Fryette Powerstation Schematic

[M3thoms]

Depends on what you mean by transparent. With a load box you're typically more concerned with feel than with sound. You can use a single 8ohm 100W resistor and call it a dummy load, but it will feel stiff and uninspiring. Most higher-end boxes (including the powerstation) use a reactive load, which has an inductive element to it aside from the resistive element.

A speaker is not a perfect load. It has a different impedance depending on the frequency of the input signal. A resistor, on the other hand, has the same impedance regardless of the input frequency. The goal of a reactive load is to mimic the imperfect response of a speaker for a more natural feel.

Now how important this is will depend on your use case; if you're going to be using the external power amp to drive speakers and that's the only use for it then you may not notice much of a difference. But if you're going to a direct out for recording or through headphones, you'll notice a different feel.

Well I want the load to react like my guitar speaker would. I want it to mimic the impedance of my guitar speaker. How do I go about accurately modeling the reaction of an 8ohm speaker. Also I've recently learned LTSpice can I use its features to model the reactive load element of my design?

 

[temol]

Sure, you can use LTSpice to model the reacive load.

Aiken's Reactive Dummy Load.

I have been planing to build a good dummy load box to my tube amp with a line-out, then re-amp with a quality Solid-State Power Amp into my Guitar Cab. After some research Aikens design seems to load the Tube amp like a speaker would...

www.thegearpage.net

 

[mnemonic]

The Aiken reactive load box design is a really good one, I would just go with that scheme and tweak values to match what you want it to do simulating it in LTSpice. Lots of seemingly-minor factors have a major effect on the impedence curve, that tgp thread is a good read. Stuff like inductor dc resistance (even very small levels), inductor proximity to metal (steel or aluminum have different affects on the inductance), can greatly change the curve. LTSpice is good for simulating this.

I built mine based on research others did in that thread. Works really well.

I would think the power amp is also quite similar to other Fryette designs, most of his amps seem to be the same basic thing with some tweaks. The power station maybe has more negative feedback to linearise it’s output.

Here is a plot of the ps100 I found a while back, for research purposes



And some other assorted loads with ps1 (must have made some revisions to the load over time)

I'm always put off by fans in this type of equipment... I'm no expert on attenuators so maybe that's common in something that is designed to dissipate power?

I had an old Peavey Classic (30?) amp that had fans inside to cool the power tubes and that really just bugged the hell out of me. You couldn't really hear them when the amp was cooking, but it sounded like a little jet engine firing up when you first flipped on the power.

I had an old peavey classic 20 combo back in high school, it got so hot after it was on for a while I couldn’t touch the metal panel. I usually ran a small fan behind it to keep air moving. Wish I still had that amp, it was pretty cool but back then all I wanted to do was play Tool songs in drop D, and it wasn’t really the right amp for that.