Would the schematic for the Weber Mass work if i replaced the speaker dummy coil with an equivalent resistor?

tschwarz

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You could get a cheap HiFi speaker rated at whatever your amp's power output is, remove the membrane / cone and somehow use flexible glue or silicone to fix the coil inside the magnet. Then flex the now superfluous basket off the magnet assembly. That should get you close.

I know I will try this with my current build, an 18W TMB derivative with ukranian 6P14P / 6N2P glass. I adore the sound of it clean and cranked but there's no MV (nor should there be!). I'll try a fixed attenuator to 1/20th the power - i.e. ~1W. I have a Marshall DSL1 that's perfectly usable @ 1W...
 

itsGiusto

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You have the answer before even asking, of course it is fine if it is seeing the appropriate load. You wont break your amp.
I don't think I have the answer necessarily. One particular thing that comes to mind:

Take a look at these calculations I did 4 years ago, which shows what the load is presented to the amp if the voice coil and speaker are assumed to be a resistive load:

You can see that the resistance presented to the amp is not constant across the sweep of the rheostat. But is it close enough?
Take for example the center image. We'd want to be presenting 8 ohms to the amp, but at some mild attenuation settings, it goes as low as 5 or 6 ohms.
And for the top left, we'd want to be presenting 4 ohms to the amp, but at some heavy attenuation settings, the load goes over 5 ohms, which is more than 25% off from desired.

How can you know if the load is too different from the optimal?
 

sds1

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I found it somewhat excruciating to use, with poor user interface, and it doesn't even have native support for potentiometers!
Terrible interface like you say, but it works.

Try Micro-Cap, this simulation software cost $5000 a few years ago but is now free. Much better UI and way more built-in component support:
 

Len058

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I've seen that John H attenuator before, but I'd much prefer to make one continuously adjustable, with a rheostat, not just with discrete switches for discrete attenuation levels. I find with the attenuators I own, I do a significant amount of tweaking of the dial to get it just right. I'm not sure discrete switches will allow me that flexibility and the fine-grained control I want.
Just put in a post phase inverter master volume and tweak with that. But that's my solution.
 




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