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Old 1st January 2013, 09:47 PM   #11
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Nice amp. Class A 2-stage amp with emitter follower loaded on gyrator.
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Old 1st January 2013, 09:52 PM   #12
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It can't seem to work without at least 2 bias diode junctions, and then harmonic distortion will still be measured in tenths to whole percents. Tube sound, maybe.
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Old 1st January 2013, 09:52 PM   #13
DF96 is offline DF96  England
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Quote:
Originally Posted by sreten
I'm assuming its a 100R and then the 220uF doesn't set the LF limit.
You could be right. That would make more sense. It would drop the gain down to a more sensible value. The extra feedback would help cope with all the crossover distortion.
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Old 1st January 2013, 09:54 PM   #14
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with 100r, 40Hz seems to be the -3db point, and overall gain makes more sense.

Last edited by Andrew Eckhardt; 1st January 2013 at 09:56 PM.
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Old 1st January 2013, 10:36 PM   #15
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Quote:
Originally Posted by Andrew Eckhardt View Post
It can't seem to work without at least 2 bias diode junctions, and then harmonic distortion will still be measured in tenths to whole percents. Tube sound, maybe.
One silicone diode for couple of Germanium transistors is just fine.
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Old 1st January 2013, 10:59 PM   #16
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Yes okay for germanium output.
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Old 2nd January 2013, 07:38 AM   #17
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My mistake, the diode is supposed to be two diodes in series. The 10 ohm resistor in the feedback circuit is right. The 47K on the capacitor is 47,000pf. The amp has alot of gain, has some ringing on square wave test, four bumps on the leading edge. This leads me to believe that the neg feedback can't be increased much. It does oddly manage to have almost no crossover distortion (can't even see it on the scope). 3db points are 80hz flat to 50khz, with usable bass down to 55hz (possible predistortion in preamp). Power supply is around 23v. There's no way it's only 3 watts, has to be at least 7 per side (it can shake the floor). It's not a serious amp power wise, it's just the only transistor amp I've ever heard that sounds like a single ended tube amp. When under 2 watts it just sounds so clear, it kind of baffles me how such cheap components, weird "or poor" design choices can come together and sound really good. I just posted it to see of the topology of the amp could be built into a more powerful amp. I just figure that if such poor components can sound good, then better parts and fine tuning of values might lead to really great sounding amp. There's something to be said for a design that has a gradual increase in distortion with power. But I do consider this amp to be hi-fi, it's just not going to rock the house. Most of the time I listen to music under 5 watts anyway, if I want loud I use a more typical transistor amp. It can go loud, then it's bass gets really sucky.


Keith

Last edited by repair guy; 2nd January 2013 at 07:53 AM.
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Old 2nd January 2013, 08:45 AM   #18
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Presenting part of the amp is only half the cake ...

behind it there is a preamplifier that is made 70's style also .. that will mean plenty of gain and raw tone controls adding an unreal but dear other wise very dear sonic signature ...

In the repair world there is many of people that preserve and repair amplifiers like that just to have the specific sonic result .

Obviously this has nothing to do with today's circuits when it comes to speed , linearity ,and accuracy .

kind regards and happy new year
sakis
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Old 2nd January 2013, 10:41 AM   #19
wahab is offline wahab  Algeria
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Originally Posted by DF96 View Post
You could be right. That would make more sense. It would drop the gain down to a more sensible value. The extra feedback would help cope with all the crossover distortion.
Mind you , a gain of 330 is quite possible since it would match
the line output level of "hifi" sources of the time , generaly about
100-200mV , it was common even with 70s japanese amplifiers ,
although with gains generaly being close to 100.
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Old 2nd January 2013, 11:00 AM   #20
JMFahey is offline JMFahey  Argentina
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Quote:
I just figure that if such poor components can sound good, then better parts and fine tuning of values might lead to really great sounding amp.
I wouldn't use the words "tube sound" simply because it's undefined, but can accept that it sounds good for guitar, why not?
And "poor components" might be part of the "magic".
Dear Repairguy, I'll ask you a personal favor: please drive it to *just* clipping, and then raise the signal 10X (20 dB)
Post both scope screenshots, I think it will probably show a quite unsymmetrical waveform, or one with a quite unsymmetrical duty cycle.
That would explain a lot, at least in the Guitar world.
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