Can anybody suggest a way to modify this little daughterboard so that it puts out 12V instead of the 18V? I suspect it may just be a latter of choosing different diodes (and possibly doubling them up), but I'm a novice to futzing with this sort of thing, and don't want to make a really bad mistake!
I'm having trouble uploading a picture, so here's the URL link to the vero layout I'm hoping to modify:
http://4.bp.blogspot.com/-SHcE0P5tEao/U9rvGU589eI/AAAAAAAAIX0/hO5n62dQ2cs/s1600/Toneczar+Openhaur+charge+pump.png
Of course, if anybody has an existing vero layout they can share for a 9V to 12V charge pump, that would be great too.
Thanks in advance.
Adding a 78L12 regulator from the 18V output is probably the simplest most stable option.
So, take the18V lead, feed it to the input pin on the regulator, take a wire from the output pin and feed it to the circuit, and then ground the GND pin? Dumb question (the pinouts seem fairly intuitive) but I'd rather sound dumb than make a dumb error.
Note -- I'm doing this to try to run a Valvecaster circuit at 12V. It just occurred to me...do I even need the 18V charge pump, or can I feed the 78L12 regulator the regular 9V source...that is, if I power the 78L12 from a 9V source, will it still put out 12V to feed the circuit?
The 78L** series has an internal voltage drop of about 2V, meaning you need to supply a 12V regulator with at least 14V to work properly. I don't know if theres any easier way to power the circuit or if a charge pump and regulator is still the best.
Okay...so if I understand correctly, then something like this would work:
1. 9V power supply to an 18V charge pump.
2. 18V out from the charge pump to the IN of the regulator; GND pin of the regulator grounded.
3. the OUT pin of the regular will provide 12V of power, which can then go to the circuit.
If I have that right (I hope I do!) would it be advisable to insert some power filtering caps between the regulator and the Power IN of the circuit, or should the power filtering be done before the current hits the regulator (or, for that matter, the charge pump)?
Refer to the datasheet for the correct filtering capacitors for the regulator. Usually it's 220nF or 330nF in and 100nF out, but check the datasheet for your brand.
Powering a tube is different, a charge pump wont have sufficient current to power the heater so if you want to use a 9V supply you'd have to wire the heater for 6V operation (300mA) from a 7806 regulator and then the rest of the circuit would be fed by the charge pump, in which case you may as well omit the regulator and feed it the 18V.
Just use the 12V supply for the valvecaster.
The current required to power the heaters will literally melt most 6V regulators. You need a regulator with a heat sink tab, and a BIG heat sink. The heat sink you'll need with be about an inch wide and and inch and a half tall. You don't want it close to your hot glowing tube because then it won't be able to dissipate the heat. You can't let it touch the case, so you need to make sure it's a big pedal.
But the voltage is only half the problem. 300mA of current isn't a small number. It's absurdly high. The One Spot can supply almost 2A of power, but even it won't be happy about giving up 300mA to a single pedal, and would likely introduce a lot of noise into the daisy chain (you know how it's a bad idea to daisy chain Strymon/Eventide/etc. stuff? same reason: high current draw). Your average power brick (like the PP+) can't even supply the current necessary to power a heater. If you're not daisy chaining it and you're not powering it from a power brick, then it's getting its own power supply anyway. So get a 12V supply dedicated to your valvecaster. You can get one for like $10 on ebay that's intended for running LED arrays, so it'll have plenty of current.
So Jon, what if I wanted to run the valvecaster plates at 18V, but run the heaters at 12V (which one of the other forums suggests is a good option for better tone/headroom)...could I use the RoadRage for that (and modify the LM78L15 to a LM78L12)? Or are you saying that even the Road Rage wouldn't work in this scenario for all the reasons you noted regarding charge pumps?
As I said above, you cannot feed a tube heater from a charge pump.
You really do need to get a 12V supply, i've powered from a 6V regulator and as Jon alludes to, unless it's the only option it's not worth the hassle.
Alright...I will move on from the charge pump option. So my question now is...what must I do to feed 12V to the heaters but 18V to the plates?
That's much easier, just wire the heaters directly to the 12V (follow the 12AU7 datasheet) and also run the 12V in to a LT1054 charge pump input which off the top of my head is okay up to 15V but check its datasheet to be certain and have its output feed in to the plate resistors, that'll be 24V (minus losses so ~22V) so an extra bit of headroom over 18V.
Neither 18v nor 12v are full plate voltage, so why bother with the 18v which will still need the giant heat sink? The starved plate is basically the point of the design. If you want headroom you should really be looking at a different design, one with a real power supply that can give you at least 120v. (Grind customs has one and has instructions for safely building it.)
I'm not even totally sure you CAN dissipate the the 6V of waste at 300mA or more with any reasonable part.
I'm not trying to discourage experimentation, but it's a good idea if someone mentions an issue with a build (like current draw in this case) to understand the problem before suggesting a slightly different mod that will just recreate the problem under different circumstances. Spend a bit of time reading about Ohm's law and the power dissipation formula, and in the meantime you can breadboard the design as it exists and see if you don't like it or easily try other plate voltages.
So Jon, since I am interested in using this primarily as an overdrive -- powering the entire circuit at 12V will work? I want to avoid the problems people report with running it at 9V, which is why I thought 18V would provide better clarity and punch (while still yielding good drive characteristics). But if I can get that with hitting both the plates and the heaters at 12V and avoiding having to use the heat sink...
If you're using a 12V DC Supply for the heaters you do not need a heat sync for anything, a charge pump will happily power the plates without getting warm.
A 12AU7 doesn't need full plate voltage to sound good, they're much better at lower voltages than a 12AX7 so 12V and 18V will make some difference or 22V as it would be with using a 12V supply in to the charge pump.
Quote from: midwayfair on May 11, 2016, 01:39:47 AM
Neither 18v nor 12v are full plate voltage, so why bother with the 18v which will still need the giant heat sink? The starved plate is basically the point of the design. If you want headroom you should really be looking at a different design, one with a real power supply that can give you at least 120v. (Grind customs has one and has instructions for safely building it.)
I'm not even totally sure you CAN dissipate the the 6V of waste at 300mA or more with any reasonable part.
Who said anything about wasting 6V at 300mA? Even his original plan was to waste 3V at 300mA which is perfectly doable really, the 7806 is fine up to 1A but of course does need heat syncing.
Quote from: Scruffie on May 11, 2016, 10:29:49 AM
Who said anything about wasting 6V at 300mA? Even his original plan was to waste 3V at 300mA which is perfectly doable really, the 7806 is fine up to 1A but of course does need heat syncing.
Sorry, I thought he was asking about using an 18V supply and dropping it to 12V.
And I meant without a heatsink re the 6V drop if he'd been using an 18V to knock it down to 12V.
>
Problems running it at 9VA single 12V supply does everything you need as long as the one you get can supply the current required for the heaters and still have some leftover mA. It's pretty much ideal for the circuit since you don't need any regulation and it'll run sound through the tubes.
A 12AU7 doesn't require as much voltage as a 12AX7 and will absolutely sound way better, but a 12AU7 might still just a bandaid if you have a problem with the sound of a low plate voltage tube circuit. If you're building a starved plate design instead of using a voltage multiplier circuit to get full plate voltages of whatever triode you want to use (i.e. not just a voltage doubler or tripler to get ~22-32V from an LT1054), then I think it's just easier to embrace the fact that it's a starved plate and say, "Well, that's what the valvecaster sounds like." Most of the problems you were reading about with the 9V circuit probably had to do with powering the heaters.
There are other types of voltage multipliers you can build if you want to make something in the future with full plate voltage. Like I said, GrindCustoms has one. (And if you want to get really fancy, theirs can also be modified to run on a dedicated 12V adapter to avoid regulating the heaters down to 6V.)
So Scruffie and Jon...do you think it would be more advisable to power this with a charge pump changing 9V into 12V, or would it be better to power it with a 12V wall wart?
(and if the charge pump is okay, could I then just use the Road Rage and modify the regular to an LM78L12 or something else like it?)
The reason I ask is because if there isn't that much of a difference, I'd rather just be able to power the effect from the powr supply I use for most of my 9V pedals (a Dunlop DC Power Brick) because then I don't need to worry about carrying a separate wall wart.
Actually, Scruffie, I looked at the Road Rage at it puts out a maximum current of 100mA. If I understand the Valvecaster-type devices correctly, they require more than that...about 300-500mA or so, or more. If you think using a RR-type charge pump will sufficiently power the circuit at 12V, why is there such concern that the circuit be run at 300-500mA?
I think I can speak for Jon and my self here when we say use a dedicated 12V DC supply for the heaters, once again, a charge pump cannot deliver the 150mA required for that job.
If you wish to use a charge pump to power the plates at a higher voltage however, that is up to you.
I say 24V vs 12V on the plates will make a noticeable difference (far more than the same change would make on an opamp) so using a charge pump (the tubes heaters will still be powered directly from the 12V dedicated wall wart) on the plates is worthwhile for a bit of extra oomph.
Jon is suggesting either just powering both the heaters and plates off the 12V supply and forgetting the charge pump or using an SMPS (think of an SMPS as a sports car instead of a charge pump being the family hatch back) which can provide 100-200V+ to the plates to get the best out of the tube but they are far more finicky than charge pumps, require specific parts choices and can give you a nasty electric shock, i'd save that for later builds when you've gotten some more experience in tube circuits.
The power supply rating of 100ma is not about the power supply limiting it's output to 100ma. The rating of 100ma is the maximum the power supply can provide the circuit. if the circuit "Draws" too much power, more than the power supplies rating, your transformer will be pushed to provide more than it's designed rating, or the circuit will suck too much juice and could smoke the power supply.
Hope this helps.
I know you probably already understand this...
Quote from: MarkL on May 11, 2016, 03:51:43 PM
Actually, Scruffie, I looked at the Road Rage at it puts out a maximum current of 100mA. If I understand the Valvecaster-type devices correctly, they require more than that...about 300-500mA or so, or more. If you think using a RR-type charge pump will sufficiently power the circuit at 12V, why is there such concern that the circuit be run at 300-500mA?
The Road Rage can actually only supply 50mA.
Anyway, I think I see where the confusion is coming from, vastly over simplifying it, a 12A"7 tube has 2 sections, the first section it has are the heaters which turn the tube 'on' these can be run from either 6V at 300mA or 12V at 150mA, they are a separate part of the circuit to everything else.
The second part of the tube is the bit where all the audio stuff happens, this is where the plate (or anode) lives which can take voltages up in to several hundred volts and only draws a small amount of current so that bit
can be powered by a charge pump.
Jon is better at analogies than me so he can probably describe it better.
Actually, I think I know really do understand what's going on here. With all of the different options, and the fact that I want to use this as an overdrive rather than as a boost, I think simply powering the entire circuit (both plates and heaters) at 12 V from a wall wart will be the best option.
Now -- anybody have any suggestions for a preferred 12v DC wall wart to use with this thing? :-)