zAh-ng amplifier, my amplifier..

[nikwal]

So this is what I've been playing around with for the last months, I think it might be ready for the vultures to tear it apart now ;-D hehe. I've been listening to it for some time now and I'm pleased with it.. sure it could be better with ccs and stuff but as usual, I'm using vicor modules with 4wire connection so, add it if you like, If I would, they would be something simple like a led and a resistor + bd139. And also I really want a low component count. Idle current is adjusted to 300mA or higher, hmm I've used somewhat lower too and It seems to work pretty ok at that too..
ps. add another couple of output transistors if you feel like it, but at 28v I'm not sure what it would be good for..

[nikwal]

I know spice is not to be trusted very much but as comparison or just for fun, here is the fourier analysis in multisim10.. My old hp thd+n analyzer stops at 0.01% or something like that so thats not of much use here. so there is probably quite much space to add emitter resistor s here and there if you'd like.. hmm also a tip I got was the transistors zvn3310, zvp3310 and 06 transistors, but I hav'nt got around trying them yet.

[jam]

Good work. The circuit begs to be converted into a balanced bridge design. Please explain the reason for hooking the junction of the 800ohm resistors to the emitters of the driver stage.

Regards,

Jam

[nikwal]

I guess it could be connected to the output ,tried that too and did'nt like it as much, then the 1k resistor was put there instead, at first it was like 33ohm and then 100 and 150 and so on , ended up with 1k . maybe 470ohm would be nice to. also, I guess I wanted a short loop there, not letting the output transistors disturb how the vas is working , letting that happen in the input stage alone. hmm maybe that's wrong I'm not a 100% sure.
Hmm the reason why I put that connection there in the first place was some vague idea that the vas transistors should see a similar voltage, hmm but that was at 03: o clock something at night so I'm not sure exacly what went on In my mind then..

[lumanauw]

The 800ohm joint connected to 150ohm joint, is this making positive feedback?

[LineSource]

Hi nikwal,

There are a few genius designers who believe that if an amp uses MOSFET outputs, then using only JFET and MOSFETS throughout the design can reduce the odd harmonic content, which they see as important for sweet, no fatigue sound. There is data to support this claim, as well as data showing that although bipolar designs may have higher odd harmonic distortion, the total distortion can be lower using higher feedback. JFETS and MOSFETs have lower gain than bipolars, and the all FET amps take advantage of lower odd harmonic distortion to use less global feedback while achieving adequate gain from a few gain stages. The Ayre V3 is one example.

I favor using JFET inputs and then all bipolar circuits and outputs, using the higher BJT gain to support local in-stage feedback. Similar the Ayre and the Nelson Pass Super Symm amps, I find using both positive and negative outputs to drive the speaker seems to remove ground noise - including AC power line crud. You've probably studied the V3, but it might be of interest to other readers.

[lineup]

Originally posted by LineSource
There are a few genius designers who believe that if an amp uses MOSFET outputs, then using only JFET and MOSFETS throughout the design can reduce the odd harmonic content, which they see as important for sweet, no fatigue sound.
-
You've probably studied the V3, but it might be of interest to other readers.

Should we use MOSFET for audio amplifier inputs?
I say YES!
They can work great both in VAS and Differential Input. Even as Complementary Diff Input Pairs.

And I have created several circuits that spice just as well as BJT.
LineSource mentions, the harmonics content can be different. True!
This makes it very interesting to experiment with MOSFET inputs/VAS.

But I find no reason to use IRF TO-220 HEXFET for input stage.
If design one bipolar input power amplifier, I would, for example,
not use MJE15030, MJE15031 for line livel input if I can use 2SC2240, 2SA970 etc.
If I did, I would not feel very good about it.

There are good TO-92 MOSFET from ZETEX. Among other manufacturers.
Better suited for small signals.
I imagine these can be a bit more 'complementary', too.

ZVN3306, ZVP3306 and ZVN3310, ZVP3310 for example.
And some other similar small signal MOSFET.
They are not difficult to find. These are worldwide distributors of ZETEX transistors [ http://www.zetex.com/ ]
http://www.digikey.com/
http://www.farnell.com/
I know Nelson Pass has used ZVN3306, ZVP3306

Lineup Selection Guide of audio transistors

[nikwal]

lumanauw: not sure, maybe both at some time ;-), I vote on back most of the time.

LineSource: Hmm good point, I'll have to study this closer. No did'nt see an ayre schematic before as I can remember hmm ,so no i've got something to look at in the bath today :-).

Got A LOT of irf's here now so.. will try them, at a later time hehe.. also to220 dissipate quite a lot of heat, i wonder how they will perform If put on a cooler and run a bit harder, I guess transconductance will be higher (good or bad?)..
maybe if using zvp/n it could be a good idea to clamp them together with some heat conductor between?..

[Nico Ras]

56K at the input and 18k NFB will create an off-set at the output. Make the input resistor the same as the NFB resistor.

[Nico Ras]

you can omit the two driver transistors and vbe multiplier if you like, make it simpler.