Preamplifier Dispre 2 - JFET

[chlorofille]

Pavel,

Although unlikely that it will ever happen, will there be any damage if I power 150Ohm headphones and use the line-level at the same time ?

 

[PMA]

You can use both headphones (even 32 ohm) and line output at the same time.

Only be careful when inserting headphone jack in, it sometimes short-circuit the output (out to GND). In case of troubles, switch the preamp off and on, with headphone jack inserted.

Best regards,

 

[chlorofille]

Thanks. I never ever unplug anything when the device is on.

 

[PMA]

Hello all builders,

I would like to place a warning here. I have received a feedback from a builder who had a problem to setup a preamp. The problem was that there is a manufacturer who produces BC560 transistors with reversed pins compared to usual and recommended type in the BOM. I am attaching images of both correct and 'wrong' (reversed) packages. Please do not use CDIL transistors. Use ON Semiconductor or Fairchild, e.g.

 

[chlorofille]

Dispre 2 Jfet complete...

Dear all,

I have finally completed the Dispre 2 preamplifier wiring and installed the boards in the Modushop 1U enclosure.

Initially, I was supposed to use 34AWG Belden RG-59 coax cable but due to such a short signal path, they were terribly inflexible. I stripped the shield and used the inner conductors as wiring. Input wire is about 3 inches long, while outputs are an inch or so.

The switch is just a dummy as I plan not to use one since the preamp will be on forever. Plastic extension shaft couples the ALPS pot to the knob. Green LED this time.

Fantastic huge sound when I pair it with Rod Eliiot's P3A amp.I have yet to find a pre that can better this Dispre.

 

[PMA]

RG 179 is a good option. It is flexible, well shielded, with PTFE dielectric and silver coated conductor and shield.

 

[Luke]

Hi Pavel, I just got my Dispre 2 going, great Pre, I am using it as a HP amp and its very good. I use a varo board LM317 pre and I am tempted to try some Salas shunts. I have a few jfets I would like to try, is it really not worth trying this on the bjt board?

 

[PMA]

Nice to hear it is working well for you. In case you speak about Dispre 2 BJT board, direct replacement of BJT's with JFET's is not possible. But, it might be possible, with some changes, to use the old BJT version PCB and to implement this circuit to it.

 

[Luke]

Thanks Pavel, I might try it sometime For now I'm enjoying listening to it.

 

[PMA]

Hello all,

just would like to let you know that my web page address has changed, please see my signature.

 

[PMA]

12 years have passed for me to be finally able to measure this preamplifier properly. So here are the results, measured with E1DA Cosmos ADC.

 

[Carl_Huff]

Pavel you should offer PCBs again. I've got to believe that there would be several interested builders out there if you did.

 

[PMA]

Carl, I remember you were one of my first customers, years ago . It is of course not impossible to start production of PCB’s of this preamp, I have all the production files. Frankly, I myself was surprised what I have measured now with better equipment, and I have also updated my web page.

 

[Carl_Huff]

I have enjoyed building all versions of your preamp. I'd buy a couple more PCBs from you if you made them available. It's a very nice preamplifier.

 

[pidesd]

is the DC servo absolutely needed or is it only to attain a certain standard of offset ? i'd like to cobble one if boards are not available.

 

[Adams_Leo]

wonderful test result,hope you can resume the pcb or kit

 

[PMA]

Set of new measurements published here:

https://www.audiosciencereview.com/...2010-with-1-5w-32ohm-output-capability.40415/

 

[Citizen124032]

@ PMA:
At what point and for what reason did you decide to add R51 (51k) as shown in #88?

 

[Antonimus]

Set of new measurements published here:

https://www.audiosciencereview.com/...2010-with-1-5w-32ohm-output-capability.40415/

Hello Mr. Pavel Macura,
I cannot find the schematic anymore for your MOSFET power follower, the version that also uses a MOSFET instead of the TIP141..I cannot even find the MOSFET power follower on your website
Can you please tell me where to find the schematic or send it to me? Many thanks
Thank you for your answer

 

[arthur]

Hi
PMA, Please offer PCBs again
Thanks