Hi all, I want to build a tape delay unit from scratch. I was just wondering if anyone could suggest a simplish circuit to generate and inject the 100khz signal to the record head.
I would like to use transistors but if there is a much simpler way to do it with an IC I am all ears. Any suggestions appreciated!
I would like to use transistors but if there is a much simpler way to do it with an IC I am all ears. Any suggestions appreciated!
You can use most anything to generate the bias any sine circuit will do, my Otari MTR-15 uses a signal generated off of the 8080 cpu inside it directly when it is in record mode.
I know this because it decided to stop recording one day and I have traced all of this in the manual , just have not repaired it yet.
The TTL signal gets filtered and applied to the tapes heads in just the same fashion as any other tape drive, through a variable cap (usually).
Or, the anti bias signal can even be fed in to the record head driving amp with a pot for adjustment mixed with the signal as it is recording.
The erase head may need its own full drive by itself from the very same signal, IIRC this comes out of a simple buffer or maybe straight TTL level IIRC, I have to get the manual out to check all of that again.
But there are many ways to do this, depending on the current level that the heads need and an opamp may not have enough drive output current (Low enough output impedance).
However you can get away with a simple current boosted opamp buffer, or get a hold off some LME49600's (Good Luck, sadly) if you can't find them, then else an opamp and two BJT's or small chip amp buffer will drive them.
I have always been wanting to do something likes this for many years, I once had a awesome tape motor that had a 1" dia. pully on it shaped like a capstan I was going to use for some High speed taped reverb tricks !!
I had a bunch of 8-track tape head's I was going to use but all that went by the wayside through the years...........................
But, It Is Still on my bucket list of things to do once I get some more tape heads again.
:Cheers:
Good luck !!
jer
I know this because it decided to stop recording one day and I have traced all of this in the manual , just have not repaired it yet.
The TTL signal gets filtered and applied to the tapes heads in just the same fashion as any other tape drive, through a variable cap (usually).
Or, the anti bias signal can even be fed in to the record head driving amp with a pot for adjustment mixed with the signal as it is recording.
The erase head may need its own full drive by itself from the very same signal, IIRC this comes out of a simple buffer or maybe straight TTL level IIRC, I have to get the manual out to check all of that again.
But there are many ways to do this, depending on the current level that the heads need and an opamp may not have enough drive output current (Low enough output impedance).
However you can get away with a simple current boosted opamp buffer, or get a hold off some LME49600's (Good Luck, sadly) if you can't find them, then else an opamp and two BJT's or small chip amp buffer will drive them.
I have always been wanting to do something likes this for many years, I once had a awesome tape motor that had a 1" dia. pully on it shaped like a capstan I was going to use for some High speed taped reverb tricks !!
I had a bunch of 8-track tape head's I was going to use but all that went by the wayside through the years...........................
But, It Is Still on my bucket list of things to do once I get some more tape heads again.
:Cheers:
Good luck !!
jer
A few years back I helped a diy'er with the the preamp section of his Melotron, and I used Circuitmaker2000 to simulate the preamp and then later added a opamp in place of the noisey BJT's that it used, I don't recall if he tried it or not I will have to re-read this thread,
https://www.diyaudio.com/community/threads/mellotron-preamp-schematic.185649/post-2532595
I have not messed with this since but I think it did work for him, at the time I was all new to tape preamps and NAB's filter's ( if there is any used), and since then I found out Mellotron used their own record EQ curve IIRC.
And was why I had a hard time understand what I was doing in the thread but it worked I think.
I never built it yet, as I don't have a unit to try it on yet, I do have a Univox Echo 100 I do need to get out and get working again, it uses 1/8" tape so when I do it I will add some more heads and make a glass cage for the tape to flow through instead of the now shot plastic cassette unit it uses, Mini 8-Track type.
Cheers!!
jer
https://www.diyaudio.com/community/threads/mellotron-preamp-schematic.185649/post-2532595
I have not messed with this since but I think it did work for him, at the time I was all new to tape preamps and NAB's filter's ( if there is any used), and since then I found out Mellotron used their own record EQ curve IIRC.
And was why I had a hard time understand what I was doing in the thread but it worked I think.
I never built it yet, as I don't have a unit to try it on yet, I do have a Univox Echo 100 I do need to get out and get working again, it uses 1/8" tape so when I do it I will add some more heads and make a glass cage for the tape to flow through instead of the now shot plastic cassette unit it uses, Mini 8-Track type.
Cheers!!
jer
Have a look at few service manuals for older cassette decks to see some simple circuits. Many used a special (purpose built) transformer such as here. If you got an old scrap deck you could find the circuit and copy the oscillator.
At the risk of sounding totally nutz and depending on quality you want there is also DC bias... doesn't come any simpler than that. If you are only experimenting and want to get something up and running and are just trying stuff out... well it might be an option.
At the risk of sounding totally nutz
and depending on quality you want there is also DC bias... doesn't come any simpler than that. If you are only experimenting and want to get something up and running and are just trying stuff out... well it might be an option.Nice to see you again mooley, thats extremely similar to the marantz PMD 222 that I have, I just struggle to understand it (and then the whole proprietary transformer thing).
I would like this to be high quality, but I may look into DC bias just to mess around with for now.
I forgot to mention, I want to build this unit to run standard cassette tapes (if that makes any difference to the complexity of the circuit).
I would like this to be high quality, but I may look into DC bias just to mess around with for now.
I forgot to mention, I want to build this unit to run standard cassette tapes (if that makes any difference to the complexity of the circuit).
Thanks
For some reason I missed seeing the notifier for this earlier. This was from a Sony TCK5 cassette deck.The supply is varied in this application to vary the bias level for different tape formulations. I'm not 100% sure what oscillator type this is... some variation of a Hartley oscillator possibly. I'm really not sure though.
Hello! I used to work with a couple of simple BJT based generators for tape heads.
To offer something I have to know a bit more:
1. What about erasing head? Does it exists in your project and if yes - where it is powered from?
2. What is your supply voltage and how stable it is?
To offer something I have to know a bit more:
1. What about erasing head? Does it exists in your project and if yes - where it is powered from?
2. What is your supply voltage and how stable it is?
Hi Mas, so to be honest i am in the very early stages of this project. I really am trying to design a general purpose cassette tape delay that will work in any studio setting.
I would like the supply voltage to be 9v but if I will get better fidelity at 12v or even 24v I have no issues changing that. Lets assume I am building a general purpose echo unit running on the best voltage needed for a full transistor unit. I am ok with op amps and such but I would prefer to not hit vacuum tube voltages.
I would like the supply voltage to be 9v but if I will get better fidelity at 12v or even 24v I have no issues changing that. Lets assume I am building a general purpose echo unit running on the best voltage needed for a full transistor unit. I am ok with op amps and such but I would prefer to not hit vacuum tube voltages.
Should work with any head but you might need to trim the capacitors to get the correct frequency. For erase duties, signal also has to be strong, something like 30Vp. I can't tell if low distortion is a requirement here.Then the same signal can be used for bias but it has to be attenuated to a specific level for each tape type, so it should pass through resistors and caps hopefully filtering some noise. Then it goes straight to the recording head. The signal to be recorded on the other hand, is not sent directly to the head. It should pass through a so called "bias trap", an LC circuit that works like a notch filter and it's tuned right on the bias frequency so it won't allow it to modulate the audio circuit. The bias trap is not very sharp, it should filter a few harmonics. The principal of operation is that the bias frequency is significantly higher than the audio signal.