Tube Preamp Project: advise and discussion

[MJ_Sound_Cubed]

First, here is a verified 555 SMPS layout:



Here is a video of guitar amplifier with a 555 SMPS played clean with a Stratocaster, and it does not have any noise issues.

Having tried both, back to back trafos ( even some I wound) and the SMPS, I have learned that the SMPS is as quiet as the power supply it is plugged in, the quality and material of the output capacitor and the layout.

I also use a 6V regulator with a schottkey between middle pin and ground for 6.3V as I don't want to cram a 5W resistor into my pedals

Now my dear friend vigilante397, Can you tell me more about that heater PSU with diodes and other parts? 

[vigilante397]

Now my dear friend vigilante397, Can you tell me more about that heater PSU with diodes and other parts? 

Absolutely. I'm on my phone so I can't draw anything up for you, but this is how I do it:

I use an L7806 regulator, or a 78M06 on SMD builds. The middle pin is the GND reference, so if you tie it to common ground you will get a 6V output. If you get a schottkey diode with a 300mV forward voltage between that pin and ground then your output will go 300mV higher, meaning a 6.3V output.

I have also seen this done with an L7805 and two 1N4001 diodes. They have a forward voltage of 700mV, so a pair of them in series between the GND pin and ground will bring you 1.4V higher for a 6.4V output. A lot of people like this better because you're more likely to already have some 5V regulators lying around.

As with any voltage regulator it's a good idea to put filter caps on the input and output. I usually do minimum 220nF on input and minimum 100nF on output. So aside from saving space over a resistor this also ensures you will get nice quiet DC voltage for your heaters

EDIT: Just remembered I had this pic on the OmniBox thread so I can throw it in here so you see what I did. And you can ignore the extra filter stages on the 555 SMPS, it was an experiment that didn't add any benefit.

[johngovan1234]

here is my pcb layout. Copied from Waltk with some traces modifications. not yet verified.

[rankot]

Nice layout, but better check inductor size. This inductor must be 3A rated, best with toroidal core.

[vigilante397]

This inductor must be 3A rated

I agree the inductor footprint should probably be bigger, but 3A seems excessive. The ones I use are rated for 1.9A and they do fine.

Definitely agree with the ferrite core though. It's not a bad idea to find an inductor first then make your footprint, rather than trying to force whatever you find into the footprint you made.

[pravudh]

My first tube pedal with SMPS it make strange resonance noise issue when I play with Flanger pedal.

I do use back to back power transformer 12VAC 300mA. it work great without problem. I did try SMPS  it have noise issue.

Amazing work! Do you have a demo of this sir?

[MJ_Sound_Cubed]

here is my pcb layout. Copied from Waltk with some traces modifications. not yet verified.

Great layout, for less thank 15mA like a single tube preamp, even a 100uH 1A ferrite core inductor is enough. Please make sure the layout has space for a radiator in the MOSFET.

My first tube pedal with SMPS it make strange resonance noise issue when I play with Flanger pedal.

This happened when the phaser was before of after the SMPS effect?

Now my dear friend vigilante397, Can you tell me more about that heater PSU with diodes and other parts? 

Absolutely. I'm on my phone so I can't draw anything up for you, but this is how I do it:

I use an L7806 regulator, or a 78M06 on SMD builds. The middle pin is the GND reference, so if you tie it to common ground you will get a 6V output. If you get a schottkey diode with a 300mV forward voltage between that pin and ground then your output will go 300mV higher, meaning a 6.3V output.

I have also seen this done with an L7805 and two 1N4001 diodes. They have a forward voltage of 700mV, so a pair of them in series between the GND pin and ground will bring you 1.4V higher for a 6.4V output. A lot of people like this better because you're more likely to already have some 5V regulators lying around.

As with any voltage regulator it's a good idea to put filter caps on the input and output. I usually do minimum 220nF on input and minimum 100nF on output. So aside from saving space over a resistor this also ensures you will get nice quiet DC voltage for your heaters

EDIT: Just remembered I had this pic on the OmniBox thread so I can throw it in here so you see what I did. And you can ignore the extra filter stages on the 555 SMPS, it was an experiment that didn't add any benefit.

This was a fantastic help Do you use SMD parts?

[vigilante397]

This was a fantastic help Do you use SMD parts?

Mostly, yup 1590B is my absolute favorite enclosure size, but I LOVE tube pedals, so I've been using Russian submini tubes and SMD to fit any tube pedal I want into a 1590B. This is my latest, a tube-driven BTDR-2 reverb. An excellent example of making a footprint before I had the component That's why the regulator footprints are so much bigger than the actual component. Whoops

[MJ_Sound_Cubed]

This was a fantastic help Do you use SMD parts?

Mostly, yup 1590B is my absolute favorite enclosure size, but I LOVE tube pedals, so I've been using Russian submini tubes and SMD to fit any tube pedal I want into a 1590B. This is my latest, a tube-driven BTDR-2 reverb. An excellent example of making a footprint before I had the component That's why the regulator footprints are so much bigger than the actual component. Whoops

That a really good looking idea, how does it sound like? Do you have a demo.

I have some of those 6n17b and 6n16b submini tubes. But never thought about something as cool as hybrid pedal sized, tube powered reverb like that

Those boards look seriously good you are ordering them from where ?

I saw your page you have some really cool work going on. Why are closing down your website next week? Thats a pitty.

Final question:

Do you like tiny tube amps?

[vigilante397]

That a really good looking idea, how does it sound like? Do you have a demo.

I have some of those 6n17b and 6n16b submini tubes. But never thought about something as cool as hybrid pedal sized, tube powered reverb like that

Those boards look seriously good you are ordering them from where ?

I saw your page you have some really cool work going on. Why are closing down your website next week? Thats a pitty.

Final question:

Do you like tiny tube amps?

In order: Not only do I have a quick demo, there's a whole thread https://www.diystompboxes.com/smfforum/index.php?topic=120732.0

The boards are from Elecrow. Now that I actually know what I'm doing in the design stage I get consistently good results from Elecrow boards.

I'm not actually closing down my page, more just focusing less on it. I mostly wanted a .com website when I was in college to impress recruiters, but now that it worked and I have a job there's less of a need So I'm keeping the URL but closing down the eCommerce because it costs quite a bit and in the 2 years the website has been up I have had $0 go through it. 100% of my sales have either been local word-of-mouth or people on Facebook that pay me with PayPal. So I stopped updating the official website and all of my updates and stuff has been on my Facebook page.

And lastly, I love the idea of tiny tube amps, and building one has been on my to-do list for years now, but I've never really gotten around to it I have all the parts I would need just sitting around my garage, I just need to clear out my backlog, which will take approximately forever. But as soon as forever is over I absolutely plan to build a tiny tube amp. Probably something high-gain, because that's the main sound I'm missing in my arsenal right now

[johngovan1234]

This was a fantastic help Do you use SMD parts?

Mostly, yup 1590B is my absolute favorite enclosure size, but I LOVE tube pedals, so I've been using Russian submini tubes and SMD to fit any tube pedal I want into a 1590B. This is my latest, a tube-driven BTDR-2 reverb. An excellent example of making a footprint before I had the component That's why the regulator footprints are so much bigger than the actual component. Whoops

What a great work sir. Very professional looking circuit.

[johngovan1234]

I found this inductor on my old router. Can i use this tho it is rated 150uH?

[vigilante397]

I'm going to go with probably. 100uH is a good number for the inductor, but not a magic number by any means. I've seen plenty of people that just used whatever inductor they had lying around and had it work just fine.

[MJ_Sound_Cubed]

Usually 100uH do the job well

[rankot]

Simulation shows that bigger the oscillator frequency, lower inductance should be.

[johngovan1234]

My next question is what are the voltage rating of coupling capacitors, tone stack capacitors and cathode capacitors? Thank you..

[MJ_Sound_Cubed]

 

I would recommend 30% higher than the anode and cathode voltages.

[vigilante397]

For coupling absolutely aim high. For preamps I usually shoot for 300V plate voltage and I use 400V coupling caps. For tone stack caps it depends on the setup of your tone stack. If there's another cap between the high voltage and the tone stack then you can get away with lower voltage caps in the tone stack.

[johngovan1234]

my buying list. i already have resistors and cheap cathode capacitors at home. I think it will do the job.

[johngovan1234]

thank you for all the responses. please bear with me through a lot of questions. can i replace te uf4007 by 1n4007 in power supply? thanks again guys. Highly appreciated.