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Old 26th September 2021, 06:08 PM   #2821
6L6 is offline 6L6  United States
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Building a Pearl 2
Almost any produced in the last 5 years or so, as “super bright” is becoming more and more common. That’s almost certainly what you have in yours, considering your comment about them being like headlights. All you need to do is make the LED resistor more ohms your tame that down.
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Old 26th September 2021, 06:25 PM   #2822
Mark Johnson is offline Mark Johnson  United States
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For front panel "pilot light" applications, I prefer LEDs with the widest possible viewing angle -- which is a manufacturer guaranteed specification on many datasheets. The wider the viewing angle, the greater the likelihood that you'll be able to see whether the LED is on or off, at all positions in the listening room. Not just dead center. Here are a couple example LEDs that specify a quite wide, 120 degree (!!) viewing angle:

3MMLED-GREEN: Jameco Valuepro : LED Super Bright Green Diffused 3mm (T-1) 520nm 5000mcd : Opto & Illumination

3MMLED-BLUE: Jameco Valuepro : LED Super Bright Blue Diffused 3mm (T-1) 465nm 5000mcd : Opto & Illumination
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Old 26th September 2021, 11:22 PM   #2823
aalewis is offline aalewis  Australia
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Thanks for the replies
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Old 20th October 2021, 03:34 AM   #2824
Anticipation is offline Anticipation  New Zealand
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Wow, what a fun journey this has been! The Pearl 2 is an amazing piece of kit. I just wish I had found this thread sooner, it would have saved me a lot of pain chasing RF (thanks to C7) and trying to balance the output. Almost there now, thanks to the input from all you awesome people. At the tweaking stage now: R14 for gain, and playing with R8 to get the voltage more in line with the ideal around Q3. Have ordered some 20R resistors. Added another 100nF under the board to lower the cut-off. I have fitted 6,800uF caps rather than the specified 10,000uF, as they're shorter, meaning I could fit it all in a low-profile 1U high case. Yes, PSU as well!! and it's as quiet as I've ever heard a phono preamp. Not a hint of hum, even with the volume cranked right up
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Old 27th October 2021, 04:21 PM   #2825
rhthatcher is offline rhthatcher  United States
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I'm getting parts ordered for my build. This project is in a queue of many, so I don't expect to build until sometime in the middle of winter. I need to order the chassis, too.

One thing I'm going to play with is the capacitor and resistor loading using rotary switches. My buddy's EAR phono has something like this, so I thought I'd build on that concept. I sent these boards off for fab last night, and the switches are inbound, too. I'll report back on how they work out. If anyone wants to beta test, I'll have extra boards.

The idea is one switch for caps on a DP6T switch with 5 cap values plus leaving one open for no cap loading.

Resistor loading will be one 16 position switch per channel. All resistors are parallel to the 47k5 on the main board. 15 resistors on the switch + one open position for 47k5 loading.
Attached Images
File Type: jpg Capacitor Load PCB Protoype.jpg (186.8 KB, 160 views)
File Type: jpg Resistor Load PCB Protoype.jpg (178.2 KB, 162 views)
File Type: jpg JLCPCB-00a.JPG (19.1 KB, 159 views)
File Type: jpg Resistor Load PCB.JPG (226.9 KB, 165 views)
File Type: jpg Cap Load PCB.JPG (144.9 KB, 124 views)
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Old 27th October 2021, 05:52 PM   #2826
Mark Johnson is offline Mark Johnson  United States
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I lost a battle against obsessive compulsive disorder this morning.


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Last edited by Mark Johnson; 27th October 2021 at 05:55 PM.
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Old 27th October 2021, 07:08 PM   #2827
rhthatcher is offline rhthatcher  United States
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Mark - nice catch! I wasn't thinking to do that at 1AM when I finished... It's easy (and cheap) to throw a few more boards into an existing order, so I added those traces. And while I was at it I made a new wider version with updated resistor footprints. So I'll have vertical and horizontal resistor PCB's to see which I like better...
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Old 27th October 2021, 08:13 PM   #2828
Dennis Hui is online now Dennis Hui  Canada
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This is very nice and looks to be a great addition to the Pearl 2.
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Old 27th October 2021, 09:24 PM   #2829
McQuaide is offline McQuaide  United States
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Quote:
Originally Posted by rhthatcher View Post
I'm getting parts ordered for my build. This project is in a queue of many, so I don't expect to build until sometime in the middle of winter. I need to order the chassis, too.

One thing I'm going to play with is the capacitor and resistor loading using rotary switches. My buddy's EAR phono has something like this, so I thought I'd build on that concept. I sent these boards off for fab last night, and the switches are inbound, too. I'll report back on how they work out. If anyone wants to beta test, I'll have extra boards.

The idea is one switch for caps on a DP6T switch with 5 cap values plus leaving one open for no cap loading.

Resistor loading will be one 16 position switch per channel. All resistors are parallel to the 47k5 on the main board. 15 resistors on the switch + one open position for 47k5 loading.
I did this with 5 position rotary switches, and added another one to control gain via R14 to select between 300, 600, and 1K ohms.
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Old 27th October 2021, 09:35 PM   #2830
rhthatcher is offline rhthatcher  United States
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Quote:
Originally Posted by McQuaide View Post
I did this with 5 position rotary switches, and added another one to control gain via R14 to select between 300, 600, and 1K ohms.
I'm planning to do a switch for Hi/Lo gain. In reality, it will run on high gain nearly all the time with an MC cart. It may get a little run time with an old beater 'table with a MM - so I'll put the switch in for that case.
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