I'm currently only using this section
All I want to do is make up for the sound drop caused by the pre-amplification I disabled by making a preamp.
What is the rule for adjusting the gain here? How to set? Can a single transistor preamp handle this volume drop? How to do it correctly?
BEST REGARDS !
All I want to do is make up for the sound drop caused by the pre-amplification I disabled by making a preamp.
What is the rule for adjusting the gain here? How to set? Can a single transistor preamp handle this volume drop? How to do it correctly?
BEST REGARDS !
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A single transistor can handle the necessary amplification but a IEC correction should be applied to have an
accurate sound, IEC curve typicaly boost low frequencies by 20dB at about 30Hz compared to 1KHz.
One transistor with a basic feedback network can be used but it will be more noisy than a two transistors regular
vintage preamplifier or an opamp like the NE5532, it will also have a less accurate IEC correction although it s still
enough in your case.
accurate sound, IEC curve typicaly boost low frequencies by 20dB at about 30Hz compared to 1KHz.
One transistor with a basic feedback network can be used but it will be more noisy than a two transistors regular
vintage preamplifier or an opamp like the NE5532, it will also have a less accurate IEC correction although it s still
enough in your case.
Ok, then your signal level is about 100mV RMS.
Your amplifier can put out maximum 9V RMS and its gain is 18X so you need 500mV to drive it to clipping.
The single transistor preamplifier you show has raw gain, as-is, of about 50X, too much.
To reduce it to needed 5X replace 33 ohm R597 by a 150 ohm resistor.
Apparently still too much gain but amplifier input impedance is too low 1 K so it will load preamplifier down.
From experience, 150 ohm {or even 120 ohm) emitter resistor should be about right.
It would also avoid using smartphone at maximum gain.
No need to add an extra volume control, amp + preamp roughly match.
If you still want one, an Audio 10k potentiometer at the input will do.
Your amplifier can put out maximum 9V RMS and its gain is 18X so you need 500mV to drive it to clipping.
The single transistor preamplifier you show has raw gain, as-is, of about 50X, too much.
To reduce it to needed 5X replace 33 ohm R597 by a 150 ohm resistor.
Apparently still too much gain but amplifier input impedance is too low 1 K so it will load preamplifier down.
From experience, 150 ohm {or even 120 ohm) emitter resistor should be about right.
It would also avoid using smartphone at maximum gain.
No need to add an extra volume control, amp + preamp roughly match.
If you still want one, an Audio 10k potentiometer at the input will do.
He said that the volume is too low, if he kept the passive tone control then it means that the total gain is about 35x
at most, and eventually lower, dont forget that the balance control reduce the signal amplitude by 2x.
He need to increase the gain by a 5-6 factor to drive the amp to clipping with about 50mV.
at most, and eventually lower, dont forget that the balance control reduce the signal amplitude by 2x.
He need to increase the gain by a 5-6 factor to drive the amp to clipping with about 50mV.
Yes, but he also said that he does't really need the tone control stack. Did you notice that somewhat uncommon balance control symbol? I know that especially Philips used potentiometers that didn' t attenuate until, or from, resp., the center position.
Best regards!
Best regards!
You are right on this one, i didnt pay attention that they used a dual potentiometer, nice catch, then the gain is about 720
without the tone control, that should be close to enough with a 100mV signal, so JMFahey is spot on with his solution.
Best regards as well.
without the tone control, that should be close to enough with a 100mV signal, so JMFahey is spot on with his solution.
Best regards as well.