25W Class A amp with Lateral MOSFETs

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AndrewT

R.I.P.
Joined 2004
Hi,
the about to become obsolete analogue TV signal here in the UK is FM modulated for the sound channel.
There is also a NICAM digital channel for the sound.
Both are good in the UK when the sound engineers are allowed to make it good.
The new DTV offers only digital sound channel. I have no idea whether they use lossless compression like NICAM or they use a lossy compression method to squeeze all that digital information into a few MUXes.

I use my FM (only) Tuner and my TV as two regular sources for my sound systems.
I have done this since about 1974, before stereo became available.
 
juma

juma

Member
Joined 2005
Laterals don't need that kind of stabilisation when there's only one pair per channel. For multiple pairs I use Source resistors to prevent current hogging. Some people advocate that even in that situation Source resistors are not needed because of their NTC. My experience is that NTC has it's limits in practical circuit and one can't rely on it to solve all the problems.

Since this amp has simple biasing procedure (just one pot to set) it's easy to have different bias settings - 1.3A in winter and the half of that during the summer (in regions with very high summer temperatures). The sonic difference is subtle if you don't play it to the max very often but dissipated heat is much lower.
 
sandyhooker

sandyhooker

Member
Joined 2005
I'm surprised there isnt more interest in this circuit. I have a ZV9 which is wonderful but a little short on oommph! I also have quite a few hitachi laterals purchashed from Randy Slone way back when . My two way quarter wave speakers arent that friendly with the Zen approach so this might be the answer.

I wonder if Juma would be so kind as to elaborate on this retro-tech circuit.ie. setup and any other vital info. If I do this it would be point to point construction.

Believe me, juma's stuff is worth the effort!

Also ,i have an etching positive for Slone's Opti-mos amp, if someone is interested.
 
G

gaborbela

Member
Joined 2005
Source resistor???

Hello JUMA

You have the another amplifier all mosfet amp. I attache the schematic. Hopefully soon I power up that.
I have a question, If the power mosfets are close matched can I leave out the 0R22 Source resistors.
Do you think those resistor has any effect on the sound ?
If not I can use them even do my power mosfets are well matched.
Your design I would be interested on your opinion.
Thank you

Greetings Gabor :)
 

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juma

juma

Member
Joined 2005
sandyhooker said:
... to elaborate on this retro-tech circuit.ie. setup and any other vital info....
Click to expand...

Hi Sandy,
I think I got it pretty much covered in post #1 :)
This is an experimenter's amp - you can try changing the current through Q1 and Q2 (i.e. their gains). Also, changing the capacitor types (especially at the output/feedback loop) gives different sonic results. Just take your time and find out what you like... ;)
 
sandyhooker

sandyhooker

Member
Joined 2005
I'm in the (slo-motion)process of planning a version of this amp and was wondering if 16 volt aluminum polymer electrolyitics might be OK for C3, C9 and C10? I have a bunch of them and wondered if anything is known about their sound qualities. Assuming the voltage level is fine , I'll probably give them a try.

Thanks much for your patience..
 
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