Hello everybody!
I just bought a Technics Rs1500 reel to reel recorder. It comes with a Nab equalization. I would like to modify it to have a switchable IEC equalization that is used on some master tapes.
I have been looking at the schematics(I have attached them). It appears to me that the equalization is obtained with the feedback circuit circled in red plus the one circled in green which changes based on tape speed (the transistor Tr127 is connected to the speed switch).
The circuit circled in red has (if I have done my calculations correctly-I got the formulas here:Andy's Active RIAA Phono Equalization Design Page) two time constants:the first around 3180 μs which is the bass lift and the second around 25μs which is not a time constant of the NAB equalization but I suspect it is then corrected by the second circuit (circled in green).
Now my questions are:
1)Is my reasoning correct? (I'm new in the electronic world)
2) If I wanted to implement the Iec equalization for 15IPS (Two time constants:∞ and 35 μs) what should I do? I think I could increment the value of the of the capacitor 162 or resistor 182 until I get a bass roll off under 20 Hz (∞ is not possible, I've read that people place it somewhere under 20 Hz) and then decrease the value of the capacitor 169 or trim pot vr105 or resistor 181 till I get the correct frequency response ( high frequency roll off at 4500Hz) taking into account the circuit circled in green (I would probably need a calibration tape to do this correctly).
Am I at least partially right? Or completely wrong?
Thank you very much
Benjamin
I just bought a Technics Rs1500 reel to reel recorder. It comes with a Nab equalization. I would like to modify it to have a switchable IEC equalization that is used on some master tapes.
I have been looking at the schematics(I have attached them). It appears to me that the equalization is obtained with the feedback circuit circled in red plus the one circled in green which changes based on tape speed (the transistor Tr127 is connected to the speed switch).
The circuit circled in red has (if I have done my calculations correctly-I got the formulas here:Andy's Active RIAA Phono Equalization Design Page) two time constants:the first around 3180 μs which is the bass lift and the second around 25μs which is not a time constant of the NAB equalization but I suspect it is then corrected by the second circuit (circled in green).
Now my questions are:
1)Is my reasoning correct? (I'm new in the electronic world)
2) If I wanted to implement the Iec equalization for 15IPS (Two time constants:∞ and 35 μs) what should I do? I think I could increment the value of the of the capacitor 162 or resistor 182 until I get a bass roll off under 20 Hz (∞ is not possible, I've read that people place it somewhere under 20 Hz) and then decrease the value of the capacitor 169 or trim pot vr105 or resistor 181 till I get the correct frequency response ( high frequency roll off at 4500Hz) taking into account the circuit circled in green (I would probably need a calibration tape to do this correctly).
Am I at least partially right? Or completely wrong?
Thank you very much
Benjamin
Attachments
You have identified the right parts that implement the equalization.
I need to look at the required changes, it's been many years...
Jan
I need to look at the required changes, it's been many years...
Jan
are you going to record or just playback? If you are recording you will have to change the record eq and of course you will have to adjust the tape bias for whatever tape you are going to use.
the playback(read) head is just after the record(write) head, you can monitor and test the record and playback functions and circuits all at once. Don't forget to align your heads up and down for amplitude and for squew/phase between channels.
I will just playback not record. Anyway I wanted to do a switchable eq. I think it shouldn't be to hard to place somewhere there a relay that can change from one equalization to the other. With this solution I could still record with the Nab equalization and then listen to it.
I've checked their forum but haven't found anything. Many users there just convert it to use it with external electronics.
You might also want to do a search on The Tape Project . The Technics is one of the decks in their lineup. They have a forum there too - A good chance the eq mod has been talked about. (eg. did a very quick search and found this link in a post.)
The last link is very useful. I have actually seen it before. It has two issues in my opinion. First it wasn't tested and the author doesn't seem to be 100% sure. I was not able to found a RS1520 service manual (the Rs1520 was a version of the same deck that came with a switchable equalization)to double check his findings. Second it doesn't change the lower frequency lift off which stays at 50Hz. On other Iec playbacks systems I read that it is usually placed under 20Hz.
I don't know how big this difference could sound but since I will anyway have to open the deck and do some soldering I thought that I should try to go with the most correct solution.
Thank you all for all the help so far! I really appreciate it!🙂
I don't know how big this difference could sound but since I will anyway have to open the deck and do some soldering I thought that I should try to go with the most correct solution.
Thank you all for all the help so far! I really appreciate it!🙂
Hello guys,
I just acquired one RS1500 and one RS1506 from Japan in good condition.
Realizing that it would be great to modify directly the EQ from NAB to IEC on the board, I would be very interested to know if Benji90 you had found a way to do so!
I also searched for the RS1520 service manual but for now could not put my hand on it.
I just acquired one RS1500 and one RS1506 from Japan in good condition.
Realizing that it would be great to modify directly the EQ from NAB to IEC on the board, I would be very interested to know if Benji90 you had found a way to do so!
I also searched for the RS1520 service manual but for now could not put my hand on it.
I know this is an old thread but did anyone ever have any success on the conversion? If so, can you share any details? I have a RS-1500 I would like to play NEC tapes on.