NEWBIE Q: Lowering output voltage of phono catridge - diyAudio
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Old 2nd November 2007, 01:09 PM   #1
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Default NEWBIE Q: Lowering output voltage of phono catridge

Hi Guys,

First let me introduce myself.

I'm Robert van Loghem living in the Netherlands and together with my father and brother have been building amps and speakers.

I've attached a picture of my amps and phono.

My current setup is 2 visaton speakers (soon to be replaced with scan speak ultimos), a pre-amplifier (called high-end battery powered amplifier with SRPP FET phono stage, without the battery part) and a amp called 50w power amp. All 3 taken from designs by elektuur.

and now for my quesion

For my phono i bought a new 2M blue Ortofon cartridge and i must say it sounds a lot better then my Ortofon OM 5!
But when the record gets loud it sounds distorted... Now i've looked at the specs of the catridge and it puts out 5.5mv whereas the OM 5 did 2.5.

My phono stage accepts nominal 2.5mv so that is where i think the problem lies. The output of the 2M Blue is too high for my phono stage.

Is there a way to lower the output from 5.5mv to lets say 3.5mv without damaging the sound too much (like loosing highs and such)

Changing the phono stage isn't an option because i'm using FET's, the other thing i could think of is building a new phono stage that accepts/can handle higher input voltages but that's a new project.

I can imagine using resistors 1% metal film and experimenting with them but i'm not sure.

Thanks for reading my post (and perhaps answering it)
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Old 2nd November 2007, 02:39 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

A competently designed phono stage will not clip with +6dB extra input.

However you can use two 22Kohm resistors in series as a divider.
Replace the 47K input resistor with these and take the input to
the preamplifier from the junction.

Personally I think the arm is poor and probably adding to the problem.

/sreten.
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Old 4th November 2007, 11:52 PM   #3
Gordy is offline Gordy  United Kingdom
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Default Re: NEWBIE Q: Lowering output voltage of phono catridge

Quote:
Originally posted by soundbites


... the other thing i could think of is building a new phono stage that accepts/can handle higher input voltages but that's a new project.

That really is your best solution!

Also, I would advise that you visit the Analogue section of the forum for more cartridge / phono amp related posts.

Good luck.
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Old 5th November 2007, 06:25 AM   #4
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Thanks for your answers!

I'm going to ask a friend of mine to bring his own phono-amp (cambridge audio) so we can test if it is the amp itself or some other thing.
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Old 5th November 2007, 11:09 AM   #5
SY is offline SY  United States
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I'll wager that the issue is cartridge/arm, not preamp. Have you double-checked alignment, tracking force, and antiskate?
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Old 19th November 2007, 08:45 AM   #6
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Yesterday i spent an afternoon re-checking the alignment, vta and made some very small adjustments. The alignment isn't optimal though better then it used to be (2M Blue needs at least 5 more degrees for it to be perfect)! The VTA and anti-skate is setup properly (and as a test i changed it, made it heavier and it didn't sound any different)

Now some records that sounded awful, sound properly now but there is about 10% of my record collection that is having the same problem. (distortion in the mid-freq spectrum... especially vocals)

Now my final question would be...is it that 10% of my records are crap where the sound gets loud . (e.g. Bjork - Vespertine (Track Frosti sounds very distorted)) or should i replace my TP 16 MK2 arm with something better and do you have any recommendations?

ps. perhaps this topic should be moved to the analogue section

ps2. I also tried a different phono amp and the sound/distortion didn't change, so i know it isn't my pre-amp!!! Yay!. (well it sounded less good but same distortion)
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Old 19th November 2007, 09:17 AM   #7
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by soundbites

.... The alignment isn't optimal though better then it used to be
(2M Blue needs at least 5 more degrees for it to be perfect)!....
Huh ? 5 degrees out is miles out ? /sreten.
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Old 19th November 2007, 09:19 AM   #8
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hmmmmmm......

then there's nothing else i can do but to replace my tonearm.....
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Old 19th November 2007, 09:42 AM   #9
h_a is offline h_a  Europe
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Did you try to increase tracking force?

This is usually the source of distortion during loud passages. The scale on the tonearm is regularly not correct, so don't trust that too much.

Try an increase of 0.1-0.2grams and see.

All the best, Hannes
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Old 19th November 2007, 09:49 AM   #10
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I did increase the tracking force and there was no noticable difference. (increased it from 1.75 to 2.0grams)
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