Mono versus Stereo reel to reel

[TIMTAPE]

Originally Posted by ben

Actually the pressure pad on these philips units can be switched in or out of use (i.e. when backcoated tape is used). It's a handy feature.

If it can work well with backcoated tapes without pressure pads, why include the pressure pads in the first place?

[DMcMahon]

I guess the pressure pads were fitted primarily for use with non backed coated tape and made removable for use with the back coated tapes that resulted in high contact friction and subsequent potential tape transport issues/excess wear. Not all back coated tapes of course have a problem being used with pressure pads.

David

[TIMTAPE]

Generally, non back coated tapes are in no more need of pressure pads than are backcoated. Pressure pads are a cost saving expedient for tape machines with an inadequate tape back tension system.

[Ted Kendall]

Originally Posted by ben

Actually the pressure pad on these philips units can be switched in or out of use (i.e. when backcoated tape is used). It's a handy feature.

I thought that widget was for dropping the tape lifters in fast wind, as it's labelled "cueing". Incidentally, the Sony 377 has no such problems, having no pressure pads, and has a scrape roller to boot.

The N4520/4522 is a different beast altogether - a sort of cheap Revox A700 clone, which performs well enough until the motor bearings fail...

[TIMTAPE]

Ted, is that the bearings in capstan or reel motors or all of them?

[Ted Kendall]

Fair point. The reel motors suffer, but the capstan motor, driving the flywheel through a belt, lasts better. The worst of it is that they are sintered plain bearings, unlike the easily replaced ballraces on the A700.

[ben]

Remember we're talking about domestic machines here, not semi-pro or pro. Comparing a Philips with a Studer is like comparing apples and oranges. The OP just want to occasionally play a handful of stereo tapes, not subject it to rigorous studio use. Let's keep a sense of perspective here!

[Martin Bush]

This has become an interesting thread, but Ben is correct.

I am imagining a small (ish) machine that will play and record acceptably and even be interesting to show visitors. I may build up a small collection of pre-recorded tapes and, if I find any old reels on my travels, see what's been recorded on them in years gone by.

The bug may bite me over time, but for now I'm looking for something I can use to play the odd tape when the fancy takes me.

I am slightly annoyed as I did get a machine a few years back and passed it on via the forum as I had not space to use it in my old house.

[ben]

Your chances of getting a stereo machine that will suit you for a reasonable sum increase enormously if you are prepared to do some work on it yourself. As a minimum, expect to do some mechanical cleaning and relubricating and changing of rubber parts. You can pick up machines in need of work on ebay all day long.

If, however, you want a fully operational stereo unit then these are more sought after and prices reflect that. You'd have to be a lot more patient!

[Martin Bush]

Thanks Ben.

I am prepared to do the kind of work you describe - I think that's within my capabilities. Where I come unstuck is electrical/ electronic work. I can solder and replace parts but lack experience in fault finding.

[DMcMahon]

One area to be aware of are machines that have multiple rubber tyred idlers, some of these may be in very poor condition (some go to sticky goo) and for the average tape recorder enthusiast not that easy to find suitable replacements.

David

[Ted Kendall]

Originally Posted by ben

Remember we're talking about domestic machines here, not semi-pro or pro. Comparing a Philips with a Studer is like comparing apples and oranges. The OP just want to occasionally play a handful of stereo tapes, not subject it to rigorous studio use. Let's keep a sense of perspective here!

Quite, a domestic machine is a domestic machine (4504 etc), but a sheep in wolf's clothing (4520) is a poor proposition for either situation.

[TIMTAPE]

Originally Posted by DMcMahon

One area to be aware of are machines that have multiple rubber tyred idlers, some of these may be in very poor condition (some go to sticky goo) and for the average tape recorder enthusiast not that easy to find suitable replacements.

David

Yes, not to mention the cost. Rubber parts perish with time,
regardless of use. This applies more to domestic machines and affects more the rare or occasional user.

[jamesperrett]

Originally Posted by Ted Kendall

I thought that widget was for dropping the tape lifters in fast wind, as it's labelled "cueing".

The pressure pad lever is on the bottom head cover while the cue lever is next to the head cover. Incidentally the N4506/4515 have a slider labelled wind speed. Most people who see it ask if it can control the weather!

[Simondm]

Just mentioning this as I don't think it's been said above:

The whole mono-stereo compatibility thing is somewhat nasty. The low-end (Akai 400-series, Sony 377, etc.) domestic reel-to-reel machines adopted the really awkward 1/4-track configuration for stereo: So if you count down the tracks going across the tape, 1 & 3 are used in one direction, allowing the tape to be turned over (without rewind) to record the other way.

I'm hoping someone who really knows will pop-up in a second, but I think this was done to make head construction easier (and thus cheaper) - there's one-track-width gap between the two heads, leaving plenty of room to put in shielding, etc., and this _probably_ makes quarter-track heads cheaper that way. They're also a bit less physically asymmetric than having both tracks on one half of the tape, so as the head wears, the asymmetry will probably cause fewer bad things to happen.

But... there are two big issues: one is azimuth adjustment, especially at the slower tape speeds of domestic machines: the one-track-wide gap between the stereo pair introduces significant timing issues if the azimuth is at all off. At best this gives weird effects in stereo, at worst you get a comb-filter effect at HF if you parallel the tracks (for mono). The other issue is crosstalk between the tracks recorded in different directions. The guard bands are small, and you're at the mercy of the setup of the machine that made the original recording.

Now that these machines are really old, I'd expect a pretty well defined wear notch in the heads. You can probably re-profile the record head to be smooth again, without dramatically affecting its electrical characteristics or performance, but replay heads are not so easy. The internal design, particularly on domestic machines, is for the pole-pieces to come together much like the jaws of flush-cutting side cutters: two bevelled magnetic poles almost touching each other. As with side cutters, if you attempt to regrind them, you'll widen the gap between the jaws as you take material away - they are one-time sharpened. It's the same with replay heads - they cannot be reprofiled without dramatic loss of HF performance. So, over time and use, the HF response will drop off as the replay gap widens.

Why does the above matter particularly? Those wear notches! If the record and replay heads weren't set to the same (correct) heights (and this isn't easy), you will have a heck of a job getting the crosstalk down, as the tape will want to follow the wear pattern, rather than the height guides that ought to be in proximity to the heads.

You can reprofile record heads (not that I've done it!) because they don't work the same way as replay heads: For a start the gap is considerably larger, and isn't anything like as critical as in the replay head design. In fact, within a range of parameters, it doesn't affect the frequency response of the system anything like as much.

Record heads are designed to have as sharp a cut-off to the magnetic field as possible. This is because recording takes place as the tape _leaves_ the head field, in the area where the flux is rapidly diminishing. The recording does NOT happen in the head gap. The short-lived 'crossfield bias' system (with a separate bias head at the back of the tape) was intended to take advantage of this, at the cost of serious mechanical complexity and inconvenience in use.

In the case of the replay head, the upper frequency limit is defined by the head gap. They might seem the same as record heads but they are definitely not interchangeable!

The other issue, this time for a record head, is how much it records into the guard bands between tracks. Poorly designed heads splattter the recording outide the track width, where it shouldn't be. So, adjacent tracks can be picked up by replay heads (predominantly at low frequency)..

So it's usual to have professional replay heads' tracks made slightly narrower than the official track width. In 1/4-track machines this becomes a challenge, because the domestic machines typically have noisy electronics, and every dB of s/n off the head is needed!

Bear in mind, too, that because of the replay head gap issue, frequency response is proportional to tape speed, for any given replay head. Double the speed and the frequency response goes up an octave (all other things being equal). So a single-track recording on a 1/4-track machine at 1 7/8" ips will probably have a poorer signal to noise than a mono cassette - the tracks are nominally the same size, but the tape of the 1/4" machine is a lot less flexible, and this will affect the machine's ability to replay the HF properly.

That said, I did a very rough experiment years ago with a Studer B67 running at 15ips - just an oscillator and known good audio test meter.

I had a bit of spare time and our maintenance department were finishing a repair job on the machine in one of our outside broadcast vans (and they did get bumped around on the road somewhat). "I wonder what the upper limit of the machine actually is..." Turned out to be well north of 35kHz record-to-replay! But that was a 1/2-track stereo machine...

... On which topic (and finally!), on professional machines, 1/2 track stereo and twin-track are not the same: 1/2 track stereo machines use 'butterfly' heads (named because of how they look from the front). There is the narrowest possible guard band, and the assumption of a little bit of crosstalk as a consequence (which, according to the idea, doesn't matter because of the large amount of signal common to both channels anyway. Stereo machines have a full-width erase head, so you cannot record separately to the two tracks*.

Twin track systems are intended for you to be able to put entirely different signals on the two tracks - they have a wider guard band and usually the ability to record independently on the two tracks. The erase head is usually split and slightly staggered, too.

You can do stereo on both, but the line-up level differs very slightly, because the signal off the twin-track heads is slightly lower.

Most domestic full-width 15ips 'stereo' machines (e.g. Revox) are actually twin-track, to give users flexibility, but there are a lot of ex-broadcast (ex-BBC Radio) machines that are stereo, and they cause some disappointment when new owners load up a twin track tape and hear horrid crosstalk! Back in the day, you could just swap out the headblock (or heads if feeling brave and having test kit and lots of time), but I very much doubt new heads are cheap now, if they can be obtained at all.

Hope that helps someone, if not the OP.

S.

*I guess you could fool a 1/2 track machine, by bulk-erasing the tape and turning off the erase head, then recording one channel at a time, but it wouldn't be easy and you'd still have replay crosstalk issues. There's a "feature' in the logicboard of the early Revox A700 I have that puts audio without bias on the record heads when the record enable button is selected for a particular channel. Yes, I was (not) delighted to find out that does wipe the recordings!

PS: bias frequency has a bearing on this too, but it's somewhat complex. To my surpise, I found that on some machines at least, the bias is actually recoverable off tape - if you hand-rock Nagra recordings (IV-S etc., whic have quite a low frequency around 30-35kHz) you can actually hear it.

[Edward Huggins]

I can't help feel that all of this is geing a bit, er, overindulged. Surely something like a Ferguson 3224 (or similar period basic Thorn product) or maybe a bit better, like a Philips 4144 (or a Philips N4xxx range product) Stereo unit with inbuit amp and speakers, is going to be ideal for Martin? Not Audiophile, but fit for purpose and relatively easy to service....and cheap starting from £10-00!

[Borderer]

Originally Posted by Edward Huggins

I can't help feel that all of this is geing a bit, er, overindulged. Surely something like a Ferguson 3224 (or similar period basic Thorn product) or maybe a bit better, like a Philips 4144 (or a Philips N4xxx range product) Stereo unit with inbuit amp and speakers, is going to be ideal for Martin? Not Audiophile, but fit for purpose and relatively easy to service....and cheap starting from £10-00!

I agree. There are probably quite a few such machines which would suit the OP's requirements and in real terms they will all have a similar performance. The problem is knowing what to avoid, and choosing a good one which isn't worn out and worth looking after.

There are some very good sticky threads here, introducing the basics of radios and record players - maybe there is scope for something similar about tape recorders?.

[Martin Bush]

Thanks for all the responses from all.

I have come to the conclusion that for my needs a mono machine would suffice. The purpose is to have something for a bit of entertainment - if I find I get into the format in a big way I may look for a better machine.

Following a bit of research I realise that I don't have the cash to pick up a stereo machine - certainly not one that wouldn't need a lot of work doing on it.

I have a machine in my sights that I have spotted for sale online. If that doesn't come off (I am not going to bid very much) I will keep searching.

[ben]

Okay. One thing though, I would go for one which takes 7" spools, many suitcase type machines only tape 5 3/4" reels. This will allow you to use a greater variety of tapes and also if you are given or find some 7" you'll be able to use them.

2 or 3 speeds would also be useful for the same reason, though if you don't have them you can still access the material by digitizing it first and slowing it in software.

4 track is perhaps more versatile than 2 track, as you'll be able to play 2 track tapes on a 4 track unit but not vice versa.

Keep us posted!

[Martin Bush]

Cheers Ben.

I have a Philips in mind that meets that description. It also has a "stereo" out socket which, if I ended up with it, I'd investigate at some point (you mention this feature elsewhere in the thread).

My dad and his friend used to get some interesting effects with the very limited features you mention when recording their own tunes - double tracking and slowed down/ sped up sounds. Primitive stuff, but effective.