of 85mH chokes some years ago, so I can´t see why it wouldn´t work. But as you say, higher inductance would of course be a good thing.