Fender Style Mosfet Reverb Board

[rp]

http://www.tube-town.net/ttstore/Kits/M ... :6830.html

The LNDVerb kit is based on a classic Fender reverb circuit, but uses LND 150 Mosfets instead of tubes. These can be operated at voltages as high as 500 V, to get as close as possible to the characteristics of real tubes.

Anyone seen? These things tend to have their equivalents from Mojo or Weber and I'm wondering if anyone has tried and their opinion.

[Stevem]

Mosfets do sound very tube like! but for this I do not like the greater frequency range they drive the pan with, I like the sound of that small OT rolling off the bottom and top range like it does for the most part!

[xk49w]

Mosfets do sound very tube like! but for this I do not like the greater frequency range they drive the pan with, I like the sound of that small OT rolling off the bottom and top range like it does for the most part!

It does use a conventional reverb transformer so there will be some bandwidth limitation on the reverb drive signal. No schematic apparently.

[M Fowler]

http://www.tube-town.net/info/datenblae ... ndverb.pdf

[R.G.]

Kewl. Someone else has tumbled to the MOSFET Follies.

From 2000:
http://www.geofex.com/Article_Folders/m ... tfolly.htm

From 2002:
http://www.geofex.com/Article_Folders/s ... remolo.htm

From 2012:
http://www.geofex.com/FX_images/Return% ... Fol....pdf

And going backwards:
http://www.geofex.com/Article_Folders/t ... be-wah.htm

There are some issues in doing high voltage MOSFET replacements for tubes. These are largely in the area of the gate-source capacitance being higher than the grid-cathode capacitance on a tube, and the very much higher transconductance that a MOSFET has compared to a tube.

IMHO, MOSFETs sound more like pentodes than triodes, but that's quibbling.

There is usually a way to tame the gate capacitance and transconductance issues. What you don't get is any softly curvy plate characteristic distortion or grid conduction effects, so the distortion characteristics aren't the same. But for places where you're not looking for the distortion results, like in a reverb or a follower, it's pretty useful.

[tubeswell]

And here's another variant of RG Keen's design for a FET-based stand alone reverb unit based on the 6G15 topology

http://surfybear.weebly.com/fet-reverb---project.html

[matt h]

Avoiding community circlejerks, I've only recently been getting into anything transistory. While I'm a fan of the LND150s now... That's an absolutely awful implementation.

Why?

- Pdss (equivalent thereof) is smaller than a 12ax7. for a reverb send? oh hellz no.

- bringing the poitn up again, you know how even robust 12at7's (2.5W per triode, so 5W total for standard fender implementation) suffer meltdowns when fed much less than 500V in silverface implementations? Even if you were using a pair of LND150's in parallel, you'd be looking at about 1.5W total available power handling. Uhm...

- Super high gain is... pointless. You typically need to *pad* the signal and supply enough current. Again (see above), LND150 is turrible choice. (as cleveland brown would say. jus turrible)

Even if you were going to keep it transformer coupled, there are much better driver options.

For the return? Oh, I'm totally on board for the LND150 for the return.


Yay transistors-- boo implementation.

[R.G.]

Yeah, you have to watch the power dissipation with MOSFET changeovers.

I tend to use the bigger power MOSFETs in TO220 packages. These will do about 2W all by themselves in free air, and up to 10-20W with a reasonbly small heat sink. It's fairly easy to get them to 5W with a small sink tied to the metal tab.

But then you could also parallel up half a dozen LND's.

[xtian]

Well that's a shame. I must say it's an attractive option to be able to drop in a premade verb for $100 in parts and less than an hour of labor.

[Structo]

I had an Ironsounds SS loop in my D'lite for a while.

Then I built a stand alone D'lator and prefer that.

[rp]

Well that's a shame. I must say it's an attractive option to be able to drop in a premade verb for $100 in parts and less than an hour of labor.

I was hoping that too.

Looks like we have concluded that tubes are better than ss

[Structo]

Have you tried the Kleinurator?

That got pretty good reviews until all the D'lators got built.

[R.G.]

While I'm a fan of the LND150s now... That's an absolutely awful implementation.

...

- bringing the poitn up again, you know how even robust 12at7's (2.5W per triode, so 5W total for standard fender implementation) suffer meltdowns when fed much less than 500V in silverface implementations? Even if you were using a pair of LND150's in parallel, you'd be looking at about 1.5W total available power handling. Uhm...

- Super high gain is... pointless. You typically need to *pad* the signal and supply enough current. Again (see above), LND150 is turrible choice. (as cleveland brown would say. jus turrible)
...

Without knowing the exact schematic, the concept might work fine if the actual transformer driver was replaced with a TO-220 MOSFET follower run from the drain of an LND150 input device. That would let the LND run at high voltage/low current and whatever gain was needed, and then have the big brother MOSFET pump out whatever current was needed to the transformer. I believe you might be able to direct couple the TO220 to the drain of the input LND150, then drive the transformer from source to ground with the TO220. That could easily get 5+W of dissipation for driving the xfmr in a board that size.

In any case, the board and parts are a trivial part of the cost. LND150s are $0.50 each, the board is a couple of bucks, and the other parts are all jellybean stuff. The real cost of any such setup is the transformer, cables and reverb pan. The board and electronics might as well be free, as they're in the rounding error on the cost of the bigger parts.

[xtian]

The real cost of any such setup is the transformer, cables and reverb pan.

Well, for people typically making one-offs like me, the real cost is the labor. So Buying a prebuilt board for the equivalent of 1.17 hours of labor versus building it myself for $10 in parts and four hours of labor...

[R.G.]

Well, for people typically making one-offs like me, the real cost is the labor. So Buying a prebuilt board for the equivalent of 1.17 hours of labor versus building it myself for $10 in parts and four hours of labor...

Yeah, there's that. Of course, populating a PCB like that is about a 15 minute job, so there's a middle ground.

And that looks like about a $5.00 board (parts included) at a contract assembly house in 500-1000 quantity. That's what led me to say that the real cost is the transformer, cables, and tank.

Sure, if you're doing a one-off on perfboard or something, it would get expensive.

And I personally **hate** perfboard.