Converting a circuit from 15v to 12v - Page 1
Forum section: electronics / beginners

author: Midphase
author_rank: Regular Contributor
timestamp: February 13, 2025, 05:35:56 pm
content: Sorry if I continue with the dumb noob questions, but I'm slowly learning and this stuff can be intimidating at first.I have been working on this +-15v circuit (schematic attached) and was wondering if it can run on +-12v just by changing the regulator?The reason for wanting to do this is that in the world of Eurorack +-12v is the standard and it would be a hell of a lot easier to feed that voltage to the circuit methinks.From the data sheets, all of the IC's seem to be just fine working at 12v. So can I just replace the regulators from 7815 and 7915 to a 7812 and 7912 and call it a day? Sounds too simple...what's the catch?Juno Chorus Clone Schematic.pdf(155.06 kB - downloaded 83 times.)

author: langwadt
author_rank: Super Contributor
timestamp: February 13, 2025, 05:49:59 pm
content: it'll probably work just fine on +/-12V, but you won't get 12V from a 7812 with 12V input, it needs at least a couple of volt extra.but if the +/-12V is already quiet and regulated you might not any regulators

author: Konkedout
author_rank: Frequent Contributor
timestamp: February 13, 2025, 05:58:39 pm
content: There is a lot in your schematic which I have not tried to understand, but I notice 1N5819 at D1 and D2. Those are rated 40V PIV. With 15V regulators shown, 25V raged capacitors at C1 and C2, there is not much voltage margin for the diodes (or you may be exceeding the ratings) and maybe similar for the capacitors.The 15V regulators really want 17-18V minimum input so that is about 35V. If you really have a 15V sinewave at P1, that = 21V peak or 42V p-p and you are exceeding the diode voltage ratings. I would go with 1N4004 diodes for mains frequency and current < 400 mA, or maybe 60V schottky diodes.Having said that I think it is fair to say that many +/- 15V analog circuits will work on +/-12 but with less dynamic range.

author: Terry Bites
author_rank: Super Contributor
timestamp: February 16, 2025, 02:49:25 pm
content: I don't see why not.None of the synth audio signals swing about more than a few volts. There's already bags of signal headroom even at the lower voltageThe clock ic circuit will run on a supply as low as 8V. No worries there.The modulator (U1 etc) might not give enough output for extreme depth, but I doubt it. Its already about 18v pp! on 15VCrazy VCO circuit, cheap but effective.

author: schmitt trigger
author_rank: Super Contributor
timestamp: February 16, 2025, 05:53:29 pm
content: Fortunately I still have my copy of Panasonic's MN3000-series BBD devices.The MN3101 clock generator can operate with a minimum Vdd of -8V; But the MN3009 BBD requires to operate a minimum Vdd of -14V.In both cases, to meet the published performance requirements, they are designed to operate at -15V.The opamps themselves would be no problem, other than reduced headroom.

author: langwadt
author_rank: Super Contributor
timestamp: February 16, 2025, 07:16:00 pm
content: Quote from: schmitt trigger on February 16, 2025, 05:53:29 pmbut the example diagram in the datasheets tells that the 15V is generated by the 3101 and it'll run from 6-15Vhttps://eadn-wc04-3257698.nxedge.io/audio/wp-content/uploads/sites/2/2021/11/Xvive_MN3009_DATASHEET.pdf

author: Midphase
author_rank: Regular Contributor
timestamp: February 17, 2025, 08:06:50 pm
content: Ok I just swapped the 78/7915's for 78/7912's.Here is what I'm hearing coming out of the circuit:1. The audio input seems to clip and distort more noticeably at 12v than it did at 15v, requiring me to turn down the input level quite a bit in order not to pick up distortion.2. The overall tone coming out of the circuit appears a bit darker and the chorusing effect is definitely not as pronounced.Any ideas on what the culprit might be? Are the two issues related? And if so, am I just better off sticking to 15v (the idea is that eventually I'd like to be able to run this as a guitar pedal with a 9v DC supply, and it's a bit easier to use a voltage boost circuit to achieve 12v than it is to achieve 15v).Many thanks!

author: schmitt trigger
author_rank: Super Contributor
timestamp: February 17, 2025, 08:32:14 pm
content: Quote from: langwadt on February 16, 2025, 07:16:00 pm-Absolutely not. The MN3101 is only a bi-phase clock generator, which also provides a gate bias supply. Gate BiasVggonly, not the actual supply voltageVdd.-Also please read my reply above. I mentioned that “to meet the published performance requirements, they are designed to operate at -15V.” Of course, you can run it at lower supply voltages, but as you also mention in another post, that at the lower supply voltages the sound is different and yet wonder why would that be the case.

author: langwadt
author_rank: Super Contributor
timestamp: February 17, 2025, 08:35:30 pm
content: Quote from: schmitt trigger on February 17, 2025, 08:32:14 pmso the schematic on page 45 is wrong?https://eadn-wc04-3257698.nxedge.io/audio/wp-content/uploads/sites/2/2021/11/Xvive_MN3009_DATASHEET.pdf

author: schmitt trigger
author_rank: Super Contributor
timestamp: February 17, 2025, 09:28:03 pm
content: Kindly show me the path that the clock generator uses to generate the Vdd to Vss rails.Mark up the schematic, please.

author: edavid
author_rank: Super Contributor
timestamp: February 17, 2025, 09:47:12 pm
content: Stop! You're both right!The datasheet is rather poorly translated. The operating conditions specify 14-16V supply, but the graphs and schematic show that it will operate at a lower voltage. The graphs also show how the performance degrades at lower voltages, but it should work well enough at 12V if that's what OP wants. The DC bias and input level need to be adjusted for that. I forget, does OP at least have an oscilloscope?

author: Midphase
author_rank: Regular Contributor
timestamp: February 17, 2025, 11:41:25 pm
content: Yes, I have a scope. I already did the calibration on the 15v circuit, but it looks like I now need to do it again on the 12v one?I guess ultimately I should clarify that my goal is to be able to power this circuit off of a regular guitar 9v DC wall wart, and as such if I can figure out how to get +/- 15v from that then going down to 12v becomes moot.Any ideas on how I should be able to achieve that goal?

author: schmitt trigger
author_rank: Super Contributor
timestamp: February 18, 2025, 12:52:24 am
content: Here you go;https://www.digikey.com/en/products/detail/dcomponents/AM6C-1215DLPZ/25994087

author: Midphase
author_rank: Regular Contributor
timestamp: February 18, 2025, 01:46:14 am
content: Looks about perfect. I guess the next question would be -- do you think that if I use something like that, I can completely bypass the 7815 and 7915 regulators?

author: Smokey
author_rank: Super Contributor
timestamp: February 18, 2025, 02:01:58 am
content: Quote from: Midphase on February 17, 2025, 08:06:50 pmthe stuff you talk about here is probably best quantified with a spectrum analyzer. If you wanted to see what "darker" and "pronounced chorusing effects" actually means in the signal (if anything) then a spectrum analyzer can do that. Then you can say things like "look at all these odd harmonics that the clipping generated in my signal"...spectrum analyzer = Dynamic signal analyzer in audio frequencies

author: Midphase
author_rank: Regular Contributor
timestamp: February 18, 2025, 02:45:53 am
content: Yeah, I get what you're saying. I looked at the signal through my audio workstation and spectrally they look pretty similar.I guess it's a less pronounced chorusing effect, which I guess might be due to slight changes in the voltages due to switching from 15v to 12v?Anyhoo...just a subtle but noticeable change that tells me that I best stick with the 15v voltage.

author: edavid
author_rank: Super Contributor
timestamp: February 18, 2025, 04:52:02 am
content: Quote from: Midphase on February 17, 2025, 11:41:25 pmI don't know what you mean by calibration, but the BBDs require different DC bias and input levels depending on supply voltage.QuoteYou would have to, since as someone already mentioned, voltage regulators require a higher input voltage than the output voltage.

author: Midphase
author_rank: Regular Contributor
timestamp: February 18, 2025, 06:21:44 am
content: I followed the Roland Service Manual in order to fine tune the RV3 and RV4 trimmers in order to adjust the LFO waves as to make sure they're not being clipped.However it sounds like you're referring to something else, how would I go about changing the DC bias and input levels? Seems like I would need to change some of the resistors perhaps? I was under the impression this is what the RV3 and 4 trimmers were for, but perhaps I'm mistaken?Juno Chorus Clone Schematic.pdf(155.06 kB - downloaded 17 times.)

author: edavid
author_rank: Super Contributor
timestamp: February 18, 2025, 03:08:42 pm
content: Quote from: Midphase on February 18, 2025, 06:21:44 amYes, those are the DC bias trimmers, and they would need to be readjusted if you changed the power supply voltage.

author: tooki
author_rank: Super Contributor
timestamp: February 18, 2025, 07:15:08 pm
content: Quote from: Midphase on February 18, 2025, 01:46:14 amYou not onlycan, youmust:as was explained to you earlier in the thread, the 7815/7819 regulators need around 2V of drop-out voltage (headroom) to regulate: you cannot supply them with the output voltage, you would need to supply them with 17V minimum.FYI: If you find the DC/DC converter to be too noisy, then a solution would be to post-regulate. Find some modern adjustable linearlow-dropoutregulators and then set them to, say, 14.5V. (Some modern low-dropout (LDO) regulators need as little as 0.1V dropout to regulate. Most are around 0.3V.)