Building a Pearl 2

mhenschel · 2021-01-23 6:45 pm

I'd be tempted to rearrange things so that the Pearl wasn't next to Wayne's preamp transformer.
Just sayin'.

Wellerman · 2021-01-23 9:07 pm

For more gain, change R14 to something between 600 and 750R. The Pearl will output something like 250mV then with your cartridge, that should be enough for most (pre)amps.

Manolo47 · 2021-01-25 8:42 pm

Would I have to set the bias voltage again after changing R14?

Wellerman · 2021-01-25 8:50 pm

I don't know, I would just check. Good to check anyway after some use to see if it stays stable. With the extra capacitor-modification it should stay stable.

bmdduck · 2021-01-26 12:58 am

I recently bought a set of Pearl 2 board and matched JFETs from PassDIY - the JFETs are 2SK170s.

I am up to the point of installing the JFETs in the board and I want to make sure I have the correct orientation. The 2SK170s have one flat face and a curved back.

Here comes possibly a dumb question: do I install the JFETs (and other transistors) with the flat faces on the flat side of the circuit board silk screening?

I looked up the data sheets for the JFETs and it based on the pinout it looks to me like they should go the other way - but all of the build pictures look like the flat faces go to to the flat side on the board.

Thanks in advance for any insight - bmdduck

mhenschel · 2021-01-26 1:05 am

Are the diagrams on the datasheet looking up from below or down from above?

bmdduck · 2021-01-26 1:32 am

Looking from below or down from above - that is a good question. I assumed it was top down - but if it's bottom up that would explain my confusion. Is bottom up the normal way?

I tried to attached the datasheet I found -

mhenschel · 2021-01-26 2:05 am

I think "from below" is assumed if there is no note otherwise.
But really, it would be truly helpful to have this important information made unambiguously.

6L6 · 2021-01-26 3:17 am

Of course it’s looking at the bottom... that’s where the pins are!

And yes, the flats of the transistors line up with the flats of the silkscreen.

McQuaide · 2021-01-26 12:28 pm

Manolo47 said:
Would I have to set the bias voltage again after changing R14?

It's DC offset voltage and if you add a cap between R14 and ground you won't have any. I switch R14 between 300R and 1K routinely with no issues.

bmdduck · 2021-01-27 1:42 am

Thanks mhenschel and 6L6 - not sure why I was reading that wrong. Looking at it again, it seems obvious!

bmdduck · 2021-01-28 11:20 pm

Ok, here goes - first time posting pictures.

The boards are done. Next up is building the power supply and picking a chassis for the PS.

My last project was a BA2018 linestage which I put in a pretty big chassis. I am removing the power supply from it, installing the Pearl 2 board and powering the linestage from the Pearls. All with an off-board power supply.

Thanks to those who answered questions along the way - this forum is super helpful!

bmdduck · 2021-01-28 11:29 pm

Trying again to post the picture.

McQuaide · 2021-01-29 3:14 pm

bmdduck said:
Trying again to post the picture.

Looks good, you could put a 47uF 25V electrolytic between R14 and ground to stabilize offset. Put the - side on ground.

bmdduck · 2021-01-29 5:34 pm

Thanks for the suggestion!

Dlkoch76 · 2021-01-30 5:34 pm

I have received my boards and JFETS from PASSDIY. completed a BOM order from mouser (thank 6L6). I have a DIYaudio psu board and looking for suggestions on populating it. I have build the board for power amps before but they where of the simple class A setup. I currently have 6800uF 50V nichicon caps for the board. was curious if anyone has resistor values for it or are the .47ohm 3 watt good? I have an AnTek AS-0522 toroid that I plan on using. I am fairly new to all this and do not have an engineering background. I have build a pair of Amp camp amp, a F6, a few tube amps and am currently collecting components for an AlephJ. I have attempted to read thru this entire thread but it has become very lengthy.
I went way off topic. With the DIYaudio PSU boards, what snubbers, resistors and such get used?

Manolo47 · 2021-01-30 6:32 pm

I ued the same board for the PS. See me pictures posted here. Your caps and transformer are OK, that's what I used. The only parts really needed are the diodes -i used Hexfreds- and even the heatsinks are not necessary. As far as resistors, only R9 and R10 are needed, and I also used resistors in the R1 and R8 -R .47 ok-positions, -left the others open- that's all. Be sure to connect the ground planes of the 3 boards as shown on the build guide. Take care in positioning of the diodes in the board to account for their polarity. There's nice photo of this in this thread but I cannot find it now.

Dlkoch76 · 2021-01-30 6:45 pm

I have a bunch of Vishay FEP30DPs that is use in amp builds. they are 200V 30A

6L6 · 2021-01-30 6:59 pm

Those will work beautifully. :yes:

I love being able to use things on hand.

Dlkoch76 · 2021-01-31 12:29 am

Well I think my power supply has an issue. I have the FEP30DPs installed, the capacitors installed and .47ohm resistors in R9, R10 and R8 and R4. have LEDs and R20 and R21 with 4.7k. hooked up my dim bulb to the transformer and it lit up and never dimmed. no DC output. to I need more than 1 filter resistor? should I have not put the led with drop resistor in? any help? will post a pic of PSU

Building a Pearl 2

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