Power supply for digital reverb from AC heater winding

[dobrota]

Hi, I need power supply for Belton BTDR2 digital reverb module (5V DC) in my DIY tube amp. It isn't problem if heater winding has central tap connets to ground, but there it isn't on my power transformer I use typical two 100 ohm resistors connent to ground to eliminate heater hum. If I add rectifier / caps / 5V regulator for reverb module, I need connect to ground also their negative points. Will it work correctly without hum or is an special technique to solve it ?
Thanks for Your advices.

[loudthud]

How much current does the reverb require? Getting clean DC from a 6.3V heater winding can be difficult. You can't use a 7805.

What you can do is connect the 6.3V to a bridge rectifier, ground the minus output of the bridge. Leave the virtual center tap connected on the AC side but connect a capacitor, maybe 100uF at 10V, from the virtual center tap to ground. It will have about 4V DC on it.

[dobrota]

How much current does the reverb require? Getting clean DC from a 6.3V heater winding can be difficult. You can't use a 7805.

What you can do is connect the 6.3V to a bridge rectifier, ground the minus output of the bridge. Leave the virtual center tap connected on the AC side but connect a capacitor, maybe 100uF at 10V, from the virtual center tap to ground. It will have about 4V DC on it.

Reverb consumption is about 70mA. Yes, I'm thinking about bridge rectifier with ground the minus output, than capacitor about 470u-1000u, 7805 regulator and an smaller capacitor about 47-100u. But I wasn't sure what to do with common ends of virtual tap resistors. Thanks, I'll try it.

[R.G.]

Maybe a simpler and easier way to do this is to find a small DC-output wall wart. Some of them even provide regulated 5Vdc out. Hide/bury this inside the amp, clamping it in place so it doesn't move around and wiring its AC prongs in parallel to the power transformer primaries.

- no dinking around with your filaments
- safe(r) if the mechanics are done well
- simpler to debug if something goes wrong

[jrfrond]

It usually isn't a problem to fit a small filament transformer in most tube amps, plus a small board to contain a bridge rectifier, two small filter caps and a 7805 regulator, which will NOT have to be heat-sinked for that current demand.

Because it is digital, you need a clean, stable +5V supply. Don't gamble using the heater supply. Another reason is that if a tube develops a heater short, you'll probably kiss the Belton module goodbye.

Since the Belton does need a few peripheral components, you can fit the power supply components on the same board.

[trobbins]

You could check if the heater hum becomes a problem if you connect one heater end, or the other end to ground (ie. don't use a humdinger). If hum is not any worse, then you could use a capacitor fed doubler rectifier to provide a DC supply for the reverb module with the same 0V reference as the heaters.

[Smitty]

The radio shack 273-1385B is a great transformer for this application. http://support.radioshack.com/suppor...oc40/40996.htm
Its small enough that you can fit it inside the chassis of many amps. Bridge rectified it will deliver almost 13V which you can use to feed a 78L09 for some jfet action and then cascade the 78L05 off the 78L09 for the digilog. Make sure you have your regulators hooked up right before you connect the supply to the Digilog.

The transformer caps and regulators take up very little space if laid out carefully. Dead quiet if you are careful with grounding. I tried everything under the sun to get those five volts off the heater supply. Never got it quiet enough for my liking.

[Steve Conner]

I also had hum troubles that wouldn't go away, trying to run a digital reverb module off the heater supply. I think it was a grounding issue, and I could probably have solved it by star grounding right at the module, but I couldn't do that as I was also running channel switching relays off the same supply.

I ditched it for a spring reverb pan (same price as the module!) but the little Radio Shack transformer would also be a good solution.

[R.G.]

While you're at it -

Since you're making a DC supply which shares the signal ground with your amp, why not make it put out 9Vdc regulated, as suggested above, but make it put out up to about 1A, which you get with one 7809? The you can put a 3.5mm/1/8" phone jack or DC barrel jack on the back of the amp and feed out 9Vdc to power a pedal board. No need for a power cable to the pedalboard then.

I did this on the Workhorse amps, and it worked very well.

[Gtr_tech]

Got a little cell phone charger in yer junk drawer? One of the little switcher types would work great.

[dobrota]

How much current does the reverb require? Getting clean DC from a 6.3V heater winding can be difficult. You can't use a 7805.

What you can do is connect the 6.3V to a bridge rectifier, ground the minus output of the bridge. Leave the virtual center tap connected on the AC side but connect a capacitor, maybe 100uF at 10V, from the virtual center tap to ground. It will have about 4V DC on it.

I tried rectifier - capacitor - 7805 - capacitor, ground minus output of the bridge and capacitors without virtual center tap and it works ! It seems both heater winding ends connected to ground through rectifier diodes it works as virtual tap, difference in hum without center tap is very little. But I'm very disapointed of reliability of BTDR-2 module. I used it in recomended circuit from Belton site, strong resistor divider to protect input, resistors and capacitors on outputs to protect shortcut and after some time of working it failed - no reverb on output, current consumption incresead from 70mA to about 120mA. I thought this way is wrong, I made some mistake, so I bought other one, I increased resistor divider, I added two diodes antiparallel to ground for better input protect and I used other small low voltage transformer, no heater winding. I checked power supply, I checked levels - max about 0.2-0.5V on input, well, all is OK.... but after some hours of working Belton module almost burned!! again, power consumption of it is even about 300mA now. I don't understand what happend and I don't wan't try it again, I'll use some digital multieffect in front or in effect loop of this tube amp.

[jrfrond]

Problems like this tend to arise a lot with people who have the tube amp thing sussed, but haven't worked much with digital. You always get multiple screw-up chances with tubes, and there's a lot of latitude in the design work. Digital, on the other hand, affords you extremely little leeway, and "dirty" DC is a common problem with digital circuits. This is why using the heater winding is a really bad idea. You need super-clean, regulated B+ Treat it as a separate entity totally, only enclosed in you amp. BTW- I don't know the temperature range specs of the Belton, but you'll need to take those into account also if burying it in an amp. The module will need to be in a cool area of the chassis, relatively-speaking.

[loudthud]

Not much info I could find online about this module except one little spec sheet on AES. http://www.tubesandmore.com/sites/de...tdr_spec_0.gif

The only things I can say are to make sure the power supply is 5V +/- 0.5V and that the input and output never get any big voltage spikes. A diode clamp on the input should protect against any problem there. Two or three diodes for each polarity.

[dobrota]

Problems like this tend to arise a lot with people who have the tube amp thing sussed, but haven't worked much with digital. You always get multiple screw-up chances with tubes, and there's a lot of latitude in the design work. Digital, on the other hand, affords you extremely little leeway, and "dirty" DC is a common problem with digital circuits. This is why using the heater winding is a really bad idea. You need super-clean, regulated B+ Treat it as a separate entity totally, only enclosed in you amp. BTW- I don't know the temperature range specs of the Belton, but you'll need to take those into account also if burying it in an amp. The module will need to be in a cool area of the chassis, relatively-speaking.

As I wrote, I tried second piece of BTDR-2 using separated power supply (small PCB transformer, rectifier, caps, 7805 5V/1A IC), not with heater winding, but it failed again I also checked temperature of 7805 and Belton module, all was OK.
I built some digital delays with PT2399 (btw the're 3 pieces of it inside of BTDR-2) and one digital multieffect with board using Alesis ALS3xxx IC before, and all it work for years without any problem.
So I really can't understand what is wrong with this Belton digital reverb.