ART Power Plant preamp

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Casey_Butt
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ART Power Plant preamp

Post by Casey_Butt » Fri Nov 14, 2014 4:38 am

Today I got an old ART Power Plant preamp from the late '80s or early '90s. Looking at it, my guess is it's been in a pawn shop or music shop for quite a while (judging by the price sticker glue imprint that's steadfast to it).

All I can say is I'm in shock over the sound this thing produces. It's one of the best, if not the best, preamps I've ever heard. No tubes, just analogue.

So I hooked it up and did a battery of frequency sweeps on it to find out what it's doing, and I'm quite surprised with what I found. Here's a shot of a frequency sweep of one of it's outputs...
ART Power Plant - OD HS on 0. tones on 0 - Cab sim out - gain down to prevent distortion.JPG
That's the Overdrive channel with all the "tone" controls set flat and the "Harmonic Superdrive" on 0. If you're familiar with these things you can see immediately that that's a 4x12 cab simulated output. In fact, it's very similar to the Palmers or a multitude of popular analog 4x12 cab sim shapes (Tech 21 Sansamps, Red Boxes, Peavey JSX, etc).

This is with the "Thrust" control on 10...
ART Power Plant - OD HS on 0. Thrust on 10, tones on 0 - Cab sim out - gain down to prevent distortion.JPG
That hump at about 130 Hz is exactly where it should be to mimic the resonance of a Marshall 4x12 1960a cab. With "Thrust" on -10 the response is notched out at that same frequency. So the "Thrust" control isn't simply a Bass pot, like I assumed, it's actually a cab resonance control.

The Mid control sweeps from about 350 Hz to 575 Hz as you decrease it, and the "Edge" control is a treble control centred at around 3.5 kHz (like a Marshall Presence control).

But the really interesting part is the "Harmonic Superdrive" - it's a pre-clipping gain control that boosts the signal before it goes to the distortion generating sections of the preamp. Here's what it does ("Harmonic Superdrive" on 10)...
ART Power Plant - OD HS on 10. tones on 0 - Cab sim out - gain down to prevent distortion.JPG
This control puts a huge hump at ~1 kHz before the signal slams into the clipping section. Then any harsh high-order harmonics are filtered off with a fairly aggressive low pass filter at about 4.3 kHz. The surprising thing about that is that it's practically identical to what a Tech 21 Sansamp does. In fact, I'd say that this ART Power Plant thing does the Sansamp thing as good or better than my Tech 21 PSA-1 that's sitting next to it ...or any other Tech 21 Sansamp products I've tried (i.e. the Character series). Now I wonder who copied who.

I got this thing on Ebay for $13.16!! It's probably the best kept secret in preamps - a Sansamp with better frequency control over the cab sim, and it has a Power amp output without an aggressive cab sim at all (like a Cab sim defeat output that people have been asking Tech 21 for for decades). So if anyone is interested in an analogue amp simulating preamp like the Tech 21 PSA or similar, look around for an old ART Power Plant.

Oh... I should add that the Clean channel is just a generic clean with mids centred around 400-450Hz (similar to a Fender Blackface). There's no cab sim on the Clean channel, even in the Cab sim out line. And I can't speak for other pawn shop finds, but this one has held up to time extremely well - everything functioning perfectly, no scratchy pots or bad jacks or anything... for under $14???
_ JVM410H: "Blackface" Clean channel, "Plexi" Crunch channel, "Dual Rec" OD2 channel, 3rd stage bias pot with switchable 100nF bypass cap, switchable 470k/470pF "treble peaker", OD1/2 Orange and Red extra gain pot, signal boost into power amp, PI voltage set to 2203 levels, 5H choke w/ 50uF on screens, -ve feedback pot.
_ Marshall 2203/1959 clone - switchable (with FX loop, resonance control and -ve fb pot) built from a Peavey Windsor 'donor' head
_ Fender Deluxe Reverb clone head
_ ADA MP-1, ART Power Plant, Tech 21 PSA-1
_ 1960A cab w/ Celestion G12-65s and G12-75Ts in X-pattern, Peavey JSX cab with Celestion G12M's (UK 6402 cones)
_ Fender Pro 185 (rebuilt) - open back 2x12" with Jensen C12Ks

Tonemeister
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Re: ART Power Plant preamp

Post by Tonemeister » Fri Nov 14, 2014 4:00 pm

thanks for sharing Casey... new toys are so much fun [smilie=banana_smiley.gif]
- Marshall JVM410H: Negative Feedback Mod (33k-500k, linear), Compression Mod, One-Wire Cascade Mod, OD2-to-OD1 Mod, P.I. Boost Mod (with 33k in R52), Plexi Cap Mod (1uF), Modified C83 Mod (1- OFF, 2- 0.68uF, 3- 1.0uF, 4- 1.5uF, 5- 2.2uF, 6- 3.2uF), Gain Reduction Mod, Blackface Mod, Mesa Rectifier Mod, 50W (two tubes: 37.5mV), LED Footswitch Mod
- Laney AOR ProTube 3012 Combo: stock
- 2x Marshall 1960B 4xG12T-75
- 2x Dean DIME (FBD, Stealth #29/50), ESP LTD MH-250HT, Fender MIM Strat
- TC Electronic PolyTune, ISP Decimator G-String, Morley Mark Tremonti Power Wah, Ibanez TS9, MXR EVH Phase 90, TC Flashback X4, TC Hall Of Fame

link to my old band "Systatic" (Line6 Vetta II days) http://www.systatic.ca

Casey_Butt
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Re: ART Power Plant preamp

Post by Casey_Butt » Fri Nov 14, 2014 4:35 pm

I'm really surprised by the Tech 21 Sansamp similarity. I've looked at the Sansamp circuits a fair bit and I know how they work and do what they do. This thing is the same exact concept... and executed brilliantly.

In the Sansamps there are two opamp low-pass filters cascaded after the clipping stage(s). Their function is to give that high-end roll-off guitar speaker cabs have. I even suspect the ART is doing that nearly identically because the response from the non-cab sim output also has a high-end roll-off, but not as aggressive as the cab sim output line. It's exactly what you would get if you tapped the output of a Sansamp off at the point between the two output low-pass filters (like a partial cab sim of the high-end). I think ART did it that way because without some high-end filtering the solid-state opamp or diode clipping would be too harsh and fuzzy (even for a dedicated preamp). So, even though ART says there's no cab sim on that particular output line, there sort of is. It's just another clue to me that the designs of the Power Plant and the Tech 21 Sansamps are very similar, even down to the output stages. I also think Tech 21 has refused to release any of their Sansamp products with a cab sim bypass feature for similar reasons. (Those 'speaker' buttons on the newer Character series pedals is not a cab sim defeat. In fact, it's the 'opposite' - it filters off even more highs with the intention of being able to plug into the front of an amp.)

There are too many similarities going on here for it to be a coincidence. ART released the Power Plant in 1990, I believe. And Tech 21 released the first Sansamp in 1989. But ART says in the Power Plant manual that they were 10 years working on the development of the Power Plant (though that may be an exaggeration or deceiving). I wonder was Andrew Barta (creator of Tech 21) in the room? [smilie=icon_wink.gif]

...Andrew bARTa. :yikes:
_ JVM410H: "Blackface" Clean channel, "Plexi" Crunch channel, "Dual Rec" OD2 channel, 3rd stage bias pot with switchable 100nF bypass cap, switchable 470k/470pF "treble peaker", OD1/2 Orange and Red extra gain pot, signal boost into power amp, PI voltage set to 2203 levels, 5H choke w/ 50uF on screens, -ve feedback pot.
_ Marshall 2203/1959 clone - switchable (with FX loop, resonance control and -ve fb pot) built from a Peavey Windsor 'donor' head
_ Fender Deluxe Reverb clone head
_ ADA MP-1, ART Power Plant, Tech 21 PSA-1
_ 1960A cab w/ Celestion G12-65s and G12-75Ts in X-pattern, Peavey JSX cab with Celestion G12M's (UK 6402 cones)
_ Fender Pro 185 (rebuilt) - open back 2x12" with Jensen C12Ks

Casey_Butt
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Re: ART Power Plant preamp

Post by Casey_Butt » Fri Nov 14, 2014 4:49 pm

...Just for reference, this is what the early ones (like mine) look like...
ART Power Plant.jpg
ART Power Plant back.jpg
_ JVM410H: "Blackface" Clean channel, "Plexi" Crunch channel, "Dual Rec" OD2 channel, 3rd stage bias pot with switchable 100nF bypass cap, switchable 470k/470pF "treble peaker", OD1/2 Orange and Red extra gain pot, signal boost into power amp, PI voltage set to 2203 levels, 5H choke w/ 50uF on screens, -ve feedback pot.
_ Marshall 2203/1959 clone - switchable (with FX loop, resonance control and -ve fb pot) built from a Peavey Windsor 'donor' head
_ Fender Deluxe Reverb clone head
_ ADA MP-1, ART Power Plant, Tech 21 PSA-1
_ 1960A cab w/ Celestion G12-65s and G12-75Ts in X-pattern, Peavey JSX cab with Celestion G12M's (UK 6402 cones)
_ Fender Pro 185 (rebuilt) - open back 2x12" with Jensen C12Ks

Tonemeister
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Re: ART Power Plant preamp

Post by Tonemeister » Fri Nov 14, 2014 5:13 pm

Casey_Butt wrote:...Andrew bARTa. :yikes:
you just blew my mind smilie=icon_lol.gif
- Marshall JVM410H: Negative Feedback Mod (33k-500k, linear), Compression Mod, One-Wire Cascade Mod, OD2-to-OD1 Mod, P.I. Boost Mod (with 33k in R52), Plexi Cap Mod (1uF), Modified C83 Mod (1- OFF, 2- 0.68uF, 3- 1.0uF, 4- 1.5uF, 5- 2.2uF, 6- 3.2uF), Gain Reduction Mod, Blackface Mod, Mesa Rectifier Mod, 50W (two tubes: 37.5mV), LED Footswitch Mod
- Laney AOR ProTube 3012 Combo: stock
- 2x Marshall 1960B 4xG12T-75
- 2x Dean DIME (FBD, Stealth #29/50), ESP LTD MH-250HT, Fender MIM Strat
- TC Electronic PolyTune, ISP Decimator G-String, Morley Mark Tremonti Power Wah, Ibanez TS9, MXR EVH Phase 90, TC Flashback X4, TC Hall Of Fame

link to my old band "Systatic" (Line6 Vetta II days) http://www.systatic.ca

Casey_Butt
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Location: Newfoundland

Re: ART Power Plant preamp

Post by Casey_Butt » Fri Nov 14, 2014 5:26 pm

Actually, the ART Power Plant cab sim is more accurate than the Tech 21 stuff. The Tech 21 high-end rolls off more gently than most cab sims or actual cabs, and they don't have that "thump" at ~130 Hz like a real 4x12 at all. Not saying they don't sound good, but they're not quite as "cab accurate" as what the ART is doing.

Here's the frequency response of a Tech 21 PSA-1 with all controls at unity (except gain and input down to prevent clipping from messing with the response... as I also did with the ART)...
Tech 21 PSA-1 all controls at unity - input low as possible.JPG
Incidentally, the PSA-1 drives the pre-gain mids at about 600-700 Hz for a more "American" type/level of gain. The ART pushes the pre-gain mids at around 1 kHz, more like a Tech 21 British pedal... not surprising considering the ART was designed to produce a Marshall sound in the OD channel.

This is the PSA-1 with "Punch" (pre-gain mids) dimed...
Tech 21 PSA-1 PUNCH on 10, others at unity - input low as possible.JPG
...Good for Rammstein. [smilie=icon_wink.gif]
_ JVM410H: "Blackface" Clean channel, "Plexi" Crunch channel, "Dual Rec" OD2 channel, 3rd stage bias pot with switchable 100nF bypass cap, switchable 470k/470pF "treble peaker", OD1/2 Orange and Red extra gain pot, signal boost into power amp, PI voltage set to 2203 levels, 5H choke w/ 50uF on screens, -ve feedback pot.
_ Marshall 2203/1959 clone - switchable (with FX loop, resonance control and -ve fb pot) built from a Peavey Windsor 'donor' head
_ Fender Deluxe Reverb clone head
_ ADA MP-1, ART Power Plant, Tech 21 PSA-1
_ 1960A cab w/ Celestion G12-65s and G12-75Ts in X-pattern, Peavey JSX cab with Celestion G12M's (UK 6402 cones)
_ Fender Pro 185 (rebuilt) - open back 2x12" with Jensen C12Ks

Andy
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Re: ART Power Plant preamp

Post by Andy » Sat Nov 15, 2014 2:50 pm

I guess you got the car fixed huh Casey ? smilie=icon_lol.gif

Always an interesting read [smilie=gt-happyup.gif]
|----- if this forum helped you, pls donate to keep it alive -----|
::: JVM410 head,modded:- Hammond 5H choke, 2 tubes pulled, 37.5mv bias :: Caseys Mods :- Plexi cap, -ve feedback, Dual Rectifier, Blackface, 1 wire Randy Rhoads, Plexi, Metaled Out ModPI Boost, OD Channel Gain Reduction Mod
::: AFD100, DSL100W head (no C83), Fender Champ 12
::: 1960AV 2xgreenbacks 2xG12H30, homemade 2x12 cab 2x Celestion Golds (100W)
::: Gibson Les Paul Standard, Dimarzio SD bridge Pup,Standard neck Pup.
::: Tokai Strat with Dimarzio SD, Epi SG-400 Iommi, Hondo Les Paul, Alhambra Acoustic fishman Pup
::: PodXTLive, Vox V848 Clyde McCoy Wah Wah,

It's better to fail in Originality than to succeed in Imitation ...

Casey_Butt
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Joined: Mon Nov 02, 2009 7:09 pm
Location: Newfoundland

Re: ART Power Plant preamp

Post by Casey_Butt » Sat Nov 15, 2014 4:45 pm

Andy wrote:I guess you got the car fixed huh Casey ? smilie=icon_lol.gif
Hahaha... well, got the engine and transmission finished and back in. I actually have to put the front lower control arms on today... which might be a bitch... hopefully not.

It's getting cold now though... I think the end of "car season" is very near. ;)
_ JVM410H: "Blackface" Clean channel, "Plexi" Crunch channel, "Dual Rec" OD2 channel, 3rd stage bias pot with switchable 100nF bypass cap, switchable 470k/470pF "treble peaker", OD1/2 Orange and Red extra gain pot, signal boost into power amp, PI voltage set to 2203 levels, 5H choke w/ 50uF on screens, -ve feedback pot.
_ Marshall 2203/1959 clone - switchable (with FX loop, resonance control and -ve fb pot) built from a Peavey Windsor 'donor' head
_ Fender Deluxe Reverb clone head
_ ADA MP-1, ART Power Plant, Tech 21 PSA-1
_ 1960A cab w/ Celestion G12-65s and G12-75Ts in X-pattern, Peavey JSX cab with Celestion G12M's (UK 6402 cones)
_ Fender Pro 185 (rebuilt) - open back 2x12" with Jensen C12Ks

F_Ostrander
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Re: ART Power Plant preamp

Post by F_Ostrander » Wed Nov 28, 2018 5:11 am

I stumbled on your thread today. Sorry it’s been so long since it was active.

As the person who designed the filter circuits for the ART Power Plant back in 1990, I was very interested to see your measurements and commentary. I have to say that the Art version was indeed the second version of the product. The original was developed by a small company, DBJ Labs, in about 1980. Somewhere I have literature on it. I also have all my design notes and original schematic drawings.

I can tell you that the ART version was based on an original unit that Buck Brundage, the originator of the concept, had cobbled together with a bunch of external EQs. He had spent years perfecting the sound. In fact, a pre-ART version of the Power Plant that Buck set up was used by Jan Hammer on the guitar sounds (actually all synth) on the Miami Vice TV show theme music.

Buck and I had worked together at a regional sound company on and off through the mid and late 1970s. In the late 1980s, after getting ART interested in producing the Power Plant he approached me for help. I had a recent degree in Electrical Engineering and an interest in analog filters. Buck, another Engineer form the original version named Dick Dussunger and I did the design and presented ART with a working prototype.

You will find that all the EQs in the Power Plant are actually based on a standard circuit used in graphic equalizers - series R-L-C (using gyrators) that are attached to an op-amp in such a way as to allow for both boost and cut. Instead of all the filters having the same bandwidth, evenly spaced at octaves or third-octaves, my filters were custom tailored for the task at hand!

Andy
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Re: ART Power Plant preamp

Post by Andy » Fri Nov 30, 2018 9:30 pm

interesting ! I have forwarded it to casey
|----- if this forum helped you, pls donate to keep it alive -----|
::: JVM410 head,modded:- Hammond 5H choke, 2 tubes pulled, 37.5mv bias :: Caseys Mods :- Plexi cap, -ve feedback, Dual Rectifier, Blackface, 1 wire Randy Rhoads, Plexi, Metaled Out ModPI Boost, OD Channel Gain Reduction Mod
::: AFD100, DSL100W head (no C83), Fender Champ 12
::: 1960AV 2xgreenbacks 2xG12H30, homemade 2x12 cab 2x Celestion Golds (100W)
::: Gibson Les Paul Standard, Dimarzio SD bridge Pup,Standard neck Pup.
::: Tokai Strat with Dimarzio SD, Epi SG-400 Iommi, Hondo Les Paul, Alhambra Acoustic fishman Pup
::: PodXTLive, Vox V848 Clyde McCoy Wah Wah,

It's better to fail in Originality than to succeed in Imitation ...

Casey_Butt
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Re: ART Power Plant preamp

Post by Casey_Butt » Sat Dec 01, 2018 12:21 am

F_Ostrander, it's a pleasure to "talk" to you. I find the Power Plant fascinating. It's obviously a very well thought out piece of equipment - one that doesn't get the recognition as an evolution in solid-state guitar preamps as it should. It was possibly the first "amp in a box" as they call them now. And quite a good one, even in today's market.

I'm particularly perplexed by the "Harmonic Superdrive" control... I really suspect that it's a high-mid boost before the downstream clipping stages. And the clipping is quite smooth for solid-state. I don't want to impose or trouble you, but if you have those schematics in digital form I'd love to have a look at them.
_ JVM410H: "Blackface" Clean channel, "Plexi" Crunch channel, "Dual Rec" OD2 channel, 3rd stage bias pot with switchable 100nF bypass cap, switchable 470k/470pF "treble peaker", OD1/2 Orange and Red extra gain pot, signal boost into power amp, PI voltage set to 2203 levels, 5H choke w/ 50uF on screens, -ve feedback pot.
_ Marshall 2203/1959 clone - switchable (with FX loop, resonance control and -ve fb pot) built from a Peavey Windsor 'donor' head
_ Fender Deluxe Reverb clone head
_ ADA MP-1, ART Power Plant, Tech 21 PSA-1
_ 1960A cab w/ Celestion G12-65s and G12-75Ts in X-pattern, Peavey JSX cab with Celestion G12M's (UK 6402 cones)
_ Fender Pro 185 (rebuilt) - open back 2x12" with Jensen C12Ks

F_Ostrander
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Re: ART Power Plant preamp

Post by F_Ostrander » Sat Dec 01, 2018 2:09 am

Here’s a block diagram:
76504783-63DC-4D44-A6E2-601DB8C8B171.jpeg
Power Plant block diagram
Here’s a photo of the title block from the hand-drawn schematic:
C6634739-55A6-46DA-9B83-D16FCB8A1B80.jpeg
Power Plant Title Block

Casey_Butt
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Re: ART Power Plant preamp

Post by Casey_Butt » Sat Dec 01, 2018 1:37 pm

Thanks for that. I assume the filter at 1.2kHz ("pre-emphasis") is the "Harmonic Superdrive". What is the "SRL" amp block? I'm assuming that's the stage where the bulk of the clipping happens and then the filters afterwards are the tone controls and speaker cab emulation (treble shelving and cab resonance, etc). If so, the Tech 21 Character Series is very, very similar in topology.
_ JVM410H: "Blackface" Clean channel, "Plexi" Crunch channel, "Dual Rec" OD2 channel, 3rd stage bias pot with switchable 100nF bypass cap, switchable 470k/470pF "treble peaker", OD1/2 Orange and Red extra gain pot, signal boost into power amp, PI voltage set to 2203 levels, 5H choke w/ 50uF on screens, -ve feedback pot.
_ Marshall 2203/1959 clone - switchable (with FX loop, resonance control and -ve fb pot) built from a Peavey Windsor 'donor' head
_ Fender Deluxe Reverb clone head
_ ADA MP-1, ART Power Plant, Tech 21 PSA-1
_ 1960A cab w/ Celestion G12-65s and G12-75Ts in X-pattern, Peavey JSX cab with Celestion G12M's (UK 6402 cones)
_ Fender Pro 185 (rebuilt) - open back 2x12" with Jensen C12Ks

F_Ostrander
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Re: ART Power Plant preamp

Post by F_Ostrander » Sat Dec 01, 2018 6:32 pm

You are correct on both counts. I believe that ART spiced up the control names when they designed the front panel. The distortion was achieved using a transconductance op-amp. I’m attaching a photo of one of the EQ sections so you can see the topology we used. This is one of a number of such circuits, some of which were switched in or out depending on which output was being used. A great deal of attention was paid to getting the response right. I should also mention that I still have the original prototype.
:
2574ECAF-747E-4585-ABB8-2CA3AAAF5D69.jpeg

Casey_Butt
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Re: ART Power Plant preamp

Post by Casey_Butt » Sat Dec 01, 2018 8:31 pm

I can imagine all the trial and error you had to go through to get all that filtering right, back in the pre-digital days. Things are so easy now - I have a fairly well-equipped home workshop where I can model circuits digitally (including transient and harmonic (FFT) analyses), run real-world frequency sweeps including harmonic distortion content, look at responses through a USB 'scope, etc. I can take the response of, say, a cab, design a circuit to emulate it, model it in spice, breadboard it and take the frequency and harmonic distortion responses on my computer, and look at the waveforms on my PC 'scope. If it's a fairly simple circuit and all goes well, you're looking at a day or two for all of that... though you can then spend forever tweaking and perfecting it. But it amazes me the work that engineers had to go through before such conveniences were at our disposal.

Thanks for the schematic! I love these sorts of things. ;)
_ JVM410H: "Blackface" Clean channel, "Plexi" Crunch channel, "Dual Rec" OD2 channel, 3rd stage bias pot with switchable 100nF bypass cap, switchable 470k/470pF "treble peaker", OD1/2 Orange and Red extra gain pot, signal boost into power amp, PI voltage set to 2203 levels, 5H choke w/ 50uF on screens, -ve feedback pot.
_ Marshall 2203/1959 clone - switchable (with FX loop, resonance control and -ve fb pot) built from a Peavey Windsor 'donor' head
_ Fender Deluxe Reverb clone head
_ ADA MP-1, ART Power Plant, Tech 21 PSA-1
_ 1960A cab w/ Celestion G12-65s and G12-75Ts in X-pattern, Peavey JSX cab with Celestion G12M's (UK 6402 cones)
_ Fender Pro 185 (rebuilt) - open back 2x12" with Jensen C12Ks

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