Vibroluxish build

[überfuzz]

The filter seems to be based on a bunch of 16u caps. How is the amp affected if this value is altered? (I think I have heaps of 20u in my stash.)

[loudthud]

20uF should work just fine as long as you don't go over the Voltage rating. You might notice a difference if you played the amp for many months with 16uF and suddenly stuck 20uF in there, but for a new build there won't be anything to compare to.

[überfuzz]

I've mustered a layout for this project. Please feel free to comment on it, specially gnarlys.

[Chuck H]

It's funny (not the ha ha type of funny) that people (especially me) tend to overlook the better things and only mention the errors in such circumstances. So let me open by saying that it looks to be a thoughtful and very functional board layout. Where the transformers are located and how the leads are routed isn't clear, but so far so good, with one exception...

The reverb circuit looks to be a loop. The signal that feeds the reverb comes from a dedicated stage that follows the triode where the reverb output is re introduced. Basically, you'll be reverberating a reverberated signal over and over. A loop. IMHE this is going to ring and feed back. I know there are some designs that do something similar, but I usually read complaints about them like weak or bad sounding reverb or feedback issues. I would change the design but YMMV.

[überfuzz]

It's funny (not the ha ha type of funny) that people (especially me) tend to overlook the better things and only mention the errors in such circumstances.

*Imagining a forum with back rubbing and Kumbaya singing.* Sigh! Ah well...

The reverb circuit looks to be a loop. The signal that feeds the reverb comes from a dedicated stage that follows the triode where the reverb output is re introduced. Basically, you'll be reverberating a reverberated signal over and over. A loop. IMHE this is going to ring and feed back. I know there are some designs that do something similar, but I usually read complaints about them like weak or bad sounding reverb or feedback issues. I would change the design but YMMV.

I'm definitely no expert so I might have gotten this all wrong. I'll attached the circuit I was aiming for.
reverb path.pdf

[Chuck H]

Actually (and I looked it over a couple of times) you DO have the reverb and dry summed at the PI grid via a pair of 220k resistors. So that's all good. I don't know the nature of your reverb unit (input sensitivity, output voltage, etc.) but the layout seems correct as a basic summing circuit. You may want to include tabs on the board to allow for voltage division on either end in case you need to tune it. Also, allow for the possibility that you may need to move grounds, which is common for reverb circuits to reduce hum and noise.

[überfuzz]

Actually (and I looked it over a couple of times) you DO have the reverb and dry summed at the PI grid via a pair of 220k resistors. So that's all good. I don't know the nature of your reverb unit (input sensitivity, output voltage, etc.) but the layout seems correct as a basic summing circuit. You may want to include tabs on the board to allow for voltage division on either end in case you need to tune it. Also, allow for the possibility that you may need to move grounds, which is common for reverb circuits to reduce hum and noise.

Thanks for the advisory, good stuff!

"Tabs" as in potentiometers where I can fine tune the resistance? I'm always kind of nervous when I wire the grounding. Mostly I go with a Fenderish grounding, but in this build there are some nodes I have to think about...

[Chuck H]

"Tabs" as in: just a couple of extra eyelets, turrets, etc. in the area so that you have a place to solder something if you have to.

[überfuzz]

Aha, yeah that's the plan. Thanks!

[überfuzz]

Where the transformers are located and how the leads are routed isn't clear...

The plan is to place the transformers in the short ends of the chassis.

[überfuzz]

I've been tinkering some more with the circuit. First of all I've tighten up the break up. In addition to this I added some other stuff like tremolo and such to the simulation: Tremolo HIGH VOLUME. Note how the tone is all distorted and funky in the beginning, when the supply voltages have levelled out the tone gets tighter. But then again, most of you'll be to dazzled by my playing to notice...

[Audiotexan]

But then again, most of you'll be to dazzled by my playing to notice...

Or deafened if you have headphones on! XD

*** volume warning ***

[überfuzz]

Or deafened if you have headphones on! XD

*** volume warning ***

I pushed the volume knob to 11.

[überfuzz]

I'm trying to add reverb to this amp. I got a slight problem with the ltspice model of the reverb tank. The problem is plainly that I don't know if I have a model that's resembles that actual tank at all. So, it would be great if I could get some advise or help on how I should add the reverb.

I have a high impedance tank that should work for a transformer-less reverb driver. The circuit I have at the moment seems to amplify the reverb to much. I attach the circuit I'm tinkering with at the moment in hope of some good advise.


Sorry about the schematics (I Though it would be a walk in the park so I started from a layout:ish circuit I have over this amplifier).

[Chuck H]

Looking at your schematic, because you have a 470k load following the dwell pot load (or what was a 2.2M load?) you could use a 1M audio dwell pot with very little difference in output.

As to the reverb showing too much output... Build it anyway. If the reverb is too loud you can always dumb it down. Plenty of simple ways to do that. Much more problematic to build it and find it isn't loud enough.