Hello,
I have a Lyrec Fred reel2reel tape recorder with a noisy head preamplifier , noise is picked up by the digital circuits that controls the tape transport (sounds like a very week "modem audio" like sound) . The design is like this from the factory since this recorder is intended for editing (tape splicing, no recording is possible) . The preamplifier is using NE5534 which is quite good , what options do I have to filter out the digital noise from the digital ciruits? should I use an isolated power supply for the preamplifier to isolate the didgtal ground ? attached is schematics of the preamplifier and the entire schematics of the unit
Thanks
I have a Lyrec Fred reel2reel tape recorder with a noisy head preamplifier , noise is picked up by the digital circuits that controls the tape transport (sounds like a very week "modem audio" like sound) . The design is like this from the factory since this recorder is intended for editing (tape splicing, no recording is possible) . The preamplifier is using NE5534 which is quite good , what options do I have to filter out the digital noise from the digital ciruits? should I use an isolated power supply for the preamplifier to isolate the didgtal ground ? attached is schematics of the preamplifier and the entire schematics of the unit
Thanks
Hi hafrse,
This may be a very challenging problem.
Your idea to use an isolated supply may be the quickest experiment for a possible solution. You could remove/open connection to transistor T1 and connect a battery for supply to the 11V head opamps rail. (eg a 9V battery plus one or two 1.5 batteries to yield about 11V or 12V.) But I'm a bit pessimistic that this will resolve the problem. If noise persists, then a next experiment: try disconnecting any shielded cable leading to the tape head and installing a short across C4. This should establish the lowest noise connection to the head amp easily obtained; if interference is STILL objectionable, then there are likely grounding/routing issues across the deck chassis.
Is the noise present only while the tape is in motion? I believe the tape position display may be multiplexed, a possible interference generator. Can you determine any correlation of the interference with operation? You may be able to route the tape directly reel to reel, without tape passing through the heads. This might allow you to stall the reel motion for insights into sources of noise generation. Keep us updated.
Good luck!
This may be a very challenging problem.
Your idea to use an isolated supply may be the quickest experiment for a possible solution. You could remove/open connection to transistor T1 and connect a battery for supply to the 11V head opamps rail. (eg a 9V battery plus one or two 1.5 batteries to yield about 11V or 12V.) But I'm a bit pessimistic that this will resolve the problem. If noise persists, then a next experiment: try disconnecting any shielded cable leading to the tape head and installing a short across C4. This should establish the lowest noise connection to the head amp easily obtained; if interference is STILL objectionable, then there are likely grounding/routing issues across the deck chassis.
Is the noise present only while the tape is in motion? I believe the tape position display may be multiplexed, a possible interference generator. Can you determine any correlation of the interference with operation? You may be able to route the tape directly reel to reel, without tape passing through the heads. This might allow you to stall the reel motion for insights into sources of noise generation. Keep us updated.
Good luck!
@BSST : thanks, I will try to perform the steps proposed. The noise is also present when the tape is not in motion , the digital circuit is running all the time (this is a special unit dresigned without a pinch roller, and the digital circuit is performing regulation all the time )
@kevnkr: Please move this thread to the analog source forum , many thanks in advance!
@kevnkr: Please move this thread to the analog source forum , many thanks in advance!
Appears the 12V digital supply also runs the analog circuit through an amplified capacitor filter.
Separating the analog and digital circuits with individual supplies should help.
Separating the analog and digital circuits with individual supplies should help.
It has a high resolution tachometer in the left roller, search for LYREC FRED you found more information 🙂
The oscillators for the erase head seem to be powered on and running even when not erasing a tape. You could simply remove power from the whole erase amp, by cutting a trace. If that fixes your problem, then, good.
The oscillators for the erase board is embedded in the preamplifier board (same board) , If I remove the digital control board for the tape transport , then the preamplifier is very quite. Noise is from the digital control board.
Two completely separate supplies should help, if there's room for a second small transformer.
Look out for digital board ground interconnections with the analog circuits.
Try adding an insulated, grounded shield under the digital board if it seems more radiated.
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If there is poor execution of grounding and/or isolation, separate supplies may not help. After all, the cap multiplier (T1, C1, etc.) and the supply rejection offered by the opamp should both help with supply noise suppression. Some experimentation to establish the path of noise ingress might point the way...
^This
Do you have a current limiting lab PSU? I think you could be surprised by the multitude of ways that logic can introduce noise into analogue paths, particularly ones that might be designed for a high-ish impedance such as a tape head. The noise can get in conductively, capacitively - and a combination of both. I would not spend the time lashing up an auxiliary PSU without working out where (and if) it's needed first via a lab PSU. The chances are that the hash is getting in via 0V somewhere, but don't take anything for granted. You may need to do some careful tracing of the 0V paths, working out where different branches meet. With digital junk, simply ensuring every 0V return meets back at the PSU common 0V may not be enough (although bearing in mind tape's inherent hiss, it likely will be here). Digital hash can be insidious and tricky to isolate from analogue paths. A lab PSU and a bleeper will be your friends here.
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That reel to reel was once as quiet as possible , otherwise nobody was able to sell it given the fact it was aimed for professionals.It was an editing machine with playback capabilities.You should find what's wrong with it first , not modify.Look for a disconected or poorly connected shield to ground first.
Signal bleeding can take place in several ways.I'd check the tapeheads alignment cause usually the tacho signal needs to be recorded either perpendicularly to the play track or on a different track.Are the recording of tacho signal and music done on the same head as well as the their playback?
Unfortunatly not, this reel2reel was intended to be used for tape splicing and erasing , it was not quiet from the beginning and not a proffesional Audio unit but used by broadcast stations
At first i thought so as well, but this logic is somehow flawed because everything you record on tape stays there until it's erased.Broadcasting equipment has to have a special filter for that tacho signal if it can be read by the playhead and that would be possible only if there was a standard approved by the whole industry which I doubt it was orall the broadcasting equipment is done by Lyrec ...
I might be wrong, but I still think that recorder should provide a clean signal if it was made for audio.If it was for other purposes that I have no ideea.
You first need to know exactly how the digital and analog signals are recorded, played and filtered from any digital carrier.
I am going to fight a 8 track fostex 08A soon myself and nothing works well with that unit... Tape units aren't that simple to debug.
I might be wrong, but I still think that recorder should provide a clean signal if it was made for audio.If it was for other purposes that I have no ideea.
You first need to know exactly how the digital and analog signals are recorded, played and filtered from any digital carrier.
I am going to fight a 8 track fostex 08A soon myself and nothing works well with that unit... Tape units aren't that simple to debug.
At first I also thought a standard tone had to be recorded onto the tape as a reference signal that would be sensed at playback. Now, I don't think so. I now think the supply and take-up spools tension the tape so that it is held in contact by friction against a freely spinning roller with a speed (tachometer) sensor. Very clever and elegant. Unless I'm completely out to lunch. 🙂
Are there any specs regarding residual noise? How far below typical playback level is the interfering background noise in dB?
Are there any specs regarding residual noise? How far below typical playback level is the interfering background noise in dB?
It may be a Danish thing? Swedish? I have seen it on other Danish/Swedish drawings.
https://www.gyraf.dk/schematics/ntp-179-270_schematic.jpg
https://www.gyraf.dk/schematics/NTP_179-140_Manual.pdf
https://www.gyraf.dk/schematics/NTP_179-160_Compressor.PDF
http://www.hansenaudio.se/Active DI box 1975.jpg
http://www.hansenaudio.se/Phantom PSU.jpg