Motown Direct Amplifier-inspired Preamp?
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adding an 82 k stopper to the grids of the 6BX7 output tube helps even more,
now the ringing looks manageable
interesting that you can not see the ringing on the input of the transformer, it takes the transformer to make all that ringing happen from the hi freq response of the preamp,
theses shots are all 10 k hz,
now the ringing looks manageable
interesting that you can not see the ringing on the input of the transformer, it takes the transformer to make all that ringing happen from the hi freq response of the preamp,
theses shots are all 10 k hz,
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there is no free lunch with those stoppers, here is a 100 K Hz sine wave input,
attenuation is not that bad with the stopper, Jeff Beck might have been able to generate 100 K Hz but i do not have that note on my guitar or bass,
last night's listening tests confirmed what i see on the scope, Dave's preamp had a bit more articulation on the high end, overall the two circuits were very close to each other, Dave's circuit was unforgiving of guitar technique, you have to play perfect or you will hear it, the smearing from my circuit made it a little less stressful when trying to play clean. i will give the circuit with the stoppers another side by side listening test,
both circuits sound wonderful compared to plugging directly into the board.
attenuation is not that bad with the stopper, Jeff Beck might have been able to generate 100 K Hz but i do not have that note on my guitar or bass,
last night's listening tests confirmed what i see on the scope, Dave's preamp had a bit more articulation on the high end, overall the two circuits were very close to each other, Dave's circuit was unforgiving of guitar technique, you have to play perfect or you will hear it, the smearing from my circuit made it a little less stressful when trying to play clean. i will give the circuit with the stoppers another side by side listening test,
both circuits sound wonderful compared to plugging directly into the board.
Attachments
spun a choke last night, 625 EI core (5/8" tongue)
got 6000 turns of #34 on a square bobbin, about 450 ohms DCR but 80 Henries
so at 120 Hz that will be 6.28 x 120 Hz x 80 Henrys = 60 K ohms of inductive reactance to squelch out that sawtooth rectification noise.
this circuit is not push pull so you do not get any free cancellation of pwr supply hum,
ripple on my circuit was 5 volts on the first cap and 600 mv P-P after the 200 ohm dropping resistor
now it is 5 or 10 mv after the choke,
there was a slight buzz with the dropping resistor, now it should be gone.
Dave's circuit has another advantage over mine, it only uses two tubes,
green choke on chassis, those end bells might cut down on noise coming in or going out, i do not know,>
got 6000 turns of #34 on a square bobbin, about 450 ohms DCR but 80 Henries
so at 120 Hz that will be 6.28 x 120 Hz x 80 Henrys = 60 K ohms of inductive reactance to squelch out that sawtooth rectification noise.
this circuit is not push pull so you do not get any free cancellation of pwr supply hum,
ripple on my circuit was 5 volts on the first cap and 600 mv P-P after the 200 ohm dropping resistor
now it is 5 or 10 mv after the choke,
there was a slight buzz with the dropping resistor, now it should be gone.
Dave's circuit has another advantage over mine, it only uses two tubes,
green choke on chassis, those end bells might cut down on noise coming in or going out, i do not know,>
