Padding down 1 input

[Thijs]

Hi all,

I hope someone can help me with the following issue.

Some background info:
Currently I'm using the Eros to drive the Stereomour which in turn is driving 99db1/w/1m sensitivity speakers.
I'm using the Dynavector 20x2H high output MC cartridge which puts out 2.8V. Volume level is very satisfactory and actually playing way louder than my Bluesound Node2 streamer/dac. At least one click louder on the coarse control, maybe even more.


I would however like to increase the signal-to-noise ratio of the analog rig as hum and tube rush come into play at louder listening levels. Which is pretty audible especially during the quieter passages of music. I've ordered the Sowter 1090 SUTs to effectively double the output of the cartridge. I would however like to maintain the same amount of 'travel' on the volume control. Maybe even extend its travel slightly. So I was thinking it would be worth the experiment to pad the input into which the Eros is playing. I could do 6db to compensate for the doubling of voltage due to the SUTs but I was thinking of taking it a little bit further to approach the digital source a little bit more. Like 10db for example.

I would like to keep the input impedance at 50k so the Eros plays into the same load as before. I've looked at the Goldpoint charts at https://goldpt.com/preattenuation.html and found that for 10db attenuation into a 50k load I would have to use R1 53.6K R2 49.9K.
Using online calculators (which are all geared towards padding tweeter units) I end up with very different values. (R1 34K R2 23.1K http://www.mh-audio.nl/Calculators/att.html)


Could someone explain to me which resistors I would need to use to attenuate the signal by 10db while also maintaining the 50k load for the Eros.

I hope I'm not too much of a bother... I've looked everywhere and just can't seem to make sense of it all. 

By the way, the Stereomour sounds wonderful with all its upgrades. It's a joy to listen to!

Cheers,
Thijs

[Paul Birkeland]

You'll have to let us know what you think of the 1090 step-ups. 

If you want to increase the SNR of the analog system, then the step-up transformers are the best way to do that. 

The Stereomour II with both the stock level/balance pot and the attenuator upgrade does not have a constant input impedance, so using a simple pad isn't necessarily going to get you where you need to go. 

Are you running out of steps on the attenuator, or are you bunched up at the bottom end of the rotation?  There are ways to increase and decrease the gain of the Stereomour circuit a little bit, and that could address that issue. 

Otherwise the simple pad just isn't so simple, unless you go with a pretty low impedance pad.  Something like a 10K pad would swamp out the problems that the level controls would otherwise cause, but it will load down the Eros. 

[Thijs]

You'll have to let us know what you think of the 1090 step-ups. 

If you want to increase the SNR of the analog system, then the step-up transformers are the best way to do that. 

The Stereomour II with both the stock level/balance pot and the attenuator upgrade does not have a constant input impedance, so using a simple pad isn't necessarily going to get you where you need to go. 

Are you running out of steps on the attenuator, or are you bunched up at the bottom end of the rotation?  There are ways to increase and decrease the gain of the Stereomour circuit a little bit, and that could address that issue. 

Otherwise the simple pad just isn't so simple, unless you go with a pretty low impedance pad.  Something like a 10K pad would swamp out the problems that the level controls would otherwise cause, but it will load down the Eros.

Thanks for your reply PB. I'd rather not load down the Eros so I might inquire about reducing gain in the Stereomour in the near future.
I'll make sure to let you know how I like the 1090 SUT. When everything is up and running I'll also have a better idea as to how much attenuation will be required.

Cheers, Thijs

[Thijs]

I wanted to get back to you and let you know my impressions of the Sowter 1090. To me, it does the job nicely. I can’t really fault it on sound quality vs improved s/n ratio.

It has made the noise level of the system at high volume much more acceptable.
I had my doubts at first since Sowter only advocates its use on low powered MM cartridges, but it suited my HOMC surprisingly well!

I’m happy! So thanks again for the recommendation.