Building a Pearl 2

Steve, what height will work?

There's just 40mm inside the 1U case so ideally 30mm caps are the limit without modifying the case a little. I struggled to find the smaller diameter caps at less than 35mm height. Bit of squeeze. You could up the diameter a little but then run into problems with component overlap on the board and leg spacing on the caps.

Small washers instead of standoffs and some sort of insulator under the boards might work.

Cheers

Steve
 
Could you post a good picture of the selector switch once you have it all wired up?

It's quite simple but perhaps a bit counter-intuitive. Select-2 is a 4 pole device. None of the grounds are common. Resistors go across the inputs (+ to gnd) and switch output (+ and gnd) goes to R14. See attached.

Since it is a "break-before-make" switch, it might be best to power the Pearl 2 down before switching gains. You definitely want to turn down the input to the down stream preamp/amp before switching gain.

Perhaps someone could weigh in on whether a momentary open at R14 under load might damage any of the Pearl's components. An alternative would be to leave some resistance on the board at the R14 location and just add resistors in parallel.

One more thing about the Select-2. I had to mill out the back side of the 10mm front panel about 6mm using a forstner bit in a drill press fitted with a drill press vise. Yhe entire body of the switch goes down into the panel.
 

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You got those into a 1U case? I thought for certain my transformer wouldn’t fit and couldn’t find caps on the RIAA short enough but apparently I didn’t try hard enough or know how to measure. I’m gonna have to build another level on the hifi rack to fit my 2U cases

Caps are 10,000 mfd Vishay's, 30mm tall (actually closer to 31mm). Standoffs are brass 4mm, Board is maybe 3mm. That leaves 2-3mm clearance to the lid.

Very little trimming was required on the regulator heat sink fins. I took off maybe 2mm which left about 1mm free and clear to the 30mm OD of the caps.

My big worry is using 25 volt 3300 mfd Nichicons. As long as the regulators don't fail in a way that supplies the unregulated 30.5 v rails to them, everything will be OK. I may yet still go to some 35 v caps that are not audio rated like the Nichicons for C4, C5, C6 and C24.
 
avdesignguru said:
My big worry is using 25 volt 3300 mfd Nichicons. As long as the regulators don't fail in a way that supplies the unregulated 30.5 v rails to them, everything will be OK. I may yet still go to some 35 v caps that are not audio rated like the Nichicons for C4, C5, C6 and C24.

Any thoughts out there on using 2200 mfd caps in the 3300 mfd positions? The 2200/35 Nichicons are only 25mm tall. Or better to use some 35V 3300mfd that are only 30mm tall by United Chemicon but not audio rated.
EGXF350ELL332ML30S United Chemi-Con | Mouser
 
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6L6

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This really runs into what your raw PSU has for filtering - if you have CRC or CRCRC there will be so little noise before the regulators that the regs will mainly be stabilizing the voltage more than making things much quieter.

As for audio rated caps, that’s mainly a marketing thing. I use them in kits when I can mainly to keep people from worrying about caps... :) Modern caps are all extremely good.

I personally would use the suggested value instead of undersizing in order to have capacitors with heatshrink that says audio.
 
6L6: I agree w/ your views on caps. I'm going to order the 3300mfd/35V that are 30mm tall and fit the 1RU chassis. They look pretty good even if they are not "audio" grade. Besides, the 3300mfd do not appear to be in the signal path, just additional supply references.

I'm also going to calculate parallel resistances for R14 so there is never less than 2000 ohms at the R14 position during the switch contact "break" while operating my gain control. Seems the safest thing to do.
 
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Made some progress this weekend and got the phono boards fired up. So far so good as the measurements all check out. The DC offset wanders a bit, like + - 10mv and stays a bit steadier after it warms ups.

I have it set up for a Hana SL MC cart that I don’t have yet so I can’t totally figure out if it’s working properly but I plugged it into my current TT and there were no alarming buzzes or noise To be concerned about. My current TT is notoriously noisy already, which is why I’m getting a new one, but it is surprisingly much quieter through the Pearl.

Hopefully I’ll have the rest of the pieces this week.

My case is unnecessarily large which bothers me but oh well.
 

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Made some progress this weekend and got the phono boards fired up. So far so good as the measurements all check out. The DC offset wanders a bit, like + - 10mv and stays a bit steadier after it warms ups.

I have it set up for a Hana SL MC cart that I don’t have yet so I can’t totally figure out if it’s working properly but I plugged it into my current TT and there were no alarming buzzes or noise To be concerned about. My current TT is notoriously noisy already, which is why I’m getting a new one, but it is surprisingly much quieter through the Pearl.

Hopefully I’ll have the rest of the pieces this week.

My case is unnecessarily large which bothers me but oh well.

Looking good so far. Which case did you go with?
 
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I’m finally got my turntable and have it set up and am Very happy with how everything sounds. It’s super quiet compared to my old TT and phono that buzzed when turned up loud. Now if I turn it up all the way on my 89db speakers, I just hear a slight hiss, but it’s not much at all. I would never turn it up that loud playing a record.

Everything sounds so much better but because I also got a new TT I can’t really tell what the Pearl 2 sounds like.

One potential issue:

The DC offset. I’m measuring it by putting one probe on the DC offset hole and the other on a ground pad. Without playing a record and nothing on input, the offset can wander over time from 0 to + or - 100mv. Is that too much drift?
 
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New turntable porn. It’s a VPI Prime Scout with a bunch of upgrades like a different tone arm and platter. Hana SL cartridge.


I always wondered what all the fuss about vinyl was but now that I have some proper equipment and some good pressings, I get it.
 

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The DC offset. I’m measuring it by putting one probe on the DC offset hole and the other on a ground pad. Without playing a record and nothing on input, the offset can wander over time from 0 to + or - 100mv. Is that too much drift?

See the conversation starting at post #753 for a solution to wandering offset.

I made this mod and offset is now fixed and stable at 0.0mV
 
Congratulations! Nice spinner!


Regarding the offset: You are measuring before the output cap. The preamp won't see it. Did you install the 220-440 uf BP cap mod between R14 & GND? Lift the lower end of R14 & install the cap between. That should smooth it out a lot. Mine varies only +/- 1 or 2 mv after the mod. Some have even removed the output cap afterwards. I prefer to leave it in just in case. :)


TJ