Phono Amp Spec’s

Hi Don,  Pretty busy so wont do the arithmetic but to help you along:

20dB margin = 10X margin. 

64 dB of gain is 1500X

So calculate backwards

hope the is helpful

@viridian 

Thank you so much for sharing the link 👍

However, I don’t know if I am using it correctly.

If I plug in the following data:

1mV@5cm/sec

1.2mV of Sensitivity 

64dB of gain

8 V rms Max Output 

it seems to solve for:

50dB Otimum gain (but I could use higher if I need to, right?)

46dB of overload margin

5mV before overloading

Am I doing this correctly? I would actually have 46 dB of overload margin if using my 1mV into 64dB of gain in this phono amps? If, yes then that is far higher than the 20dB that is often recommended 👍

Somehow, I feel like I’m doing something wrong  

Any thoughts?

Thanks much!

Don

@viridian 

As I relook at your previous reply, you mention that …

Overload is 5.7mV@64dB of gain

20dB above 1mV=10mV

So, does that mean I’d only have around 10dB or less of overload margin?

if yes, then that would mean I would probably clipping the phono amp quite often, right?

Im very sorry that my brain is having trouble trying to comprehend this.

Any thoughts?

I really appreciate everyone’s help 😊

Best wishes,

Don

I don’t think you can use the kAB calculator to determine the overload margins as this is specific to your phono pre. However, if I plug in your specific figures it yields an optimal gain of 50 db, and if you go to the chart at the very bottom, this is confirmed as optimal gain is specified as 43db minimum, and 53db maximum. And realize, if your phono pre is putting out 8V as suggested, you may be overdriveing your preamp or overloading the phono preamp. And yes, I think your math’s are correct and you would only have 10db of headroom before overload.

Rather than skiing uphill, and trying to make something work that inherently doesn’t, the best options might be to buy a phono pre with the correct gain settings for that cartridge, replace the cartridge with low output at the same time as buying the Accuphase, or using a 1:5 SUT with your current cartridge and running it into the MM setting of the Accuphase.

@viridian Thank you again for your reply.  Believe me, it is very much appreciated!

I understand that the KAB is suggesting the optimal gain for my cartridge is from 43 to 53dB.

However, as @tablejockey had correctly posted above... the Benz website says my cartridge is ideally suited for tube phono amps that have 50-60dB of gain.

I have used my cartridge with phono amps that had 40dB, 52-54dB and 60 - 62dB.  I have found that "in my system" the cartridge really comes alive and is full bodied with at least 60dB of gain and it works beautifully with my current 62dB all tubed phono amp.

Based on these experiences, I was hoping 64dB would be close enough and still work well, but obviously I am concerned about the overload margins with this new phono amp.

I was really hoping to avoid the use of step up transformers, because oftentimes you may have to deal with hum - due to placement, etc.

I do have an extremely nice vintage Hirata Tango step up transformer that offers 1:6.6 ratio.  There are times when I get no hum and then other times when I do... it can be frustrating at times.... but when there is no hum - it's simply stunning!

Anyhow, I'm at a point in my life, with all of my health issues, etc I don't want anymore stress.  So, I guess that is why I'm trying to avoid using my SUT if at all possible.

Best wishes,

Don