I have been experimenting for a while now with transistor amplifiers say for the last 50 years or so
I now feel that the heart of any good amplifier lies with the VAS stage
Over the lockdown I have been experimenting with a no of circuits What I am after is a super VAS does any one have details re device and schematic
emitter follower cascode etc All advice and guidance gratefully received
Trev
I now feel that the heart of any good amplifier lies with the VAS stage
Over the lockdown I have been experimenting with a no of circuits What I am after is a super VAS does any one have details re device and schematic
emitter follower cascode etc All advice and guidance gratefully received
Trev
"the heart of any good amplifier lies with the VAS stage " ---I am sure D.self would agree with you he came out with various VAS designs have look at his designs .
JLH added cascodes to some of his designs and included the theory behind it and I built them.
JLH added cascodes to some of his designs and included the theory behind it and I built them.
Jam Somasundram taught me to cascode the VAS to reduce the Early effect. But he's even more of a fan of a current mirror loaded LTP.
I'm building a couple of different versions, but none are finished yet so I can't speak from personal experience yet.
I'm building a couple of different versions, but none are finished yet so I can't speak from personal experience yet.
I'm I huge fan of the folded cascode VAS stage. Highest GBW you can get, and good linearity. It's a effectively a single stage amplifier, and compensation is easy. Just a cap from the VAS output to GND.
If you want a super VAS, then put a feedback servo around the cascode transistor to further boost the gain of the VAS. I did an IC headphone amp using that technique, and it had better than 110 dB linearity across the audio band.
If you want a super VAS, then put a feedback servo around the cascode transistor to further boost the gain of the VAS. I did an IC headphone amp using that technique, and it had better than 110 dB linearity across the audio band.
He wouldn't agree. The core of an amplifier is the input stage because it controls all the circuit. However, in the standard "blameless" topology, the input and VAS do their job better than the output stage where most of the non linearity comes from.
Read D.Self,s many articles / heated arguments over the years in EW/WW and the VAS stage figures prominently in his "self publicized /promoted advertised "Blameless amplifiers " .
Its a wonder he hasn't "patented " the word yet.
Its a wonder he hasn't "patented " the word yet.
I don't know how the super A got into this ?
I was thinking of cascode or even enhanced cascode ! maybe a cascode with an emitter follower with a constant current source in the emitter of the follower
I shall experiment soon
Trev
I was thinking of cascode or even enhanced cascode ! maybe a cascode with an emitter follower with a constant current source in the emitter of the follower
I shall experiment soon
Trev
Iatala, a cascode has many benefits and while some people like "minimalist " I have found it to be worth the extra circuit installation,don't be put off it.