Switches on Aleph Ono with Grado

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Currently, I only have the MM part of the Ono soldered but plan to populate the MC section as well and give the Grado Statement a try.
http://www.gradolabs.com/product_pages/statement.htm

The Ono can be set for a variable impedance of 10 to 1000 ohm but the cartridge needs an input load of 47k.

I’m a bit confused on how to set the switches or do I solder a 47k resistor in?
Perhaps I don’t need the MC input at all, given the high gain of the Ono in MM mode.
I found a post that might indicate that the previous is valid:
http://www.diyaudio.com/forums/showthread.php?postid=27218#post27218

Also, are there any particular tweaks possible to perfectly mate the Statement to the Ono?

/Hugo
 
It appears they are all from the same lot so i guess they will do fine without matching then.
Is there any advantage in paralleling even more devices?
I happen to see Sansui using six in a row in the AU-919 MC section.
In other words, what determines the amount of FETs?

/Hugo
 

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There has been an article about the noise cancellation when using parallel input devices.
In theory the noise halved every time the number is doubled, in real life it is a little less, about 5,4dB
If I remember correctly, the conclusion was that 4 in parallel has optimum efficiency (cost) 8 in parallel make sense.
Going beond like 16 or 32 would only add very little to noise cancellation.

I can send you the article if you are interested.
 
Hi Hugo,

when using the BL version you can´t use the highest gain setting. Be sure to disable that.
The cause is the Idss that is too high causing a voltage drop higher as the cascode voltage.

It is no problem as such. Mine also runs with BL´s.
Matching them is no big deal and I would do this because they do vary quite a lot. I´ve measured Idss and Vp and drew the (theoretical) Vgs/Id lines. Then used the ones that matched best.

William
 
For some unknown reason I made a recording today and noticed that the waveform was different than it has been until now.
The sound was not at all what I'm used to hear from the phono stages and when taking a closer look to the waveform I could clearly see distortion, increased in the lower octaves, say the bass region.
I connected a sinewave generator to the MC inputs and made a frequency sweep; the picture is taken at about 400Hz.
When I sweep the MM input, I get far lower distortion.
It's not my soundcard as I attenuate the inputs, the distortion remains.
I measured some voltages and instead of 15V at the drains of the input Jfets, I have 12V.
Could this be the reason? Although the problem occurred only since today and nothing really changed, I'm clueless. The only thing I did was fine-tuning the cartridge for VTA.

/Hugo
 

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hi just a curiousity:

what program/ sound card do you use to make this graphs posted in here?
it looks like a cool analysis....

Do you have external hardware to adjust the input sigal level to the input range of your sound card?


Thanks for the information and sorry for the intrusion :)
 
I had to put the –10dB jumper in place on top of the –4dB one to get a non-clipped signal.
Ahh, now I know. The cartridge has reached its final burn in cycle and delivers the full output swing of 0.5mV.
Anyway, it looks like the MC amp has suddenly decided to get more sensitive…

Nelson,

Do you have a rough idea at what input level the amp should start clipping?

Stefano,

The program is Audition, before known as Cooledit.
Soundcard is still SB Live! and all levels are set within the windows software.
I plan to upgrade soon. :)

/Hugo
 
I’m still puzzled about the gain settings.
As said, I have the –4dB and the –10dB jumpers in place.
The statement is a fairly low output cartridge (0.5mV), still without the bridges the amp clips like hell.
Not having perfectly matched Jfets for Idss, I played with the source resistors to have +/- 4mA Id on all of them.
Without the –4dB switch in place, the cascode (Q14) is saturated. I can live with that lower gain and now the Vce is 5.5V on the one channel and 5.8V on the other one.
The Drain voltage should be 15V according to the manual but mine is exactly 12V.
Here’s a part of the song La Llave from Carlos Santana’s The Swing of Delight.
Until about halfway you can see the peaks flatten out while the music itself is louder than the second part. There, the peaks reach their full potential while the music is recorded quieter.
First part is without the –10dB jumper, second part with jumper and higher input level settings on the soundcard to match the overall loudness.
Could anyone confirm these voltages and get me on the way to solve this?

/Hugo
 

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