Convert cartridge output voltage to db gain

Ok, thank you for the responses. That does explain the volume difference to some extent. According to John's calculations, my phono stage has an output of 0.5V, while my CDP has an output of 2.5V. So, I'm guessing (since I can't find my old sceintific calculator) that I would need a cartridge with about a 2.0 mV output with 66 db of gain to make a closer match to the 2.5 V output of my CDP.

Is this correct? Or as Kal suggest, I should try changing the preamp tubes in the integrated amp? (1 12AX7, 1 12AU7)

Cheers,
John

A cartridge with 2.0mv output will need a higher input impedance than your .24mv cartridge, typically something from 10K-47K ohms. Can your phono stage provide that *without* switching to the MM inputs and reducing the gain you're trying to increase?

Even if you can get a suitable impedance without losing gain, I'm not sure I'd replace the cartridge. The higher noise floor is in the new line stage, not the phono stage or cartridge, so address that.

Your old (seperate) line stage had an acceptable noise floor with phono, the new (integrated) line stage does not. It's not really a gain issue, as already discussed. Any decent line stage should play with a similar noise floor at both 10 o'clock and 2 o'clock. Those are not extreme settings.

It's worth trying different tubes. Which will work best depends on the circuit of course, but FWIW the best new production JJ 12AX7 and 12AU7 both have a low noise floor in my preamp, and they won't break the bank.

If that doesn't help, the quality of the line stage circuit and/or the power supplies in this new integrated begin to become suspect.

You haven't described just what this higher noise floor sounds like. That might help...

Phono preamp gain computer at kabusa.com (click on phono preamps and scroll to the bottom of the page) shows you need 63 db of gain. I'm with Kal above; unless you are running a system with very low overall gain in your actual preamp further up the line (say a passive) or extremely low efficiency speakers you need less gain not more or, a lower output cartridge. Sounds like the integrated you are running has a bit more gain than the component(s) you replaced.

Once you hit into low output MC's, getting the gain right is very critical. My guess is that the "higher noise floor" you are hearing is a result of too much gain and the noise and hiss being amplified as a result of that. You might also have a very slight hardening of the sound as a result of too much gain. Go higher gain and your problems will become even worse and your sound quality will deteriorate even more.

Hi John,

I second Doug's excellent comments, and I agree with him and Kal that the noise you are hearing is most likely being generated in the front end of the integrated amp.

Re aiming for a 2mv cartridge to match the level of your cdp: The actual number is 1.25 mv. 66db corresponds to a voltage gain of exactly 2000 (20log2000 = 66). 2.5V/2000 = 1.25mv. However, that still may be high enough to unduly limit your selection of a new cartridge (if you can't resolve the problem via tube rolling), and might still lead to the kind of impedance matching issues with your phono stage that Doug referred to.

1.25mv is about 14db greater than 0.24mv. A 10db increase in level (which was your initial rough guess) would correspond approximately to a 0.75mv cartridge (20log(0.75/0.24)= 9.9db).

Another thought altogether: Although the problem is most likely in the line stage section of the amp, I'm wondering if it might be noise coupling that involves the interconnect between phono stage and amp (assuming the interconnection is unbalanced; if it is balanced that is almost certainly not an issue). That may differ with the new amp compared to the old preamp + amp, due to differences in ac-related leakage paths. Are the ac power plugs of the phono stage and amp plugged into separate dedicated ac lines, or into separate outlets or separately filtered power conditioner outputs? If so, try plugging them into the same ac source (which will minimize differences in potential between the two chassis, which might otherwise result in extraneous inter-chassis noise currents flowing through the interconnect shields, in common with signal return currents). Also try unplugging the cdp completely, to make sure digital noise it may generate is not somehow coupling into the phono signal path. And consider whether there may be any nearby sources of rfi/emi, such as dimmer switches, that the new amp may be more sensitive to than its predecessor.

Best regards,
-- Al

Thank you Doug, Kal and Al for your very informative replies. I think I have some ideas of were to head here. First let me make a few points of clarification. Kal, you are right, I looked it up, and the preamp stage in my integrated amp has 11 db more than the gain of my seperate preamp. So more gain may be a bad thing.

Secondly,I have owned this integrated for over a year now, but due to personal reasons, have not listened to analog for about the last 8-9 months. As I recall, the last I listened to this setup regularly, the noise was more apparent than with my seperates, but not nearly as loud as the noise floor is now. Doug, the noise sounds like surface noise, steady hiss, easily audible from the listening chair when I turn the volume up to my normal listening levels (70-90 db). Also thanks for the JJ tube reco Doug, I may try that.

Here are my current thoughts. First, my phono stage is the Walker Audio Signature. Walker recommends that the DC offset be adjusted monthly. When I had the rig running regularly, I checked it about every 3 months, no issues after the original adjustment. However, I have lost the manual, and can't recall how to adjust the DC offset using the supplied DMM. I sent Lloyd an e-mail yesterday and I'm awaiting a reply. I think I should check the DC offset before tube rolling. Second, once I have made sure the Walker phono preamp is in spec, if the issue still exists, change out the preamp tubes. As far as everyone has said, and I tend to agree, one of these two steps should solve my problem.

I do not expect a $6500 integrated amp to be as quiet as $20K seperates, but I do remember it being enjoyable before, so I should be able to make it enjoyable again for much less than buying a new cartridge or phono stage.

I'll keep you posted once I've heard Lloyd's reply. Thanks again for all of your help.

Cheers,
John

BTW, all cabling is single ended, not balanced.