Germanium investigations

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#441
All good info PRR.

My religion is 'if it sounds good, it is good'

I lowered the collector resistors from 200 ohms to 75. Distortion dropped below 0.4% at -10dB of soundcard max. I suppose at normal listening level it is close to 0.1%.

I may experiment with 50ohm, or even 25ohm, but that may lead to more heat. So far its barely warm.

Still some hum problem, actually, even bigger after lowering the resistor values.

Will see, cheers!
 
#442
folks, still have not solved the 120hz hum problem
i tried four power supplies, the better, more filtered or more stabilizer, more hum I get
best result so far was with an old stabilizer board which looks like it may have germanium transistor in it 🙂
really not sure how to proceed any further, unless I take it all apart, and to better wiring or shielding
but I do not think this is the case, there must be something else
perhaps this circuit has positive as ground, which my cd player has negative? nah that should not be it
 
#448
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Change the polarity of the power supply and take VT1 type npn.
Filtering or stabilization can be introduced into the bias circuit (RC or RD).
Sell a germanium transistor for the price of a cow? 🙂
 
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#450
thanks for the tips

unfortunately, I do not have complementary pair, neither npn germanium power transistors
I am using what I have
no worries, I will eventually solve the hum problem
otherwise it sounds nice, I got distortion below 0.4% at very high level, likely below 0.1% at normal headphone listening, so its not all lost
 
#451
analog_sa said:
Low Ft?

I think it is a bad idea to run it as CE. As EF you will get lower distortion, better HF response and higher input impedance. If you do need voltage gain add another stage in front.
Click to expand...

analog_sa, the emitter follower is certainly a good idea, and it works, I moved the output from collector to emitter and hum is gone
so is gain, but that was expected

i do have plenty of small balancing transformers, 600:10k, I will put it on the input, should boost the signal enough for headphones

thanks
 

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#452
just measured 0.141% distortion at -10dB level
not bad
I can see second harmonic ~-60dB, and third ~ -80 to -90dB, depending on the current I set with trimmers
I can set anywhere between 40 to 100mA comfortably, and increasing the current decrease the 3rd harmonic mainly
I am thinking of making trimmers into pots and put them on the front, so I can adjust current based on headphones impedance and desired harmonic spectrum

I was wrong, hum is gone in headphones, but on the measurements, still significant left
need to work on filtering the bias setting, likely...

and hf rollof is still there
but it sounds awesome
 

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