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Ortofon carts are too hot for my phono preamp?

When I need hardware advice, I always come to Audiogon for the true experts.  Thanks in advance and happy Easter!

So after much trial and error, I THINK I have deduced that my Ortofon 2M Bronze and 2M Black cartridges are too hot for my Avid Pulsus phono preamp.  Some softer recordings are fine, but I think I am hearing some distortion with loud transients and even sometimes on relatively loud vocals.

I have a Pro-ject tube phono preamp I swap in and I don’ t hear that distortion. I never hear that distortion with other sources. 

Given my investment in 3 Ortofon 2M carts (1 Bronze, 1 Black, 1 Black SE) and the Pulsus, is there anything I can do to step down that signal from the carts without doing any damage to the sound?  

Any other thoughts?

(BTW the 2 turntables I am using are a Rega P3/24 and an older Rotel.  Meridian preamp has variable gain settings on inputs and I can hear the distortion at any setting.)

jji666
jji666 OP
589 posts
 

Actually, the math above was helpful.  I just set inputs on the preamp to 2.8v - up from 2.0. If the Bronze and the Black are really closer to 8mV then 2.0 was too low. 

Checking now to see if there is any improvement. 

billstevenson
579 posts
 

I know this is kind of a crazy idea, but desperate times call for desperate measures and all that.  What you need seems to me is a bit of line loss between the cartridge(s) and the phono stage.  Do you have an extra long set of phono cables you could try?  I have a set that I use for my subs, for example, that reach across the room.  If you have something like that you might give it a try just to see if it helps.  The guy I get all my wires from could make a set of special phono cables that would provide the mathematically correct amount of resistance to get the job done.  If you have a guy like that you might give him a call.  If you want my guy's contact info send me a private message.

jji666 OP
589 posts
 

Thanks!  Well I suppose a passive line stage would be similar. I do worry about loss of quality with such measures. 

lewm
13,688 posts
 

Bill, Not a good idea because of capacitance.  Capacitance will cause a HF roll off probably before you notice a loss of gain. That’s throwing the baby out with the bathwater.

"I just set inputs on the preamp to 2.8v - up from 2.0."  What does that mean? And are you referring to the phono stage or to your linestage?

If the cartridge actually puts out 8.6mV RMS at 5 cm/sec, that is quite a bit off of the factory spec of 5mV, presumably representing peak to peak voltage. "RMS" voltage I think if memory serves is calculated by dividing the peak to peak voltage by 1.414 or square root of 2.  That means peak to peak V was higher than 8.6V.  I don’t get it; I doubt Ortofon specs would be that far off from reality. Then I found this on the Steve Hoffman forum:

"Recently, I have attempted to make sense of some conflicting measurements of the output voltage of various phono cartridges from different sources. The infamous one here are the measurements of the 2M Black in particular, comparing the results of HiFi World (HFW) with those of Miller Audio Research (MAR). I ended up emailing HFW and got a response from them that may explain the discrepancy.
To recap, HFW said the output of the 2M Black measured at 8.6mV (5cms/sec). From my email exchange, it appears they actually measured at 3.54cms/sec and "converted up" to 5cm/sec. MAR’s test said 5.79/5.73mV (L/R 5cms/sec).  HFW thinks the difference is due to different test records (yes, I’ve experienced that) but also the differences between peak vs. RMS standards for measuring the output. Of course that wasn’t mentioned as far as I can see in either test result.Using a quick conversion calculator, it looks like 8.6mV peak voltage is equivalent to 6mV RMS. That’s pretty close to the MAR results, so this appears to make sense."
The next post says that HiFi World (HFW) probably erred in labeling their result "RMS".  So their number should be divided by 1.414. In other words, the HFW value of 8.6mV is probably not an RMS voltage and is in other ways erroneous.  Stick with the idea the 2M Black makes 5mV, like Ortofon says it does. Even the above explanation of why the HFW value is wrong is fuzzy.
 
 
jji666 OP
589 posts
 

"I just set inputs on the preamp to 2.8v - up from 2.0."  What does that mean? And are you referring to the phono stage or to your linestage?

Referring to my line stage, just in case the distortion was happening there.  It may actually be both,  in the sense that the hotness of the cart combines with the high gain of the phone preamp to create a cascade of distortion issues. 

I don't think it is an alignment issue, in the sense that it happens with two different TTs and I recall having had this issue for a long time - I just hadn't focused on vinyl for a number of years and am now re-living what I had thought was the issue years ago. 

The challenge is that I really do not want to waste my investment in all of these 2M carts or in the Pulsus phono stage.  But they don't seem to like each other too much.  The Pro-ject phonostage sounds OK...but it isn't at the same level that the Pulsus is "supposed" to be...at least judging by price and reviews.  

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