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|19th May 2004, 06:06 AM||#1|
Join Date: Mar 2004
non global nfb balanced MM ss phono preamp/amp
Sorry for chaotic thoughts, but please read.
I always loved the tubes,
But it is time to think serious about ss (not about the wasted live). So I made this project.
Whatever you will build with tubes it sounds beauty.
With the transistors usually does not! Unless you will know about a few rules:
1. BJTs needs a large NFB (I prefer local so use rather large Re) but are useful only with small signals.
2. FET in SE mode are dying in hearing or simulating even from the local NFB, but in the differential inputs some of the local feedback is accepted, unless class A was introduced.
3. Tubes are MUCH better but in this project lets forgot about this.
4. When a SE mode is chosen 2nd harmonic even when is up to 11% is not heard (power amps only with no global NFB). Especially tube power amps, so way not to try FET/BJT instead, like N Pass? I have never understand this why he do not use a source resistor? Now I know and heard. My small MOSFET power amp with a no NFB explained this to me. By the way, I spoilt no tube versus the kilograms of the transistors during the starts! The only reason I found is that the single MOSFET gives only a little worse sound that a tube. So this is a challenge!
5. Odd harmonics are not invited (but exists).
After this you would build SE triode power amp: I agree!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
But where is the challenge?
Attached schematic after simulation with the 1 mV source showed 93mV at out1. Nothing special? But 2nd harmonic is –120 dB, 3rd almost –130 dB.
Of course I have a lots of the projects,
But let’s focus at the MM balanced phono preamp.
· Input stage BJT (because of the low level signals), and differential,
· Differential FET (small NFB but differential),
· Between out1 and out2 there is a possibility to connect a RIAA circuit but it also is good enough to connect the power N-MOSFETS that would be controlled of the current sources on the scheme, which may consist only from of the regulated J-FET!
· But how to realize the volume control?
That indicates that a power amp designed to work with only a MM cartridge was thought? But to build this ;-) not obey. And please do not beware of rather low power. You may overdrive this up to 11% on the 2nd harmonic with a blind love.
Please understand that this wold be an only a project, and please do not vote that the resistors might be chosen by the ccses which might be regulated, and so on, please discuss this!
Attached are schematics and simulation results as pdfs and *ckt circuit ready for the simulation in BB2spice
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