What is the purpose of this network? - Page 1
Forum section: electronics / beginners

author: WimWalther
author_rank: Regular Contributor
timestamp: September 15, 2023, 07:19:56 am
content: Looks a bit like an FM detector to me; others have suggested a sine converter.Do you know what it is? Input is on the right, output on the left.

author: srb1954
author_rank: Super Contributor
timestamp: September 15, 2023, 07:37:49 am
content: Quote from: WimWalther on September 15, 2023, 07:19:56 amLooks like a sine shaper to me but there would need to be some series resistance, or current limited drive, on the input side for the clamping action of the diodes to work.

author: liaifat85
author_rank: Regular Contributor
timestamp: September 15, 2023, 08:11:55 am
content: Looks like neither to me completely.

author: Vovk_Z
author_rank: Super Contributor
timestamp: September 15, 2023, 09:59:32 am
content: Quote from: srb1954 on September 15, 2023, 07:37:49 am+1. I found several similar circuits with a "triangle-sine wave shaper diagram" keywords.For example:(eevblog.com/forum) Creating a sine and triangle reference wave from analog stuff

author: WimWalther
author_rank: Regular Contributor
timestamp: September 15, 2023, 12:23:16 pm
content: Here's the circuitry on the input & output sides. U9A/B seem to be an LFO - but - apparently the output waveform isn't suitable for direct-driving the flip-flop(?), so they interposed the (presumed) sine converter? The flip-flop provides complementary clock signals which drive a TDA1022 (BBD delay chip, not shown).Someone suggested that U9 is a relaxation osc., but I'm not seeing how. My experience with IC oscillators is limited to feedback around a Schmidt trigger inverter.

author: MrAl
author_rank: Super Contributor
timestamp: September 16, 2023, 10:48:36 am
content: Quote from: WimWalther on September 15, 2023, 12:23:16 pmShow the whole circuit.Part of it looks like a PLL but can't be sure without seeing the whole circuit and what it's for.

author: iMo
author_rank: Super Contributor
timestamp: September 16, 2023, 11:35:33 am
content: It looks like a sine shaper..But why a sine when it drives a TTL divider or what..

author: golden_labels
author_rank: Super Contributor
timestamp: September 16, 2023, 11:47:18 am
content: What’s the role of the node marked with bottom-pointing empty triangle (under R132, R137, R141)? I assume it’s not a power symbol, given it’s shorted (under R141) to the signal.

author: Bud
author_rank: Super Contributor
timestamp: September 16, 2023, 01:21:40 pm
content: Ground symbol. It is not shorted to the signal, there is no dot on the intersection.

author: WimWalther
author_rank: Regular Contributor
timestamp: September 16, 2023, 01:42:37 pm
content: Ok, so the circuit block in question is definitely a triangle-to-sine shaper. The oscillator on the right, formed by U9A/B outputs a triangle which is fed into the shaping network through R145 (68k).Probing R145 with a scope shows a tri on the right and a sine on the left, both of the same frequency. The sine is output by emitter follower Q9 to drive the flip-flop, which itself outputs a complementary pair of clocks which drive the BBD.The entire schematic is attached, by request. It's the most complicated guitar amp I've ever seen - and note that Channel 3, the power amp and the chassis wiring aren't even shown (though the deleted distortion channel, is.)

author: MrAl
author_rank: Super Contributor
timestamp: September 16, 2023, 04:12:34 pm
content: Hi,That's nice but parts of the drawing are still missing. The parts missing may be important.Is there any place that mentions the actual part numbers of the IC chips?I looked up that one IC chip marked PT2201 and it comes up with an 8 pin package which does not match the schematic.

author: WimWalther
author_rank: Regular Contributor
timestamp: September 16, 2023, 05:57:05 pm
content: As I mentioned, the drawing is incomplete - chan. 3 is missing as is the whole PA and most all chassis wiring. To confound matters, it does contain circuits that are not present in my model (like distortion and remote channel switching).The chip U7 is a TDA1022P BBD delay. The flip-flop is a MC14011B. Opamps are MC4458 / LMT358 types. There is no parts list and the part numbers on the drawing do not match my board. =)ETA: In addition, the opamps in the drawing are 14-pin devices, while those on my board are the more typical 8-pin style. Due to this difference, the pin numbers on the drawing are fairly meaningless.If you can locate a better diagram for a Polytone Taurus Elite, I'd love to have one.

author: MrAl
author_rank: Super Contributor
timestamp: September 17, 2023, 10:51:24 am
content: Quote from: WimWalther on September 16, 2023, 05:57:05 pmHi,Lucky for you I have one of every single schematic ever published since the year 1801 (ha ha).Sorry don't have that one and that reminds me when I looked online for a guitar amplifier some years ago and found it one day. The next week it was gone, nowhere to be found again and i searched and searched. Damn internet.

author: WimWalther
author_rank: Regular Contributor
timestamp: September 18, 2023, 02:30:23 am
content: There isn't much info available out there on this model (Taurus Elite). The only schematic I've found that even mentions it is the one I've posted. My sense is that it was relatively low-production and may have appeared later in company history.Mine was built in or around September of 1997, and is serial #12XX. Mine is covered in standard black Tolex, though there are blue Tolex versions also.

author: MrAl
author_rank: Super Contributor
timestamp: September 18, 2023, 04:27:50 am
content: Quote from: WimWalther on September 18, 2023, 02:30:23 amI wish I could help more but without a complete or very nearly complete schematic there's no way to know how to modify it correctly.You had suggestions already of the most basic things and since they could not be used you have to dig deeper.You do not have to create a full schematic in one sitting you know. I took maybe 5 days, working on and off, to finish the fuel pump controller board. I worked maybe 1, 2, or 3 hours a day, then did other things the rest of the day, then came back to it the next day, etc., etc.Aside from tracing the circuit out, I would spend some time thinking about how it might work and what some of the parts were that were not immediately identifiable. It takes time and patience, but the rewards are pretty nice. You get what you need that way.I was able to repair the fuel pump relay/controller and save a bunch of money, and I could bet it worked better than the original because I spotted a bad choice for one of the capacitors that had the original voltage rating too low for an automobile circuit. I also was able to use high quality electrolytic caps too.If you create a schematic and some of the parts are not known, myself and others here could probably figure out what they are.BTW, welcome to the world of reverse engineering.

author: WimWalther
author_rank: Regular Contributor
timestamp: September 19, 2023, 01:03:05 am
content: Quote from: MrAl on September 18, 2023, 04:27:50 amOh, I have a fairly complete schematic, it's posted in a couple of my recent threads. There's also a second drawing that covers just the PA.

author: jwet
author_rank: Frequent Contributor
timestamp: September 19, 2023, 04:04:36 am
content: I took this on as a puzzler. (what can I say, I'm retired...). I think you've got it doped out mostly, U9A is a comparator that resets U9B, an integrator, overall this creates a triangle wave. That circuit with the diodes and transistors is a waveform converter, not necessarily a sine, as someone verified. What follows the "sine" converter is a discrete flip flop that is triggered by the "sine" wave to generate a 2 phase clock for the bucket brigade delay. I can only surmise that they wanted a special overlapping 2 phase clock and this specially shaped wave gave them the right timing and duty cycles- the "sine" isn't used elsewhere. I think this was an analog guru's way of making an unusual 2 phase clock. I found a circuit on line from a Korg Synth of the same era (attached ) that uses a BBD device. They develop the triangle in the same way but then run it into a transistor multivibrator that must get them the 2 phase clock they want. Its really quite ingenious. Wooden ships and iron men in those days...

author: WimWalther
author_rank: Regular Contributor
timestamp: September 20, 2023, 02:43:13 am
content: Yeah, I think we're on the same page. So here's a question or two for you:It seems that there are in fact TWO oscillators in play here. One is the dual-clock for the BBD, which I measure at ~50KHz. The second is a variable rate LFO which frequency-modulates the clocks.. I am roughly guessing it as having a range from 0.5Hz to 5Hz.The LFO frequency is controlled by the Speed control (and foot switch). This allows the player to control the speed (of "rotation") of the virtual Leslie effect.So where are the two oscillators created? And how is the FM implemented? Do you see the correct components for the two time constants (~50khz & ~1hz)?

author: WimWalther
author_rank: Regular Contributor
timestamp: September 20, 2023, 02:47:55 am
content: Also.. with a 50khz clock driving the 512-element BBD, I make the max delay to be only 5mS.Is that correct? Doesn't seem very useful, isn't 5mS limited to like slapback range?

author: jwet
author_rank: Frequent Contributor
timestamp: September 20, 2023, 01:27:44 pm
content: Got your PM, had another look at this and those subtleties you mention.The U9 clock generator driver has some subtleties. U9B is an integrator. RC is 22k x .47u, it get a bit of postivie output bias depending on its present input voltage from R150/151. The overall inegrator rate is a positive input through R156B, the speed pot. That pot can get pulled down by Q10 depending on the modulator switch Fast/Slow- that's the source of some effect. The speed pot is conditioned by R154, R155, C86 and CR20. This network low pass filters the speed and modulation, R155 and CR20 makes it ramp down faster that it ramps up when slewing. Finally the integrator voltage is presented to U9B. Its feedback C85 is .47 (uF?) and has R152 of 22K, This is a VERY slow integrator that integrates in the negative direction. Some thing is wrong here. Verify C85 value? U9B output trips U9A positive V/2 with some hysterisis. The integrator is reset when U9A triggers Q11, this effectively makes the ramp reverse. This all looks very slow.There is a bit of low frequency modulation applied through Opto OP5. This looks like AM or tremelo?I assume that there is a micro or some digital logic that drives these optos.Isolate U9A and U9B and let's see if we can get a handle on that BBD clock source, etc.

author: WimWalther
author_rank: Regular Contributor
timestamp: September 21, 2023, 02:04:02 am
content: Thank you, that's fairly in-depth and will take some tome for me to digest it. I'm just a technician, mostly acquainted with tube-based audio & radio gear. I also dabble a bit with computer / micros etc.I'll verify the things you pointed out and get back with you. I'll also post the full (as it is) schematic below.The circuit under discussion ("Polytone modulator") is a Leslie loudspeaker emulator effect that's built into a Polytone Taurus Elite (TE) guitar amp. The Speed and Intensity controls are on the amp panel and can be used without connecting the footswitch.When the footswitch is connected, it has two SPST switches that control on/off & hi/low speeds for the modulator effect. A switching style 1/4" TRS jack transfers control to the footswitch when connected, though I believe the Speed control still sets the "hi" speed of the effect.There is no uC onboard, the unit is straight analog unless you want to count the quad-nand flip-flop IC & U7 the TDA1022 BBD.

author: jwet
author_rank: Frequent Contributor
timestamp: September 21, 2023, 02:56:10 am
content: I'm happy to help. Let me know what you learn. PM me if lose you- I don't follow the board very closely, its just nice diversion.

author: WimWalther
author_rank: Regular Contributor
timestamp: September 22, 2023, 04:38:27 am
content: C85 is definitely a 0.47uF (474) polyester type.

author: WimWalther
author_rank: Regular Contributor
timestamp: October 08, 2023, 04:45:31 am
content: Bump bump.. one more round.