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Old 26th February 2013, 05:39 PM   #1991
6L6 is offline 6L6  United States
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Using budwieser's example of PSU is fantastic. It is very well done... emulate what you see there and you should have no problems.

As for your questions, they are not dumb. The only dumb questions are the ones you don't ask.

Dual red/black wires. These are the transformer primaries, the ones that attach to the wall. (The secondaries are the wired that attach to the rectifier and PSU, and are usually a different voltage than the primary) The reason for the 2 wires is so you can attach them in paralell for 120v input from the wall (North America and other places) or in series for 240v from the wall (Europe, etc...)

The Secondary wires are the ones that you attach to the rectifiers/capacitor/etc -- the PSU. Which leads are which should be clearly marked on the transformer itself.

You say you are a beginner, and that's awesome! There are lots of people here who will be happy to help. The Pearl isn't really an ideal project for a beginner, but, if you take your time and are super careful, it will be fine. This is a circuit that need patience during construction no matter who you are. The rewards are that it's amongst the very best phonostages I have ever heard. Seriously, it's that good.

Anyway - please read every word of this webpage --

Building a Gainclone chip amp power supply.

Although this is specific to Gainclone powersupplies, there is tons of fantastic information that applies 100% to the Pearl PSU. It will clear up many of your questions. The unregulated Pearl PSU is basically a gainclone PSU with a smaller transformer...

The screw terminal thingy you asked about is called a Barrier block, screw terminal barrier block, terminal block, or some other variation of those words.
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Old 26th February 2013, 11:18 PM   #1992
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I swapped out Q4 and Q5. I can now easily tune P16/P17 to around +/- 50 mv of 0 V. I swapped back in the 499R at R28 instead of the POT. Connected to the TT and amp and I now get music. It sounds good on my cheap test system. I think I am good.

One thing to note. When I was trimming P1 with the amp board on the bench, I did not have TT hooked up at input or output to amp and I was getting wild voltage oscillations at P16/P17. Hooking up to the TT and amp (while on) made it more stable to trim P1. Does this make sense? You should only trim with input and output connected some sort of load?
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Old 27th February 2013, 03:32 AM   #1993
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Default The Beginner's Climb to The Pearl2

Quote:
Originally Posted by 6L6 View Post
...
You say you are a beginner, and that's awesome! There are lots of people here who will be happy to help. The Pearl isn't really an ideal project for a beginner, but, if you take your time and are super careful, it will be fine. This is a circuit that need patience during construction no matter who you are. The rewards are that it's amongst the very best phonostages I have ever heard. Seriously, it's that good...
The Pearl2 can be tricky, especially that second stage discrete opamp.
That's why I'm getting there in steps ...

Got the Pearl2 PCB but haven't started yet? (Pearl1.5)

And if you want, you can build in small successful steps:

The Beginner's Climb to The Pearl2

1) 1 JFET input, RIAA network, 1 JFET output and batteries ('pacific' or 'boozehound' style) easy as pie! Actually pie is hard compared to this ... seriously that easy (and safe, just batteries)!

2) Get AC and 24V chip power-supply working (careful and safe with AC)

3) Beef up the input with 4 JFETs in parallel and cascode (sort of Pearl1)

4) Beef up the output with 2 JFETs in parallel and cascode (Pearl1.5)

5) Add negative supply and beef up the output with discrete opamp (Pearl2)


All on the Pearl2 PCB (and matched FETs) to make sure you're doin' it right and you upgrade one project rather than building many (no 'wasted time' or v1.1 boards).

It starts easy and safe--perfect for the beginner--but you're also up and running (no long, boring learning curve) and enjoying your own phonopre! This satisfaction is overwhelming!


Listening to a proto-Pearl before even touching AC! :-)

Then slowly and safely upgrade, climbing to the sublime summit of the Pearl2!




Oh ... and that connector is called a terminal strip/block, a screw-down terminal strip/block

Last edited by AudioLapDance; 27th February 2013 at 03:59 AM.
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Old 1st March 2013, 10:10 PM   #1994
poli is offline poli  Germany
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Hi 6L6,
thanks for the link about building the PSU - I will have a closer look - 'cos my Pearl 2 has a wonderful "hum" sound :-)
Not sure why this is, but that's only half the fun, finding out the problems and trying to solve it, isn't it?
Probably I did not get the earthing right and have a ground loop. Will sort it out...
How are you guys doing it? Do you have signal ground and enclosure ground completely seperated? And if not - is it connected through a 10 Ohm resistor and 0,1 uF capacitor? What about the connection amp enclosure to PSU enclosure? Does that need to be chassis-wise connected, so that the amp enclosure is also earthed? Signal ground also connected to amp chassis ground?
Thanks
Poli
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Old 1st March 2013, 10:24 PM   #1995
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I did the grounding like the article. Earth ground from the mains connected to the chassis of the PSU. Signal ground in the PSU connected to the chassis via the bridge. Only the PSU is connected to a wall socket with earth ground, other components are not (not really usual for audio equipment over here to have earth ground).

0V (signal ground) in the Pearl II enclosure is star grounded to a single point on the chassis. RCA inputs are floating from the chassis.

This way I have no hum whatsoever.
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Old 1st March 2013, 10:55 PM   #1996
6L6 is offline 6L6  United States
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Poli - Regarding the earthing the basic layout is this -

PSU is only chassis attached to AC Mains earth. PSU ground (at capacitor) is attached to earth via the rectifier block as loop-breaker.

ALL connectors on RIAA chassis (RCA, phono ground post, PSU umbilical) are not connected to chassis. Both PCB grounds connect to phono ground post. Phono ground post connects to chassis via a wire only if that is quieter than floating it. (In both my pearls, it is quieter to connect to chassis. According to Wayne, thins isn't always the case, you need to try both ways.)

And lastly, the transformer (I.E., PSU chassis) needs to be 3 feet (1M) from the RIAA to be truly silent.
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Old 1st March 2013, 10:58 PM   #1997
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I picture would be realllllllly good here!
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Old 1st March 2013, 10:59 PM   #1998
6L6 is offline 6L6  United States
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Check out my awesome drafting program --

Click the image to open in full size.




The important thing to remember is that all the connectors are floating. Ground them to the screw in the chassis only as you need to. (which will likely only be 2 things, the AC mains earth/ground breaker bridge, and the phono ground post.)

Last edited by 6L6; 1st March 2013 at 11:28 PM.
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Old 2nd March 2013, 12:45 AM   #1999
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That is one fancy CAD program you have there! You must have loaded a fastener library!

How would the grounding look in ... gulp, one chassis?

Last edited by AudioLapDance; 2nd March 2013 at 12:48 AM.
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Old 2nd March 2013, 01:19 AM   #2000
6L6 is offline 6L6  United States
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One chassis, actually quite similar, but the phono ground post would attach to the loop-breaker bridge, and the PSU likely wouldn't.

It wouldn't be very quiet with the transformer in the same box. Just getting a cheap plastic radioshack box to mount the transformer remotely would solve the problem. Have the rest of the PSU on board. Both the Pearl and the Pearl 2 are not truly quiet until the transformer is 3ft away.

Last edited by 6L6; 2nd March 2013 at 01:28 AM.
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