Common Source versus Common Drain output stages

[Tube_Dude]

Yes Ampman!

And more:as the openloop output impedance is high and if you have a load with a phase shift (thats you have with a speaker)the feedback will be not in phase wih the input signal,but with the phase of the load inprinted in it!
Second and more important all the EMF of the peaker is not dissipated in the low output impedance of the output but will be conected to the input stage where it can intermodulate with the input signal...puting in another way the amplifier will be subjected
at two input signals...the normal input signal and a delayed and distorted that comes from the speaker...is obvious that one will intermodulate with the other.
This is nothing new as Matti Otalla have call it interface intermodulation distortion
This is a great forum!
Regards

Jorge

[AMPMAN]

first of all,signals sent back in phase with the input will be positive,signals sent back negativly reduce gain and distortion. regarding interface modulation this amp's output impedance is 30 milli ohms, it has not been proven that low output impedance amplifiers sound any better.So tell me what is wrong with this topology.

[Peter Daniel]

So here it is:

[AMPMAN]

further to my reply to you I browsed through my old wireless world mag's and found an article by robert cordell which refutes what you say.its too long repeat here but I'll fax it to you or anybody else who is SERIOUSLY INTERESTED. OK thanks to HP for the schematic,I would point out that the power tranny's are obsolete, replace with 2sc5200/2sa1943, the ssm input transistors are matched pairs in integrated circuit form. I used 2n3904/2n3906 transistors replacing the two 100 ohm resistors with a 200 ohm pot,is interes if anyone is interested in this circuit I'll be happy to supply more info.

[sonnya]

Originally posted by HPotter
So here it is:

I wish it was me who had come up with this outputstage!!!

Sonny

[alaskanaudio]

Originally posted by AMPMAN
further to my reply to you I browsed through my old wireless world mag's and found an article by robert cordell which refutes what you say.its too long repeat here but I'll fax it to you or anybody else who is SERIOUSLY INTERESTED. OK thanks to HP for the schematic,I would point out that the power tranny's are obsolete, replace with 2sc5200/2sa1943, the ssm input transistors are matched pairs in integrated circuit form. I used 2n3904/2n3906 transistors replacing the two 100 ohm resistors with a 200 ohm pot,is interes if anyone is interested in this circuit I'll be happy to supply more info.

AMPMAN

I'm interested in more information on the article you mention and the circuit. Perhaps you could mail me the information you have available or send them to me via fax at a pre-arranged time.

Please use my email johnf@audioamps.com to respond.

Best regards,

John Fassotte
Alaskan Audio

[janneman]

Ampman,

I know some articles by Bob Cordell and have a high regard for him, but I don't recognise your reference. Can you give my magazine & issue or publishing date?

Thanks, Jan Didden

[hugobross]

For every one who is seeking the sound of a tube amplifer in a solid state design the first thing you have to get rid of is the source follower in the output stage. Then adjust the negative feedback around the output stage to reasonable values.

I've just read an article on rod's page about variable amplifier impedance (project 56: http://sound.westhost.com/project56.htm)
He's comparing voltage amplifiers with current amplifiers and amps with the two compared. I'm just wondering if anyone here has experienced with that?? Although, the conclusion of Rod himself about the sound of tubes and the output impedance of amps is interesting.

I'm going to read it again a few times because my English isn't that good.

best regards,

HB.

[AMPMAN]

the article appeard inW.W. feb 1983

[Ian Macmillan]

Would anyone care to summarise how this circuit works for those of us who do not have access to the article in question? I recognise various parts of the topology and the front end is conventional enough, but I am not clear how the driver and output stage operate.

Ian.