Add Gain and Load settings for Pearl 2 Phono? - diyAudio
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Old 3rd April 2013, 08:22 AM   #1
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Default Add Gain and Load settings for Pearl 2 Phono?

Whats the best way to go about adding a selection of gain levels and load settings for the output in this design? It would be nice to not have to remove the case to make changes on the fly.

Gain output of the Pearl 2 is controlled by a resistor ( R 14 ) on the PC board (right?) The standard value for this Resistor is 1K and the gain is 55 db in standard configuration. Substituting a 300 Ohm resistor for ( R 14 ) bumps the gain up to 65 ohm, for those wishing to use a LOMC cartridge.

This had me wondering why phono stages don't have variable gain selections to allow LOMC, MM and High output MM.


What about adding a 3 position switch, or a 5 position rotary switch. and a few resistors.

what about using pots?

Any noise issues to consider in doing so?

Could this be done for the input Loading as well??

has anyone tried this, or is everyone sticking to the basic build? What do you think?
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Old 3rd April 2013, 11:20 AM   #2
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Someone did try this. It is in the original Pearl 2 forum thread posted in the past 3 months.
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Old 3rd April 2013, 12:47 PM   #3
6L6 is offline 6L6  United States
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I can think of 3 instances in the last 6 months or so where it was done. One used a bank of DIP switches, another a couple of toggles, and one used a rotary for input loading, but I don't think he switched the gain...

Don't use a pot.

Have you read the entire Pearl 2 thread? It's worth it.

Stick to the basic build first. Adding a function like that is fairly easy to do as a modification later.
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Old 3rd April 2013, 11:23 PM   #4
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Based on what I've read Ive decided to go with 10pole rotary switches (from digikey) for gain and resistance settings. Pots will be poorly L/R balanced and noisy and too variable, proving difficult to match channels on the fly. Shouldn't be tough to build switches and wire it in instead of the respective fixed value resistor in the schematic.

Wire the switch as follows: One resistor to each tab (except v in) and then a common wire to all and out to the board.

---but capacitance selection might prove more challenging to implement..

DIP-switch from 50's or rotary switch to separate board and rows of series caps....?
can a 100pf and 50pf cap be wired in series to safely make 150pf?

Would like to add a few capacitance settings.. . rotary switch would be nice to operate, but dip switch might be easier to build. i Plan to have multiples of 50 and 100.
(50,100,200,300,400, 500..) ... Based on the limited number of pF cap values it looks like a dip switch would be the easiest idea... But I've never worked with one, and believe the caps must be in series to add... Is this correct?

For cas, radial C0G ceramics or pp film? Other ideas?
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Old 4th April 2013, 12:00 AM   #5
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The project is a fair undertaking - I second 6L6 advice. Keep it simple - get it working first (get psu working first), add the functionality second.
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Old 4th April 2013, 02:42 AM   #6
omishra is online now omishra  India
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I have a suggestion which I will be trying in fact. I have MV102 (for MW radio)vericap diode and NSL-32SR2 optocoupler. So i plan to use vericap diode for tuning capacitance which will be controlled with some single pot variable DC voltage or stepped switch for pre configured voltages through fixed resistances. This will keep signal wires up to only PCB.

Same thing for resistance loading through voltage controlled switch and optocoupler. What you say?

Last edited by omishra; 4th April 2013 at 02:44 AM.
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Old 4th April 2013, 03:00 AM   #7
omishra is online now omishra  India
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Sorry it's MV 109 diode. Also there are lot of 1SV 149 diodes are available which could used for changing capacitance ~20-500pF.

Last edited by omishra; 4th April 2013 at 03:05 AM.
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Old 4th April 2013, 03:01 AM   #8
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I built this for Pearl II loading.

MC and MM Resistor and Capacitor Loading
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Old 7th April 2013, 10:06 AM   #9
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Quote:
Originally Posted by vdi_nenna View Post
I built this for Pearl II loading.

MC and MM Resistor and Capacitor Loading
Very elegant solution! I was thinking the same. I like the job you did. Im ultimately going to attempt to build rotary switches to allow changing settings on the fly. Id like to be able to experiment and accomidate various cartridges on headshells.
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Old 7th April 2013, 10:22 AM   #10
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Quote:
Originally Posted by omishra View Post
I have a suggestion which I will be trying in fact. I have MV102 (for MW radio)vericap diode and NSL-32SR2 optocoupler. So i plan to use vericap diode for tuning capacitance which will be controlled with some single pot variable DC voltage or stepped switch for pre configured voltages through fixed resistances. This will keep signal wires up to only PCB.

Same thing for resistance loading through voltage controlled switch and optocoupler. What you say?
Hi! I not so well aquanted with those components because im new to this hobby. I dont know if i perfectly understand your idea, but i think i have a faint idea. i believe if you want to try something you should! That sounds like a more sophisticated idea than mine. I feel that using a rotary switch to select between capacitor and resistor values would be most convenient and easier for me to understand and build at this point... Though my idea will take up a good amount of space in the case.

I breifly considered variable capacitors and reisistors for loading and gain but i decided against them for a couple of fundamental reasons. With continuously variable components or potentiometers it would take alot of time to dial the settings in and make sure both channels match exactly.. however you be able to get more exact match. im guessing you would need a very stable voltage. With basic components i feel im not changing the signal path or circuit voltage too much.

for me, Fixed value capacitors and resistors have close enough tolerances and can be matched so easily. also several can be installed and wired to dip switches or other types of switches to allow quick selections between them and make it easy to return to a previous setting if desired.

I like thinking of ideas to add because it makes me feel more creative and it challenges me to learn more than how to follow directions. Im glad to see you are also thinking of ideas too!


If i can leanr more about the riaa section i might contemplate adding alternative equalization schemes for older recordings... But thats a long way away for me.
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