2nd Gen Build Started (that didn’t take long…)

[Raoul Duke]

Understood. I was planning on the high Vdd, but now I’m wondering which way serves this build/generation best?

One other question:

I plan on using your adaptation of the relay and have a 12v NTE R40-11D2-12 for my relay board. The F313x is 6.3. Does the relay PS board double it somehow?

I see in the original layout that the ice cube was 12v with the F313x, but never noticed the mismatch in voltage until now.

Thanks Martin!

[martin manning]

The 2nd Gen layout shows a voltage doubler which will produce enough voltage for a 12V regulator using the F-313X transformer. Since you have the higher voltage clean boost on your 102, maybe it would be nice to go with the low voltage off-center bias for this one.

[Raoul Duke]

Hey, I think that’s a great idea actually.
I gravitated toward clean boost just because the clean on my 102 is really something fantastic. Making this one two shades of “scream” sounds great. Is there math to scale the 18v result down or do I need to figure out how to get 12v into that board?

Anyhoo, where’s that voltage doubler; in the relay board? If I follow that layout - am I covered?

I know, probably basic questions.

Thanks!

[martin manning]

Is there math to scale the 18v result down or do I need to figure out how to get 12v into that board?

Not really, you need something close to the eventual operating voltage. You can put 12V across the 8k2 and bias it now, or wait until you have the amp working and power it from the B+ rail.

Anyhoo, where’s that voltage doubler; in the relay board? If I follow that layout - am I covered?

The 2nd gen layout relay supply board is a doubler, and the schematic is the same as #040 here: https://ampgarage.com/forum/viewtopic.p ... 834#p57834 The 56k resistor should be 56 ohm as shown in the layout. It is unregulated, but you can put a 12V regulator where that resistor is, on the chassis or on the board, like this:

[Raoul Duke]

I may try and come up with a way to bias it ahead of time. Maybe a lantern battery might do? Or run down the two 9v some? What exactly is low voltage off-center bias in relation to what the FET will sound like? Fuzz pedal? Raw, old tweed? Just curious because this will be a new facet of Dumble tone that I’m unfamiliar with - but I like the idea of, lol.

Do I actually need the regulator or is the regulator an improvement? I understand improving reliability and agree with that; just curious why HAD wouldn’t have included it? Evolving designs?

Since I have the board built I’d likely put it in the usual spot in the corner. Luckily I have a 7812 on hand also if needed. Just checked and I have the 56R installed - so somehow I caught that one, lol.

Thanks again!

[martin manning]

I may try and come up with a way to bias it ahead of time. Maybe a lantern battery might do? Or run down the two 9v some? What exactly is low voltage off-center bias in relation to what the FET will sound like? Fuzz pedal? Raw, old tweed? Just curious because this will be a new facet of Dumble tone that I’m unfamiliar with - but I like the idea of, lol.

Any way you can put 10-12V across the 8k2 will work. One 9V plus a 1.5V AA in series would be fine, I think. Per observations of real Dumbles, the man seemed to favor the lower voltage, lower headroom approach rather than a big clean boost. An additional flavor of distortion, maybe? You can play with that ad nauseam after it's all working.

Do I actually need the regulator or is the regulator an improvement? I understand improving reliability and agree with that; just curious why HAD wouldn’t have included it? Evolving designs?

The regulator is an improvement, and since the relay will work with a pretty wide range of coil voltage, it's not really necessary.

[Raoul Duke]

Understood, thanks Martin,
I like the idea of the different flavor the more I think about it

One last regulator question and I promise I’ll quit bugging you about it, lol:

What are the advantages to including it in this build? I figure the only disadvantages are cost (which I’ve already covered by having spares on hand), time/effort to install (which isn’t a huge factor for me at this point), increase in parts count which introduces some increased risk of potential failure, and not staying true to the original (which I’m not a slave to if it increases reliability/performance).

In other words; if the juice is worth the squeeze - I’ll squeeze it. If it’s a case of solving a problem that has a low probability of existence - maybe not.

Any wisdom you can provide is always appreciated!

Thanks!

[martin manning]

Well the cost is negligible at $1.50 or so. You could just add one eyelet to your relay ps board and put it there. Personally I would feel better doing that, and power the relay and the footswitch LED with regulated 12VDC. The doubler will probably deliver 17 VDC or more, depending on the transformer's regulation..

[Raoul Duke]

Easy enough and makes a lot of sense. I’m sold.

So I’m adding an eyelet for pin 2 running to ground, getting rid of the 56R and jumpering straight to the cap in its place?

I’m assuming based on the low voltages involved heat won’t be an issue? I ask because I’ll likely shorten the 7812 pins due to space constraints, so it won’t be “flappin’ in the breeze” as much, lol.

Thanks Martin - I learn something pretty much every time you pop in. I appreciate that!

[martin manning]

All correct. My math says you don't need a heat sink, but you could bolt a little u-shaped one on if you like.

[Raoul Duke]

Looks like I have the space to add a second 1k for the footswitch feed (per your first drawing with the regulator) - can I just daisy chain it to the original 1k? I imagine one is for the relay board and one is for the footswitch?

[martin manning]

Relay coil(s) are fed directly from the reg output (from the positive end of the output cap, as shown in the 2nd Gen layout). Adding another 1k would be exactly as in my earlier drawing, both of them coming off the 12V output, and separate leads to the foot switch jack. In that drawing, one was for the footswitch and the other was for an LED panel indicator. Daisy chain implies series to me, this is more like parallel.

[Raoul Duke]

Understood, thanks Martin.
I’ll stick with the second drawing then; my indicator light is 6v. Been making my cabinet yesterday and today, but now I’m going to try and get this relay board sorted.

Is there a limit on how much I can clip from the regulator pins? Probably a silly question…

I appreciate the help!

[martin manning]

I'd leave 1 cm or 3/8" above the eyelets.

[Raoul Duke]

I planned on it being free-standing above the board - but then noticed I’m close to the screw that fastens the board. I don’t think I need to fasten it down with the screw, do I?