Please help me wire this IC - Page 1
Forum section: electronics / projects

author: Explodey
author_rank: Contributor
timestamp: September 12, 2017, 10:46:17 pm
content: Please see the attached PDF. I bought ten of these TA7668BP chips on eBay to experiment with for this tape loop project I'm working on. I don't have a lot of experience wiring directly to IC's, and I'm not sure I understand all the pin designations in the PDF. Mainly, I'm not sure which pins I should apply power to. Also, I'm not sure how the pins are numbered. Left to right, facing the top of the IC? And I assume the notch is used for orientation somehow?Hmm... I guess I can't attach files. Here's a link:https://www.dropbox.com/s/lanre79yt3vn6fg/TA7668BP_datasheet.pdf?dl=0Any help you can give would be most appreciated!

author: Benta
author_rank: Super Contributor
timestamp: September 12, 2017, 10:53:04 pm
content: Your user name is revealing...

author: helius
author_rank: Super Contributor
timestamp: September 12, 2017, 11:10:14 pm
content: Maybe this would be better in the Beginners section...Try these intros, they aren't terrible; I guess they could be better.https://learn.sparkfun.com/tutorials/integrated-circuitsOne of the things missing is a discussion of power pins.Vxxor GND means that a pin is for power. Sometimes there are also dedicated grounds for analog or digital signals separate from the power ground. V+ and V- mean that power is bipolar: a chip uses a positive voltage and a negative voltage of the same magnitude.VCCis the most common power supply name. "CC" is short for "Collector" since the collector of a NPN transistor is connected to the positive supply. Sometimes the power supply is named VDDin CMOS chips. "DD" is short for "Drain" because the drain of a N-channel FET is connected to the positive supply. VSSalways refers to a 0V or ground return of the power supply. "SS" stands for "Source" and comes from N-channel FET circuits as above. VEEis a negative supply voltage, like -5.2V: this comes from emitter-coupled logic.

author: Audioguru
author_rank: Super Contributor
timestamp: September 12, 2017, 11:33:56 pm
content: Tape? Scotch tape, packing tape, duct tape or masking tape?About 37 years ago we used cassette tape recorders and players. I haven't used mine since about 17 years ago.My video tape recorder was replaced by a digital PVR also a long time ago.Why are you using an old way to record and playback sounds?

author: helius
author_rank: Super Contributor
timestamp: September 13, 2017, 01:18:12 am
content: Tape loops are used in delay units like the SE-201, very highly regarded by musicians. I'm pretty shocked that an "audio guru" is unaware of that.OP: In the example circuit in that datasheet, it shows a single power supply, VCCat around +9V on pin 16. That is the last pin counting counterclockwise from the notch (also the upper left pin when the notch is in its usual position facing left). There are two grounds that should both be connected to the power return, pins 1 and 9. They are separate so you can use bypassing capacitors on each one to control noise and crosstalk. You would also ground pin 8 to defeat ALC and ground pin 15 to defeat muting.

author: Explodey
author_rank: Contributor
timestamp: September 17, 2017, 06:39:16 am
content: Thanks for your help everyone. If you're curious why I'm working with tape in the 21st-century, here's why:https://youtu.be/4LkZMmxRAB8It's actually been a surprisingly fruitful endeavor for me!Anyway, I'm hoping to use this IC for the playhead preamp and the record/erased head in my latest prototype, but so far I haven't had much luck. Tonight I wired it up just to test the preamp function, but I couldn't get any sound. And I breadboarded it, so I know the connections are all good. I must've just wired it wrong. Perhaps someone could tell me where I went wrong? Here's what I did:12v DC to pins +16 and -9Two-channel playhead to pins 7/6 and 10/11Left channel output to pins 5 and 9Right channel output to pins 12 and 9And I tried a few other things, like grounding 1 and 8. I should also mention that because of the way the playhead is wired, pins 6 and 11 are connected. I'd really appreciate it if anyone has any suggestions. But if not, it's cool; I'll go back to using this little preamp PCB that I bought on eBay. I was just really excited at the prospect of having a solution for the playhead signal and the record head signal all in one.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 17, 2017, 07:15:59 am
content: Those integrated circuits require perhaps a dozen additional components around them to use as a tape playback (or record) amplification stage. Using a "raw" integrated circuit is NOT as simple as wiring to a board-level preamp module. Until you have significantly more experience with low-level audio circuits, suggest sticking with board-level amplifier modules. Else you will need some months or years of experience with audio circuits, or else find a "reference design" for that chip and try to copy what the manufacturer suggests. Note that constructing low-level audio circuits on breadboards is quite susceptible to ambient noise incursion, just another reason to stick with board-level solutions where the circuits have been designed, manufactured and tested (or at least very likely to work "out of the box."

author: helius
author_rank: Super Contributor
timestamp: September 17, 2017, 08:18:13 am
content: I suspect that the mute circuitry is active as you didn't mention any connection to pin 15. It should turn off (unmute) when pulled to ground.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 17, 2017, 04:24:15 pm
content: Here is the "reference design" from the manufacturer. This chip was created for cheap/simple tape/cassette recording gadgets. So they re-used the same chip for both recording and for playback. Note in several places there are switches labeled "P" and "R". (Play and Record) They are all sections of a single switch, but shown in various places throughout the circuit. Of course if you wanted to create a circuit only for playback (or only for recording) then you could "hard-wire" the circuit without the P/R switch.You could probably design a board that would use these chips, but IMHO, there would be no significant advantage over using existing off-the-shelf solutions of preamp boards as you have already been experimenting with. Developing a circuit and then a board for these chips seems like distraction from your primary project. I would rather get on with the main project and not fool around with these obscure chips.

author: Explodey
author_rank: Contributor
timestamp: September 17, 2017, 06:32:09 pm
content: Thanks Richard. Yes I suspected that would probably turn out to be the case, but I wanted to give it a shot. I'll go back to using the kit boards. I think what I really need is a partner who can help me with the wiring. When my video started blowing up on Facebook, I got a lot of offers of help, but unfortunately, not from anyone who was local.As my project comes along, I'm sure I'll be back on the forums with more questions, but for now, I think I know what to do.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 18, 2017, 05:40:24 am
content: Quote from: Explodey on September 17, 2017, 06:32:09 pmNobody here knows where "local" is?

author: Nusa
author_rank: Super Contributor
timestamp: September 18, 2017, 08:37:29 am
content: Quote from: Richard Crowley on September 18, 2017, 05:40:24 amText at the end of the video says "South Bay" which is a bit ambiguous, but most likely refers to San Francisco Bay Area.

author: Explodey
author_rank: Contributor
timestamp: September 19, 2017, 12:18:51 am
content: Sorry, to clarify -- I live in Santa Cruz, CA.