New PS-2A Overdriving

Stage & Studio Power Station PS-2
1

Hey folks, posting this here since the email auto reply said to.

Earlier this week (1/8/25) I bought a PS-2A from Zzounds. It arrived Thursday (there’s a reason Zzounds has had all my business for the last decade plus) and I tested it out with my Marshall Silver Jubilee Reissue (2555X). When playing through the PS-2A, I noticed that the low end kinda flubs out, it sounds for all like the low/low mid frequencies are overdriving something in the signal chain. This happens even if all the controls are set to middle (5) and power set to 50w.

One is an anomaly, two is a trend. Tested it out with my Carvin VL100 Legacy yesterday. I set it to 50w, tried the drive channel with my favorite settings, seemed like there were no issues. Switched to 100w, seems good still. Tried the clean channel…and it behaves exactly like the Marshall. Switched to 50w, same thing. So I’m not sure if the issue is there on the drive channel and I didn’t notice it, or if there’s something intermittent occuring. (Update, I tested further today, it is happening on the drive channel. It just wasn’t as noticable because the distortion/overdrive of the PS-2A melded “better” with the Legacy than it did on the Marshall.)

Any help y’all can provide would be appreciated. I’ve been doing all my own amp tech work for the last 18 years now. I’m a technician by trade, though admittedly I don’t have a low of professional experience with guitar amps. I currently don’t have any balanced 12AX7s on hand, or any spare 6L6s, else I’d have just started there. (I do have ones in amps, but if it’s not broken, don’t mess with it…)

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Hi Phil,

Thanks for the question—I’m finding it hard to follow exactly the testing you have done. Would you be able to post a clip so we can hear it and understand better? This could be audio (.mp3) you can upload recorded directly by your phone, or you could upload and link to a YouTube video. Looking forward to understanding more!

Regards,

Dan

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Roger that, I’ll try and get something recorded tonight once I get off work.

I’m not sure how to describe it other than it sounds overdriven/distorted, focused on the low frequencies. Clean channel, switch the PS-2A on, it sounds distorted, like there’s a fuzz with a ton of gain on the low/low mid freqs. Switch to bypass, it’s crystal clean.

4

Hi Phil,

Can you change the reactive load toggle switches to flat? Does this help? What about changing the resonance control all the way on or off?

Looking forward to the clip!

Regards

Dan

5

Haven’t had more than about ten minutes to test things this week, sorry.

However, I am now unusable to reproduce the problem myself. Same amps, same guitars, same settings on everything. I’m not sure what happened. Hopefully this weekend I’ll have more time to focus on a full test.

1 Like
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I think I’ve figured it out!

I was running 8 ohms out on both amps when I experienced the distortion…Since the Fryette is only rated for 150w at that setting…and both amps likely output that much or more cranked…

I was bouncing back and forth between amps/cabs when troubleshooting, and at some point switched to 16 ohms, likely before the stretch were I couldn’t test anything. (Both amps have selectable impedance out, and of course everything matched.)

Without realizing it at the time, this preceeded when everything started working.

Hopefully this will save someone else some headache: Check rated power at the different impedances.

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Hi Phil,

Thanks for coming back and letting us know!

So what’s the conclusion? Was the distortion due to a mismatch impedance selector?

Regards

Dan

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Not a mismatch, rather using the PS-2A transformer to match to the cab. Both amps “feel” better to me with 8-ohm loads, (Like 2x16ohm cab load) hence why I started that way.

But I can confirm, using 8-ohm outputs from the Carvin VL100 Legacy and the Marshall 2555X, into the Fryette input set to 8 ohms, recreates the issues I had before. Both amps, same settings, but using the 16 ohm outputs, again into the PS-2A input set to 16 ohms results in a clear sound, no distortion.

Legacy 8 ohm out → PS-2A 8 ohm input = overdriven
Silver Jubilee 8 ohm out → PS-2A 8 ohm input = overdriven

Legacy 16 ohm out → PS-2A 16 ohm input = distortion free
Silver Jubilee 16 ohm out → PS-2A 16 ohm input = distortion free

Therefore, my theory is that both amps exceed the 150w rating of the 8-ohm PS-2A input, but are fine with the 200w capable 16-ohm option.

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Hi Phil,

This is definitely piquing my interest!

Could you capture a clip of that? Even with your mobile phone.

I would be surprised if this was due to PS-2A being rated for 150W at 8 Ohm and 200W at 16 Ohm and I would be equally surprised if your amps were generating that much continuous average power.

Also can you try this…

Regards,

Dan

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Dunno man, the way I’ve got these amps gained out (about 6 out of 10 for each) and cranked (again, 70%ish, maybe a little more) they’re going to be compressed/saturated enough that whatever they can give, they are. Both are biased on the warm side, Legacy is at about 70-75%, I’d have to measure the Marshall to give you the numbers.

FWIW, this is how we get max power out of our TWTa’s at work, despite that not being my goal in this case. So the theory backs that these amps are working hard.

Since the distortion is linked to the bass…and area under the curve being a thing, could easily be a thing.

I’ll try an post clips, but be advised I won’t have time till the weekend, and it’s not guaranteed even then.

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OK, looking forward to hearing those when you have some time!

It sounds like a good way of using those amps; they don’t sound good with a full right-hand sweep. I mean, Eddie did that, but he also ran his amp at 90V so it was putting out 30W.

I think the power thing is described by the crest factor. They put out around 100W average power (“sine wave power”). For an 8 Ohm load; this waveform will have a nominal voltage of around 30V. As the amp is pushed more and more, the shape of the waveform changes from sine to square. This could account for extra power output, even though there is not more voltage coming out of the amp.

To get back to your question: yes, please post the clips, and we can take it from there. If you hear distortion in bass frequencies, then try changing the deep toggle switch to flat and see what happens (this is the 3rd time I have asked this by the way :slight_smile: )

Regards,

Dan

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Changing the toggle switches, or the knobs for that matter, hasn’t changed anything, but I’ll verify that again.

Sorry, things have been busy lately, and when I’ve had any time I’ve been playing vs. troubleshooting/rewiring gear.

As much as playing amp tech is fun, being a tech at my day job takes priority.

As for the Henning mess that’s cropped up alongside all this…well, I wouldn’t blame a load for exposing flaws in an amp/tubes.

However, Steve really missed an opportunity to show how a sine wave at a single freq generates a different (and lower) power level than a range of frequencies will. Show a guitar signal into the amp, and use an RSA/SpecAn to show the total power (area under the FFT) across all frequencies. He’s not wrong, but this method would better get his point across, as well as show a more “typical” use case.

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No worries, just when you get around to it.

Maybe he could do a follow-up video? Personally, I think he nailed it: did not dumb down any of the technical details and at the same time made it accessible. A guitar signal would have just confused things even more—the world is not ready for that just yet; :slight_smile: let’s leave the Illuminati with some esoteric knowledge.

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Dumb the description of my day job, and it’s basically measuring analog power levels. IMO, not using real-world signals only further deepens the misunderstandings rampant in musical equipment engineering.

Running a basic sine wave into an amp and noting the power out isn’t unlike advertising the wattage of a kitchen blender without discussing the RPM/torque relationship. Or like the guy bragging that his car makes 500hp but it’s all at the top end and it makes no torque. The more you look at numbers, and not what the power curves are telling you, the more you miss.

Again, I’m not an amp tech, but I am a tech (and EE dropout. Well, maybe not dropout, the school ended the program…) The worst engineers I’ve worked with all say things like “You wouldn’t understand this, so I’ll dumb it down and leave things out.”

Don’t be like them. Even apprentices will surprise you with what they retain. They may not understand it in the moment, but given time and experience, they might.

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I could not agree more with this. Those engineers are defining themselves as close-minded and incompent for any type of leadership role.

For a concept to be useful, we all need to understand and agree on what it means. Same for power rating of guitar amps and loads. We need to all agree on what 100W average (sine wave continuous) power means; like it or not, this is defined as by the whole electronic engineering displine.

P = I^2 R

or

P = V^2 / R

where I and V are the RMS values for sine waveforms for current and voltage, respectively, and R is the load resistance.

I agree this waveform is not similar to guitar; it is definitely not music.

If we move away from this definition, what do we replace it with? Me strumming an A chord from my JMP-1 on the OD 1 channel with the volume set to 7… you get my point. We would need to all standardise around a specific, more realistic waveform just to quote power.

But such a concept already exists. We can convert from power dissipation figures from one waveform type to another using Crest Factor.

For example, the crest factor of a voltage of a current sine wave is \sqrt(2)\approx1.414 and the crest factor of an equivalent square wave is 1.

So if you measure the power dissipation using sine waveforms and want to convert to the square wave, you find that the power dissipation would double.

P_\text{sine} \propto V^2

P_\text{square} \propto (C V)^2 = ( \sqrt{2} V )^2 = 2 V^2

Therefore, square wave power is twice as much as sine wave power,

P_\text{square} = 2 P_\text{sine}

This sounds ridiculous, but I have been worrying and thinking about this stuff for years. I actually played the isolated guitar track from Crazy Train into my load box on a loop to see how much it differed from sine wave heating. Should we say on the back of the Power Station

“Rated for 150W or 200W Crazy Train Watts”…

And yes, the sine wave rated caused more heating than Crazy Train, because a sine wave is not music.

Sorry to rant and reply with maths, I know that will mean most people will not even read this post, but I think we mostly agree :slight_smile:

Regards,

Dan