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Musical Fidelity DAC/pre & technics 1200 incompatibility gain distortion

B

Bigbobby666

pfm Member
Ongoing problem here and wondered if anyone had any thoughts:

I have a Musical Fidelity M1SDAC which is a DAC/Pre and into the aux inputs I have tried several phono stages from my technics 1200 which has an Ortofon 2m blue plug and play on it.

The phono stages I have tried are: rega fono mini a2d, musical fidelity M1LPS, and trichord Dino ii. All of these phono stages played through the MF DAC will distort when I play a record with louder recording levels (usually 45rpm singles).

Now, I have talked to Musical Fidelity and they say that the aux 'level in' is limited to a 1volt input, but they say that the Dino phono stage with its .5 volt output should not distort, they thought it was the unit at fault and advised that I return it. As I bought the MF new I borrowed another unit to test; and the same thing happened.

I have also tried the set up through another pre/amp a naim Nait 5 and through a passive amp I have: when I do this using the same record player/phono stage there is no distortion!!!

I'm kind of at a loss as to where to go next, any suggestions? Could it be the wiring in the technics? It's stock.

Cheers for any suggestions.

R
 
I thought the standard line level voltage was 2volts, seems a little odd the MF is set at 1v?

You could try attenuated cables, or phono plugs, but its not solving the problem either. I don't think the TT's at fault, although the Ortofon has a healthy output, its not unusually high either.


Can you live with a pre in the system?
 
divedeepdog said:
I thought the standard line level voltage was 2volts, seems a little odd the MF is set at 1v?

You could try attenuated cables, or phono plugs, but its not solving the problem either. I don't think the TT's at fault, although the Ortofon has a healthy output, its not unusually high either.


Can you live with a pre in the system?
Click to expand...


Hi Divedeepdog

Yup I have a set of phono attenuators -11db and they work for the rega phono, but the other stages need more attenuation.

I have a little passive pre now that works. But I bought this DAC/pre so that it could be the center of my system so really want to get it running! The less boxes the better for me!

MF said that the level is 1volt as they were only really expecting digital inputs like analogue from a TV, seems stupid to me as the obvious use for the analogue ins is to allow you to have digital music and analogue music through the same pre, is exactly the reason I bought it! They do offer a service to increase the line level to 2 volts but the guy at the hifi shop I bought the pre from advised against this route... Don't know why will have to email him!
 
Which gain setting did you use on the Dino? I've noticed (since I can monitor it) that a lot of techno vinyl seems to be cut extremely hot and will sometimes redline my ADC unless I back things off by 3dB from the calculated value, at the phono stage.

Edit: Just noticed the 11dB comment. That's a lot! I notice that the 2M has a 5.5 v output (quoted at 1KHz), are you overloading the phono stage rather than the pre with loud cuts? Not familiar with the Rega but does that offer gain adjustment like the Dino?
 
You are clipping the MF DAC's ADC input.

So you need less gain. Either an attenuator after the phono stage, a phono stage with sufficient adjustment in gain, an adjustment to your ADC or a cartridge with a more 'normal' output. Probably a combination.

The peak from a record will be within 20dB greater than the 5cm/s 'standard'. So for your cart that's an output of 55mV, which at 1kHz the MF phono stage will turn in to 6.6v, an overload of about 16dB.

Paul
 
Or you could use a properly designed for purpose preamp instead of the sales attracting "feature" of you DAC.
 
johnfromnorwich said:
Which gain setting did you use on the Dino? I've noticed (since I can monitor it) that a lot of techno vinyl seems to be cut extremely hot and will sometimes redline my ADC unless I back things off by 3dB from the calculated value, at the phono stage.

Edit: Just noticed the 11dB comment. That's a lot! I notice that the 2M has a 5.5 v output (quoted at 1KHz), are you overloading the phono stage rather than the pre with loud cuts? Not familiar with the Rega but does that offer gain adjustment like the Dino?
Click to expand...

I use the following setting:

Cartridge Loading : switch 1 on, 2 3 & 4 Off = 47K
Amplifier Gain: 1, 2, 3 & 4 Off = MM High

These would seem to be the correct settings right?

Is there any way of changing the gain to lower the output?

Image of switches here: http://i262.photobucket.com/albums/ii114/jandl100/DSCF9005_zpsfce31390.jpg
 
Paul R said:
You are clipping the MF DAC's ADC input.

So you need less gain. Either an attenuator after the phono stage, a phono stage with sufficient adjustment in gain, an adjustment to your ADC or a cartridge with a more 'normal' output. Probably a combination.

The peak from a record will be within 20dB greater than the 5cm/s 'standard'. So for your cart that's an output of 55mV, which at 1kHz the MF phono stage will turn in to 6.6v, an overload of about 16dB.

Paul
Click to expand...

Thanks Paul

Very interesting! 6.6v would then distort even if the Line level in was altered to 2 volts. Right?
 
Paul R said:
The peak from a record will be within 20dB greater than the 5cm/s 'standard'. So for your cart that's an output of 55mV, which at 1kHz the MF phono stage will turn in to 6.6v, an overload of about 16dB.

Paul
Click to expand...

Paul - thanks for the reply.

Excuse my stupidity, but could you expand this comment out slightly.

I get the jist of it but don't quite grasp the specifics.

Thanks
Rob.
 
According to that photo you have DIP 3 & DIP 4 with number 3 on - that is for an MC cart according to the instructions. Try flipping it to off :)
 
Bigbobby666 said:
Now, I have talked to Musical Fidelity and they say ... that the Dino phono stage with its .5 volt output should not distort,
Click to expand...

Hear the experts!

A Dino, nor any other phonostage, has a '0.5 volt output'. Its output is what the cartridge delivers with loud records, times the phonostage gain. And the Dino's 'MM' gain, being 48dB, is already bloody loud.


If you know someone handy with a soldering iron you can have them make up a pair of suitably-dimensioned attenuators. Or go for a phono stage with variable output control.

(Dino was made for MCs, and not really MMs, hence its bias towards loud gain settings and lack of configurable input capacitance.)
 
Had a similar problem with 2M Bronze/NVA Phono 1 combination overloading my ADC on some records and solved it making attenuated interconnects - relatively simple if a little fiddly trying to fit two resistors into a phono plug without them shorting out and with some trial and error to get the level right. I used this as a guide to how to go about it and what resistor values to use:

http://www.goldpt.com/mods.html
 
Ibbots said:
Had a similar problem with 2M Bronze/NVA Phono 1 combination overloading my ADC on some records and solved it making attenuated interconnects - relatively simple if a little fiddly trying to fit two resistors into a phono plug without them shorting out and with some trial and error to get the level right. I used this as a guide to how to go about it and what resistor values to use:

http://www.goldpt.com/mods.html
Click to expand...

Hmmmmm Interesting, well i already make my own Mogami interconnects so soldering in some resistors isn't a massive stretch of the imagination! Where did you buy the resistors from?
 
Bigbobby666 said:
Paul - thanks for the reply.

Excuse my stupidity, but could you expand this comment out slightly.

I get the jist of it but don't quite grasp the specifics.

Thanks
Rob.
Click to expand...
Magnetic cartridges produce voltages proportional to the sideways velocity of the stylus. The notional reference level is at a velocity of 5cm/s. So your Ortofon has an output of 5.5mV at 5cm/s. The highest level that can be cut is about 20dB above this, it's limited by the cutter and physics. 20dB is a voltage ratio of 10, so a voltage of 55mV

Phono stage gains are defined at 1kHz, this is a frequency in the 'flat' part of the RIAA curve. Werner says the Dino has a gain of 48dB. So the peak output of your cartridge/phono at 1kHz is 68dB above 5.5mV. Which is about 14V. You might be marginal on the Dino itself at that level, but we'll assume it's happy.

Which implies that if you want to use the Ortofon/Dino into your MF ADC with very little probability of clipping whatever the record you will need an attenuatiion of 1/14. Which is 23dB.

This may mean you end up with the volume up near max sometimes, however this is a good thing.

Paul
 
Bigbobby666 said:
Hmmmmm Interesting, well i already make my own Mogami interconnects so soldering in some resistors isn't a massive stretch of the imagination! Where did you buy the resistors from?
Click to expand...


I've recently made a few 26dB attenuated ICs with a 10K series and 510R drain - I used 1% metal films from CPC - 1/4W for the series and 1/8W for the drain. I measure them on a digital multimeter to get the pairs as closely matched as possible.
 
Paul R said:
Magnetic cartridges produce voltages proportional to the sideways velocity of the stylus. The notional reference level is at a velocity of 5cm/s. So your Ortofon has an output of 5.5mV at 5cm/s. The highest level that can be cut is about 20dB above this, it's limited by the cutter and physics. 20dB is a voltage ratio of 10, so a voltage of 55mV

Phono stage gains are defined at 1kHz, this is a frequency in the 'flat' part of the RIAA curve. Werner says the Dino has a gain of 48dB. So the peak output of your cartridge/phono at 1kHz is 68dB above 5.5mV. Which is about 14V. You might be marginal on the Dino itself at that level, but we'll assume it's happy.

Which implies that if you want to use the Ortofon/Dino into your MF ADC with very little probability of clipping whatever the record you will need an attenuatiion of 1/14. Which is 23dB.

This may mean you end up with the volume up near max sometimes, however this is a good thing.

Paul
Click to expand...

Very clear explanation, thanks Paul.
 
ultrawomble said:
I've recently made a few 26dB attenuated ICs with a 10K series and 510R drain - I used 1% metal films from CPC - 1/4W for the series and 1/8W for the drain. I measure them on a digital multimeter to get the pairs as closely matched as possible.
Click to expand...

OK so its more than simply placing a resistor between the 2 soldered connections of the phono plug then?
 
Yes, you are creating effectively a single value potentiometer - you may see it called an L-Pad due to the layout of the two resistors used.
 
I got mine from maplin, 0.6w metal film jobbies. Bought a few of each and matched them. Following the Goldpoint site, soldered R1 into the live contact on the plug and the live wire to the other end, soldered R2 between the live connector and the earth tab. stuck some heatshrink over R1 to stop it shorting out. I ended up with R1 4.7k and R2 75K which is just enough to stop the overload light from coming on in the ADC on all but the most vigorous music.
 
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