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Tape deck impedance matching

H

Harlyquin

Anti speed-camera member
I wonder if the boffins in the DIY room can help me? I'm trying to connect a Sony TC-153SD cassette recorder to my Nait-3. Playback performance is fine, but I'm getting distortion with recordings, which I suspect indicates an impedance mismatch.

The TC-153 has a DIN record/playback socket, which has input/output impedance of 'less than 10K ohms' according to the manual. The Nait manual gives tape output impedance at 600ohms.

Its almost impossible to set the record levels, as the slightest movement on the sliders sends the VU meter needles way over the limit. Is there a simple way to sort this mismatch? - I don't want to spend a lot of time and money on it as I'm only testing the m/c prior to offering it for sale - any suggestions?
 
Originally posted by Harlyquin
I wonder if the boffins in the DIY room can help me? I'm trying to connect a Sony TC-153SD cassette recorder to my Nait-3. Playback performance is fine, but I'm getting distortion with recordings, which I suspect indicates an impedance mismatch.

The TC-153 has a DIN record/playback socket, which has input/output impedance of 'less than 10K ohms' according to the manual. The Nait manual gives tape output impedance at 600ohms.

Its almost impossible to set the record levels, as the slightest movement on the sliders sends the VU meter needles way over the limit. Is there a simple way to sort this mismatch? - I don't want to spend a lot of time and money on it as I'm only testing the m/c prior to offering it for sale - any suggestions?
Click to expand...

Have you checked the sliders to see if they are ok? I would start there with some Servisol.

Mark
 
Mark,
The sliders seem to be fine, as they work OK when recording from other sources. It's just the Nait I'm having trouble with which leads me to think its an impedance mismatch. With all the combined electronic knowledge on here I'm quite surprised nobody else has come up with any suggestions. Thanks for your anyway :)
 
The Din inputs on old decks were far more sensitive than phono types. An attenuator will be required if the Sony is to work with a modern amp. The signal from the Nait is overloading the inputs - there is nothing wrong with the sliders.

Rob.
 
Originally posted by Harlyquin
Mark,
The sliders seem to be fine, as they work OK when recording from other sources. It's just the Nait I'm having trouble with which leads me to think its an impedance mismatch. With all the combined electronic knowledge on here I'm quite surprised nobody else has come up with any suggestions. Thanks for your anyway :)
Click to expand...

Like most connection level problem solving I offered the above on the assumtion the tape deck is not new...

What is the source type and which input in the Nait?

Mark
 
Have used the tape and aux inputs. The Nait has in input impedance around 100k I think which is probably why there's no apparent mis-match problem on playback, only on record where the Naits 600ohm output seems to be overloading the 10K input on the Sony. The Sony has switchable 15/30db attenuators built-in but according to the manuel they only work with the two mike jacks.
 
Originally posted by Harlyquin
Have used the tape and aux inputs. The Nait has in input impedance around 100k I think which is probably why there's no apparent mis-match problem on playback, only on record where the Naits 600ohm output seems to be overloading the 10K input on the Sony. The Sony has switchable 15/30db attenuators built-in but according to the manuel they only work with the two mike jacks.
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Tape output @ 75mV over 600R is quite standard. That is not the issue.

Are you trying to record from cd player on one of the inputs?

Btw, when you are listening to music what is the Nait volume knob setting for non aggressive sound level from the speakers - 9 o'clock or higher/lower?

Mark
 
Btw, when you are listening to music what is the Nait volume knob setting for non aggressive sound level from the speakers - 9 o'clock or higher/lower?
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Around 11 on phono or 9 for all other inputs. Yes I'm trying to record from a CD to the Sony tape m/c.
 
I say again, The Naim will not work with the Sony.

You are attempting to connect a 1970s tape deck built to DIN european standards to a modern amp. This a bit like connecting a CD player to the MM phono input on your amp - it will cause gross overload.

Most Japanese tape decks had phono and Din inputs to cater for both standards.

The only way this combination will work is to reduce the output form the tape sockets on the Nait. Personally, I'd buy a cheap late 80s deck on ebay (even good ones go for peanuts) made to the correct standards. 30 quid should land you a decent JVC, Akai or Denon machine.

Rob.
 
Sony tape deck(cassette) specifications in the 70's is the same as with later and modern machines - namely -20db(circa 100mv) below standard line level @ 775mv=0db @ 1kHz at a tape input impedance >= 10k ohm. Additionally, the 600 Ohm output impedance on the tape deck was standard for professional tape machines(both cassette & reel-to-reel). Nothing wrong there.

The problem lies with the fixed input sensitivity on the Nait(and a lot of other pre-amp aux fixed inputs) with a CD player in that the nominal CD player output is 2vrms(2000mv) where as the input sensitivity on the Nait fixed inputs is 75mv. This gives an overload ratio in excess of 26...

For this reason I purchased the variable input level boards for my Nait to use with a CD player. This does however mean having no phono input on the Nait which for me is not an issue as the Nait is the workshop ghetto blaster. It does also mean I don't get blown out of my socks when I switch from, say, tuner to CD source.

For cassette recording I use a 32.5 with the variable level input boards, set for maximum attenuation, being fed by my CD player.

Hope this helps.

Mark

PS It does baffle me as to why this situation exists and the manufacturers have done nothing about it. Duh!
 
Thanks for the help and useful info. I think I shall give up on it for now. I havn't used the TC153 for several years, since I disposed of my A&R A60 amp which used to work with it fine. The TC153 is now a 'collectable' piece of retro audiophilia so I wanted to test it out with a view to offering it for sale.

Replay works fine into the Nait3 - no problems at all, its just that I can't record via the Nait w/o getting massive distortion. Maybe I'll be able to find another source that matches better with the TC153 inputs? I had hoped there would be a simple way to make the two work together but it seems not.
 
Originally posted by Harlyquin
Replay works fine into the Nait3 - no problems at all, its just that I can't record via the Nait w/o getting massive distortion. Maybe I'll be able to find another source that matches better with the TC153 inputs? I had hoped there would be a simple way to make the two work together but it seems not.
Click to expand...

By replay I assume you mean a tape recorded elsewhere?

Mark
 
Quick update - managed to connect the TC153SD to my Sony CD Walkman, which has a much higher output impedance than the Nait (47Kohms against 600). Recorded a CD from that and replayed it throught the Nait. Sounds really good for a 20 year old cassette deck - so off it goes to eBay :)
 
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