Recording on magnetic tape media  - Page 1
Forum section: electronics / projects

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: June 07, 2021, 12:37:52 am
content: So I have yet again purchased a dead reel to reel tape deck. This time I have bigger plans for it. But I need to sort this problem. Recording on tape and playback takes fair bit of mumbojumbo. You cant just record flat and play back flat. Which is the problem I have. Now thankfully I have the graphs for these operations (both record and playback). I only need to design the active filter itself. Which is a problem since I never really did any active filters that would match the frequency reponses here in the graphs.There are two speeds as which the tape player records and plays back. Both speeds need a slightly different curve. The graphs are labeled 9 and 19 indicating the tape speed (9cm/s or 3 and 3/4ips and 19cm/s which is 7 and 1/2ips)I need to build a active filter to match these curves as close as possible while being able to switch them for both tape speeds (by relay or transistor whatever will work).I hope that there is a knowledgeable engineer here who could help me with the design of the circuit and or at least give me the knowledge to make it work. Many thanks in advance.

author: bob91343
author_rank: Super Contributor
timestamp: June 07, 2021, 02:50:59 am
content: Perhaps you are doing this as an educational exercise but you are reinventing the wheel. This has been done in analog fashion for well over a half century. The curves were devised with the limitations of analog filters in mind and so are relatively easy to implement. In analog. The final result is excellent, as seen in some of the very good recordings made when tape was the way to go.The main problems were head wear and cleanliness, and wow and flutter. Frequency response was lower on the list. One main flaw of slower tape speed was dynamic range. And poorer high frequency response. However the lower speeds had better low frequency response.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: June 07, 2021, 03:28:51 am
content: Yes I am aware of problems and things with tape recordings. I have a reel to reel that is more than due for service...so much so PCBs have delaminated to shit beyond repair. So I want to instead make my own electronics into it. Normal people would have thrown all this garbage out but not me.Perhaps this problem is simple for you but ain't for me. As I stated I have absolutely no idea how to design such filters that would do this. Preferably opamp based active ones for simplicity sake.And just a small note with new LPR35 my other tape player that I tuned up completely can reach up to 15kHz at 9cm/s and 22kHz at 19cm/s which is pretty damn good so I guess not that bad either. I will be mostly using the higher speeds but for playing back older already recorded tapes I need the lower speed corrections aswell.Wow and flutter will be taken care of since I am designing a 3 motor chassis to retrofit the old single motor one. I can do the entire tape player by myself except the filters. You would be actually pretty suprised how well can a R2R tape machine perform with good new tape. Almost digital quality (if you leave out the noise). And also the heads last actually quite a while if you use good tapes not the sandpaper ones...The frequency curves I have there are speciffic for the heads I plan to use. That is why I need to match the curves as best I can.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 07, 2021, 03:48:32 am
content: Would it not be preferable to reverse-engineer the existing design, and probably reuse sections of it, rather than design the whole thing from scratch? These are solved problems, why leave them behind (literally)?Tim

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: June 07, 2021, 07:33:46 am
content: Unfortunately no. The original circuitry used gain and noise selected transistors and I am really not able to get a hold of any of those high gain ultra low noise components... I would prefer a op amp playback amplifier for convenience sake. Someone already stated it's gonna be easy so I don't see a problem why it would be necessary to go out hunt for those pretty difficult to get hold of components...

author: Terry Bites
author_rank: Super Contributor
timestamp: June 07, 2021, 03:35:55 pm
content: Tape uses NAB to set the response. Loads of referrences out there. eghttp://blog.dddac.com/reel-to-reel-tapedeck-equalization/Here's a good readhttps://www.logosfoundation.org/g_texts/Orfeus/tape_recorders.html

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 07, 2021, 05:18:29 pm
content: Well, like what? 2N5088 isn't hard to find... JFETs, there are likely substitutes. Transistors rarely need exact replacements. Even if you drop in 2N3904s, a few dB extra noise isn't going to ruin anything.Tim

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: June 07, 2021, 06:17:16 pm
content: I would prefer to just build a active filter insteadPer manual states that the transistors were hand picked for noise and bias at the factory. Got no chance at that.Easier and more repeatable will be to just make a active filter that does what it should according to the curves. And I really dont see a reason to try to painfully recreate the old one whem as one user already said it's simple. Only If someone could help me to actually design it.Thanks.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: June 08, 2021, 01:30:10 pm
content: Quote from: Terry Bites on June 07, 2021, 03:35:55 pmAll that is absolutely great but they just mention the existence of 9cm/s speed. They don't go deep enough into the speed as the others. They only state "recording amplifier with proper equalisation". That's all there is there. Also the problem is the nit every head is the exact same. 1980s Czechoslovakian manufactured TESLA heads are pretty speciffic to their own. Lucky me I have the curves for the head. Just to design the tone correcting circuit. Which is my problem. I can make a simple band pass or band stop or a low cut high cut with op amps but with the requirement of boosting certain frequencies and leaving the other at 0dB well it has become pretty confusing to me. Same about the correcting amplifier of the playback circuitry. I have never seen or worked with equipment that would have such filters.Any further help will be appreciated. Especially if someone could please help me design a active filter for this purpose.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: June 09, 2021, 10:33:06 am
content: I wonder why everyone refuses to help..I guess that's it for this project going to the trash bin..

author: Renate
author_rank: Super Contributor
timestamp: June 09, 2021, 12:43:22 pm
content: Not much, but figure 9 here:http://www.industrial-electronics.com/aole_8.html

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 09, 2021, 01:21:32 pm
content: For archival purposes, what about digitize the signal with no equalization and then correct for it in software afterwards?

author: tooki
author_rank: Super Contributor
timestamp: June 09, 2021, 05:31:45 pm
content: Quote from: SK_Caterpilar_SK on June 09, 2021, 10:33:06 amGetting pissy after just a day or two will only put people off. Lots of us have lives outside of the forum and can’t read every thread the moment it’s posted.Take a look athttp://sim.okawa-denshi.jp/en/Fkeisan.htmI often use it to do filter math. Makes it easy to play around.Don’t forget that you can (and likely will need to) run the signal through several filters to get the curve you need, e.g. one to boost the low end and one to boost the high.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 09, 2021, 09:51:55 pm
content: You will likely find the filters are simple 1-2 order high and low pass/boost/cut affairs. They went simple in those days, and intentionally so.Since you're heart set on doing it, there's nothing left but to... go out and do it, right? Don't wait for us to catch up.Set up some simulations if you want to get a head start, or just start breadboarding passive and active filters and have a play with values, get something that plots the same. What, do you need help with tools? Just ask.We don't know what you want, and we can't do the work for you, you have to do it yourself!Tim

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: June 10, 2021, 02:13:51 pm
content: Quote from: NiHaoMike on June 09, 2021, 01:21:32 pmI thought of that too but I dont really intend to use a computer with the tape machines...while it would be great for testing the mixer final ampthat drives the record head itself but I will have to make a hardware solution for this since if I have to use my pc for record and playback well I guess ill just play the stuff from pc in the firts place.

author: jonpaul
author_rank: Super Contributor
timestamp: June 10, 2021, 03:12:42 pm
content: SK ...BRAVO to restore an old tape deck...you will learn a LOT.Many NAB and EBU equalizer designs exist, for valves as well as transistors and ICs.The technique of frequency shaping is préemptais and deemphasis.There is also a need for an ultrasonic bias current on the record head to linearize... normally ~ 40-100 kHz.The circuits are easy in analog, and the transistors or ICs do not have a huge noise requirement, as the dynamic range of a tape is perhaps 50-65 dB at best.Be patient and sendus sume photos and sketches, YOU WILL get the help you need here...Best Regards and Bon Chance,Jon

author: ccktek
author_rank: Regular Contributor
timestamp: June 10, 2021, 06:49:26 pm
content: Best of luck with your interesting project; you are certainly not the only one among us interested in tape recorder technology or resurrecting old decks.Here's a link to an online book that contains design formulas for the filters that you need. The circuits use tubes, so they need to be adapted for IC's.http://www.tubebooks.org/books/burstein_tape.pdf

author: jonpaul
author_rank: Super Contributor
timestamp: June 11, 2021, 05:48:16 am
content: SK: The post title is a bit OT...Band reject filters are either a very sharp null at one frequency or a "notch" that removes a small band, eg a DVM may use a 50/60 Hz rejection notch, or a carrier tramsmission system could have band reject filters to put a guard bands between channels.https://en.wikipedia.org/wiki/Band-stop_filterthe equalizers you seek are NOT "band reject" filters but tape head equalizers, for pre and de emphasis.http://www.ant-audio.co.uk/Tape_Recording/Library/EQ.pdfhttp://www.mrltapes.com/equaliz.htmlThe analog filters are easy to implement in any type gain device, valves (tubes) transistors, FETs or ICs.Depending on your country choose NSA, CCIR or DIN EQ.The filters are proportioned according to the tape speed, so a 3 3/4 ips will scale differently from a 7 1/2 ips tape.The commercial tape decks have switches or relays to select the EQ.The Nagra and other professional studio and cinéma decks had not only ips speed but some could allow choice of EQ thype eg NAB or CCIR.Bon Chance,Jon

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: June 11, 2021, 09:57:56 pm
content: Quote from: jonpaul on June 10, 2021, 03:12:42 pmThank you.I have three old tape decks two pieces of Tesla B115 and one B113 which was in a horrible state of disrepair. I took it fully apart properly washed everything however this is bound to be the most complex single motor chassis ever to exist in the 1980s and no matter how well ill put it together it still be a singke motor belt drive.. so I decided to scrap the insides all together.... I plan to completely redo the whole thing except the outside look. I have been sketching in fusion 360 a 3 motor direct drive chassis. If it will work out it should be much quieter and smoother in operation than the original was. This one is more of a first experiment on building a R2R tape deck before I will begin to work on a prototype that was neber actually made functional in the 1980s. Rest in piece project Tesla B135. A museum was very much interested in making a functioning one so that there would exist one working machine of a deck that was only a dream.I will have a current drive mixer amplifier that will drive the record head with 150kHz of bias. I dont really have a exact solution how ill do that but I have some ideas..VERY MUCH THANK YOU for telling me how are even these filters called. Until now I couldnt even search properly for the thing I need.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: June 11, 2021, 10:01:14 pm
content: Quote from: ccktek on June 10, 2021, 06:49:26 pmTUBE CIRCUITS??? IM INI will definitely check it out . I have a mono compact half track tube reel to reel too. Amazes me how great it sounds for its age of 57 years. However I dont really want to make a huge heads for myself yet with going full tube. Thank you.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: June 29, 2021, 10:25:42 pm
content: subject name has been changed from : "active filters for rec and playback functions for a reel to reel tape deck"Hello. I am back here. I have figured out a few things about recording with the heads I own and machines I own.First of all is that the recording amplifier frequency characteristics are mostly there to compensate for tape head losses (due to reactance at higher frequencies).Also. Every tape reel to reel deck ever manufactured to my knowledge has the high frequency bias frequency (in my case 100kHz) taken from from the erase heads with a cappacitor.. Now the important thing here I learned was never to voltage controll the heads (as they are in most tape players) but what is important here is the current. Since current generates magnetic fields Its more important to current drive such a record head to ensure that you dont get skewed results with the heads own inductance.. This would be a easy do with op amps, except when I measured my properly set up heads from a working reel to reel deck I found that the peak to peak voltage was 10-38V. Now thats just the bias voltage across the heads there is no audio yet modulated into it. So a regular op amp wont do since op amps are rated up to 30V (roughly without a rail to rail opamp its a little less). So I looked for "extent op amp voltage swing", and I have come up with the schematic down below. I am higly considering just removing the driving op amp and just building a a classic "audio" amp that I can only hope will work at 100kHz. Currents were talking here are at most I assume up to 50mA so this doesnt have to be such a high power performer.I wonder if anyone would have a different idea at this. This would essentially take the head tolerances out of the equation. Set it for current and forget it. and even if it comes to replacing the head well you have same current set still (assuming you have the same model of the head yes this would be true).Biggest bonus is that this kind of arrangement does not take the bias from the erase heads so youre not affecting the erasing.While this works beautifully in the simulator I have absolutely no trust in this working in the real world.. I want to build this just to see if I can come even close to the 100kHz mark with this contraption but I have serious doubts that it wont oscilate on itself. I wonder how would YOU make a amplifier such a purpose...to current drive a load at 100kHz mixed with the audio and into a inductive load above all. This is my one and only idea so far...if anyone has a better one and another idea how to tacle this problem well I would be glad if anyone could contribute to this.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: June 30, 2021, 12:33:04 am
content: here is my other option...good ol diifferential in the input side..I know this will need some bias adjustments so I anticipate a few changes...also there are no emitter resistors for the output transistors...just didnt want to make the schematic too large in the simulator. otherwise this would be preffered in my view.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: June 30, 2021, 01:50:14 am
content: http://hparchive.com/appnotesAN-89

author: jonpaul
author_rank: Super Contributor
timestamp: July 06, 2021, 08:41:49 am
content: Hello again, BRAVO to SK!1/ Tesla tape deck..is the OP in CZ or HU? Photos of the machine inside and out are appreciated! Very interesting.2/ Museum: Had old connexions at Nagra and StuderStuder in Regensdorf, Switzerland had a huge tape recorder museum, from the beginning. All gone now for a decade.3/ Pre/De emph: Not just for head losses, but also the physics of the magnetic circuit will result in lower signal as the frequency changes. The Pre/De results in a better SNR over the band.Similar techniques for FM radio and phono records.4/ NAB and DIN have standard pre/de for various tape speeds.5/ Diff amps seldom needed for tape decks as the head is shielded and has a floating winding.6/ Recorder side MUST have AC ultrasonic bias, to linearize the transfer curve!!! Absolutely required!https://en.wikipedia.org/wiki/Tape_biasStrongly suggest to search for tape deck electronics, and old app notes, and see some modern deck manuals eg Studer, RevoX, Nagra, Stellavox for fine transistor designs.excellent text book: Handbook of Recording Engineering by John Earglehttps://www.amazon.com/Handbook-Recording-Engineering-John-Eargle/dp/0387284702Bon Chance, and ENJOY!Jon

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: July 06, 2021, 10:18:24 am
content: Thank youThe HP AN89 document provided by Alex has been a huge eye opener to me so far. Made things that seemed so easy more difficult but clear and things that looked difficult it made look easy.My máme suggest im SK so I am Slovakian. I know for many people outside EU have no idea that czechoslovakia is not a thing anymore since 1989 ( I think) and they only consider CZ and HU as major countries. No hard feelings thought I hate this place too.About my collection of tape playersI have the Tesla B series and a Sonet Duo (half track mono full tube small deck)I have the B93, B700, B113 B115 B116.The entire series of B70 up to the CM130 is the same exact concept but with improvements over time. They have lots of problems. Mechanical and electrical problems too. Some came patched from the factory. Springs get weak overtime, rubbers get turned to black Nutella after 30-40or so years. And it has the absolute craptaculariest possible final power amplifierbut for casual feedback listening of 10W it performs rather surprisingly well.The differences between the B113 116 and 115 are theseThe B113 being the predecessor to both 116 and 115 was the father of the 11x series. It had a capacitively coupled final amp and no sensing of tape tension..and by that I mean if the tape rips the machine won't stop so no sensing on the take-up side. It has a constant torque clutch powering the take-up reel which would be fine for 13 or 15 cm reels but it's quite the stretch for 18 cm reels as the tension on the tape at the beginning of the reel (when the take-up is empty ) is far too much for my comfort levels and at the end it barely spins up the 18cm reel. BUT WAIT there is more...what if you poor soul decide to play a 13cm reel. Well the diameter of the plastic is already smaller than a 15 or a 18 cm reel. So guess what you start stretching tapes. The reason they opted to go with this instead of let's say a pressure operated clutch like various Phillips machines is because the machine was supposed to be able to operate standing up and laying down too. So you can imagine how that would play out with a pressure essentially take-up reel weight dependent constant torque clutch. These are no advanced machines whatsoever arguably its the crappest tape deck out there. They are not really worth the time u less you get it free. And not to mention that it's a absolute nightmare to tune the mechanical side of the thing ..especially the pinch roller is a absolute nightmare. And at the end of the day you find out that when the supply reel is full you have a constant feed speed but as it gets close to emptying it begins fluttering like crazy because the tension spring pulling the pinch roller against the tone shaft has gone weak. Great.Also O kimd of got carried away lol. B115 is a later version of the 113 it has a small tape tension sensor that would switch the deck off if your take up reel was not spinning for some reason or the tape got snapped, and they received the same final power amplifier but it was upgraded from a capacitively coupled one to a directly coupled one (since they now had a simetrical power supply). The B115 also recieved long life hardened headsThe B116 is essentially a B115 without a power amp. That's it. Gets the better heads but it still sucks if you don't give it the caressing hand.Besides there is a fundamental flaw with these machines...they go mechanically bad even if you treat it with upmost respect like a fragile baby... The flywheel..or as I like to call it, tremolo (it really is) eventually overtime turns into a cracked mess. The reason being is the absolute shittastic zinc aluminium casting... Overtime the zinc crystalizes in the flywheel and it's a unavoidable problem. Making matters worse most people stored the machines for 20+ years in attics or cellars where temperature swings are humongous. Guess what that makes it 10x worse..freezing temperatures though those make vibratos from the flywheel. You can literary feel the entire desk vibrating at 330 rpm or 760 rpm (the speed at which it turns) at which point you know you're getting nowhere. I'm fortunate enough to be a electronics nerd ever since I can remember my brain (and I am a 19 year old student so assume as much you want) and also I have machining experience and thankfully aachine shop not too far away from me. So I also plan to manufacture a fer replacement flywheel so I can throw the zinc aluminium garbage where it belongs...I will send some images from my computer because my phone just outright refuses to cooperate ..

author: Terry Bites
author_rank: Super Contributor
timestamp: July 06, 2021, 03:21:14 pm
content: Do you have a copy of Walt Jungs book?https://www.amazon.co.uk/Audio-op-amp-applications-Walter-Jung/dp/0672215586An oldie but a goody!seehttps://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjQrITO3s7xAhXBilwKHftmCDgQFnoECAcQAA&url=http%3A%2F%2Fwww.jrfmagnetics.com%2FNortronics_pro%2Fnortronics_silver%2Fpdfs%2FNortronics_Silvr_pp1-9.pdf&usg=AOvVaw1RVQa5BCamXSnNN1P-LevlYou'll find it interesting I'm sure.Lots of older desings used a Royer Inverter for the bias generator. A CCFL backlight controller may be a good starting point for that.

author: Dcline
author_rank: Newbie
timestamp: November 16, 2021, 07:38:11 pm
content: Congratulations on your endeavors to build a record/playback tape system. I have been playing around with Revox A77 dolby and a Ferrograph model 7 for some time. The suggestion to look at Jung's books on op amps is great and I have attached more info on this book plus some other material including some of the service manual for the A77. Seems that yo need to choose the type of tape that you plan to use if you want to get the best results. If you want to get interchangeable recordings then you will need to choose an equalization NAB, IEC DIN etc and then buy a calibration tape to get a flat playback response. Normally the calibration tape is at a specified speed ie 7.5ips and you can do some adjustment for other speeds. If you want to add Dolby B to the process there are additional circuitry requirements and calibration steps. If you get the playback side done first, you can go on to the record side. This is where your choice of tape becomes important. The tape chosen will have a "best" bias amount in the recording mode. This will balance high frequency response, distortion and noise floor. You cannot get one without affecting the others. The tape chosen will also affect the "overhead" that you have in maximum recording level. Pick a tape that you can get. My preference is Scotch 207. Good luck!