Convert cartridge output voltage to db gain

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

Hdm, I respectfully disagree. Lowering the cartridge output will make things worse. It will result in the signal being lower relative to the level of noise that is being summed onto it, presumably in the preamp stages of the integrated amp. The lowered signal level will result in John setting the volume control at a higher setting than he is presently using, which will further boost the noise (assuming the noise is being introduced at a point in the system that is prior to the volume control, which appears to be the case).

What is called signal-to-noise ratio (s/n or snr) is what is important, and what needs to be improved, either by raising the signal level prior to the point at which the noise is being introduced, or by reducing the amount of noise that is being introduced, or both.

Too much gain or too little gain is only an issue if the volume control ends up being used near the top or bottom of its range, or if the input of a component is overloaded, neither of those situations being present here, or if the additional gain comes at the expense of degraded s/n ratio in the particular design (which may be the case here).

Regards,
-- Al

Correction. The last paragraph of my previous post should have read:

Too much gain is only an issue if the volume control ends up being used near the bottom of its range, or if the input of a component is overloaded, neither of those situations being present here, or if the additional gain comes at the expense of degraded s/n ratio in the particular design (which may be the case here).

Regards,
-- Al

Hdm -- If the preamp section of the integrated amp is introducing a certain amount of noise into the signal path, how is reducing the signal level that is going into that amp going to help? Answer: It will not, it will make things worse, because the ratio of signal to noise will be degraded.

The statement that the higher gain of the new amp is exacerbating noise resulting from a cartridge/phono stage mismatch makes no sense. The signal level, noise level, signal-to-noise ratio, and distortion level of what is being fed by the cartridge + phono stage into the new amp is the same as what was being fed into the prior preamp + amp. If the new amp provides higher gain than the prior preamp + amp, the volume control would be adjusted down correspondingly, with no difference in the resulting noise EXCEPT for the difference in s/n performance of the new amp compared to the prior preamp + amp.

Regards,
-- Al

Actually, the specs on the Avatar SE indicate that its preamp section has a gain of 24db, and its power amp section has a gain of 25 dB ultra-linear and 23 dB triode mode. It also indicates "Maximum input signal: Infinite (attenuation precedes line stage)."

So with the phono stage set for 66db gain, the 0.24mv cartridge output would result in 480mv into the preamp section, which certainly will not overload it (in addition to the quoted statement, additional evidence of that being the fact that it can handle the cdp cleanly).

The 24db of available gain in the preamp section would boost the 480mv to 7.7 volts (into the power amp section) IF the volume control is turned all the way up. However, John indicated that the 2pm position provided a comfortable listening volume, as did the 10am position for the cdp.

I don't see any problem in any of that; all of these numbers, and the volume control settings, seem very reasonable.

I note, though, that the Avatar SE specs indicate 60W/channel, while John mentioned 80W/channel. John, can you clarify?

Best regards,
-- Al

Yes, there don't seem to be any published specs on the gain of the line stage or power amp section of the Avatar Super, but the manual does indicate, as with the SE, that "attenuation precedes line stage" and consequently there is no practical limit on input voltage.

And if 2.5V from the cdp doesn't overload anything, 480mv from the phono stage certainly won't.

BTW, John, if I may I thought I'd point out that Hdm, to whom you've addressed a couple of comments, is not Kal. Kal is Kr4.

Best regards,
-- Al