I can't change the title so I make here an update on the topic which abandoned the initial Telefunken deck mods in favour of a Denon DRM 700A.
have this deck for about 5 years, never used , not even tried it until today...I suspect it wasn't used for at least 20 years before that.It's manual specs...modest.It's transport...simple and modest, but in working condition right out of the batch. It's sound right out f the shed : although a bit too much hiss when no noise reduction is used really f... good and I mean it! The needle vu-meters...hypnotic. It's schematic... discrete for most of it leaves some room for improvement and it's also a very serviceable deck.
You can find a lot of photos and videos over the internet on it.The Tapeheads forum would probably be the place to discuss it...but I am going to start working on it right here.Replacing a lot of capacitors...no problem.A taste of the 70's cassette deck technology guaranteed.Any good suggestion appreciated.
I have much better decks in terms of specs and functionality except having a Hicom NR system, but not many that are much better good looking.I think it deserves all my attention.Possibly my germanium headphones amp will find a place inside..
Although the tapehead looks like a very nonlinear one in need for too much damping, I think this guy has a lot of potential.
There's also an ideea I might wanna try as I never heard anyone trying it and the playback section already suggests it can be worked that way: trying to make it a total current feedback damping design.Not sure I have the right ideeas at this moment, but something makes me think it's a better way to work with highly nonlinear tapeheads.I really welcome any ideas heading that way or better.
have this deck for about 5 years, never used , not even tried it until today...I suspect it wasn't used for at least 20 years before that.It's manual specs...modest.It's transport...simple and modest, but in working condition right out of the batch. It's sound right out f the shed : although a bit too much hiss when no noise reduction is used really f... good and I mean it! The needle vu-meters...hypnotic. It's schematic... discrete for most of it leaves some room for improvement and it's also a very serviceable deck.
You can find a lot of photos and videos over the internet on it.The Tapeheads forum would probably be the place to discuss it...but I am going to start working on it right here.Replacing a lot of capacitors...no problem.A taste of the 70's cassette deck technology guaranteed.Any good suggestion appreciated.
I have much better decks in terms of specs and functionality except having a Hicom NR system, but not many that are much better good looking.I think it deserves all my attention.Possibly my germanium headphones amp will find a place inside..
Although the tapehead looks like a very nonlinear one in need for too much damping, I think this guy has a lot of potential.
There's also an ideea I might wanna try as I never heard anyone trying it and the playback section already suggests it can be worked that way: trying to make it a total current feedback damping design.Not sure I have the right ideeas at this moment, but something makes me think it's a better way to work with highly nonlinear tapeheads.I really welcome any ideas heading that way or better.
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The real reason I want to work on this deck is that the output level on the headphones as it has no volume pot is the exact volume i wanna hear when listening to a tape: loud and clear.At least for the playbacl signal treatment the electronics is pretty much identical with their better RC200, RC300 models .
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Here's the lesson of the mindless recaps: replaced all the filtering and some of the decoupling caps and ALL of the original ones measure as new.I mean it, the original 42 years nichicons are as they were made yesterday.So I'm gonna use them to recap more expensive decks 😉
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More crazy things happened ...more caps replaced op-amps replaced with opa2132 and 2134 for now.Better highs...a bit too much boomy base due to the use of 4.7uf and 2.2uF instead of 2.2uf and 0.47 uf here and there...it seems that the frequency response was rigged to have way more base than highs so that a final output cap of 22uF is absolutely fine for 250ohms headphones helping the op amp.I probably need to make the headphones amp gain a tiny bit lower too.Enjoying some Richard Clayderman before going to bed....
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Seems like the true gate to Sparta is the coupling cap into pin 7 of U401, but looking into Nakamichi highcom2 manual for a "refference" I saw they used this chip very differently.Couldn't find a datasheet to u401...going to 0.15uf input cap into highcom chip as in rc 300and hc3000.
Yeap...0.15uF made it .Next step...make it cool! Its tiny heatsink for the cap multiplier was hot after just 1 min of working.I have the feeling that this deck wasn't used more than 20 hours before me.So I'm replacing the original cap multiplier made of two trz with one darlington trz.Possibly adding a third trz ksc1845 to make it a triplet if needed, but I don't see that need yet.The pnp darlington is placed there just to hold the two heatsinks one against the other.Not sure yet if I'll give it a meaningful life...I might try the ESP Szikai cap multiplier.I will add another transformer for the motor as I plan to put those secondaries in series for a phono stage supply .
There's too much empty room in this deck...
There's too much empty room in this deck...
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The real mods are comming next.At the moment I just placed the new darlington trz for the cap multiplier on a huge heatsink in order to get the heat out.Next step is to place a separate 9 v transformer outside the deck for the motor .
Kendall Castor Perry's phono preamp will be tried and placed inside to replace the microphone inputs as it was simm'd a few years ago and exhibited trully remarcable performance.The original tape head preamp is really noisy by itself and will be transformed into the phono preamp while the tapehead preamp will be using an opa2228...
https://www.linkedin.com/posts/kend...=linkedin_share&utm_medium=member_desktop_web
James Last sounds unbelievably good...although a bit of noise is there undoubtedly...yet the drums are killing me!
Kendall Castor Perry's phono preamp will be tried and placed inside to replace the microphone inputs as it was simm'd a few years ago and exhibited trully remarcable performance.The original tape head preamp is really noisy by itself and will be transformed into the phono preamp while the tapehead preamp will be using an opa2228...
https://www.linkedin.com/posts/kend...=linkedin_share&utm_medium=member_desktop_web
James Last sounds unbelievably good...although a bit of noise is there undoubtedly...yet the drums are killing me!
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I gave up on improving this deck .It's hopeless.It's first stage collector current asked for a lm394 which I wasn't ready to sacrifice on it .So I took out all the electrolitics to recap a more modern design, the Denon DRM 700.I have it for 3 years with a damaged door, so I won't be able to sell it soon.As it looks like a stripped version of a better deck I also started to change all the low quality non polar caps in all the filters , damping caps, etc...Just trying to see how good the cxa20187 really is. First op amp m5220 replaced with opa2228, second and third ba15218 replaced with opa2132...
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The main difference was that Nakamichi divided the audio band into two per xover networks and used four (!) Telefunken U401B High Com chips instead of just one or two.
No wonder about the availabilty of U401B datasheets: Telefunken launched their High Com system in 1978 and initially gained some success over Dolby B, which was the predominant mass market noise suppressor system in those days. High Com was superior in terms of noise reduction (-20 dB vs. Dolby's -9 dB), but suffered from other issues, caused by it's broadband operation (Dolby B only worked in the higher audio frequencies). Anyway, in 1980 Dolby Laboratories launched their Dolby C which could reduce noise almost as much as High Com (about -16 dB), but didn't suffer from High Com's issues. In the end, as we all know Dolby C became the predominant noise suppressor for consumer cassette decks, displacing everything else, including Telefunken's High Com. Consequently, U401B chips only were produced during a very low number of years and are quite forgotten nowadays.
In the early 1980ies I've had an external DIY HobbyCom unit that per description/build instruction could be adapted to any cassette deck or reel2reel. I have to admit that I never managed to get it operating satisfyingly.
Best regards!
Thanks for your comments! Truth is that there's very little feedback and review on Highcom, most of it being in German and Google still finds difficult to show german sites unless I type in german words which I barely know any, yet some say Nak's highcom 2 didn't suffer of dbx2 breathing, but it went down DBX 150 path which split the band in three having no pumping either. Others dare to say the most professional Dolby SR was a Telcom c4 in disguise...but I have no proof of that andthey were aimed at high speed professionsl transports anyway.
Now if you go into professional product range you don't see a reason in using a cassette at 4.76cm/s.
The best half breed try I saw was a Fostex 24 track 1 inch dolby S reel to reel, but that came too late.
Highcom2 on the other hand had the same problem as all Telefunken cassette decks and Toshiba's ADRS AD4 or 5.It wasn't a 3header unit offering no monitoring .You'd need thus 8Highcom chips for a serious recording session that would allow real time monitoring.That means that I'd need to buy 4 separate functionsl telefunken cassette decks to build a good highcom system which I simply can't even think of...
Asc 3000 and Eumig Fl1000 are 3 headers that featured highcom and dolby so I assumed they must have 4 U401 chips to allow monitoring, while buying 2 units of Nakamichi highcom2 is way out of my rangeso I'll probably never know how a proper highcom system sounds.
I could try a few dbx chips from Fostex and Tascsm multitrackers if I'd want experiencing some dbx150 flavout but time....
I'm stuck with late Dolby c/s chips as most of us because with two of them I can still have a proper 3header system.
A friend gave me a defective Tascam A8 reel to reel which has 16 lm1111 dolby b chips to offer dolby c on 2 header/8track (universal head) at 38cm/sec and I though I could try a multiband 2 track 3 head multiband system with them but it's so damn complicated to fix that unit in the first place...
Showing some real love to my Denon...couldn't find yet some good quality 820pF and 390pF caps for the hx pro section...but replaced virtually every cap with higher quality species.Also rewired the headphones amp for 5x gain in inverted mode so that I can use opa2228 there too if necessary.OPA2132 is still my first choice for headphones though.
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I own a Denon DRM-800 CC deck which supposedly is somewhat superior than your's, whatever that may mean. I bought it as a new unit in about 1990 and used it enthusiastically, as it is a really good deck. I eventually retired it in it's original box in 2017 when I definitely gave up the use of CC's. Perhaps I should reactivate it?
Best regards!
Best regards!
Why not?
My Drm700 a a a stripped version of yours, just one more cd4066 on your inputs while drm800 seems to have a better playback head as it's damping is more resistive. If you look into different tapeheads the main important thing is the tapehead damping.Top decks have only resistive damping.
The top of the line versions also replaced the active switches with relays and usually added one more op amp buffer at rec dolby input, more rec buffers for switching different rc networks after the dolby chip and some tones generator to allow for automatic callibration , but the main rec playback functions are allowed by simpler decks with just bias and rec callibration potentiometers.
When I looked first into drm700a schematic I realized it would allow me to implement a Playtrim function as in Yamaha kx990 and Nad 6300.
Now these decks have cxa20188 dolby chip which is said to be better than cxa20187 but seeing how bad cxa20187 decks treats the dolby section I'm thinking that maybe it's more a marketing thing. Some people said that an rc filter in the cxa20188 dolby section should be superior to the lc version found in cxa2017.I am in no position to judge that so I thought giving it a chance then compare it to Pioneer ct777which uses cxa20188, a lower noise input , buffers everywhere and automatic callibration .
Yet I have a Yamaha kx400 where I saw something interesting, they treated very well the hx pro section giving it the best passive components and that deck has a really good sound.It was the first deck that impressed me with its headphones section which is identical to kx990 version so I copied it for a few times.It was based on njm4556 but it is in inverted mode and its sound is so damn good that you forget about every other njm4556 based headphones amp except the one found in technics sl-p990 but hey...that's using two njm4556 and Sandman's like topology.
I'm really late in this sport at 45 yo, but I never had a phone until 27, a laptop until 39 and a bike until 40...It happens that I really like these deck sound with Dolby on! I had 2 Nak cr4 and I know what a Nak can do without dolby and good tape , but I sold them for food a decade ago and I can't go back in time. In the end all Nak's magic stays in its tapeheads property and naks tapeheads wear too.Nak cr 4 headphones amp is really one of a kind as it explored the common mode cancelling resistor option talked by D Self 10 years before D Self wrote anything on that.It's also the only headphones amp that sounds well in nakamichi tapeheads except one or two lx and zx decks that used it too as all the others including the Dragon added a class B buffer for njm4556 and I haven't heard good things about it.
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There's also somehing I really like in this Denon.It's using darlington capacitor multipliers instead of regulators and there's no noise I can hear in this deck althouth it only has 2 x 100uf caps at the output for the whole deck.I added some more caps here and there , but with the new op amps I know they're useless.It's only the headphones amp that is now filtered with sanyo oscons and some more parallelled 10uf electrolitics and today I'm adding more 220uf /10v oscons next to cxa20187 and mictocontroller chips , but they're really unnecessary. The original 2x 100uf/16v , 2x 10uf/10v , 2× 10u/16 v and 1x 22uf/25vnippon chemicon sme caps measure as new.That's all this deck is actually using for decoupling the rails and It doesn't need more!
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This itches me. I see, I need performing some research for a SM for my DRM-800 😉 !
Best regards!
Best regards!
I didn't have the patience yesterday to add a relay instead of 4066 so I just removed it and wired only the playback to the output cause the monitoring is usually done on vu meters anyway while the digitalsources are very predictable in levels , but't I'm thinking of it today once again.
There's at least one 4066 replacement with significant better, almost audiophoolish data available! No need to tinker with relays.
Best regards!
Best regards!