Hi all,
I've identified an issue with my Uher tape recorder and I'd like your opinion. There's a problem with the audio amplifier chain. I've
eliminated all other possible causes like dirty heads or faulty tape
etc etc. So when I'm listening to playback, the quality is frequently
varying from 'pretty good' to 'really quite crappy'
...What,
in your considered opinion, is the most likely cause of this problem
and how would you go about identifying the culprit? Distorted output's
a lot trickier than a break in the signal path to track down!
Cursitor Doom <cd@notformail.com> wrote:
Hi all,
I've identified an issue with my Uher tape recorder and I'd like your
opinion. There's a problem with the audio amplifier chain. I've
eliminated all other possible causes like dirty heads or faulty tape
etc etc. So when I'm listening to playback, the quality is frequently
varying from 'pretty good' to 'really quite crappy'
Does it become good and bad at the same places each time you play the
same tape? If it does, the problen is in the recording.
in your considered opinion, is the most likely cause of this problem
and how would you go about identifying the culprit? Distorted output's
a lot trickier than a break in the signal path to track down!
Make a probe to feed the signal into on a high-impedance, high-gain
amplifier and trace the signal through the machine. Is it diistorted at
the playback head? At the volume control? At the line-level output?
At the loudspeaker terminals (you could have a damaged loudspeaker)?
On Sat, 10 Jan 2026 18:12:35 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Cursitor Doom <cd@notformail.com> wrote:
Hi all,
I've identified an issue with my Uher tape recorder and I'd like your
opinion. There's a problem with the audio amplifier chain. I've
eliminated all other possible causes like dirty heads or faulty tape
etc etc. So when I'm listening to playback, the quality is frequently
varying from 'pretty good' to 'really quite crappy'
Does it become good and bad at the same places each time you play the
same tape? If it does, the problen is in the recording.
Yes it does. But that recording still had to be processed through the
amp chain.
in your considered opinion, is the most likely cause of this problem
and how would you go about identifying the culprit? Distorted output's
a lot trickier than a break in the signal path to track down!
Make a probe to feed the signal into on a high-impedance, high-gain >amplifier and trace the signal through the machine. Is it diistorted at >the playback head? At the volume control? At the line-level output?
At the loudspeaker terminals (you could have a damaged loudspeaker)?
A scope would function in such a role just the same AFAICS., would it
not?
Cursitor Doom <cd@notformail.com> wrote:
On Sat, 10 Jan 2026 18:12:35 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Cursitor Doom <cd@notformail.com> wrote:
Hi all,
I've identified an issue with my Uher tape recorder and I'd like your
opinion. There's a problem with the audio amplifier chain. I've
eliminated all other possible causes like dirty heads or faulty tape
etc etc. So when I'm listening to playback, the quality is frequently
varying from 'pretty good' to 'really quite crappy'
Does it become good and bad at the same places each time you play the
same tape? If it does, the problen is in the recording.
Yes it does. But that recording still had to be processed through the
amp chain.
I can't follow your logic. If the tape sounds good in some places and >distorted in others - and these are the the same places each time you
play it - the fault is clearly something to do with the tape and not the >amplifier.
Turn down the volume and listen carefully to the tape transport - is it >squealing during the distorted passages? Does the tape each side of the--- Synchronet 3.21a-Linux NewsLink 1.2
head block appear to be running normally or is it shuddering because of >patches of sticky-shed? Rest your finger gently on the feed spool and
feel for any vibration, then try gently putting a bit of load on it
until the tape slows down a fraction. If it is unduly sensitive to the
load test or stops dead with little pressure, there is some sticky gunge >lurking somewhere you haven't looked yet.
[...]
in your considered opinion, is the most likely cause of this problem
and how would you go about identifying the culprit? Distorted output's
a lot trickier than a break in the signal path to track down!
Make a probe to feed the signal into on a high-impedance, high-gain
amplifier and trace the signal through the machine. Is it diistorted at
the playback head? At the volume control? At the line-level output?
At the loudspeaker terminals (you could have a damaged loudspeaker)?
A scope would function in such a role just the same AFAICS., would it
not?
Depending on the type of distortion, it might be quite difficult to see
on a 'scope but very obvious to hear through an amplifier. On a 'scope, >distortion of 10% on a sinewave will show up if you know what you are
looking for - but on complex programme material even 30% may not be >detectable on a 'scope trace. On a listening test, as little as 2% is >detectable on sinewaves and 'clean' programme material - but with
material that has been distorted for 'musical' effect, all bets are off.
On Sat, 10 Jan 2026 20:17:23 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Cursitor Doom <cd@notformail.com> wrote:
On Sat, 10 Jan 2026 18:12:35 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Cursitor Doom <cd@notformail.com> wrote:
Hi all,
I've identified an issue with my Uher tape recorder and I'd like your >> >> opinion. There's a problem with the audio amplifier chain. I've
eliminated all other possible causes like dirty heads or faulty tape
etc etc. So when I'm listening to playback, the quality is frequently >> >> varying from 'pretty good' to 'really quite crappy'
Does it become good and bad at the same places each time you play the
same tape? If it does, the problen is in the recording.
Yes it does. But that recording still had to be processed through the
amp chain.
I can't follow your logic. If the tape sounds good in some places and >distorted in others - and these are the the same places each time you
play it - the fault is clearly something to do with the tape and not the >amplifier.
Makes no sense to me, that observation. The tape is brand new and from
a well-respected manufacturer. Think about it, the signal on the tape
didn't get 'impressed' there direct from a microphone or whatever, it
had to be amplified. It had to pass through the amplifier chain and be
mixed with the output from the bias oscillator, so whatever defects
were present at that moment from moment to moment from the amp as the
tape passed, will be faithfully recorded and re-playable.
I assume we're not on the same page, so will not address your
follow-up until we're straight on this one.
Cursitor Doom <cd@notformail.com> wrote:
On Sat, 10 Jan 2026 20:17:23 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Cursitor Doom <cd@notformail.com> wrote:
On Sat, 10 Jan 2026 18:12:35 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Cursitor Doom <cd@notformail.com> wrote:
Hi all,
I've identified an issue with my Uher tape recorder and I'd like your >> >> >> opinion. There's a problem with the audio amplifier chain. I've
eliminated all other possible causes like dirty heads or faulty tape >> >> >> etc etc. So when I'm listening to playback, the quality is frequently >> >> >> varying from 'pretty good' to 'really quite crappy'
Does it become good and bad at the same places each time you play the
same tape? If it does, the problen is in the recording.
Yes it does. But that recording still had to be processed through the
amp chain.
I can't follow your logic. If the tape sounds good in some places and
distorted in others - and these are the the same places each time you
play it - the fault is clearly something to do with the tape and not the
amplifier.
Makes no sense to me, that observation. The tape is brand new and from
a well-respected manufacturer. Think about it, the signal on the tape
didn't get 'impressed' there direct from a microphone or whatever, it
had to be amplified. It had to pass through the amplifier chain and be
mixed with the output from the bias oscillator, so whatever defects
were present at that moment from moment to moment from the amp as the
tape passed, will be faithfully recorded and re-playable.
I assume we're not on the same page, so will not address your
follow-up until we're straight on this one.
My apologies, I was assuming you were playng back a tape that had been >recorded some time ago and it had recently begun sounding distorted. I >hadn't realised you were looking for the cause of distortion in the >*recording* amplifier.
In that case you need to monitor the signal going to the recording head >(preferably just before the point where the high-frequency bias is
added). If that is clean, suspect there is poor contact between the
head and the tape. The head-tape contact is far more critical on record
than on playback. If the bias is varying, that can cause all sorts of >problems but that is much less likely to be happening. Frequency
modulation of the sound by tape head squeal is another possibility, >especially with new tape that might have a manufacturing defect, or very
old tape that has begun to deteriorate.
Dirty contacts in the record/playback switch can manifest themselves as >variations in signal level and distortion and are more likley to occur
in a machine that hasn't been used for recording for a long period..
....But, the head-tape contact should be your first suspect.
My previous remarks about distortion being much easier to detect by >listening, rather than with an oscilloscope, still apply. If you have a >sinewave signal generator, that will make it much easier to hear
distortion than trying to spot subtle changes by listening to programme >material.
Cursitor Doom <cd@notformail.com> wrote:
On Sat, 10 Jan 2026 20:17:23 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Cursitor Doom <cd@notformail.com> wrote:
On Sat, 10 Jan 2026 18:12:35 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Cursitor Doom <cd@notformail.com> wrote:
Hi all,
I've identified an issue with my Uher tape recorder and I'd like your >> >> >> opinion. There's a problem with the audio amplifier chain. I've
eliminated all other possible causes like dirty heads or faulty tape >> >> >> etc etc. So when I'm listening to playback, the quality is frequently >> >> >> varying from 'pretty good' to 'really quite crappy'
Does it become good and bad at the same places each time you play the
same tape? If it does, the problen is in the recording.
Yes it does. But that recording still had to be processed through the
amp chain.
I can't follow your logic. If the tape sounds good in some places and
distorted in others - and these are the the same places each time you
play it - the fault is clearly something to do with the tape and not the
amplifier.
Makes no sense to me, that observation. The tape is brand new and from
a well-respected manufacturer. Think about it, the signal on the tape
didn't get 'impressed' there direct from a microphone or whatever, it
had to be amplified. It had to pass through the amplifier chain and be
mixed with the output from the bias oscillator, so whatever defects
were present at that moment from moment to moment from the amp as the
tape passed, will be faithfully recorded and re-playable.
I assume we're not on the same page, so will not address your
follow-up until we're straight on this one.
My apologies, I was assuming you were playng back a tape that had been >recorded some time ago and it had recently begun sounding distorted. I >hadn't realised you were looking for the cause of distortion in the >*recording* amplifier.
In that case you need to monitor the signal going to the recording head >(preferably just before the point where the high-frequency bias is
added). If that is clean, suspect there is poor contact between the
head and the tape. The head-tape contact is far more critical on record
than on playback. If the bias is varying, that can cause all sorts of >problems but that is much less likely to be happening. Frequency
modulation of the sound by tape head squeal is another possibility, >especially with new tape that might have a manufacturing defect, or very
old tape that has begun to deteriorate.
Dirty contacts in the record/playback switch can manifest themselves as >variations in signal level and distortion and are more likley to occur
in a machine that hasn't been used for recording for a long period..
....But, the head-tape contact should be your first suspect.
My previous remarks about distortion being much easier to detect by >listening, rather than with an oscilloscope, still apply. If you have a >sinewave signal generator, that will make it much easier to hear
distortion than trying to spot subtle changes by listening to programme >material.
On Sat, 10 Jan 2026 22:25:54 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Cursitor Doom <cd@notformail.com> wrote:
On Sat, 10 Jan 2026 20:17:23 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Cursitor Doom <cd@notformail.com> wrote:
On Sat, 10 Jan 2026 18:12:35 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Cursitor Doom <cd@notformail.com> wrote:
Hi all,
I've identified an issue with my Uher tape recorder and I'd like
your opinion. There's a problem with the audio amplifier chain.
I've eliminated all other possible causes like dirty heads or
faulty tape etc etc. So when I'm listening to playback, the
quality is frequently varying from 'pretty good' to 'really quite
crappy'
Does it become good and bad at the same places each time you play
the same tape? If it does, the problen is in the recording.
Yes it does. But that recording still had to be processed through
the amp chain.
I can't follow your logic. If the tape sounds good in some places and
distorted in others - and these are the the same places each time you
play it - the fault is clearly something to do with the tape and not
the amplifier.
Makes no sense to me, that observation. The tape is brand new and from
a well-respected manufacturer. Think about it, the signal on the tape
didn't get 'impressed' there direct from a microphone or whatever, it
had to be amplified. It had to pass through the amplifier chain and be
mixed with the output from the bias oscillator, so whatever defects
were present at that moment from moment to moment from the amp as the
tape passed, will be faithfully recorded and re-playable. I assume
we're not on the same page, so will not address your follow-up until
we're straight on this one.
My apologies, I was assuming you were playng back a tape that had been >recorded some time ago and it had recently begun sounding distorted. I >hadn't realised you were looking for the cause of distortion in the >*recording* amplifier.
In that case you need to monitor the signal going to the recording head >(preferably just before the point where the high-frequency bias is
added). If that is clean, suspect there is poor contact between the
head and the tape. The head-tape contact is far more critical on record >than on playback. If the bias is varying, that can cause all sorts of >problems but that is much less likely to be happening. Frequency >modulation of the sound by tape head squeal is another possibility, >especially with new tape that might have a manufacturing defect, or very >old tape that has begun to deteriorate.
Dirty contacts in the record/playback switch can manifest themselves as >variations in signal level and distortion and are more likley to occur
in a machine that hasn't been used for recording for a long period.. >....But, the head-tape contact should be your first suspect.
My previous remarks about distortion being much easier to detect by >listening, rather than with an oscilloscope, still apply. If you have a >sinewave signal generator, that will make it much easier to hear
distortion than trying to spot subtle changes by listening to programme >material.
Thinking about your very valid suggestion about using the sound rather
than looking at a waveform, I'm guessing a crystal earpiece would work
just as well rather than making up a hi-z probe+ amp would it not?
Cursitor Doom <cd@notformail.com> wrote:
On Sat, 10 Jan 2026 22:25:54 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Cursitor Doom <cd@notformail.com> wrote:
On Sat, 10 Jan 2026 20:17:23 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Cursitor Doom <cd@notformail.com> wrote:
On Sat, 10 Jan 2026 18:12:35 +0000, liz@poppyrecords.invalid.invalid >> >> >> (Liz Tuddenham) wrote:
Cursitor Doom <cd@notformail.com> wrote:
Hi all,
I've identified an issue with my Uher tape recorder and I'd like >> >> >> >> your opinion. There's a problem with the audio amplifier chain.
I've eliminated all other possible causes like dirty heads or
faulty tape etc etc. So when I'm listening to playback, the
quality is frequently varying from 'pretty good' to 'really quite >> >> >> >> crappy'
Does it become good and bad at the same places each time you play
the same tape? If it does, the problen is in the recording.
Yes it does. But that recording still had to be processed through
the amp chain.
I can't follow your logic. If the tape sounds good in some places and >> >> >distorted in others - and these are the the same places each time you
play it - the fault is clearly something to do with the tape and not
the amplifier.
Makes no sense to me, that observation. The tape is brand new and from
a well-respected manufacturer. Think about it, the signal on the tape
didn't get 'impressed' there direct from a microphone or whatever, it
had to be amplified. It had to pass through the amplifier chain and be
mixed with the output from the bias oscillator, so whatever defects
were present at that moment from moment to moment from the amp as the
tape passed, will be faithfully recorded and re-playable. I assume
we're not on the same page, so will not address your follow-up until
we're straight on this one.
My apologies, I was assuming you were playng back a tape that had been
recorded some time ago and it had recently begun sounding distorted. I
hadn't realised you were looking for the cause of distortion in the
*recording* amplifier.
In that case you need to monitor the signal going to the recording head
(preferably just before the point where the high-frequency bias is
added). If that is clean, suspect there is poor contact between the
head and the tape. The head-tape contact is far more critical on record
than on playback. If the bias is varying, that can cause all sorts of
problems but that is much less likely to be happening. Frequency
modulation of the sound by tape head squeal is another possibility,
especially with new tape that might have a manufacturing defect, or very
old tape that has begun to deteriorate.
Dirty contacts in the record/playback switch can manifest themselves as
variations in signal level and distortion and are more likley to occur
in a machine that hasn't been used for recording for a long period..
....But, the head-tape contact should be your first suspect.
My previous remarks about distortion being much easier to detect by
listening, rather than with an oscilloscope, still apply. If you have a
sinewave signal generator, that will make it much easier to hear
distortion than trying to spot subtle changes by listening to programme
material.
Thinking about your very valid suggestion about using the sound rather
than looking at a waveform, I'm guessing a crystal earpiece would work
just as well rather than making up a hi-z probe+ amp would it not?
You really need something that gives good sound quality so that you can
hear the difference when the distortion occurs. My experience of most >high-sensitivity earpieces siggests that they could give more distortion
on undistorted signals than the distortion you are listening for - so
you may not hear much difference.
If your distortion is really gross and isn't likely to be caused by the >loading of the amplifier by the earpiece itself, you might be able to
hear it and track it down by that method. Although crystal earpieces
may read open-circuit on a DC test, they have a fair bit of capacitance
and long leads, which could upset the circuit you are trying to monitor.
You haven't really described the distortion but if it sounds like harsh >bursts of sound on loud notes with almost silence in between, that is
usually an indication of a weak or failed bias oscillator. Overloading
the recording gives very sudden onset of bad distortion on loud peaks,
so watch your recording level meter closely (assuming it is correctly >calibrated).
[OT]--- Synchronet 3.21a-Linux NewsLink 1.2
Overloading would have much worse consequences if you were disc
recording; it may cause groove inter-cutting, which renders the disc
useless, or it may set fire to the cutterhead which will cost a few
weeks wages to repair (if the nitrate swarf doesn't catch fire too). As
most professional tape recording engineers either began their careers
with disc cutting or worked with disc-cutting engineers, watching the
meter becomes second nature. Turning down the volume control as soon as
the recording has finished is another useful habit, to prevent loud
studio noises from blowing up the cutterhead when not actually
recording.
No, it's not coming in bursts. As I said in my original post, it
really does sound for all the world like an old 45 vinyl record that's
been played with a worn stylus. Then a few minutes later it might be
fine again - for a while.
I made up a test tape of a 5khz sine wave using my Ferrograph deck and
played it on the Uher. I could hear the distinct difference in quality cutting in and out periodically when I played it back. I then tried to
make another test tape of the same tone on the Uher to play back on
the F'graph, but didn't have sufficiently low source impedance from
the generator in this instance so I had to use a radio broadcast
instead. Not ideal, but the distortion is still readily noticeable on
high quality audio recordings.
Hi all,
I've identified an issue with my Uher tape recorder and I'd like your opinion. There's a problem with the audio amplifier chain. I've
eliminated all other possible causes like dirty heads or faulty tape
etc etc. So when I'm listening to playback, the quality is frequently
varying from 'pretty good' to 'really quite crappy' and I'll expand on
what I mean by that. There's a distortion which comes and goes intermittently. You know how vinyl records start off life being really
great sounding, but that gets progressively worse the more times
they're played? Now imagine if you will a vinyl record which has been
played repeatedly with a worn stylus until the recording is very
noticeably impaired; scratchy and gritty sounding and you will have a
good sense of the kind of distortion we're talking about here. What,
in your considered opinion, is the most likely cause of this problem
and how would you go about identifying the culprit? Distorted output's
a lot trickier than a break in the signal path to track down!
Cheers,
CD
Cursitor Doom <cd@notformail.com> wrote:
[...]
No, it's not coming in bursts. As I said in my original post, it
really does sound for all the world like an old 45 vinyl record that's
been played with a worn stylus. Then a few minutes later it might be
fine again - for a while.
That distortion is a combination of intermodulation and
noise-behind-signal. Really severe tape squeal is the only thing I can
think of that sounds like that on a tape recording
I made up a test tape of a 5khz sine wave using my Ferrograph deck and
played it on the Uher. I could hear the distinct difference in quality
cutting in and out periodically when I played it back. I then tried to
make another test tape of the same tone on the Uher to play back on
the F'graph, but didn't have sufficiently low source impedance from
the generator in this instance so I had to use a radio broadcast
instead. Not ideal, but the distortion is still readily noticeable on
high quality audio recordings.
Have I understood this correctly?
1) A tape recorded on the Ferrograph shows intermittent distortion
when it is played back on the Uher.
2) A tape recorded on the Uher shows similar intermittent distortion
when played back on the Ferrograph.
3) The distortion occurs at the same place each time the tape is played
back and isn't related to signal level.
By elimination: 3) rules out any problems in either playback amplifier,
2 ) shows the problem isn't in the Ferrograph recording amplifier and 1) >shows the problem isn't in the Uher recording amplifier. The only
things left are the tape itself or one of the transports.
Years ago there were problems when one or two tape manufacturers
produced tape with a backing that caused squeal in pressure-pad machines >(which both the Uher and the Ferrograph are) but you would be able to
hear that by turning down the sound and listening to the tape going past
the heads.
I'm surprised the signal generator didn't have low enough source
impedance to feed a signal into the Uher; most audio signal generators
have an output impedance around 600 ohms and most Uhers have inputs of
around 600 ohms and 'high' (around 47k).
Why were you using 5Kc/s as your test tone? The second harmonic of
that, which is the first spurious frequency created by distortion, is
10 Kc/s which you may not be able to hear and which won't be recorded at
any tape speed below 7.5 ips. (Intermodulation distortion would be
audible as spurious low frequencies if there were other tones present,
but you wouldn't get them from a single sinewave tone.) I would have
chosen something around the middle of the audio band e.g. 630c/s so
the harmonics fell in the area of the greatest hearing sensitivity.
On 10/01/2026 16:35, Cursitor Doom wrote:
Hi all,
I've identified an issue with my Uher tape recorder and I'd like your
opinion. There's a problem with the audio amplifier chain. I've
eliminated all other possible causes like dirty heads or faulty tape
etc etc. So when I'm listening to playback, the quality is frequently
varying from 'pretty good' to 'really quite crappy' and I'll expand on
what I mean by that. There's a distortion which comes and goes
intermittently. You know how vinyl records start off life being really
great sounding, but that gets progressively worse the more times
they're played? Now imagine if you will a vinyl record which has been
played repeatedly with a worn stylus until the recording is very
noticeably impaired; scratchy and gritty sounding and you will have a
good sense of the kind of distortion we're talking about here. What,
in your considered opinion, is the most likely cause of this problem
and how would you go about identifying the culprit? Distorted output's
a lot trickier than a break in the signal path to track down!
Cheers,
CD
Thoroughly clean the pinchwheel. It could be accumalating microscopic
bits of ferrite embedded in the rubber. Chech one of the tapes on
another machine as if that is the case you will be corrupting all your
tapes each time you play them as the ferrite is in a sense recording or >deleting microscopically on each passage
On Mon, 12 Jan 2026 10:34:12 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Cursitor Doom <cd@notformail.com> wrote:
[...]
No, it's not coming in bursts. As I said in my original post, it
really does sound for all the world like an old 45 vinyl record that's
been played with a worn stylus. Then a few minutes later it might be
fine again - for a while.
That distortion is a combination of intermodulation and >noise-behind-signal. Really severe tape squeal is the only thing I can >think of that sounds like that on a tape recording
I made up a test tape of a 5khz sine wave using my Ferrograph deck and
played it on the Uher. I could hear the distinct difference in quality
cutting in and out periodically when I played it back. I then tried to
make another test tape of the same tone on the Uher to play back on
the F'graph, but didn't have sufficiently low source impedance from
the generator in this instance so I had to use a radio broadcast
instead. Not ideal, but the distortion is still readily noticeable on
high quality audio recordings.
Have I understood this correctly?
1) A tape recorded on the Ferrograph shows intermittent distortion
when it is played back on the Uher.
2) A tape recorded on the Uher shows similar intermittent distortion
when played back on the Ferrograph.
3) The distortion occurs at the same place each time the tape is played >back and isn't related to signal level.
By elimination: 3) rules out any problems in either playback amplifier,
2 ) shows the problem isn't in the Ferrograph recording amplifier and 1) >shows the problem isn't in the Uher recording amplifier. The only
things left are the tape itself or one of the transports.
Years ago there were problems when one or two tape manufacturers
produced tape with a backing that caused squeal in pressure-pad machines >(which both the Uher and the Ferrograph are) but you would be able to
hear that by turning down the sound and listening to the tape going past >the heads.
I'm surprised the signal generator didn't have low enough source
impedance to feed a signal into the Uher; most audio signal generators
have an output impedance around 600 ohms and most Uhers have inputs of >around 600 ohms and 'high' (around 47k).
Why were you using 5Kc/s as your test tone? The second harmonic of
that, which is the first spurious frequency created by distortion, is
10 Kc/s which you may not be able to hear and which won't be recorded at >any tape speed below 7.5 ips. (Intermodulation distortion would be
audible as spurious low frequencies if there were other tones present,
but you wouldn't get them from a single sinewave tone.) I would have >chosen something around the middle of the audio band e.g. 630c/s so
the harmonics fell in the area of the greatest hearing sensitivity.
Thank you for your observations. I had hoped to devote some time to
this issue today, but other events kind of took over, so the next slot
will be Weds afternoon.
It's a real nuisance not being able to record the test tone on the
Uher. I'm surprised as well. In fact I'm wondering if there's
something else going on there.
I'm going to follow up on your suggestion of cobbling together a hi-z
amp for probing stage-by-stage. I think I've got some FET front-ended
audio op amps somewhere in my parts stash which should be ideal for
this purpose. Can't recall what I originally bought them for, but
whatever it was never got finished, clearly!
I did notice that for some reason on the slowest speed (the 15/16"ips) there's considerable variation in the tonal reproduction with music
off the radio, as if the speed is wandering during transport. Not
noticed any such effect at the higher speeds so not sure what that's
all about. Fortunately, it's only music where it's noticeable; speech
just sounds normal and at that speed, it's really only speech that one
would use it for anyway.
Cursitor Doom <cd@notformail.com> wrote:
On Mon, 12 Jan 2026 10:34:12 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Cursitor Doom <cd@notformail.com> wrote:
[...]
No, it's not coming in bursts. As I said in my original post, it
really does sound for all the world like an old 45 vinyl record that's
been played with a worn stylus. Then a few minutes later it might be
fine again - for a while.
That distortion is a combination of intermodulation and
noise-behind-signal. Really severe tape squeal is the only thing I can
think of that sounds like that on a tape recording
I made up a test tape of a 5khz sine wave using my Ferrograph deck and
played it on the Uher. I could hear the distinct difference in quality
cutting in and out periodically when I played it back. I then tried to
make another test tape of the same tone on the Uher to play back on
the F'graph, but didn't have sufficiently low source impedance from
the generator in this instance so I had to use a radio broadcast
instead. Not ideal, but the distortion is still readily noticeable on
high quality audio recordings.
Have I understood this correctly?
1) A tape recorded on the Ferrograph shows intermittent distortion
when it is played back on the Uher.
2) A tape recorded on the Uher shows similar intermittent distortion
when played back on the Ferrograph.
3) The distortion occurs at the same place each time the tape is played
back and isn't related to signal level.
By elimination: 3) rules out any problems in either playback amplifier,
2 ) shows the problem isn't in the Ferrograph recording amplifier and 1)
shows the problem isn't in the Uher recording amplifier. The only
things left are the tape itself or one of the transports.
Years ago there were problems when one or two tape manufacturers
produced tape with a backing that caused squeal in pressure-pad machines
(which both the Uher and the Ferrograph are) but you would be able to
hear that by turning down the sound and listening to the tape going past
the heads.
I'm surprised the signal generator didn't have low enough source
impedance to feed a signal into the Uher; most audio signal generators
have an output impedance around 600 ohms and most Uhers have inputs of
around 600 ohms and 'high' (around 47k).
Why were you using 5Kc/s as your test tone? The second harmonic of
that, which is the first spurious frequency created by distortion, is
10 Kc/s which you may not be able to hear and which won't be recorded at
any tape speed below 7.5 ips. (Intermodulation distortion would be
audible as spurious low frequencies if there were other tones present,
but you wouldn't get them from a single sinewave tone.) I would have
chosen something around the middle of the audio band e.g. 630c/s so
the harmonics fell in the area of the greatest hearing sensitivity.
Thank you for your observations. I had hoped to devote some time to
this issue today, but other events kind of took over, so the next slot
will be Weds afternoon.
It's a real nuisance not being able to record the test tone on the
Uher. I'm surprised as well. In fact I'm wondering if there's
something else going on there.
Have you got the correct connections to the input socket?
I'm going to follow up on your suggestion of cobbling together a hi-z
amp for probing stage-by-stage. I think I've got some FET front-ended
audio op amps somewhere in my parts stash which should be ideal for
this purpose. Can't recall what I originally bought them for, but
whatever it was never got finished, clearly!
Easier than that: connect a piece of screened cable to the input of an >amplifier with reasonable gain and make a probe from a 1 megohm resistor
in series with a 10 nf capacitor at the free end. For an earth
connection you can use a crocodile clip, either on the end of a long
piece of wire coming from the amplifier or on a shorter piece connected
to the screen of the cable.
I did notice that for some reason on the slowest speed (the 15/16"ips)
there's considerable variation in the tonal reproduction with music
off the radio, as if the speed is wandering during transport. Not
noticed any such effect at the higher speeds so not sure what that's
all about. Fortunately, it's only music where it's noticeable; speech
just sounds normal and at that speed, it's really only speech that one
would use it for anyway.
Speed variations are much more obvious at slower tape speeds, 15/16 ips >wouldn't normally be used for music. 3+3/4 ips is the bare minimum for >domestic music and 7+1/2 ips is the minimum for professional recording.
I recorded a few folk music items at 7+1/2 ips for local radio and they
were happy enough with that - but for orchestral music nothing less than
15 ips was considered good enough for mainstream radio.
The speed variation could be caused by dirt on the surface of the
capstan or pinch wheel, or their bearings could be getting a bit tight >(unlikely for the capstan). The pinch wheel or the tyre of the flywheel >could be a bit dirty or oily - or it could have an indentation where the >machine has been left 'in gear' with the motor not running for long
period of storage. Other casues include dragging friction clutches, >unevenly-wound spools and binding in the guides.
The frequency of the speed variations and their 'waveform' can often
give a clue to their cause. Does the speed vary smoothly and
sinusoidally (unven pinch wheel) or does it 'hiccup' slightly (dirt or >indentations)? Watch the rotating components and try to work out which
one's rotation corresponds to the speed of variation.
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