Very interesting.
Personaly I detect 2nd harmonic at 0,63% and 3rd at 0,22% during an extensive test of sensitivity of different distortion components.
You are very close to that relationship but a magnitude lower so I suspect that it can handle some complex music too before being noticed as colouration.
Hope for a very neutral, musical and transparent sound character with that harmonic distortion pattern.
Will follow your progress...
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I do not plan other experiments, its installed in the box playing beautifuly. Its clean and musical.
0.6% distortion may be confusing on complex music. That reminds me when i started my experiments with hamtone pre. Its ideal as mic preamp for one voice. But as for complex music its too much distortion. Some hamptones depending on the jfet i used got very clean and great sounding down to 0.02%. Worth exploring.
0.6% distortion may be confusing on complex music. That reminds me when i started my experiments with hamtone pre. Its ideal as mic preamp for one voice. But as for complex music its too much distortion. Some hamptones depending on the jfet i used got very clean and great sounding down to 0.02%. Worth exploring.
A simulation of a variation on the same theme...
Similar distortion character. Very high Zin.
Zout 600 ohm.
Gain 4,5
I don't favour global negative feedback, but in this case it seems to work well. Very low distortion in simulation.
Not really global though.
Similar distortion character. Very high Zin.
Zout 600 ohm.
Gain 4,5
I don't favour global negative feedback, but in this case it seems to work well. Very low distortion in simulation.
Not really global though.
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I have no issue building it with jfet on input, but after storm one of my F1J amps developed dc on the output. Just one channel. Need to deal with it first.
Nice preamp project Adason. Just easy enough for a P2P build.
You went with your napkin schematic values and a basic CCRC (unregulated) psu?
You went with your napkin schematic values and a basic CCRC (unregulated) psu?
I built this exactly. Except i used bipolar capacitors on the input and output (two double the value back to back). And a1145/c2705 complementary pair.
Yes, simple unregulated. But i used lots of Cs.
Yes, simple unregulated. But i used lots of Cs.
Attachments
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The simplicity of this circuit was enough to motivate me to build a one and check it out.
I followed the attached circuit, minus the 1K output resistor and added sockets for easy gain changes. (10uF caps, Q2-BC550, Q1-BC557, 48V supply)
Adason,
The DC offset takes about 30secs to get below 50mV before I turn the power amplifier on.
Measured current draw for the circuit is 2.5mA.
Do you get similar results?
I followed the attached circuit, minus the 1K output resistor and added sockets for easy gain changes. (10uF caps, Q2-BC550, Q1-BC557, 48V supply)
Adason,
The DC offset takes about 30secs to get below 50mV before I turn the power amplifier on.
Measured current draw for the circuit is 2.5mA.
Do you get similar results?
Attachments
I can open the preamp tomorrow and measure current draw. Preamp is followed by akai amp, which has dc protection, and yes, there is few seconds settling, as amp speakers click in. This is normal.
Yup, offset settling time is not out of the ordinary. Power amp last on/first off is a sure way to avoid any 'nasties".
No setup for distortion measurments.
The current draw is so low I wasn't sure if I messed something up.
Is the 1K output resistor needed?
Actually, I am quite happy with what I'm hearing with this mono channel using a bench DC supply, Class D amp and small speaker. Super quiet, I can't hear anything with my ear up to the speaker.
I will proceed building the second channel.
I'd like to pair this preamp up with a 10K ohm relay/resistor attenuator in my stash.
No setup for distortion measurments.
The current draw is so low I wasn't sure if I messed something up.
Is the 1K output resistor needed?
Actually, I am quite happy with what I'm hearing with this mono channel using a bench DC supply, Class D amp and small speaker. Super quiet, I can't hear anything with my ear up to the speaker.
I will proceed building the second channel.
I'd like to pair this preamp up with a 10K ohm relay/resistor attenuator in my stash.
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I thought of that and re-installed 4K7 + 820R in the feedback line, no change in current draw. All resistors are same as the schematic.
I have typically ~5mV DC on the output. Settling time depends on what is connected to it, but its typically 2-3 seconds.
DC on output climbs to few volts only briefly, as its being discharged by 100k resistor. Or volume pot on next stage.
Yes, power the pre first, then amp. Or leave pre on all the time.
Listening to it now, sounds fantastic. Even on test speakers.
DC on output climbs to few volts only briefly, as its being discharged by 100k resistor. Or volume pot on next stage.
Yes, power the pre first, then amp. Or leave pre on all the time.
Listening to it now, sounds fantastic. Even on test speakers.