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THD Hot Plate; post-amp effects


Photos. 1

Dealer Pages. 2

Amptone.com Commentary. 2

Improving the Hot Plate. 3

Doing a real amp demo in the guitar store. 3

Official THD Email Information about Hot Plate. 4

Guitar Player Magazine Review.. 5

Newsgroup Posting by Attenuation Expert Steve. 5

Preserving Speaker Distortion when Using a Power Attenuator 6

Using a Power Attenuator as a Dummy Load Enables Post-Amp FX Placement 7

Research links. 7



Above picture is from Emerald City Guitars in Seattle. The new black rocker switches, like in the THD BiValve amp, are sturdy.

Pictures above are from Steve's excellent site.

Picture above is from the dealer Plexi Palace.

Dealer Pages

Official product page

THD site - Where to buy

Hot Plate info at Vintageamps.com (Plexi Palace)

See also

thdunivalve.htm - THD UniValve head with 1 power tube, integrated Hot Plate, and Line Out

thdyellowjackets.htm - THD Yellow Jackets tube convertor sockets

Amptone.com Commentary

The Hot Plate is packed with features, including dedicated Line Out with Level control, and variable attenuation between 16 dB and infinity, and Treble and Bass boost switches. The Power Brake is a reactive load. I A/B'd them and concluded that the essential response of the Marshall is slightly rounder and has slightly more dynamic depth than the Hot Plate. However, the Hot Plate has equalization boost switches which apply to heavy attenuation settings, providing more flexibility. I'm looking forward to A/B'ing the Hot Plate against the Power Soak. I suspect that the Hot Plate sounds like a Power Soak with equalization boost switches added. The Hot Plate is smaller, sleeker, better looking, and lighter than the Power Brake.

Only the -16 dB setting on the left engages the pot on the right, with range marked -infinity to -16 dB. On the units I heard, there's a problem with the pot on the right: it's much too trebly when extremely reduced. That's a serious problem at low volume (just louder than the unplugged solidbody guitar); when that pot is turned up, the EQ is balanced, but then it's too loud. Here's the perfect, though lame, solution I use, to make the Hot Plate EQ balanced at low volume (just louder than the unplugged solidbody guitar): chain attenuators -- that is, put a speaker volume control device after the Speaker jack of the Hot Plate -- the device only needs to handle about 1 watt.

I'm skeptical about the importance of a reactive load as opposed to a resistive load, but what could possibly sound the best, with the most features, is a reactive version of the Hot Plate.

It's interesting that guitarists cannot easily or obviously find a Hot Plate for purchase. I asked a music store associate why power attenuators are rarely found in the stores, given that many guitarists love power attenuators. Some amps have output transformers that are not designed to take the full saturated power of the tube power amp -- so manufacturers can see power attenuators as a warranty risk. And I think that stores like guitarists to mistakenly assume that you must buy multiple amps, one for each size of venue and a practice amp for home.

A Guitar Center salesman told me only 1/4 of guitarists know what a Power Brake does. That's terrible. Every rock guitarist needs at least one good power attenuator.

Hot Plates are easily available, are hugely popular, are recommended by leading amp designers, and are a thriving product at THD.

>Have you had any contact with Groove Tubes? They apparently have (according to their sales staff) Rick, I think was his name, a speaker emulater combined with a power attenuator that has an FX LOOP!!! For $599.

I was unhappy that my original STP-G spk emulator had no FX loop -- I had to make my own, to insert an EQ pedal. Even then, that early model had no brightness at all. I sold it -- if I had it today, I would have Groove Tubes put in an FX loop and make it brighter.



>I thought that was an absolutely fabulous idea that shows their interest in providing the player with really truly useful tools that are above and beyond the usual doodads that fill the pages of Musicians Friend etc. Am very interested in trying that unit.

The Hot Plate is more exciting as an add-on that's the perfect fix for an existing tube amp. The Spk Emu. was designed as a monolithic, all-in-one solution, so it has that kind of elegance. The Hot Plate is more widely relevant -- traditionalist-compatible.


>How do you like the THD Hot Plate?

I haven't tried all power attenuators. The Hot Plate is at the top of my list of recommended products. The Hot Plate sounds much better than the Power Soak and significantly better than the Power Brake and handles more power.


Every guitarist with a tube power amp ought to run out to the store or website and buy a Hot Plate (or more), and two (or more) EQ pedals (with Level control) -- and read my site for hookups. Even for rig purists, this gear is essential for research and experimentation and ear training. I'm adding a photo of the new switches on the Hot Plate.

Improving the Hot Plate

Power attenuator makers should add flexible passive EQ, adding more than treble and bass boost 2-position switches.

THD ought to change the fine-tune volume control so it's not too bright below 12:00.

I did the eq/preamp/eq/poweramp/poweratten rig hookup in the store as demonstration, proof, and for practice. It produced great results, both with clearing up the preamp distortion voicing of the amp and with bringing down the speaker volume while retaining power-tube distortion. The salesman played a strat with neck pickup and I dialed through the tones -- clean, quasi-clean, various blends of preamp dist and power-tube dist. Used a big VHT Pittbull combo amp that has two 10" speakers and one 12" speaker.

The only limitation on the tone, aside from lack of speaker distortion at this level, was that the volume fine-tune control on my Hot Plate has too much upper treble when set below 12:00. 12:00 is a bit too loud for private playing; 9:00 is the right volume level but then there's too much high treble. This is not a psychoacoustic effect; mics pick it up as well and it's clearly excess upper-treble when played at the very lowest part of the range. I'm now regularly using a voltage splitter after the Hot Plate (a wall-mount speaker attenuator like ) so that I can keep the volume fine-tune control set to 12:00 or higher -- thus I have some control of speaker EQ, like a single conventional Tone control that just happens to be tied to a volume control, in addition to the bright and deep switches. I plan to contact THD to demonstrate my workaround and ask if the control can be made to sound right throughout its sweep.

A few people have slight criticism of the imperfection of the Hot Plate, and this fix -- adding a wall attenuator -- solves it for me.

Doing a real amp demo in the guitar store

I demo'd the BiValve amp with EL84 power tubes driving a Marshall 4x10 cab. I cranked an EQ pedal in the amp's fx loop with impressive, tight-distortion, slammed-Marshall Tone, at low volume. The amp has no evident preamp distortion stage -- though the store, shockingly, only had a single EQ pedal, so I couldn't try the Amptone.com-approved sequence of eq>preamp>eq>poweramp>power atten>guitarspeaker. I'll have to go back to the store bringing my own EQs. The "Hot Plate" circuit in this head is a continuous pot -- probably not a stepped switch because this amp is just 30 watts, not 100 watts. -- mh Jan. 2003.

I feel like I'm breaking the rules by going into the store and hooking up their power attenuator to a bunch of amps, or bringing in my own power attenuator. If the stores want to have a glimmer of a hope of selling me an amp, they must let me hook up a power attenuator. In heaven, all guitar stores will have a power attenuator hooked up to every amp in the store, or each amp will have power attenuation built in, like the THD UniValve or Aiken Invader. Guitar amps in heaven have no "Volume" controls -- they have "Preamp Dist", "Power Tube Sat", and "Spk Dist" controls (which are known in this mortal life as "gain, volume, and attenuation" controls). What I really must force myself to do is bring in a MiniDisc player with dry direct guitar as my input signal for the store amps, and then push the amps' output through a power attenuator.

Power attenuation works well enough, if not perfectly. I read everything on the Net and created a FAQ. http://www.amptone.com/powerattenuatorfaq.htm Especially I recommend only driving 1 speaker, if you are playing at the private, 50 mW "tv" level where the speaker is barely louder than the unplugged guitar. Guitar speakers are simply not designed to sound their best when barely engaged.

Steve's page about Hot Plate, 5.5, CAE, str6v6 Lennon amp

Be sure to turn up the variable control on the right at least to 10 o'clock -- the pot itself sounds fizzy and thin at extreme attenuation. I cascade a wall attenuator after the Hot Plate sometimes to control the EQ and volume in this low range.

For home studio recording at 10 p.m., I suggest Hot Plate -> 1 guitar spk pushed by 1 watt -> isolation cab/box.

I have a Power Brake now. What year did that come out? Hot Plate has more features than the Power Brake, with treble and bass boost switches added for the lowest couple of notches. When not using these boost switches, the Hot Plate is a little muddy at the lowest settings, and I expect the Power Brake to sound like that all the time, at its lowest settings (greatest attenuation). As you turn the Hot Plate selector to make the speaker louder, the switches have progressively less of an effect. Has anyone modded these Tone switches to add in-between settings? These tone switches are emphasized in the THD description of the Hot Plate.

THD - Hot Plate Attenuators. $329-379. Tube-amp attenuator/dummy load. Forced-air cooling, line-out, noise reduction. Frequency compensated;bass and treb boosts. 2, 2.7, 4, 8, and 16 ohm versions. Does not included speaker cabinet simulator.

The Hot Plate has a Line Out.

The Hot Plate has 4 steps of 4 dB increments to -16 dB, then an continuously adjustable knob below -16 to -infinity. The knob seems to be just a resistive L-pad. The THD has a resistive dummy load/no speaker mode.

There is a direct, straight-thru position with no attenuation on the Hot Plate and Power Brake, allowing easy A/B-ing of the tone with and without attenuation.

"The A/B capability is what convinced me of the transparency of the THD device, at least to -12 dB. I think too many things have to change to really get that same cranked tone at very low levels. I live on a large property, so my main concern was for preventing ear damage while making minimal to no sacrifices in the area of overdrive tones. Once you throw out the speakers working hard and the acoustic feedback to the guitar, you've removed some important tonal contributors."

-- D.R.

One reviewer of several attenutors wrote:

"The THD Hotplate has been gaining popularity... I didn't know about it at the time of my review. In fact, I think it had just came out. Honestly, the Hotplate is one of my most valuable pieces of gear. What goes in comes out the same. Very little coloration. Don't buy the Groove Tubes Speaker Emulator or the Marshall Power Brake before you try the Hotplate or an equivalent. Great tone should be priority, so I must steer you away from the Groove Tubes Speaker Emulator; it's ok... maybe for recording. On a scale of 1 to 10, the Hotplate is a 10 and the emulator is a 4. No lie, the Hot Plate is that much better. I'm sure you will agree, after you compare the two. And without extensive EQ treatment, the Speaker Emulator is flat-out useless."

I agree, at least with the original STP-G design I owned. What was worst, is that my original STP-G Speaker Emulator lacked an fx loop to help straighten out the eq.

Official THD Email Information about Hot Plate

The THD Hot Plate is a power attenuator that lets you play your amp with full distortion at quiet volumes. Do you love the sound of your amp wide open, but don't want to be deaf in 2 years? The THD Hot Plate is what you need.

What is a power attenuator? - A power attenuator is a device placed between the amp's speaker output and the speaker cabinet. It acts like a huge master volume control and permits the amp to be turned up most or all the way while absorbing most of the power generated by the amplifier and turning this power into heat. It passes a small part of the power to the speaker.

Why do I want one? - Our customers use attenuators because their amps sound good at high volumes, especially with full distortion, but in rehearsal, small clubs, or at home, they can't turn the amp up. They are also used in recording studios for better separation between the instruments, and for use when the speaker sounds best at low levels, or if it can't handle the amp's power output. The Hot Plate also makes a perfect dummy load.

We needed a good attenuator for our in-house testing of THD amplifiers. The amps have to be tested at all volumes, clean and pure to wild distortion, and we were tired of our ears hurting. We tried all the attenuators on the market, but they muffled the sound and made even THD amps sound dull. Now our design engineers don't have to worry as much about hearing loss, and neither do you.

How does a Hot Plate work? - A THD Hot Plate is a tuned network of capacitors, resistors and inductors which adjusts the overall EQ as the volume is turned down to compensate for the human ear's frequency response. Your ear perceives sounds differently at different volumes: the louder the sound, the more sensitive your ears are to highs and lows. As the volume drops, your ear becomes more sensitive to the mid-range, and less so for highs and lows. The Hot Plate compensates for this, working like the "Loudness" switch on a hi-fi. The THD Hot Plate is the first, and for now, the only attenuator that is frequency compensated.

How do I use it? - The THD Hot Plate is designed for use strictly with vacuum tube guitar amplifiers, and each version is optimized for a specific impedance (2, 2.7, 4, 8, or 16 ohms.) These inductive loads are frequency compensated, which means it will give you the best possible sound for that impedance speaker and amplifier combination. To use one: connect the speaker output of the amp into the input of the Hot Plate, then connect the speaker cabinet to one of the two speaker outputs of the Hot Plate (doesn't matter which one). The amp thinks the Hot Plate is a speaker, so the sound stays true even when you turn the volume down.

Built-in Noise Reduction - The THD Hot Plate is the only attenuator on the market with built-in noise reduction to reduce the hiss and hum between notes. We've designed a passive, single-ended noise reduction system which provides approximately 10 dB of broad band noise reduction without gating or pumping, and without affecting the tone of the amp. A by-product of the noise reduction circuit is that it generates light as you play. The harder you play, the brighter it glows.

Tone Controls - The Hot Plate is also the only attenuator offering a Bright switch and a Deep switch for tailoring your sound. The Bright switch gives you two different high frequency levels so you can compensate for an overly bright, or dull speaker cabinet. The Deep switch offers two distinct bass settings to help you fill out the bottom end, or reduce the bass in a cabinet with too much low end.

Adjustable Line Out - THD Hot Plates also feature a Line Out, which is adjustable by its own volume control giving it a wide range of applications. [Does not have speaker cabinet simulation circuitry.] At higher settings, it can provide enough signal to drive the input of a separate power amp for slaving. The middle range of settings is useful for most rack mount effects. And turned most of the way down, the Hot Plate's Line Out will drive the instrument input of another guitar amplifier for extra power and volume.

Will it hurt my amp? - The THD Hot Plate will not damage your amplifier. When you play continuously at full output, you cause your tubes to age more quickly than they would at lower volumes. Using a Hot Plate will maintain the life of your tubes at exactly the same rate, no more or less, as when you play straight through the speaker.

Using a Hot Plate will also not hurt your amp's transformer any more than playing through a speaker, as long as the impedances are matched (i.e. 8 ohm setting on the amp, 8 ohm speakers and an 8 ohm attenuator). If you are using a well-made amp, then the transformer should last indefinitely, regardless of whether you are driving a speaker or attenuator. If you are using an inferior amp and the transformer blows, it would have done this whether you play through a speaker or an attenuator. The Hot Plate puts the same load on the transformer as a speaker (which is why it makes such a good dummy load).

How do I get one? - First, figure out the impedance of your amp (call us or the amp's manufacturer if you're not sure.) Then call your local music store (many dealers who don't carry the THD amplifier line do carry the Hot Plate.) If they are out of stock, call your closest THD dealer, or call us here at the factory. We will be happy to answer any questions you might have on any of our products.


         Output distortion [power tube/ output transformer saturation] at low volumes

         Better control over your final sound

         Optimized for specific impedances

         Only attenuator with noise reduction built-in

         Only frequency-compensated attenuator

         Only attenuator with tone controls

         Adjustable line-out.

THD Electronics, Ltd.

1925 8th Ave.

Seattle, WA 98101

(206) 292-5500

Guitar Player Magazine Review

Reviewed in Guitar Player, June 1995. "Rich harmonic density, extreme dynamic sensitivity, smooth creamy sustain -- these are some of the characteristics that output-tube distortion and output-transformer saturation contribute to an amp's sound. ... The Hot Plate allows you to use your favorite amp like a giant stompbox [with on/bypass switch], by using the Load (rather than attenuate) setting, along with a selector/router footswitch [not included]. An extremely wicked-sounding tube-overdrive stage indeed. Yow! ... ability to maintain the dynamic feel of a tube amp. The -4dB [that's minimal attenuation] and -8 dB settings were especially impressive at reducing volume without sacrificing tone. Has continuously variable attenuation between -16dB and zero output. A great-sounding, elegantly designed, and versatile tone tool. If you're a tube amp player who's ever wrestled with the problem of being too loud, we highly recommend THD's power attenuator."

George Brickner wrote:

>The Hot Plate needs a guitar speaker cabinet simulator [that is, equalization such as low-pass filter] on the Line Out signal. I bought the Red Box Pro. The Red Box Pro is very good, but it assumes that the Line Out signal from the amp is from the pre-amp! [Is this correct? -mh] Therefore the Red Box has a power amp simulator included. But my Boogie's line out is *after* the power tube section [of course! so was my Marshall 4010 DI Out]. So is the THD's line out, and they don't need the extra compensation.

Newsgroup Posting by Attenuation Expert Steve

The following large block is from a newsgroup posting by attenuation expert Steve.

A Hotplate will be much more flexible than Yellow Jackets in reducing volume--and maintaining the original amp tone. The Yellow Jackets are less about reducing volume than getting a different amp tone.

"A THD Hotplate is a tuned network of capacitors, resistors and inductors which adjusts the overall EQ as the volume is turned down to compensate now for the human ear's frequency response....the louder the sound, the more sensitive your ears are to highs and lows. As the volume drops, your ear becomes more sensitive to the mid-range, and less so for highs and lows. The Hot Plate compensates for this, working like the "loudness" switch on a hi-fi. The THD Hot Plate is the first, and for now the only attenuator that is frequency compensated...

A bright switch gives you two different high frequency levels so you can compensate for an overly bright or dull speaker cabinet. The Deep switch offers two distinct bass settings to help you fill out the bottom end, or reduce the bass in a cabinet with too much low end..." Adjustable Line Out can drive input of a separate power amp...or rack mount effects...or instrument input of another guitar amplifier..."

It also has a built-in passive noise reduction circuit (which can be easily de-activated...)

Something you should consider: The relation of wattage (power) and volume (perceived loudness) is logrithmical. It takes approx. 10 times the power to double the volume/and vice versa.

For example: to double the volume of an 50 watt amp you must have 500watts!

To cut the volume of an 50 watt amp in half you must go down to 5 watts!"

Preserving Speaker Distortion when Using a Power Attenuator

Steve wrote to WeberVST speaker manufacturer:

SPEAKERS are of course, a ABSOLUTELY CRUCIAL element to consider in the quest for great tone at moderate volume. I e-mailed Weber VST with a question in this regard:

From: Steve

"I have a 20/50 watt THD 'plexi' amp which I run either 2-EL84s or 2-EL34s. In order to get rich distortion and compression, it must be played loud. I would like to get that sound at lower levels, so I intend to purchase a THD HotPlate or similar attenuator. I understand that at lower volumes, the sensitivity of the ear changes according to a Fletcher-Munson curve, so I'm wondering what kind of speaker cabinet or system I should use to compensate at the lower volumes?"

WeberVST's response:

"Steve, that's true about the F-M curve and the correction needed at the lower volumes. I would have to recommend though, before using a power attenuator that you go through the calculations or have a professional amplifier technician advise you on its use with regards to steady state power handling and thermal dissipation capabilities of your output circuit. There's some 'sonic psychology' involved here, in that as you are listening comfortably to the lower, attenuated level of acoustic power, the output circuit is still giving it all it's got. So, since your ear hears the lower level, it isn't quite so evident that the output circuit is working so hard. The bottom line is that the output transformer is heating up, it might be in saturation alot of the time, you lose some bass due to the saturation as well as increased resistance of the windings due to heating, etc. As far as speakers go, depending on how much attenuation you want to dial in, you'll probably want to get the most effecient speakers you can find. Celestions and WeberVSTs are probably the most efficient speakers available at this time.

"The bottom line is that you are attenuating the big amp down to the power level of a small amp, so you need a speaker that will make the small amp sound huge. If you want to restore alot of the highs, you might go with a Kendrick 10, which is known for accentuated highs. As far as AlNiCo vs Ceramic goes, since you aren't going to really blast the speakers with a high average volume, that is to say alot of your tone (distortion plus compression) will be coming from your output circuit, I think Ceramics would work just fine, and save you some money. Additional comments submitted by Joe Pampel: Another option you might consider is the use of a closed back or sealed cabinet. With an open back, you lose a little bass due to cancellation between the rear and front. In a closed back, that problem diminishes, however it takes more power to get the same loudness. Also, rather than using high efficient speakers as suggested above, you might actually prefer lower efficient speakers. Assuming you'll have plenty of power to put into either the power attenuator or the speaker, you can put less in the attenuator and more in the speaker for a given loudness. You might find that this arrangement will give you more overall control of your tone at the loudness you desire."

"great tone should be priority... so for that matter I'll have to steer you away from the GT Emulator, it's ok... maybe for recording. On a scale of 1 to 10, the Hotplate is a 10 and the emulator is a 4. No lie, it's that much better. I'm sure you will agree once you compare the two. And without extensive EQ treatment, the emulator is flat out useless."

"Nothing beats the sound of good output tube/output transformer saturation... makes my mouth water just thinking about it!"

"And like I said, you want to stay away from the GT Emulator... take my word for it, I used it for over 7 years. You can dial in a so-so sound, and probably get a good tone with some extra effort, but it's more of a hassle than it's worth. If I were you, I would be focused on the Hotplate or the Kolbe. If you want to find out more about the Hotplate and possibly the Kolbe, call Freds Guitars. You'll probably have to leave a message. I got the number from THD. Fred certainly knows a lot about the attenuators he sells. He also discounts the Hotplate ($225), most others sell them at full retail: $325!"

"I do feel that the best tone is achieved when all components of the tone chain are overdriving, whether it is the electronics or the speakers. To that extent, I find that high sound pressure is unavoidable regarding having the speakers overdrive. [At least push each spk to 1 watt - mh] I agree completely that the speaker size, design, and quantity is very instrumental in the nature of the overdrive tone produced, the amount of power the amp has to produce to overdrive the speakers, and the sound pressure level that has to be tolerated at the break-up point of the speakers involved."


"I believe that the best overdrive comes from the power amp section (the EL34's and 6L6's etc), and less so from the pre-amp (the 12AX7's...). The power section is where you get all your dynamics from. It has a ballsier sound which is more responsive to changes in picking dynamics and changes in your guitar's volume knob position. It's also a much more "live" feel. It actually takes a more sensitive touch to control it but it kicks butt."

"It does have a totally different feel, though, than the preamp distortion. It's fuller and rounder. It's very hard to describe but it may take some getting used to if you're accustomed to hearing only preamp distortion. I wouldn't consider buying a tube amp without being able to try it out with a power attenuator. I want to hear the amp with the full potential of what it can achieve - full power!!"

[Bring your Hot Plate -- and 2 eq pedals, and instrument and speaker cables and 1/4" Phone-to-3/16" tabs cable -- to the store when amp shopping.]

"As far as doing damage to your amp....I've never had a problem with any of my amps. I've only changed power tubes a few times in the last 15 years of playing and I only changed the tubes because I thought you had to do that at some point and I felt kind of silly with my old tubes. When I got new tubes, though, I could hardly notice a difference. Granted, I've played only, say, an hour a day on average over that period of time. However, I wouldn't hesitate to recommend using a properly designed attenuator to anyone as long as they're playing through a beefy amp.

In order to make your amp sound great through a soak or break you're obviously going to set the volume and tone controls a little differently than you would otherwise. With a high-gain amp like a JCM900 you'll probably notch the preamp gain down somewhat since the power amp section is likely going to be providing a large part of the overdrive and you don't want to fuzz the thing out completely. Just twiddle the knobs a bit and see what you like. On my Hiwatts I crank the HIgh, Mid, Presence, and Master up Full. The bass is about 1/2 and the two preamp volumes are on about 2/3. If I have the bass or preamps up any further than that the amp gets way overdriven and starts to compress too much."

"Using an attenuator you can pretty much forget about getting a nice crystal clear clean sound out of your clean channel because that too is going to be compressed and fattened up quite a lot. On the other hand. If your amp is like mine, you can get a pretty crisp clean tone by backing your guitar volume off to about 1 1/2 and learn to pick with a gentle touch. It works great if you can manage some subtlety in your picking."


"Tom, I have owned and used three types:

1. the orginal Scholz Power Soak - bad tone...

2. Marshall Power Brake - good tone, no problems running my amps full up into it for extended periods of time. I believe maximum power handling is 100 watts.

3. THD Hot PLate - best tone, no amp problems, equalization capabilities, line out, maximum power handling is 185 watts RMS.

Of the three, I much prefer the THD for its transparency of tone and other features. The only drawback as that it's impedance is not switchable, and you must buy the correct 2, 2.7, 4, 8, or 16 ohm version depending on the speaker load your amp will be driving and what load your amp wants to see."

Using a Power Attenuator as a Dummy Load Enables Post-Amp FX Placement

>Put the fx AFTER the power tubes?


jonathan at callnet.com (Jonathan Schneider) wrote:

>Here is one way to do this (which is what I do):

>'71 Marshall JMP 50 head into THD Hot Plate into 4x12 cab.

>Hot Plate Adjustable Line Out into Lexicon effects processor.

>Effects Processor into Mesa/Boogie power amp, run clean, from the Boogie slave amp into a separate 2x12 cab.

>OK, it's a pretty big set-up, but it works great, and you have total control over the wet/dry mix. And, a big plus is the dry tone through the 4x12 is uncontaminated by any effects processing artifacts resulting from A-D conversions and other crud going on in the processor. It allows the same setup for live playing or home studio or practice, with the only change being how much output attenuation is set on the THD Hot Plate. This THD device is a very good match for the old Marshall amps and cabs, and I wouldn't be suprised if that is what it was designed to work with. The attenuation "effect" is very transparent and adds no ugly coloration, unlike many effects devices I have tried. You get a great overdrive tone, only it is less loud. And, it allows the time-domain processing to be _after_ the power tube distortion of the Marshall head.

>Dave R.

D.R. wrote:

>I've owned a THD Hot Plate for almost a year and use it with my '71 Marshall JMP 50 and a matching Marshall 4x12 greenback cab (straight). The Hot Plate does have an adjustable line out, but its primary intended purpose is speaker attenuation, as with the similar Marshall power Brake product. In my setup, I can leave the Marshall amp's volume control at between seven and ten (there is no Master Volume), and get everything from an acoustic-sounding clean tone to metal distortion just by varying the volume knob on the guitar. The THD unit is very transparent in this setup, at least to the -12 dB atten step. At -16 dB or greater attenuation, you start to detect some rolloff of the highs and lows. There are "Deep" and "Bright" switches on the THD to compensate for that. I don't really use the Hot Plate for bedroom quiet type practice-- the amp is still loud at -12dB attenuation through the 4x12, but it takes it down far enough to avoid severe ear ringing afterwards. As you know, the '68-72 Marshalls have some of the best sounding power stage overdrive/distortion ever invented. I carefully hand select Siemens NOS EL-34 power tubes to be perfectly matched and bias them to 40 ma idle current per tube. Guitars sound best with healthy output humbuckers. I generally use a stock Les Paul Custom or a USA Jackson Pro with an active mid-boost circuit on it. The whole rig is very quiet at idle, I can sit there with the Marshall on "Ten" and hear almost no hum or buzz, just a little hiss.

>To fully utilize all the features of the Hot Plate, I can also take the above set-up and add an effects processor fed by the post-distortion Hot Plate Line Out, then from the processor (I'm using a Lexicon LXP-15 II) into a Mesa Boogie 60W slave amp into a separate 2x12 Celestion cabinet. So the effects are completely after the Marshall-generated power tube distortion in this setup, while the slave amp is run clean. Meanwhile, the 4x12 is completely uncontaminated by any effects processing artifacts since it is using the speaker output of the Hot Plate. Another great thing about using the Hot Plate on vintage amps is that with the above rig you don't have to mod the amp with any kind of effects loop. I will admit it is a rather large setup, but if you want pro sound...

>I paid $230 for the THD Hot Plate and the quality is superb. The thing is solid as a rock, milled from one big piece of aluminum and anodized a dazzling purple color on the 8 ohm unit. There is a built-in fan driven by the guitar signal, no power supply is used. The unit is about 10" wide, 8" deep, by 2.5" tall.

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