Juma's LSK Preamp - through hole version

[tinitus]

I sent this morning with registered mail PCBs to all of you who made a payment. Thanks for support and if you find that appropriate please let me know when they arrive to you.

 

[prasimix]

prasimix:

Fantastic! Any chance you could provide some advice (or a build guide) for adjusting the multiturn resistors?

Regards,
Scott

Real authority for that should be Juma. I'm still in the phase of collecting required parts and hope that I'll be in position to share some building experience with all of you very soon.

 

[prasimix]

The 2.7 BOM says V grades for the FETs,I have BL grades can they be used?

V grades JFETs are in the BOM list from the beginning. Other possibility is to use 2SK246/2SJ103 pair.

 

[tinitus]

 

[prasimix]

Oh, that was very fast

 

[prasimix]

Schematic v2.8 and BOM list

Folks:

I've started the process of adding Mouser and Digikey part numbers to V2.7 of the BOM for prasimix' through hole version of Juma's LSK preamp, but your help would be appreciated. In those instances where the part listed in the Farnell column is also available from Mouser or Digikey, the spreadsheet has been updated. Mouser and Digikey don't offer Welwyn brand resistors and I wasn't sure what would be a good alternative (PRP from PartsConnexion or SonicCraft, or something else that Mouser or Digikey has in stock?). Also, I couldn't tell if the Hammond transformers offered by Mouser and Digikey were in fact drop-in replacements for the ones mentioned in the spreadsheet or decide which capacitors were good alternative solutions.

In any event, would someone be kind enough to pick up where I've left off?

Regards,
Scott

Here is an updated BOM, v2.8, all change are maked with purple color. Changes include adding of ground loop breaker diodes and resistor, and four additional diodes for reverse voltage protection for 78/79 regulators.

Scott, if Farnell is not an option for US, what's about Newark (i.e. for PCB transformer, part.no. 25M9497)?

 

[prasimix]

Mounting BF862 on the PCB could be a small challenge since that part is really tiny. That didn't require more that few minutes for me and I hope that shouldn't be a problem for most of you. As an assistance I used simple 20x magnifing glass and of course very sharp soldering tip (i.e. Farnell 416848).

Alternative for direct on board mounting is usage of small adapter as dobrivoje suggested here. In that case take in account that pinout should be mirrored (you also do not need gate resistor shown on picture because it is already on the PCB).

 

[potepuh]

Boards arrived

 

[brianco]

MAny thanks, my set has arrived in Scotland safe and soon sound!

 

[Ryssen]

Got my board!

 

[SRMcGee]

Here is an updated BOM, v2.8, all change are maked with purple color. Changes include adding of ground loop breaker diodes and resistor, and four additional diodes for reverse voltage protection for 78/79 regulators.

Scott, if Farnell is not an option for US, what's about Newark (i.e. for PCB transformer, part.no. 25M9497)?

prasimix:

Sorry for the belated response -- I'm travelling on business in Europe and haven't been able to log on very often. I found one of the transformers you had recommended at Allied Electronics (Allied Electronics ? Electronic Parts and Components Distributor, part no. R1070245) and ordered from them; their prices on many items were substantially less than the same item at Mouser, so my order was split between the two.

I'll post an updated version of your BOM for the North American audience when I get a moment (perhaps over the weekend?); my current version reflects your v2.7 BOM.

Regards,
Scott

 

[prasimix]

(Almost) all components arrived and I finalized PS section and upper channel from dual PCB. So far everything is ok except one minor mistake with hole diameter for 1K/2W resistors (R4, R5, R31, R32) which at least im my case should be 1mm.

I skipped ground loop breaker section in PS since I have it on another board. Mosfets for +/-33V really don't need any heatsinks, and for 78/79 regulators I used twice as shorter then listed in current BOM and that is more the enough.
You can see attached some of the first measurements (signal source is recorded CD not function generator).

Input transformer is 2x18V.

Unpopulated section of upper channel is intented for building of phase splitter as Koja requested.

Now I'm going to find somewhere P5 (50R) that I need to finalize lower channel on dual PCB

 

[Ginum]

PCBs arrived.
Thanks Denis!

 

[JimT]

Boards arrived in Canada today.

Thanks
Jim

 

[prasimix]

Dual channel board is finished. Both channels works as expected. Please find below how it looks like.

 

[prasimix]

Oh, I forgot to mention one 'unimportant' detail. This version is built around 2SK170V/2SJ74V which I found in Japan. I bought 8 matched pair (see picture), two of them is used on this board and 6 pairs is available so if someone is interesting in them can send me a PM.

In following days I'll try to complete PS board and two single channel board but this time using 2SK246/2SJ103 pair.

 

[soundchaser]

Hi Denis;

Got my PCB just now. Not bad time for a trip across the pond!

Thanks for all of your work

Matt

 

[Ryssen]

Dual channel board is finished. Both channels works as expected. Please find below how it looks like.

How did you adjust the pots?

 

[Tripmaster]

My board arrived today. Thanks for your help Denis!

 

[prasimix]

How did you adjust the pots?

I started with middle position, and didn't change that for now, since it looks fine.