Modification Of DB Meter In Technics Receiver Amplifier Model SA380S
This set had visited me a few months back and I had posted my report and I request the readers to see the article using the following link, before reading further:
This time, the customer brought it in for two purposes: Firstly to modify the DB Meters so as to function in play mode and secondly to test it with a locally built sub-woofer amplifier he brought. The interfacing with the Sub-woofer was found ok, when checked in front of him.
I removed the bottom cover as well as the top cover of the Technics to look at the DB Meter control IC. It was TA7318P.
I looked at the datasheet of this IC from my collection.
I traced the Pins (4) and (6) which were the inputs. I located the tracks and pulled one side up of the two resistors that were going to recording level circuit. Then used two 103 Capacitors (0.01uF/630V) and linked the inputs to the outputs of the volume control.
The VU Meters worked very well when I played the tuner and there was no need to adjust the pots at the IC level. Mission accomplished with satisfaction of different kind, which also got added to the collection!
This article was prepared for you by Parasuraman Subramanian from India. He is 74 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
Please give a support by clicking on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments.
P.S-If you enjoyed reading this, click here to subscribe to my blog (free subscription). That way, you’ll never miss a post. You can also forward this website link to your friends and colleagues-thanks!
You may check on his previous article on Mismatching Current In New Edge LED Necessitated Bypassing In SONY KD-43X7000E
(37)Dislikes
(0)
10 Comments
Leave a Reply
Albert van Bemmelen
December 29, 2024 at 1:31 am
After this badly tampered with Technics audio set already was successfully restored, it now even got a good db-meter upgrade to work with an external connected sub-woofer amplifier. Nice work on the TA7318P circuit modification although it was not entirely clear how the final circuit after modification exactly looked! Because only the original TA7318P circuits were shown.
Parasuraman S
December 29, 2024 at 5:16 pm
Nothing special. The input to the TA7318 was shifted from the record switch to volume control; that's all! Many thanks for your keen observation and comments, dear Albert!
Mark J
December 29, 2024 at 4:53 am
Technics are a good brand. You are the master of tape deck and CD repair. Well done Parasuraman.
Parasuraman S
December 29, 2024 at 5:17 pm
Yes, good products. Many thanks for your comments, dear Mark!
Yogesh Panchal
December 30, 2024 at 1:05 am
Good Job!Sir
Parasuraman S
December 30, 2024 at 11:37 pm
Thanks!
Waleed Rishmawi
December 30, 2024 at 2:36 am
Interesting modification; so what you basically did was shifting the inputs of the IC from record to volume? So now recording and external signal can be monitored? A job well done. Thanks for sharing
Parasuraman S
December 30, 2024 at 11:38 pm
Yes, precisely that is what I did! Thanks for your comments!
Justice
January 2, 2025 at 4:59 pm
Yes yes yes I am quite laughing trying to fully comprehend, record sig to volum sig to VU but still able to control recording. Its genius , keep up good interesting article.
Parasuraman S
January 2, 2025 at 9:39 pm
Tape section has been disabled as it was not being used. The record switch therefore does not have a function. That's why it was modified to make the VU meter work for the volume. Many thanks for your comments!