Federmann,
1) these Toshiba JFETs are perfect for high quality of sound, for many reasons (noise, linearity, HF immunity). The single devices, 2SK170/2SJ74, are still available, though not easily. And I hope for Linear Systems to develop LSJ74 sometimes, though they are quite late.
2) Toshiba JFETs and Hitachi MOSFETs prevent from fakes. I have even very bad experience with mass produced BC5XY parts, especially from CDIL.
As you know, I have an option designed completely from easily accessible parts. This option is Dispre II complementary-symmetrical preamplifier
Anyway, sound of that fully BJT preamp cannot compete neither with Dispre2-JFET, nor with PRE3.
Regards,
1) these Toshiba JFETs are perfect for high quality of sound, for many reasons (noise, linearity, HF immunity). The single devices, 2SK170/2SJ74, are still available, though not easily. And I hope for Linear Systems to develop LSJ74 sometimes, though they are quite late.
2) Toshiba JFETs and Hitachi MOSFETs prevent from fakes. I have even very bad experience with mass produced BC5XY parts, especially from CDIL.
As you know, I have an option designed completely from easily accessible parts. This option is Dispre II complementary-symmetrical preamplifier
Anyway, sound of that fully BJT preamp cannot compete neither with Dispre2-JFET, nor with PRE3.
Regards,
PMA
"Originally Posted by AMV8
Have you found that adjusting R1/R2 instead of Re gves lower distortion?
Hi AMV8,
yes, because the key is to keep input JFETs in the most linear portion of the transfer characteristic, and R1/R2 serve only to set appropriate Vgs bias of the output MOSFETs. For more info, please visit
Distortion in JFET input stage circuits"
Thanks for the reply
Don
"Originally Posted by AMV8
Have you found that adjusting R1/R2 instead of Re gves lower distortion?
Hi AMV8,
yes, because the key is to keep input JFETs in the most linear portion of the transfer characteristic, and R1/R2 serve only to set appropriate Vgs bias of the output MOSFETs. For more info, please visit
Distortion in JFET input stage circuits"
Thanks for the reply
Don
The spectrum on my website is measured, not simulated. In fact, I am unable to measure real level of the spectrum components by my sound card, as the soundcard is worse than my preamps regarding all higher harmonics above 3rd, and just similar regarding 2nd.
I still have not found ANY relationship between THD and IMD spectrum and sound of the amplifiers. I have lost any trust in possibility to predict amplifier sound from measurements published, provided these measurements do not indicate serious flaw.
I still have not found ANY relationship between THD and IMD spectrum and sound of the amplifiers. I have lost any trust in possibility to predict amplifier sound from measurements published, provided these measurements do not indicate serious flaw.
Pre3 complete
Hi Pavel and gang,
The PRE3 is all setup and driving Rod's P3A amplifier. Firstly, I found no difference with the preamp in or out of the system. It is behaving invisible to the audio chain, but providing huge gain (10X) without any hum/hiss.
This is a preamp for those who want to hear how the power amp sounds like, without adding any distortion/tone/sound signature.
I don't have the Dispre 2 Jfet with me now to compare, but if I recall, they both are almost identical in nature. Transparent and clean and absolutely quiet.
Hi Pavel and gang,
The PRE3 is all setup and driving Rod's P3A amplifier. Firstly, I found no difference with the preamp in or out of the system. It is behaving invisible to the audio chain, but providing huge gain (10X) without any hum/hiss.
This is a preamp for those who want to hear how the power amp sounds like, without adding any distortion/tone/sound signature.
I don't have the Dispre 2 Jfet with me now to compare, but if I recall, they both are almost identical in nature. Transparent and clean and absolutely quiet.
Attachments
Pavel,
That's exactly right. I have friends coming over and they want to test their tracks on MP3 players etc. My current source has a digitally controlled volume and it's output is quite low so the 10X gain is very handy. No noise at all so I guess the gain is good to have.
My new speakers (currently in building) have a sensitivity of around 86dB and will require a full 50W minimum to come alive.
Anyone else built the PRE3?
How about any comparisons between PRE3 and Dispre 2 Jfet?
That's exactly right. I have friends coming over and they want to test their tracks on MP3 players etc. My current source has a digitally controlled volume and it's output is quite low so the 10X gain is very handy. No noise at all so I guess the gain is good to have.
My new speakers (currently in building) have a sensitivity of around 86dB and will require a full 50W minimum to come alive.
Anyone else built the PRE3?
How about any comparisons between PRE3 and Dispre 2 Jfet?
Several pieces were built by the guys who do not post at diyaudio.
Regarding noise, you are right. This preamp has very, very low noise, for the reason of the very low noise input JFETs used. The output noise does not change with gain (set by input divider), so you do not get higher noise for 20dB setting than for 0dB setting.
Regarding noise, you are right. This preamp has very, very low noise, for the reason of the very low noise input JFETs used. The output noise does not change with gain (set by input divider), so you do not get higher noise for 20dB setting than for 0dB setting.
I have to confirm the fact, that jfet-dispre is extremely natural sounding preamplifier. I have tested many discrete and opamp designs, but this is really what preamp should be: piece of wire with gain or impedance converter
Only area where I can see some place for improvement is to add some stepped atenuator like DACT instead of Alps, or remote control relay volume controler...something like this: vicol audio : r-2r volume controller
The question is, if adding relay volume control could somehow degrade noise performance of this preamp? Output impedance variations also concerning me...
Have anybody already tested it with some volume controler like this or similar?
Only area where I can see some place for improvement is to add some stepped atenuator like DACT instead of Alps, or remote control relay volume controler...something like this: vicol audio : r-2r volume controller
The question is, if adding relay volume control could somehow degrade noise performance of this preamp? Output impedance variations also concerning me...
Have anybody already tested it with some volume controler like this or similar?
Attachments
I have to confirm the fact, that jfet-dispre is extremely natural sounding preamplifier. I have tested many discrete and opamp designs, but this is really what preamp should be: piece of wire with gain or impedance converter
Hi supernet, your choice of components looks very similar to mine. Are those PS caps Panasonic FC's ?
Did you notice any sonic signature of the dispre2 ? I found slightly less bass(compared to Rod's P37A discrete preamp) as all the frequencies are so clean with ultra low distortion. Glad you are happy with the preamp.
Yes, the bigger caps are Panasonic FC and smaller one FMs.
The sonic signuture is very transparent and natural...maybe a bit more on warm side of neutral. Actually it suits my needs very well
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