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4-transistor linestage [message #7846] Wed, 17 August 2005 18:54 Go to next message
Thrint is currently offline  Thrint
Messages: 43
Registered: May 2009
Baron
OK, back to the MOSFET cascode buffer.

Some nice cascode properties: very low input capacitance. THe lower device is screened by the upper, and it ( globally ) is acting as a buffer/source follower.

Instead of rigging the lower gate to the current set resistor( as in a CCS ), it is the input from the volume control. Current is regulated by a full-circuit CCS on a negative rail. +/- 25 volts should be adequate.

5-10 uF of coupling cap, and at low voltage.

Always wandered what a good L-C filter in a SS amp's power supply would do. Of course, we'll need two of them for the bi-polar rails.

Of course, we'll do rectification with vacuum diodes, preferably IDH cathodes, like 6AX4's.

The trouble is that my sleeve of DN2540N5 MOSFET's dissappeared in my move....:( along with my coffee can full of salvaged photo flash caps from disposable cameras.
regards,
Douglas

Re: 4-transistor linestage [message #7847 is a reply to message #7846] Wed, 17 August 2005 19:12 Go to previous messageGo to next message
colinhester is currently offline  colinhester
Messages: 1349
Registered: May 2009
Location: NE Arkansas
Illuminati (3rd Degree)
I'd love to build one. As for the MOSFETs and caps, did your wife help you "pack?"

Re: 4-transistor linestage [message #7849 is a reply to message #7846] Thu, 18 August 2005 13:52 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
Messages: 4973
Registered: May 2009
Illuminati (13th Degree)
Man T; you hop around more than a flea on a griddle. Whats with this SS stuff now; are you trying to experiment or is this something you heard that had a great sound? I admitt, I am baffled.
People have to have reasons for why they do stuff.

Re: 4-transistor linestage [message #7850 is a reply to message #7849] Fri, 19 August 2005 18:38 Go to previous messageGo to next message
Thrint is currently offline  Thrint
Messages: 43
Registered: May 2009
Baron
The SS plate load sounds good. A few have asked me about unity gain linestages. Some of my friends have TX linestages. I think the buffer is a critical part of the job.

Sooooo, how simple can it get? The cascode is a complication, but it gets around the variable capacitance induced by varying D-S voltage, and G-D voltage.

Partially, it is an experiment to take something which is not 'supposed' to sound good and demonstrate the conventional wisdom isn't so wise afterall. Like PP Pentodes, no?
regards,
Douglas

Re: 4-transistor linestage [message #7851 is a reply to message #7850] Sat, 20 August 2005 13:42 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
Messages: 4973
Registered: May 2009
Illuminati (13th Degree)
Boy that is some can of worms you are opening there. But I am not the right guy to discuss this; I still think the Dyna ST 70's sound pretty good. My favorite amp sound so far is the Fisher 50AZ and the Threshold Class A transistor amps.

and an option [message #7852 is a reply to message #7851] Mon, 22 August 2005 16:45 Go to previous message
Thrint is currently offline  Thrint
Messages: 43
Registered: May 2009
Baron
Hey-Hey!!!,
I am exploring a 1:1 bifilar output TX for this beastie. It will also serve to bias it. No second CCS required. Intact audio is the likely winder of these OPTx's. Bit of a research project I think. Requires a better filter for the negative rail( and a lot smaller voltage too).
regards,
Douglas

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