You could generate negative voltage using an MC34063 or similar switching regulator. To get the quietest supply, make -18V and follow it up with a linear regulator. Linear Technology's' adjustable regulators were supposed to be even better than the LM317/LM337.
If you don't have any MC34063 lying around, have a look inside some cheap car USB adapters or phone chargers. A high proportion of the 5V/1A sort of charger used that chip or a no-name copy. The MC34063 data sheet/app note provides clear directions on using them, and board layouts. The older data sheets had layouts that were easy to copy by covering blank board stock with plastic packing tape and then cutting out the pattern with an X-Acto knife. Current data sheets assume the use of SMD parts and were created using new-fangled CAD instead of sharp objects. Or, possibly it'll be easy enough to cut a few traces and rearrange parts on the old charger PC board.
If you don't have any MC34063 lying around, have a look inside some cheap car USB adapters or phone chargers. A high proportion of the 5V/1A sort of charger used that chip or a no-name copy. The MC34063 data sheet/app note provides clear directions on using them, and board layouts. The older data sheets had layouts that were easy to copy by covering blank board stock with plastic packing tape and then cutting out the pattern with an X-Acto knife. Current data sheets assume the use of SMD parts and were created using new-fangled CAD instead of sharp objects. Or, possibly it'll be easy enough to cut a few traces and rearrange parts on the old charger PC board.
Maybe it's because I'm used to having 6VAC around, but I would just use a multiplier from a filament transformer and slap 7815 and 7915 on the end of it.
Of course, you could just buy one... It costs ~ 6.50$CAD
http://kit-amp.com/bipolar-power-converter-en
They make an isolated one for under 20$CAD
http://kit-amp.com/converter-bipolar-voltage-galvanic-isolation-en
http://kit-amp.com/bipolar-power-converter-en
They make an isolated one for under 20$CAD
http://kit-amp.com/converter-bipolar-voltage-galvanic-isolation-en
Fully assembled +15V/-15V unit with transformer costs about 20-25 usd.
Here is an example of the device you can search on ebay:
https://www.aliexpress.com/item/1005002632317522.html
I believe that for old preamp that should be sufficient. I'm using similar in headphone amp and it's acceptable.
If you plan to further develop your device and are after sound quality - pick Jan Didden offer.
Here you have good starting page to get mode knowledge about power supplies: https://sound-au.com/articles.htm#psud .
Yes, this is what I was talking about "slapping" onto the end of the voltage multiplier I posted in #22.
Interesting - is this kit amp company really based in Kyiv and still shipping parts? Would much rather support them than a Chinese business 😛
The typical AC-AC wall-wart does not have a secondary center tap which means the power supply caps are charging alternately 50 % of the time. Bigger caps are needed to keep the rectified DC well above the regulator drop out voltage.
One option is to use a TLE2426 to split the rectified DC. The plus-minus loads must be balanced with the TLE2426 limits but you will have full-wave rectification which might be seen as better performance.
One option is to use a TLE2426 to split the rectified DC. The plus-minus loads must be balanced with the TLE2426 limits but you will have full-wave rectification which might be seen as better performance.
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real ground results in a far superior spec. amp. Doubling the capacitors is much simpler than any virtual grounding schemes
hhttps://nwavguy.blogspot.com/2011/05/virtual-grounds-3-channel-amps.html
one can buy 2 trannys and make dual isolated supply, if C.T. is hard to find
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Don't fret too much, whatever we buy, majority of stuff comes from PRC. Nowadays, I usually scavenge e-scrap for salvaging components. Saves environment and stuff made 20y back was good in quality
If you were from my area, I would have given away trannys and regulators for free to you, too bad shipping trannys is super expensive
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How will you use you preamp?
IF with a new supply+poweramp , it will probably have a split supply, you can get your +/-15V from there.
Or maybe you can mount a new power amp inside your old guitar amp, same thing.
Now if you will use it as a standalone unit, say in a rack case or something, yes, you´ll need an independent supply ... but not otherwise.
FWIW you can make a simple +/- 15V supply (actually closer to +/-12V, no big deal) from a simple cheap 12VAC transformer, the smallest you can find, even a tin y 100mA on e.
Purists will be horrified but it actually works quite well.
Humble 12VAC secondary feeds 12VAC to tube filament, +/-15V to Op Amps and tube. 😱
Thanks and I am 100% with you on this one. I love to repurpose old electronic junk and dumpster-dive the local surplus store for parts. I never regret taking a few minutes to scavenge resistors and wiring from junk amps and so on, because I always end up having a use for them. My initial thought here was maybe I have the parts, but in this case it's more practical to just order one. Can you imagine how much fossil fuel gets burned when people like me pay $9 to get one resistor shipped from Mouser? Yikes.
Yes unfortunately we're all propping up China's repression machine, but one can hope that gradually other countries are elbowing in to take advantage of decoupling. I think Ukraine should take over Russia's niche manufacturing vacuum tubes for guitar amps, once this thing is over. Ukrainian branded tubes would sell like hotcakes.
How will you use you preamp?
IF with a new supply+poweramp , it will probably have a split supply, you can get your +/-15V from there.
Or maybe you can mount a new power amp inside your old guitar amp, same thing.
Now if you will use it as a standalone unit, say in a rack case or something, yes, you´ll need an independent supply ... but not otherwise.
FWIW you can make a simple +/- 15V supply (actually closer to +/-12V, no big deal) from a simple cheap 12VAC transformer, the smallest you can find, even a tin y 100mA on e.
Purists will be horrified but it actually works quite well.
Humble 12VAC secondary feeds 12VAC to tube filament, +/-15V to Op Amps and tube. 😱
I love that tube unit. Have you built one of these? I have actually been working on my Super Reverb for months, and while it has been challenging, it's much easier for a novice to do hand-wired tube stuff than solid state on circuit boards. I even have spare 12ax7 sockets.
I am going to just use this amp as a preamp and pretend it's a rackmount thing. I have a 200w tiny class-D TC Electronic bass head that works well, but the EQ is voiced wrong, with the bass control at 80hz, whereas the GK has real bass at 40hz and can cut a lot more mids in two bands. I play a 5-string, so I need something at 30hz. Small thing but makes a big difference. I know I could just buy an eq unit and it would probably sound the same, but I'm just here to reuse old junk, learn how these things work, and generally be a cheapskate. I tried it with a huge Crown power amp (I actually succeeded in getting the 15v off the board of the Crown in a super dodgy way) and it sounded fantastic, but the fan on the Crown sounds like a helicopter over the house, and at 940w it's much bigger than I need. The Crown's fan is AC and can't be separated from the power supply and replaced.
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I reviewed the NwAvGuy article which is very good. I revised my model to have rail-splitter without shared ground. I do not like "virtual ground" since it is a vague abstraction. Absolute ground is always needed and exists before components are added to a circuit.
It is best to start with the simplest idea that can possibly work .. such as the O2 which has half-wave diodes and regulators. It is not necessary to worry about the lack of wall-wart center-taps.
There are a few use-cases where a rail-splitter is needed for portable operation from one battery. There are a few constraints such as the split loads must be equal. Crosstalk is more likely and must be managed in the PCB circuit structure. That is, the split supply sections must have own ground with a track leading to the absolute ground. I try to show this in the attached schematic.
I have seen some instances where a TLE2426 is used without regulators. I say don't do this since the TLE2426 is not a regulator like 7812 or LM337.
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I found a board I bought that was designed to do 12V in, +-12 out.
I can't find it on eBay though.
I can't find it on eBay though.
I used a +/-15VDC P/S supply like the one you posted #1. However, it powers 3 XO boards with linear regulators (+/-12VDC using LM7812, LM7912) and I added an LC filter to reduce SMPS noise. There are some waveform pics in the linked thread. The only caution is the amount of load capacitance could effect the soft start power up. I had to reduce my XO boards input capacitance to 3000uF, because 7700uF (total for 3 boards) caused startup "foldback hickups".