ValveCaster Mods

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ValveCaster Mods

Postby snk » 02 Mar 2018, 09:53

Hello
I am willing to build a modded Valvecaster, and i would need some advices from the community.
I picked some hints from the nice document found here : https://cdn.instructables.com/ORIG/FXM/ ... 1FLK5B.pdf

The mods are :
1- feeding it 12V (instead of 9V) to get more headroom and have the tube work at the texpected specs.
2- adding a regulator to get rid of hum and buzz.
3- being able to have more gain if desired, by adding a switch.
4- bass boost mod.

My questions are the following :

1- Is the overall wiring correct (For the 3PDT, i followed the general MadBean/TagboardFX wiring) ?

2- I am not a total newbie, but still a beginner. So, i don't know at all if the "gain mod" would work (original circuit use a 50K pot, and some users complain there is not enough gain. One user said that with a 1M pot, the gain allowed for "massive saturation", so i thought that adding a 470K resistor in serie would give a 530K value, and thus giving more gain : am i correct :scratch: ) ?

3- is the wiring for the bass boost mod ok ?

4- I have read that the overall tone is dark, and that even when fully clockwise, the tone pot sucks high frequency : is there any way to know it from the component values ? And, can i change some component to have the pedal sound brighter (full spectrum) when the tone pot is full clockwise ?

5- I am planning to use the pedal with synths (not guitars) : i would like to know if some capacitors in the early signal path are cutting low frequencies or high frequencies ( = is the pedal tuned for guitar, or "general purpose") ? Getting rid of the some bass mud before hitting the tube is fine, but i would like to know, to learn about it :D

Thank you in advance ! 8)

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Re: ValveCaster Mods

Postby plush » 02 Mar 2018, 11:04

Hi
Why won't you supply your anodes with 15v instead of 12v?

c1 at the input cuts down the low freqs
Increase it's value to allow more low freqs into your signal path

Btw, it's not the regulator, that removes buzz/hum from ac heater, but correct wiring/cable management.
You are dealing with dc heaters, since your power input is DC, so noise is not the issue.

Also 2200uf power cap is a total overkill, why would you need that?

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Re: ValveCaster Mods

Postby snk » 02 Mar 2018, 17:00

Hi, Plush
Thank you for your answer.

c1 at the input cuts down the low freqs
Increase it's value to allow more low freqs into your signal path

Ok, thank you for the hint.

Why won't you supply your anodes with 15v instead of 12v?

Also 2200uf power cap is a total overkill, why would you need that?

I don't know : it is my very first tube project (and, as far as DIY goes, i'm also quite a rookie)... As the tube is specified for 12V, i first planned to feed it with a regular 12V power supply. But a friend avised me (as i also have read on the PDF quoted above) that adding a regulator would get rid of possible hum, buzz and hiss, so i went that route.
It's the same for the 2200uf power cap : i just followed a schematic i found on the web, but as i am not familiar with regulators, i must say i am not really knowing yet what i'm doing (still learning) :lol:

I think I will first build the original version, with fewer features and no regulator, and, once it's working, i will fine tune it with more features and the regulator.
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Re: ValveCaster Mods

Postby snk » 02 Mar 2018, 18:13

Ok.

- I built the basic version : it somewhat works, but i must have done something wrong in the wiring, as i have a loud hum, nearly as loud as the "clean" signal. I need to find the source of the humming, maybe a wrong ground wiring ?
When I touch the C2 capacitor, most of the hum disappears.

- I have tried a 22nF value for C1 : it rolls off some bass from the input. I am considering adding a switch with two resistors values : one "bass friendly" cap, and one with a low end roll off to ease up the tube.

- I have tried to put a 470K resistor after the Gain pot, to see if the input volume would me much louder :it is the opposite, ah ah! :( :slap:

- The tone knob seems to sound a bit strange, not the expecteed smooth lowpass. But i think it is as it should be, i need to first fix the buzz issue to listen to the processed sound better :blackeye

- I have used an electrolytic cap for C3, and a polyester film for C1 : does it matter ?

- I have also read that "adding resistance to R1 and R2 will increase gain". Does this mean that if i swap R1 (1M) for a 1.5M resistance value, and R2 (220K) for a 470K value i will have more input gain ?
Quelle valeur, alors ?
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Re: ValveCaster Mods

Postby snk » 02 Mar 2018, 18:58

So, i tried with a 9V power supply : it's hum & buzz fest. With a 15V power supply : it sounds gorgeous, noise free 8)
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Re: ValveCaster Mods

Postby deltafred » 02 Mar 2018, 20:29

Content removed because I misread your posts.
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Re: ValveCaster Mods

Postby deltafred » 02 Mar 2018, 20:45

snk wrote:So, i tried with a 9V power supply : it's hum & buzz fest. With a 15V power supply : it sounds gorgeous, noise free 8)

This is not surprising, you were feeding a 12v regulator with 9v! A 7812 regulator needs at least 14v at the input to to work correctly.
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Re: ValveCaster Mods

Postby snk » 02 Mar 2018, 21:19

Hi, and thank you all for your replies.

This is not surprising, you were feeding a 12v regulator with 9v! A 7812 regulator needs at least 14v at the input to to work correctly.

Sorry, Deltafred, i wasn't clear enough : i didn't build the exact schematic i posted, with the regulator, bass boost & other features, i just built the regular Valvecaster as a "workbench", to hear the core sound, check if it works and try some mods afterwards.
So, as the original Valvecaster was supposed to run on 9V, i didn't expect such buzz and humming :shock:
Trying it on 12V gavbe me more volume... and more buzz accordingly :lol:
15V was plain clean and juicy :)

I socketed every capacitor, and it's easy to desolder the resistances, so i will try tonight to change some values and check how it sounds/work.

On my build, with 9V, the tone pot changes the sound (but it's hard to tell accurately what it does, as the buzz is a loud as the signal), but fed with 15V, i don't hear any change from the tone knob.
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Re: ValveCaster Mods

Postby snk » 03 Mar 2018, 01:47

I realized there was an error with the level pot not wired to the output sleeve.
Once wired, everything worked fine... until i decided to wire my build to a 3DPT :evil:
Now, i hear a strange noise (like white noise, not really a 50hz hum), the tone pot doesn't make much change... and when i turn the level knob anticlockwise, it obvioulsy reduce the output volume but it also damp the signal :scratch:
This is the schematic i used, i tried and checked many things, but i can't figure out what's wrong with it...
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Re: ValveCaster Mods

Postby ppluis0 » 03 Mar 2018, 04:11

Hi snk,

You can employ a 12AU7 tube that have reported to has better sound than 12AX7 or 12AT7 as suit better low voltage at it's anodes.

Also can modify your circuit to have a transistorized constant current source feeding pin 1 on the tube and put pin 3 directly to ground. This way the first triode section have plenty of gain and the scratchy 50 K potentiometer can be avoided. 8)

valvecaster_CCS.jpg
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Re: ValveCaster Mods

Postby snk » 03 Mar 2018, 10:38

Hi, Ppluis0

ppluis0 wrote:You can employ a 12AU7 tube that have reported to has better sound than 12AX7 or 12AT7 as suit better low voltage at it's anodes.

Yes, i am using a 12AU7 tube right now :wink:

ppluis0 wrote:Also can modify your circuit to have a transistorized constant current source feeding pin 1 on the tube and put pin 3 directly to ground. This way the first triode section have plenty of gain and the scratchy 50 K potentiometer can be avoided. 8)

This is my first tube build : i'm planning to do some more later, ah ah ! :D

... any idea where the noise can come from since i added the 3PDT (the signal was clear before) ?
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Re: ValveCaster Mods

Postby marcao_cfh » 03 Mar 2018, 17:03

snk wrote:But a friend avised me (as i also have read on the PDF quoted above) that adding a regulator would get rid of possible hum, buzz and hiss, so i went that route.

The regulator's job is, well, to regulate an DC voltage. It's not the regulator that would get rid of possible hum in tube circuits, it's the DC voltage feeding the tube heater. To keep things short, in tube amps the heaters are usually feed by AC current. The wires need to be twisted together, so the electromagnetic field around each wire cancels the other wire's field, avoiding inducted hum. But if you feed the heaters with DC voltage, you don't need twisted wires.

snk wrote:- I built the basic version : it somewhat works, but i must have done something wrong in the wiring, as i have a loud hum, nearly as loud as the "clean" signal. I need to find the source of the humming, maybe a wrong ground wiring ?
When I touch the C2 capacitor, most of the hum disappears.

Probably a ground issue. Check your wiring for ground loops or some place that had to be connected to ground but it isn't.

snk wrote:- I have tried to put a 470K resistor after the Gain pot, to see if the input volume would me much louder :it is the opposite, ah ah! :( :slap:

Yes, adding a resistor in the signal path would reduce the signal. To get volume boost, you'll need a gain stage.

snk wrote:- I have used an electrolytic cap for C3, and a polyester film for C1 : does it matter ?

Most of the times, it doesn't matter. Just be sure they can handle the supplied voltage. To be safe, if you power the effect with 9V, have eletrolytics at at least 16V. Ceramic and polyester caps have higher voltages.

snk wrote:Trying it on 12V gavbe me more volume... and more buzz accordingly :lol: 15V was plain clean and juicy :)

Probably your 12V supply doesn't have a good filtering. If yes, your effect will be noisy.

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Re: ValveCaster Mods

Postby marcao_cfh » 03 Mar 2018, 17:20

snk wrote:... any idea where the noise can come from since i added the 3PDT (the signal was clear before) ?

Since you got it working before adding the 3PDT, the problem is in the 3PDT or in the extra wires.

Just to be clear, you did made it using the schematic you've posted, and it worked fine before adding the 3PDT? I ask this because I didn't checked the circuit itself, just the 3PDT wiring, and it's fine.

One possible solution is to keep the wires as short as possible. Another one is to try to swap the 3PDT, you may have a faulty one.

But you should also note is that the schematic you've posted, as it is, have a ground loop. If you don't know what's a ground loop, I'll explain: let's start at the input. Ground wire goes to power jack, then to output jack. So far so good. But ground from output jack is connected to the switch, that's also connected to input jack. So you have 2 ground paths that connects the input and output jack: one via the power jack and other via the switch. The same means for almost all the other ground connections. For example, the input jack and power jack grouns are connected directly and also are connected via in jack->switch->out jack-power jack path. Also, if you put everything inside a box made of metal, you add another ground path: the enclosure itself connects in jack and out jack sleeves together (if they're not made of plastic). That is what a ground loop is, two or more ground paths in the circuit.

So, I suggest you to try this before trying anything else: see that black wire that goes from switch to output jack sleeve? Remove it. Also, when you put the circuit is inside a metal enclosure, if you use 2 jacks with metal nuts, the enclosure itself will connect input jack sleeve and output jack sleeves, so you need to use at least one plastic jack or remove this connection made by wires. Just remove the black wire that connects input jack and power jack OR the black wire that connects power jack and output jack.
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Re: ValveCaster Mods

Postby snk » 03 Mar 2018, 19:09

Thank you very much, Marcao :thumbsup

I know what a gground loop is, from my studio experience, but dealing with a ground loop when building a pedal is something completely different for me :D I know that the nasty hum i am hearing may be related to a ground loop, but i don't know how to fix it myself in the circuit. With your explanation, it gives me great hints.

I know about the black wire going from the input sleeve to the output sleeve : it's here only while my circuit is enclosure-less. But since it will be put into a metal enclosure, i will remove it (yes, my jack nuts are made of metal, as well as my enclosure).
I will remove the black wire that goes from switch to output jack sleeve, and see what happens, thank you very much !

I will read all your post, it's full of nice suggestions for this project, as well as for others.
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Re: ValveCaster Mods

Postby marcao_cfh » 03 Mar 2018, 19:29

Usually, I like to have 3 ground points on the circuit board:
- one goes to power jack;
- one goes to input or output jack sleeve;
- one goes to the switch.

Of course, besides all the pots/switches that have ground connections. If the don't have their connection on the board, I just connect them together if there's more than one, then connect them to input or output jack sleeve. Not necessarily the same one that's connected to circuit ground. That way, I'm sure there's no ground loops caused by wiring (there may have ground loops on the circuit board layout itself, but that's another story...)

Also, you said about something like a white noise. That may be solved when you put everything inside a metal enclosure.

And forgot to said about using it in synths. Yes, the valvecaster can be used in synths. Check this video: https://www.youtube.com/watch?v=FHOXIhWkpss

One cool mod you can add to the Valvecaster is a pair of clipping diodes to ground after the output cap. Just connect two diodes in parallel, one pin of the pair connected to lug 3 of the volume pot and the other pin of the pair connected to ground. You'll get some distortion from the clipping diodes, but also will get a lower output volume, so it's a better idea to make the diodes switchable (just add a spst switch between volume pot and the diodes).

Let us know if you get the problem solved.
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Re: ValveCaster Mods

Postby snk » 04 Mar 2018, 01:14

Hello
In the end, i managed to make it work :horsey:
I desoldered everything, put the compenents in the enclosure, and started to rebuild everything from scratch.
My 3PDT wiring was wrong (i made several schematics, involving various mods, and in the end i messed everything up i guess, ahah). I draw a new 3PDT wiring schematic, and then i compared with other pedals i built last year.

Also, I noticed a couple things :
1- I tried 3 power supplies, and voltages : The Valvecaster is really clean @15V, but when fed with 9V or 12V there is a loud huzz coming from the power supply. It was expected with 9V (underpowered tube), not really with 12V. Is it really harmful for the tube to be ran at 15V ?
2- I understand why i was confused yesterday : the tone pot seems to be acting backwards (like the RAT : it filters the high freq when turn clockwise, which is strange), and also its action seems really tied to the level knob : when the level is at max position, the tone has no effect. You have to lower the level to have the tone effective :scratch:
I guess that i just have to wire pin 3 of the tone pot to pin1 to have it working as expected, right ? The strange thing is that i don't think i wired it the wrong way, it seems that it is set like that by design ?
About the tone pot amplitude being tied to the level amount, is there any way to fix that ? I also noticed that the level pot acts as a low pass filter too : if you decrease the level value, you filter out some high frequency... that's rather strange.

All in all, i enjoyed building the Valvecaster, and i am willing to use this build to try some mods (bass boost mod, input bass cut mod, mayeb also the diode clipping mode you suggested). But i understand that it is a very simple design with several limitations and imperfections. Is there any more advanced, well designed tube overdrive project which would be still easy and safe to build ?

If you want, i can post pictures of my build ?
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Re: ValveCaster Mods

Postby marcao_cfh » 04 Mar 2018, 04:38

About the tone pot, try this:
- disconnect the tone pot and C4;
- connect C3 to lug 3 of the volume pot;
- connect one pin of C4 to lug 3 of the volume pot, and the other pin to lug 3 of the tone pot;
- connect lug 2 of the tone pot to ground.
The schematic you've used have signal>tone pot>filter cap>ground path for the tone pot, while others have signal>filter cap>tone pot>ground path. Doing these things changes the path from the first option to the 2nd. Try and see if this fixes this issue.

Also, if you think it's working in reverse, just move the wire from lug 3 to lug 1.

About the power supply, if the circuit works fine with one power supply and bad with other, the problem may be at the "bad" power supply. First check the current capacity, 12A_7 heaters @ 12V needs 150mA, so your power supply needs to have more than that capacity (let's say 200mA to 300mA to be safe). Or maybe it have poor filtering. You can do this test if you want: add a power filtering cap to the power jack. Something like 100uF or 220uF (rated to at least 25V), then try your 9V or 12V supply. If noise is gone (or you have less noise) you have poor filtering on your power supply.

I saw some Valvecaster schematics fed by 24V. A 12A_7 can handle way more than this at the plates, a lot of preamps are fed with 250V or even more, the main issue in this case are the heaters, which needs 12,6V (or 6,7V and 300mA if you wire them in parallel, but it's not the case). So, if you use voltages more than 12,6V, you'll need an regulator. To add it, keep pin 4 connected to ground and disconnect pin 5 from power supply. Connect the regulator to the power supply and fed the regulated voltage to pin 5. But maybe 15V won't do too much harm to the heaters (let's wait some opinions from the guys who knows more about this, I'm still a beginner on tubes too).

About more advanced and safe circuits, well, there's some tube projects around the internet that works at 12V. But they're opamp gain stages and "starved plate" tube stages. Or also you can do 2 Valvecaster in series. If you want that true tube tone, you'll need to go high voltage. But it's not as dangerous as you may think, you just need to be careful on working with high voltages. And there's a few options to get high voltage to power a tube amp besides using specific transformers. You've just did your first step into tube circuits, sooner or later you'll be building a tube amp :wink: .

Also, post pictures of your build if you want. Postimages.org is nice for uploading photos. Easy, free and doesn't ask for registration.

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Re: ValveCaster Mods

Postby Manfred » 04 Mar 2018, 05:34

Is the value of R1 with 100 Ohms right?
In such case a current of 120 Milliamps into the LED would be feed in.
ValveCasterRichHoltModCS.jpg
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Re: ValveCaster Mods

Postby ppluis0 » 04 Mar 2018, 19:50

Hi Manfred,

Perhaps was a mistake of Mr Holt at the time to draw his schematic. :roll:

I think that a constant current source should look like this:

Image

The current is calculated as: (Vled-Vce)/Re and the Hfe of the transistor is irrelevant.

Cheers,
Jose

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Re: ValveCaster Mods

Postby snk » 04 Mar 2018, 20:04

Once again : thank you all for your advices :hug:
Here is a picture of the enclosure build. It was my first time trying to bend a metal sheet, and i'm quite please with the result ;)
Image
... And the final build :D
Image
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