Pearl 3 Burning Amp 2023

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#363
Have been wanting to build a phono pre for a long time - it's the one component of my setup that's not a Pass DIY build. My soldering iron has been cold for a couple years and it's time to fire it back up. Was planning to build to Pearl 2 but now I think I'll wait for the P3 kit! 🙂 Very excited for this and incredibly grateful to everyone working on assembling the kits and to Wayne for sharing the design!
 
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#366
jackinnj said:
Small thing to note, probably only of note to those of us fetishists who enjoy measuring things. In Groner's ULN amplifier article in Linear Audio he suggests that when the JFET runs cooler, it also runs quieter. Next thing you know we will be using liquid helium to cool them in a Dewar flask.
Click to expand...

Hello,

I have been looking at several JFET data sheets.

What I see in the data sheets is that JFET noise decreases with increasing frequency and/or increasing current.

An example:

https://www.mouser.com/datasheet/2/308/MMBFJ113_D-2303036.pdf figure 12 and figure 13

Thanks DT
 
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#369
Hello DualTriode,

perhaps you know this article about noise in JFets with measurements?

https://www.mvaudiolabs.com/diy/modern-jfet-noise-measurements/

Then you know, why the good old TOSHIBA JFets are still 'running' in front.
But there are some good alternatives for N-JFets in SMD with low and lower noise (Toshiba 2SK209,
ONSEMI 2SK2394 / 2SK3557, ... BF862 is obsolete.
Cheers
Dirk
 
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#372
6L6 said:
@DualTriode

I have two built, one with 2SK209GR, they are reading 0.018v across the 10R resistors.

The 2nd has 2SK370 and they are measuring 0.030v across the 10R.

On the bench they both sound the same.
Click to expand...
Did you prefer the lower IDSS or the higher IDSS? What Cartridge are you using? The feedback at the first stage won't negatively affect in this application ignore my earlier comments on removing feedback to the first stage. Have you tried a jfet with a lower IDSS?
 
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#373
Please note “on the bench they both sound the same” in that post.

I’ve used AT-OC9 moving coil in high gain, Ortofon OM10 and AT-VM95SH Moving Magnet, and B&O MMC5 Moving Iron in low gain. I have more cartridges and just need time to mess with them, but initial listening says this is an incredibly good sounding phonostage.

The feedback in the first stage is imperative as the front-end is now a composite amplifier. If you want to remove the feedback, you’ll need to design a new board. Please share those findings in this thread.

Yes, the K209 are lower Idss than the K370. (In my builds)
 
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#374
6L6 said:
I can’t take credit for that as I was chatting about testing soldering continuity a week ago with @thomasnadeau , and he remembered that Jfet will measure as diodes from Source to Gate and from Drain to Gate…

So on this PCB you can set your DMM to diode test, place the red probe on the through-hole pad for gate, and black probe on through hole pad for Drain, and then black to the pad for Source. In each instance if it shows about 0.7v from D-G and then S-G, you’ve verified that 1) the SMD have continuity to the pcb, and 2) you don’t have blown jfet. Cool!

This will be shown clearly in the guide.
Click to expand...
And to add to what @6L6 said - if you measure 0V you need to go back and try your solder again, or you could have a blown / defective JFET. 🙂

--Tom
 
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#375
6L6 said:
Please note “on the bench they both sound the same” in that post.

I’ve used AT-OC9 moving coil in high gain, Ortofon OM10 and AT-VM95SH Moving Magnet, and B&O MMC5 Moving Iron in low gain. I have more cartridges and just need time to mess with them, but initial listening says this is an incredibly good sounding phonostage.

The feedback in the first stage is imperative as the front-end is now a composite amplifier. If you want to remove the feedback, you’ll need to design a new board. Please share those findings in this thread.

Yes, the K209 are lower Idss than the K370. (In my builds)
Click to expand...
Thanks, lets first build as is
 
#376
Pearl 3 is a very enjoyable phono preamp, nice voicing, not too resolving as to make one hear the imperfections of the cartridge, tone arm and turn table and also not too vague as to have a veil. Here's a comparison to direct OPA134 pickup.

Pearlfourier1k.png

Pearl 3 fourier 1k above

Pearl3OLG.png

Pearl 3 OLG 1k above

OPA134fourier1k.png

bare OPA134 pickup fourier 1k above

OPA134OLG.png

OPA134 OLG above, load 2k

OPA134pickup.png

OPA134 bare pickup above
 
#378
The pearls are nice phono preamps. Pearl2 and Pearl3 are each in a camp of its own and the AB test recordings might be interesting, Pearl4 doesn't seem all that far off
Vogel, B. (2011). The Sound of Silence: Lowest-Noise RIAA Phono-Amps: Designer's Guide (2nd ed., illustrated). Springer Science & Business Media. ISBN 3642197744, 9783642197741.
 
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