Reel to reel deck directly to power amp ?

Ralph hasn’t responded yet about the dbm question I raised, so I did some further research and it appears that what I said was correct. dbm in this context represents decibels above 1 milliwatt into 600 ohms. So the voltage numbers I calculated were correct.

It also happens that the 0.775 volt maximum output of the Technics deck that was referred to corresponds to 0 dbm, since 0.775 volts into 600 ohms corresponds to 1 milliwatt.

So the bottom line is that with some combinations of tape decks and power amps it will be possible for the power amp to be driven to full power, and with some combinations it will not be possible. Generally speaking a problem is likeliest to arise in cases in which the amp is high powered (and most or all of its power capability is actually required by the user, at least occasionally), since there tends to be a **loose** correlation between the power capability of various amplifiers and the input voltages required to drive them to full power. Although there are many exceptions to that, of course, where a higher powered amp may require less input voltage to be driven to full power than a lower powered amp.

Regards,
-- Al

Almarg, if you’re saying that .775 volts is enough to drive an amp, you’re more mistaken than the rest.

I certainly didn’t say that, and I was not addressing the Technics deck you referred to. (Although there are in fact some amps that can be driven to full power by less than 0.775 volts, the Coincident Frankenstein and Coincident Dynamo being examples). And for that matter I didn’t express agreement with Ralph’s statement that +4 dbm would necessarily be adequate.

Regarding Inna’s questions that followed my post, let’s wait for Ralph to confirm (or correct) my understanding of what the dbm numbers mean, which I’m not completely certain of.

Regards,
-- Al

I took a look at the manual for the Studer A810 that was mentioned in the OP. (The manual can be found at hifiengine.com if one is registered at the site).

Depending on the version of the deck and on how the magnetic flux reference level is defined the maximum output is either +10 dbm, +16 dbm, or +24 dbm. Apparently only balanced outputs (and balanced inputs) are provided.

Ralph, would I be correct in thinking that these dbm values, as well as the ones you referred to, mean decibels above a milliwatt into 600 ohms?

If so, +10 dbm corresponds to about 2.45 volts; +16 dbm corresponds to about 4.9 volts; and +24 dbm corresponds to about 12.25 volts. The lowest of those numbers won’t be enough to drive the balanced inputs of **some** power amps to full power, although it would be enough for many and probably most of them.

Output impedance, btw, won’t be any problem at all in this case, as the deck is specified as having an output impedance of 50 ohms max across the frequency range, and as being capable of driving a load impedance as low as 200 ohms. However the line-level input impedance is only 10K, which would not be optimal for some sources, especially some tube-based ones.

Orpheus10 11-13-2018

The RS 1500 puts out a max signal of .775 volts, while a good pre puts out a max of 20 volts for the power amp.

To be sure it’s clear, preamp output specs that are stated to be in the tens of volts, or even in the high single digits, represent the preamp’s maximum output voltage **capability.** A preamp’s actual output voltage will be the input voltage it is provided with multiplied by its gain (expressed as a ratio, rather than in db), and reduced by the amount of attenuation the volume control is set to provide. No preamp in any home audio system would ever be called upon to provide an output of more than a few volts balanced, and usually not more than one or two volts unbalanced.

From my point of view, this is a case of the blind leading the blind, and then running with it.

From my point of view, this comment is uncalled for as well as inaccurate. I commend Ralph for not responding in kind.

Regards,
-- Al