Using the Ampeg PF-20T as a DI without a speaker

[Dreamcaster™]

Hi everyone,
I've recently bought a second hand PF-20T. A friend of mine who is good with electronics and amps told me that a (valve) amp should never be used with no speaker hooked up because that'll end up damaging both the valves (I suppose he means the power valves, not the preamp ones) as well as the transformer. I understand why he's saying that, but wasn't this new portaflex series known to be great as a studio di? There's no way of excluding the speaker output (no headphones out like in other heads I owned before), so how can I use it as a di in the studio if I don't want to use it speaker? He recommended some sort of "dummy" resistence...

 

[Hoochie Coochie Man]

The PF20T and the PF50T may be operated safely with no speaker connected.
See page 6 of the owners manual here:

https://ampeg.com/data/6/0a020a3f12c8b5e0b88f60b5ae/application/pdf/Owner%E2%80%99s%20Manual%20-%20English%20.pdf

 

[KevInDaBassment]

Yup ^^

Part of the sales pitch for those, it also some incorporates some of that tube power section magic into the DI signal too.

 

[Wasnex]

Hi everyone,
I've recently bought a second hand PF-20T. A friend of mine who is good with electronics and amps told me that a (valve) amp should never be used with no speaker hooked up because that'll end up damaging both the valves (I suppose he means the power valves, not the preamp ones) as well as the transformer. I understand why he's saying that, but wasn't this new portaflex series known to be great as a studio di? There's no way of excluding the speaker output (no headphones out like in other heads I owned before), so how can I use it as a di in the studio if I don't want to use it speaker? He recommended some sort of "dummy" resistence...

The PF20T and PF50T have built in dummy loads, so they can be safely operated with no speaker plugged in.

PF20T block diagram:

@hodgy indicated the switch should be in the 8 ohm position when no speaker is attached. See this specific post: HOT AMPEG NEWS! PF20T, PF50T, PF112HLF

Whether the amp will sound good on the dummy load is another matter. FYI, a tube amp's output section interacts with the reactance of a speaker. I have seen some comments that suggest the Transformer DI Out tone is not as good using the dummy load as when the amp is driving a cab. IMHO try it both ways and judge for yourself.

 

[LahLeylah95]

I have a PF50T at my desk without a speaker cabinet for 2 years now.
I use the transformer out DI on the back silently with headphones and it sounds fantastic!

 

[Iristone]

Could be a bit expensive for the way you use it, but it's doable. The new Portaflex valve amps come with built-in load boxes, and you could also connect it to a larger power amp and rock a huge stage!

 

[Deleted member 271037]

Whether the amp will sound good on the dummy load is another matter. FYI, a tube amp's output section interacts with the reactance of a speaker. I have seen some comments that suggest the Transformer DI Out tone is not as good using the dummy load as when the amp is driving a cab. IMHO try it both ways and judge for yourself.

This could definitely be worth testing. I never realized how much difference the interaction with the speakers means until I tested two different attenuators in my home studio.

The first one was a Tone King Ironman II. This is a traditional, reactive attenuator, where the guitar amp will actually "see" the speakers, and interact with them.

The second one was a Fryette Power Station. While it is supposed to deliver a reactive load, it is also really more of a reamp device than a traditional attenuator. Forgive me if I don't get the technical details right, but I believe these Power Stations attenuate the signal all the way down to line level, and then reamps the signal through the onboard 6L6GC-based power amp. In any case, your guitar amp will never "see" or interact with the speakers when using the Fryette Power Station. The speakers will only interact with the re-amped signal from the Power Station output stage. While this design offers some interesting features, it also turned out to have some rather severe disadvantages IMO.

In real life tests I found the difference between these two devices to be HUGE.

The Ironman retained the "feel" and the touch sensitivity of my playing FAR better. I massively preferred it for everything except clean guitars through Fender-style amps. For "airy" cleans, particularly through Fender-style amps, the Ironman sounded slightly congested and lacking in detail compared to the Power Station.

The Power Station had a very lovely "airy", detailed tone with clean Fender-style guitars, but that was the ONLY thing I preferred it for (but the Power Station also had an inherent level of noise/hum that unfortunately made it borderline useless for clean guitars...). The playing experience, touch sensitivity, dynamics just didn't feel quite right. The Toneking was far superior in this respect. I also found that the Power Station colored the tone a bit too much, to the point where for example a Marshall amp didn't really sound like Marshall anymore. It didn't sound BAD per se, but certainly different. Also, with the tone switches set to flat the Fryette Power Station doesn't even deliver a reactive load. So unless you're willing to boost either the lows or the highs you're stuck with a resistive load, and a noticeably duller tone/feel.

This really was an eye-opening test for me. The playing experience was so much better with the Ironman, where the guitar amp was actually interacting with the speakers (rather than having just the re-amped signal from the output stage on the Fryette Power Station interacting with the speakers).

So yeah, don't underestimate the importance of your amp interacting with the speakers, although my experience with attenuators isn't directly comparable to using the DI on the pf20 with/without a speaker connected.

 

[logdrum]

This could definitely be worth testing. I never realized how much difference the interaction with the speakers means until I tested two different attenuators in my home studio.

The first one was a Tone King Ironman II. This is a traditional, reactive attenuator, where the guitar amp will actually "see" the speakers, and interact with them.

The second one was a Fryette Power Station. While it is supposed to deliver a reactive load, it is also really more of a reamp device than a traditional attenuator. Forgive me if I don't get the technical details right, but I believe these Power Stations attenuate the signal all the way down to line level, and then reamps the signal through the onboard 6L6GC-based power amp. In any case, your guitar amp will never "see" or interact with the speakers when using the Fryette Power Station. The speakers will only interact with the re-amped signal from the Power Station output stage. While this design offers some interesting features, it also turned out to have some rather severe disadvantages IMO.

In real life tests I found the difference between these two devices to be HUGE.

The Ironman retained the "feel" and the touch sensitivity of my playing FAR better. I massively preferred it for everything except clean guitars through Fender-style amps. For "airy" cleans, particularly through Fender-style amps, the Ironman sounded slightly congested and lacking in detail compared to the Power Station.

The Power Station had a very lovely "airy", detailed tone with clean Fender-style guitars, but that was the ONLY thing I preferred it for (but the Power Station also had an inherent level of noise/hum that unfortunately made it borderline useless for clean guitars...). The playing experience, touch sensitivity, dynamics just didn't feel quite right. The Toneking was far superior in this respect. I also found that the Power Station colored the tone a bit too much, to the point where for example a Marshall amp didn't really sound like Marshall anymore. It didn't sound BAD per se, but certainly different. Also, with the tone switches set to flat the Fryette Power Station doesn't even deliver a reactive load. So unless you're willing to boost either the lows or the highs you're stuck with a resistive load, and a noticeably duller tone/feel.

This really was an eye-opening test for me. The playing experience was so much better with the Ironman, where the guitar amp was actually interacting with the speakers (rather than having just the re-amped signal from the output stage on the Fryette Power Station interacting with the speakers).

So yeah, don't underestimate the importance of your amp interacting with the speakers, although my experience with attenuators isn't directly comparable to using the DI on the pf20 with/without a speaker connected.

What version of the PS do you have? V1 had issues to a certain SN. All the cons you listed , I and most people I know who used it have never experienced but I stopped using big amps and just mic small amps and use pedals nowadays, I have stopped following the guitar forums even before COVID. I got mine around 2015 and V2 in 2016. I have only used a Weber, and Lpad + resistor that me and my buddy made and the HotPlate in my THD UniValve and the BiValve I used to own, The PS is definitely much better than those.

 

[Hoochie Coochie Man]

You could also get an Ampeg PF112hlf cabinet and enclose it in an isolation box with interior and exterior sound dampening material if you wanted to be fanatic about the idea of having a complete reactive electromechanical load on the amp. Mount a microphone in the box and take the DI and mic signal out as well. It would not be very difficult to build something like that. In accordance with Lens's Law, a speaker acts like a motor and a generator all at the same time when being driven, so this setup may allow any effect the amplifier damping factor has on the sound to be represented in the signal as well. (Way too much trouble as far as I am concerned but I bet we could make some money selling such a setup to a few guitar players I know).

 

[King Harvest]

Yep great DI sound, no speaker necessary.

 

[Deleted member 271037]

What version of the PS do you have? V1 had issues to a certain SN. All the cons you listed , I and most people I know who used it have never experienced but I stopped using big amps and just mic small amps and use pedals nowadays, I have stopped following the guitar forums even before COVID. I got mine around 2015 and V2 in 2016. I have only used a Weber, and Lpad + resistor that me and my buddy made and the HotPlate in my THD UniValve and the BiValve I used to own, The PS is definitely much better than those.

I had the PS-2A 50w (the current version). I've seen several other Power Station users online complain about the same issues with this version. The hum was the worst problem. Unfortunately it seemed to be the result of cramming too much stuff into a tiny metal box. The hum seemed to somehow leak into the audio signal path from the power transformer. It was particularly bad between approx. 50-150 Hz. At first I thought mine was faulty so I sent it for repairs, but it couldn't be fixed and I was told it was "normal"...

In the end I got rid of mine because I found it close to useless, and preferred the Ironman 2 anyway. It's a shame, because if Fryette had done a better job with the design, it would have been a very cool little device, with a couple of nice features that "normal" attenuators don't have. I sold mine to a local amp tech. I told him about the problems, but he probably thought he could fix it. I have no idea if he succeeded.

The PS and the Ironman are the only attenuators I have spent some time with and compared directly. Personally I massively preferred the Ironman, mainly for it's superior response/feel, but also because it seemed to retain the tone/vibe of the amp much better. With the Ironman it felt like actually playing the amp/cab I was using. If the Fryette had less noise/hum it would have been a much closer call, but I would probably still have gone with the Ironman (although the flimsy wall wart power cable is very disappointing for a product in this price range). The Fryette newer sounded bad (apart from the noise) but it seemed to alter the tone/vibe of certains amp a bit too much. With clean sounds from my Matamp Series 3000 or Deluxe it sounded fantastic. With dirtier tones from an AC30 or a 4-hole Marshall JMP... well it didn't sound bad, but it didn't sound quite like an AC30 or a Marshall either. It felt kinda softer, less edgy in the mids.

Smaller amps are definitely the way to go in most situations, but I needed something that would enable me to make recordings of real tube amps in my home studio, without my family/neighbours going crazy. I absolutely detest digital modelling so it was an attenuator or nothing, even with smaller amps. Even a 5w guitar tube amp can be a bit loud for home use if you crank it.

 

[JimmyM]

There was a time when it was thought that the 8/4 ohm switch had to be in the 8 ohm position for use without a cab, but that turned out to be a misunderstanding and you can use it in either position.

 

[Wasnex]

There was a time when it was thought that the 8/4 ohm switch had to be in the 8 ohm position for use without a cab, but that turned out to be a misunderstanding and you can use it in either position.

Are you saying Hodgy is wrong?

Hey, good catch Beans! If using the amp without a speaker attached, the impedance select switch needs to be in the 8-ohm position. I'll get this to the manual makers and the movers and the shakers.

Original Post here: HOT AMPEG NEWS! PF20T, PF50T, PF112HLF

 

[JimmyM]

Are you saying Hodgy is wrong?


Original Post here: HOT AMPEG NEWS! PF20T, PF50T, PF112HLF

That was a good while back. My AR guy at the time said it was a mistake in the manual and maybe Hodgy hadn’t caught up with it at the time . But it won’t hurt anything to set it at 8 ohms.

 

[Dreamcaster™]

You could also get an Ampeg PF112hlf cabinet and enclose it in an isolation box with interior and exterior sound dampening material if you wanted to be fanatic about the idea of having a complete reactive electromechanical load on the amp. Mount a microphone in the box and take the DI and mic signal out as well. It would not be very difficult to build something like that. In accordance with Lens's Law, a speaker acts like a motor and a generator all at the same time when being driven, so this setup may allow any effect the amplifier damping factor has on the sound to be represented in the signal as well. (Way too much trouble as far as I am concerned but I bet we could make some money selling such a setup to a few guitar players I know).

I do have a PF-112HLF and I could indeed do this test.

@Wasnex mentioned that the transformer DI output isn't clean when no speaker is connected. I must say that it's definitely more "gritty" than the preamp DI even when the speaker is attached.

 

[el jeffe bass]

Harmoni Kelley, the bassist with Kenny Chesney uses a Pf20-T into a PF115HE in an iso box as part of her signal. It must sound good or she wouldn’t use it. That band doesn’t need to compromise much in regards to equipment.

 

[Wasnex]

I do have a PF-112HLF and I could indeed do this test.

@Wasnex mentioned that the transformer DI output isn't clean when no speaker is connected. I must say that it's definitely more "gritty" than the preamp DI even when the speaker is attached.

I own a PF50t, but FYI I haven't tried it. I have read comments from multiple people who reported the tone was better with a speaker attached. I didn't interpret this to mean the Transformer DI is more distorted when using the dummy load.

 

[Howlin Mad Mac]

Hi everyone,
I've recently bought a second hand PF-20T. A friend of mine who is good with electronics and amps told me that a (valve) amp should never be used with no speaker hooked up because that'll end up damaging both the valves (I suppose he means the power valves, not the preamp ones) as well as the transformer. I understand why he's saying that, but wasn't this new portaflex series known to be great as a studio di? There's no way of excluding the speaker output (no headphones out like in other heads I owned before), so how can I use it as a di in the studio if I don't want to use it speaker? He recommended some sort of "dummy" resistence...

Yes, normally a tube amp would require a “dummy load” however in the case of the PF-20T/PF-50T one is built into the amplifier’s design offering a pre/post preamp DI and a 2nd power tube/output transformer DI that’s like mic’ing the cabinet.