Dummy load to feed a valve amp

[mcgruff]

I can only speculate that they've not bothered with an inductive/reactive load on the basis that if it is coupled to a valve power amp then that will deal with all the tone shaping that comes from the power amp response from the interaction with the speaker impedance so if they did this on the dummy load you'd effectively be applying the impedance response twice.

I think the aim here is different to a normal guitar amp. It's much more about accuracy and fidelity - and hence a reactive load.

I've built a version of Aiken's reactive load with a reactive/resistive switch (switches in a simple resistor). The resistive option has the same tone, more or less, but loses the dynamic, responsive feel. It sounds very compressed. Once that information is gone it's lost forever.

Check out this gearpage thread if you want more info on the Aiken design. Seems that you need to use some high-quality inductors to avoid saturation for example.

[Zozobra]

And it's a bump from me. I've come into possession of a reasonably high powered laptop PSU (19VDC@7.3A) which looks like a good candidate to power a class D power amp module. So on the suggestion of Juan I'm going to build a simple dummy load with a line out to feed a class D amp as I have the parts to hand for this. I'd also like to try out adding a reactive component. I was looking at common mode chokes as they're readily available and reasonably cheap but it looks like they'll saturate so I guess I'll have to look into where I can source air core inductors at sensible prices.

[J M Fahey]

Cool.

Remember the power supply rail voltage determines peak output voltage so RMS so available power on a given load.

19V supply allows for 18V peak voltage if power amp is very efficient Class D so if bridged you'll have:
18^2/2Rl=40W RMS if 4 ohm load.

FWIW EH Magnum 44 claims 44W with 24V supply.

[CarylAlbert]

Hello everyone..i am new here. I read your posts for this thread and as per my experience there may be a problem with a hum loop. I'm assuming the ground on the left is part of the 'first amp' and will be connected to its own mains ground? The grounds in the middle and on the right are part of the 'second amp' and will also be connected to mains ground via another power cord? If I have got that right, the signal return current from the dummy load side to the first stage of the second amp will have to flow via the mains grounds.