question about using an old reel to reel as a preamp

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Mac:
That is a goodly amount of hiss.  

Are you positive that it uses tubes for the mic preamps?  Very well might be solid state transistors in that section, could possibly be a hybrid design.  I don't remember all the Roberts/Akai decks and circuits that well, although at one time I worked at a joint that did warranty work on 'em, they were a lot newer back then, of course, and we really didn't see all that many of them, come to think of it.  Built like tanks.  

It is indeed warm sounding, but not as warm as one would suspect of an all tube mic preamp.  

One way to tell is to turn it off, let it cool for an hour or more, with the mic and everything still hooked up, then start a recording on the daw, power on the recorder and see if you can record immediately or have to wait several minutes for tube warmup.  If its instant on, then the preamp is certainly solid state.  

Remember this too:  Noise in audio is a ratio.  

Laymen's terms, what that means is the hiss at the beginning and end of a recording where there's silence, will be a lot greater sounding than that same hiss once the music starts.  Easily handled in the DAW with and Audio Editor, highlight the silent heads and tails and turn them into total silence.  Then play it back and see the difference.  

That's why we always must refer to it as the Signal-to-Noise Ratio.  

The hiss might be more than 60dB down from the actual music level.  That's a lot.  

What that means is that it is difficult if not impossible to detect the hiss once the music content starts.  

Check that thing out to see if it is really a tube mic preamp in there, though.

"I just snagged a Roberts 1630 (better known as Akai 1710)"  -- if you beat me to digging up an online schematic, or even circuit description, post it here.  


--Mac

Mac:
[!--quoteo--][div class=\'quotetop\']QUOTE[/div][div class=\'quotemain\'][!--quotec--]
The 1700 (ca. 1966), the 1710 (ca. 1968-ca. 1970) and the 1720W (ca. 1970-ca. 1972)

These recorders are tube models. Although the 1700 only has one VU meter they are stereo sets. Like I mentioned earlier they all have a built-in main amp and built-in speakers. Both 1700 and 1710 have 4 speeds. The "W" behind the model number means this recorder has a wooden case. The "L" behind the model number means this recorder has a wooden case with leather finish.
The 1720W is an alternative version of the 1710W without tubes but with the older germanium semi- conductors which means it's a "solid-state" machine. The 1720W has a 6W built in power amplifier and built-in reel retainers.[/quote]

[!--quoteo--][div class=\'quotetop\']QUOTE[/div][div class=\'quotemain\'][!--quotec--]
The 1700 (ca. 1966), the 1710 (ca. 1968-ca. 1970) and the 1720W (ca. 1970-ca. 1972)

The 1700 is strictly a Tube recorder; the 1710 has tubes and also a few transistors. The 1700 only has one VU meter which can be switched between the left and right channels, so they are stereo sets. Like I mentioned earlier they all have a built-in main amp and built-in speakers.

Both 1700 and 1710 are 4 speed capable by changing capstan sleeves and pinch rollers. The "W" behind the model number means this recorder has a wooden case. The "L" behind the model number means this recorder has a wooden case with leather finish.

The 1720W is an alternative version of the 1710W without tubes but with the older germanium semi-conductors which means it's a "solid-state" machine. The 1720W has a 6W built in power amplifier and built-in reel retainers.
[/quote]

soul&folk:
Thanks for looking into this for me Mac.

It seems I have the equivalent of the Akai 1700 and NOT the 1710 which I read somewhere, because there's only one VU meter on mine with a switch. So if the information you cited is correct I have 2 all tube preamps. -- Looking into the back of the unit I saw a large transformer and 2 small transformers, there were 3 tall tubes and 2 shorter ones withe metal sleeves on the shorter ones. --- Also, when the unit sat for a while, the sound seemed more robust, if that makes sense. I think that would also indicate that the pramps are being powered by tubes, right?

I received the dual channel phantom power supply today and if I can I'm going to try and record something with better mics that I believe are quite a bit hotter than what I used yesterday. This should be the litmus test I'm looking for as I can turn down the volume of the Roberts when I record some more. The recording you heard had the volumes set at 3 o'clock. If I can bring it down to 12 o'clock that would help a lot.

- BTW, when I removed the hiss from the opening few seconds I attempted to change the entire track using the noise level the program had arrived at based on the first seconds. Bad idea! Good thing for undo! It sounded like it had gone through a phase shifter. So my second attempt was to do that again but remove less noise. But I was still removing some of the dynamics of the song in the process of removing the noise. I removed the signal and the noise. Not too smart, eh? - Based on what you just said I need to just select the opening and completely remove the noise. Same with the final few seconds of blank sound. And then leave the rest alone. That's where signal to noise comes in, right?  - I'll have to experiment and see if that's going to work. A lot of my music is finger picking on acoustic guitar without much else going on in the mix. The hiss might be noticeable. We shall see.

Mac:
1)  Do not use noise reduction algos here.  Simply do what I told ya, highlight the silent areas and make them silent in the audio editor.  You can do that by simply invoking a gain change, turn the gain all the way down as far as the software can in that area and done.

2)  Find out what the two small tubes covered by the shields numbers are.  Hopefully they will be readily available tubes like the 12AX7A, 12AU7, etc.  Try replacing both with new.  

3)  The fact you say it brightened up a bit after running may indicate that the thing has been sitting idle a long long time, very likely is the case, the tubes may well have some gas in them, running them heated up the getters and absorbed a bit of the gas.  Try replacing the tubes, also try leaving the thing on and idling 24/7 for a day or two and then try another recording, see if the thing sounds  tad nicer after that.  The capacitors may also get reformed by letting it sit and idle like that, too.


--Mac

soul&folk:
Quote from: Mac

2)  Find out what the two small tubes covered by the shields numbers are.  Hopefully they will be readily available tubes like the 12AX7A, 12AU7, etc.  Try replacing both with new.  


The smaller ones are NEC 4X

The taller ones are

one NEC 48

and two NEC 49

are these the equivalent of another name perhaps? are these available

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