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Old 14th November 2011, 01:16 PM   #1
nar is offline nar
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Default Aleph_Ono reduce gain ?

Dear all, Wayne and Nelson,

Recently hooked my diy AlephOno with a Rega P3 and an Elys cart mounted on

Volume is too loud, compared to the Ortofon MC3 turbo in the same place, resulting in a less crisper sound layering, with "ear tiring" mediums when playing the record loud. As I experienced also with Pearl II and my Ortofon cart, I needed to reduce stock gain. So I would like to reduce gain for the MM stage of AlephOno in order to match the Elys

My question is how do we calculate it, given the feedback loop is 2 resistors and 3 capacitors and also operates RIAA eq. ?

As 40 dB @ 1kHz is x100, I would like to go and try x50, so about 33,98 dB.

A second question would be : the 32V supply. I changed supply and now it is 30V symmetric instead of 32V. Is it bad, or can I keep it ? the PSU is UGS based, so basically Pearl One regulator but fully symmetric. I can finetune the voltage up to the 32V originals if needed.

Thanks for your answers,

Best

nAr
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Old 15th November 2011, 04:54 AM   #2
6L6 is offline 6L6  United States
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When you have the phonostage adjusted for the Elys cartridge, I will bet you a bottle of your favorite whiskey that you won't like it... (The cartridge, not the adjustments to the AlephONO)
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Old 15th November 2011, 06:13 AM   #3
nar is offline nar
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Quote:
Originally Posted by 6L6 View Post
When you have the phonostage adjusted for the Elys cartridge, I will bet you a bottle of your favorite whiskey that you won't like it... (The cartridge, not the adjustments to the AlephONO)
Lol, I know, I'm not really fan of Rega's products, with the Elys there is actually same output level from MM stage than CD version ...

But the AlephOno is at my brother's and we found that sonically, there was a problem with mediums when playing a LP loud. When listening @ more confidential levels it goes Ok, so same thing I encountered with Pearl II and Ortofon MC3 turbo. I ended up doing the gain mod and everything went in place.

Now, I'd like to do the same on AlephOno. In order not to mess up with a bad eq. setting, i thought about setting R21 to 50R instead of 100R ... it would perhaps keep the eq. curve the same whilst lowering gain ???

Best,

nAr
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Old 15th November 2011, 08:20 AM   #4
Zen Mod is offline Zen Mod  Serbia
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don't do this

put 10K multiturn pot between drains of 2SK389

if needed - put drain resistor on right Jfet
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Old 15th November 2011, 12:03 PM   #5
nar is offline nar
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Quote:
Originally Posted by Zen Mod View Post
don't do this

put 10K multiturn pot between drains of 2SK389

if needed - put drain resistor on right Jfet
Thanks for the input. I thought altering drains figure would only cut in OL, not in closed loop gain ? Maybe i'm mistaken.

Best,

nAr
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Old 15th November 2011, 12:41 PM   #6
Zen Mod is offline Zen Mod  Serbia
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uff

sorry - my brainfart , probably because of not sufficient speed of caffeine going in my system

it was long time ago when I was playing with RIAA networks , and now I even forgot what I wasn't knew then , let alone that I can't remember what I knew

anyway - it's easy : just calc impedance of RIAA chain for 20, 50, 1K , 20K , then calc what db ratios between extremes are when divided with regular value of R21 and altered one .

hmm ..... lemme see if I can calc that on back of napkin ....

yup - for 6db decrease of gain , you need to increase feedback for same amount - so you need to increase R21 for 100% and you'll be in ballpark

so - take 200R for start

fine tuning of circ will still demand reverse RIAA filter , and any of common methods for freq sweep

I reckon that 20Hz will be 19,27db above 1K , which will be around 19,9db above 20K ; that's quick and rough calc
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Last edited by Zen Mod; 15th November 2011 at 12:47 PM.
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Old 15th November 2011, 04:42 PM   #7
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Thanks Zen Mod

nAr
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Old 16th November 2011, 08:29 PM   #8
wayne is offline wayne  United States
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How much lower gain do you need?
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Old 16th November 2011, 08:42 PM   #9
Zen Mod is offline Zen Mod  Serbia
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nar wrote in post #1 :

Quote:
As 40 dB @ 1kHz is x100, I would like to go and try x50, so about 33,98 dB.
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Old 17th November 2011, 07:06 AM   #10
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Quote:
Originally Posted by wayne View Post
How much lower gain do you need?
About 34 dB

Best,

nAr
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