Reel to reel deck directly to power amp ?
Yes, I was thinking about output/input match, but Ralph didn't mention there might be a problem.With any pro audio or semi-pro reel to reel, you have a volume control to control output. On my Otari 8-channel, not so easily accessed as you have to put a screwdriver though a hole in a panel. But the two channel machines have a regular volume control and are typically set to at least +4 dbm at full volume (some might be at +10); either way that's more than plenty to clip any amplifier made, and the output is robust enough to drive any amplifier made. IOW just do it :) I of course prefer tubes, and used to do this with my Ampex 351 machine. It was a bit harder, as the volume controls were on each channel and so a bit harder to adjust. But more modern machines have made that bit easy. |
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?Yes. However: 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.Usually higher powered amps have more gain. This is because they are often used on lower efficiency loudspeakers, and the gain is need both to make use of the preamp signal and also to make the voltage swing needed to drive the output devices. The result is that with a pro audio tape machine usually has more than enough drive to work in most situations. Depending on the machine, if its output is not loaded at 600 ohms, it may well make more voltage. At any rate I've run tape machines directly into power amps many times with no worries. The exception as you correctly point out is that older consumer decks often do have lower outputs, the standard for many cassette machines was 1 volt. But I think we aren't talking about consumer machines here. Next step could be asking Ralph to custom make playback head tube preamp or maybe playback head/phono stage unit, and match it precisely to his amps, and match the amps to speakers. Now that would be high end.:) We offer tape EQ in our MP-1 and MP-3 preamps and they work pretty well with our amps... |
@inna Our 30 watt amps don't do very well if the impedance is less than 8 ohms. IEC and NAB are a good idea. At 15 i.p.s., the difference is basically where the turnover is; NAB is at 3150Hz while IEC is at 4500Hz. There has been debate over the decades about whether or not bass emphasis is needed for the NAB curve and some pretty good arguments for why its not seem to win out. So the playback curve is essentially a 6db per octave rolloff; the designer has to choose where that should start. We have enough gain that we can do it at 16Hz. To use your machine for record, you would need a switch on the playback head which directs the head signal to an XLR or uses the internal electronics. To use our phono circuit for recording onto this deck, I recommend a Jensen transformer to make the match- the phono section otherwise by itself will be bass-shy driving a 10K load. |
One more cable plus transformer - this will degrade the sound. Separate phono with appropriate output impedance will be better. What is the good range of output/input impedance proportion, 1/5-1/10 or so ?Ideally 1:10 or better is the rule of thumb. It will be tricky to come up with a tube phono section that is OK driving 10K ohms. While the output impedance might look low enough on paper, the defining spec is what the output impedance is at 20Hz, not 1KHz. That is why I recommended the transformers. BTW, input and output transformers are quite common in studio gear, from whence most of our recordings come. I don't like transformers, but they have their place and when they are needed, they can be really helpful! Where will the extra cable be used?? |
