Slaving a Plexi Project

[leadguy]

It seems to be a 4:1 (10k 600 ohm) stepdown transformer to reduce the voltage a bit on amp 2's side. Without the stepdown transformer there might be 28 volts hitting amp 2 if the level pot is at it's max setting. With the stepdown transformer the 28 volts gets reduced down to 7 volts max before it hits the voltage divider level pot. The same thing can be done with a 1:1 (600 ohm 600 ohm) transformer and a voltage dropping resistor before the voltage divider pot to bring the 28 volts down to 7 volts before it hits the voltage divider level pot. In the circuit below the 10k resistor is the 1:1 transformer voltage dropping resistor before the 5k voltage divider pot. If a 4:1 stepdown transformer is used instead of the 1:1 transformer then the 10k voltage dropping resistor is left out of the circuit like Mark Cameron says.

So a 1:1 transformer with a voltage dropping resistor is basically the same thing as a stepdown transformer.

"Its not a 1 to 1 transformer its a 600 ohm to 10 k or something like that. The readings say so def not 1to1. Dave"

http://forum.metroamp.com/viewtopic.php ... 34#p202534" onclick="window.open(this.href);return false;

"This is something like it but no resistor(10k) and a 250k pot with a 68k from the wiper to ground and I think its a step down transformer not 1:1 also."

http://forum.metroamp.com/viewtopic.php ... a&start=30" onclick="window.open(this.href);return false;

[dnatronic]

Here's the missing ingredient on using the second amp. It must be a low gain plexi circuit - a la a JTM45; a higher gain preamp on the 2nd amp such as a 12000 series won't work. Use the Vol I input but use the lower one because you don't want to distort the 2nd amp. Then you need to do "impedance matching" from the line out of the first amp to the input of the 2nd plexi - this is the key and is the function of the transformer in the Jose load box. It matches a line output impedance to the guitar input impedance. If you just stick a standard line out signal directly into a guitar amp input it won't sound exactly right, which many have tried with no luck. By using the preamp section of the second plexi, you get the benefit of the tone stack on the second amp. Jose was a genius.

from Mark Camerons post at

"This is something like it but no resistor(10k) and a 250k pot with a 68k from the wiper to ground and I think its a step down transformer not 1:1 also." http://forum.metroamp.com/viewtopic.php ... a&start=30" onclick="window.open(this.href);return false;

The step down transformer seems to be 10K on amp 1's side and 600 ohms on amp 2's side which will step down amp 1's output by roughly a 1/4. http://forum.metroamp.com/viewtopic.php ... 34#p202534" onclick="window.open(this.href);return false; A 1:1 no step down or step up transformer could be used just as well.



Rough calculations

A Marshall 100 wattt amp delivering 100 watts to it's load outputs around 28.28 volts.

Power = current * voltage
Voltage = current * resistance or current = voltage / resistance

so Power = (voltage * voltage) / resistance

so 100 watts * 8 ohms = (voltage * voltage)
so the square root of 800 = voltage

= 28.28 volts into a 8 ohm load


A 600 ohm to 10K transformer will step up the voltage by the turns ratio which is 4.1.

Turns ratio = the square root of (secondary impedance / primary impedance)

So there would be 28.28 * 4.1 volts (116 volts) hitting the voltage divider (10k resistor and 5 k pot).

A 600 ohm to 600 ohm transformer has a turns ratio of 1 so it doesn't step the voltage up or down so there would be 28.28 volts hitting the voltage divider (10k resistor and 5 k pot).

Very high output pickups can output around 1 volt so the 28.28 volts or 116 volts has to be voltage divided down to at least 1 volt so why have 116 volts from the 600 ohm 10 k step up transformer hitting the voltage divider when 28.28 volts hitting the voltage divider from a 600 ohm 600 ohm transformer would be more than enough.


What is the point of a 600 ohm to 10K step up transformer? It doesn't need to match impedances like a mic as the Marshall input is a high impedance voltage transfer input and not a power transfer input. The Marshall input is designed to be high impedance for maximum voltage transfer (bridging impedance) from the high impedance guitar pickups and not for maximum power transfer from the high impedance guitar pickups.

If the transformer is a 10K (primary) 600 ohm (secondary) step down transformer then the turns ratio is 0.245 and the voltage hitting the 10k and 5k pot voltage divder is 6.9 volts and this makes sense and this is what Mark Cameron describes.

http://www.tape.com/resource/impedance.html" onclick="window.open(this.href);return false;

http://www.bnoack.com/index.html?http&& ... ormer.html" onclick="window.open(this.href);return false;

WIth all due respect, you are missing the big picture. Try this experiment. Run Marshall amp #1 into a hot plate set as a load, and then then run the line out of the hot plate into the input of Marshall amp #2. You will find it doesn't work very well. Why not? Now imagine yourself as an electrical engineer whose job it is to solve this problem. First, identify why it doesn't work very well and then second, provide a solution to the problem. The solution is a block box stuck between the hot plate line out and the input of amp#2. What's in your block box that solves the problem?

[T.J.Fuller]

[quote="dnatronic]WIth all due respect, you are missing the big picture. Try this experiment. Run Marshall amp #1 into a hot plate set as a load, and then then run the line out of the hot plate into the input of Marshall amp #2. You will find it doesn't work very well. Why not? Now imagine yourself as an electrical engineer whose job it is to solve this problem. First, identify why it doesn't work very well and then second, provide a solution to the problem. The solution is a block box stuck between the hot plate line out and the input of amp#2. What's in your block box that solves the problem?[/quote]

The block box would have to knock that signal WAY down ( pickup output level) since you are talking about going thru the front of amp #2.

The main reason Mark's clips sound so good is it looks like he approached this a whole NEW way- there is no need to knock anything down , if you just bypass the whole pre-amp section of amp #2- its the amp pre-amp section that usually gets in the way.

way to go Mark ...something original that sounds great...and with the tone he is getting on these clips ...why does he even need to mess with a 4:1 transformer set-up?? ... seems thought out like an engineer/ mad scientist.

[Krinkle]

I agree.

I think the load box issue has been solved, at least for Mark. I'm not sure that it needs to go any further (or that he wants to). That's why he is inclined to keep saying to connect it like he does.

Here's what I think the difference is between what Mark is doing and what everybody else is trying. If you look at the schematic for the Power Brake you will see that it is Marshall's version of a load, obviously. It is essentially a speaker electrical "model", consisting of inductance, capacitance and resistance, all 3 of which are needed to properly simulate the speaker load. Some of the circuitry is also probably used to roll of some treble response, as the cabinet does in real life. So the head is connected to a load that it thinks is a 4x12 cabinet.

So Mark is sending the best suited signal, from a level and frequency perspective, to the second amp. Is it what Ed did? The saga goes on. I just know that it sounds right to me. I would be inclined to blame any differences from the magic moments in the 70's on the rest of the signal chain, Mark included, as good as he is. While it may not be true we say it over and over, the studio, Donn Landee, Ed's picking technique, etc, adds to the equation.

There is a chance that Sozo's load is missing the Power Brake elements with the transformer and resistors only and the treble roll off is perceived as loss of bottom end. But if he is semding it to the input of the sedon amp it could be a different story.

Exactly what ED did may not have been electrically "correct" but may have worked in spades. I just think that Mark has it already, when sending the signal into the effects return of another amp.

I guess part of the equation here is that we may believe that Ed slaved into the input of the second amp. In that case you will have to play around with the load box because it's very likely that it wasn't done "properly" from an engineering point of view. If that's the case, then it's likely that only the exact same circuit will work. I'm inclined to say just do what Mark is doing.

Sorry for the long post.

Darrin

[rgalpin]

hey stan - don't you use a Marshall Power amp as your second amp?

what model is it? your clips have always stood out as having some of the more elusive qualities of ed's sound. i wonder if the Marshall Power amp has similarities with what mark is doing.

??

[leadguy]

WIth all due respect, you are missing the big picture. Try this experiment. Run Marshall amp #1 into a hot plate set as a load, and then then run the line out of the hot plate into the input of Marshall amp #2. You will find it doesn't work very well. Why not? Now imagine yourself as an electrical engineer whose job it is to solve this problem. First, identify why it doesn't work very well and then second, provide a solution to the problem. The solution is a block box stuck between the hot plate line out and the input of amp#2. What's in your block box that solves the problem?

Well I am an electronics engineer and Mark Camerons Jose load box is a well designed line out for a Marshall and is probably the only box you need. It's a design that's been around for years and years and Jose who was an engineer based his design on those older designs. There is really nothing new about the Jose load box. There could be lots of reasons why using a hotplate or anything else for that matter doesn't sound too good when you couple amps together.

I have never heard of anyone making a Marshall line out box to be like a guitar pickups impedance and as I've said before it makes no sense to do it as Marshall and effect inputs are voltage driven inputs.

The Jose load box is not the only way to do it but it's pretty good as it breaks any ground loop noise problems with it's isolation transformer and gives pretty good output voltage level control.

[T.J.Fuller]

WIth all due respect, you are missing the big picture. Try this experiment. Run Marshall amp #1 into a hot plate set as a load, and then then run the line out of the hot plate into the input of Marshall amp #2. You will find it doesn't work very well. Why not? Now imagine yourself as an electrical engineer whose job it is to solve this problem. First, identify why it doesn't work very well and then second, provide a solution to the problem. The solution is a block box stuck between the hot plate line out and the input of amp#2. What's in your block box that solves the problem?

I have never heard of anyone making a Marshall line out box to be like a guitar pickups impedance and as I've said before it makes no sense to do it as Marshall and effect inputs are voltage driven inputs.

I was meaning bringing the voltage down ( should've worded it differently)
to more of the guitar pickup output. millivolt range, even though some power amps
handle 3v input.

regardless, when using a 2nd amps preamp and power amp, it does sound wrong.

when Rgalpin did it - it was more of a nailing of the Diver Down tone.

which is killer ,for that VH type tone, it's because you are marrying the tones of a Marshall driven amp with a Fender tone stack and power amp section.

I think this is why Ed went H&H , he probably did want that sound. H&H has a unique bass filter arrangement , EXTREMELY hi-bandwith, and it gave him that super clean fender-clear sound when he backed off the volume knob.

both ways rock...Rob's and Rockstah's set-ups.

but one is the Largo tone and one is clearly the elusive early club/VH1 tone...

[leadguy]

I think it's a good idea to bypass Amp 2's preamp and tonestack but how did Ed do that with a Marshall for VH1 or did he use something else for amp 2. Later on he used the H&H power amp as amp 2.

[dnatronic]

WIth all due respect, you are missing the big picture. Try this experiment. Run Marshall amp #1 into a hot plate set as a load, and then then run the line out of the hot plate into the input of Marshall amp #2. You will find it doesn't work very well. Why not? Now imagine yourself as an electrical engineer whose job it is to solve this problem. First, identify why it doesn't work very well and then second, provide a solution to the problem. The solution is a block box stuck between the hot plate line out and the input of amp#2. What's in your block box that solves the problem?

Well I am an electronics engineer and Mark Camerons Jose load box is a well designed line out for a Marshall and is probably the only box you need. It's a design that's been around for years and years and Jose who was an engineer based his design on those older designs. There is really nothing new about the Jose load box. There could be lots of reasons why using a hotplate or anything else for that matter doesn't sound too good when you couple amps together.

I have never heard of anyone making a Marshall line out box to be like a guitar pickups impedance and as I've said before it makes no sense to do it as Marshall and effect inputs are voltage driven inputs.

The Jose load box is not the only way to do it but it's pretty good as it breaks any ground loop noise problems with it's isolation transformer and gives pretty good output voltage level control.

I'm glad you're an electronics engineer. I have a degree in electrical engineering.

But that's not the point I was getting at. Most folks have a commonly available attenuator or load box such as a hot plate, weber mass, etc., and don't have the time or inclination to build a Jose load box. Hot plates and weber masses only have line level outputs.

Assume you have two Marshalls and one hot plate. That's it. So my question to you, is why can't you just plug Marshall #1 into the hot plate, set the hot plate to load, and run the line out of the hot plate straight into the guitar input of Marshall #2? I don't disagree that the Jose/Mark Cameron solved this problem with their load box, however the modern attenuator devices I mentioned don't.

Trust me, there is a very simple electrical engineering reason why a line out straight into a guitar input doesn't work very well. Do a search of this website and you will hear anecdotal evidence of folks saying doing that sounds bad. I have tried it myself personally and verified this. So I have applied my electrical engineering skills have solved this problem with fantastic results, because I know my stuff.

[fivecoyote]

Okay, I want to know -- sorry if i missed it -- what is your solution dnatronic?

Also, in another current thread rgalpin is swearing he's getting good tones I believe going into the input of amp 2 (right?), though he has some boosts between the line out box and amp #2.

[leadguy]

Hot Plate Line Out Specs

II. Line output:

Type: Mid-impedance (approx. 35Kohm), unbalanced, negative ground.
Connector: 1/4' phone jack.
Level: Continuously variable line out level (+10dB(V) to -40dB(V)).

http://www.vintageamps.com/va/thd/thd_hotplate.html" onclick="window.open(this.href);return false;

Q. Do the settings on the front panel of the Hot Plate affect the line out signal?
Only the bright and deep switches. These have a very slight effect on the line out tone, and actually CUT the treble and bass respectively in the line out signal when they are switched on (up), because they are directing more of the highs or lows to the speakers.


Q. Sometimes when I run a slave amp out of the line-out there is substantial signal to the slave amp even when the line-out level control is turned all the way down. Why is this?
This signal is generated in the cable due to the very high currents involved. To eliminated it, use a cable from the Hot Plate to the slave amp that has its shield connected on only one end.

http://www.vintageamps.com/va/thd/thdfaq.html" onclick="window.open(this.href);return false;

The THD Hotplate has filters in it's circuit and a pretty high output impedance so there are a number of things why it might not sound great when used as a line out.
With a line out that is going to a high impedance input like a guitar amp or effects, the line out should deliver guitar pickup like voltage levels at a low impedance output so that maximum voltage gets transferred to the high impedance input and there are tons of circuits all over the net. The Jose load box also has the advantage of breaking ground loops due to it's transformer.

I don't really know what you mean but tell about your solution.

[leadguy]

Here are some interesting articles on what happens to a pickups frequency response and output when the pickup gets connected to a amp or effect pedal with varying input impedances and how the cable affects it as well. I know it gets a bit technical (just read it in a basic way and ignore the technical stuff) but it shows a lot of the problems that line outs and other things can suffer from like impedance problems and cable problems etc.

http://www.ozvalveamps.elands.com/pickups.htm" onclick="window.open(this.href);return false;

http://www.terrydownsmusic.com/technote ... cables.htm" onclick="window.open(this.href);return false;

[dirtycooter]

Hi-been lurking a long time and I must say this is the home of all that is brown!!!!

I would like to share some slaving knowledge with all of you though-I feel somehow sharing this stuff will someday break the code to obtaining the brown sound as a simple method or recipe so many of us won't have to struggle for it any more.

I don't have any recording gear so I cannot post any clips. But here is some insight on ss power amps and slaving.
I have found many problems trying to go wet/dry/wet with a ss power amp.

Here is the mystique behind the palmer speaker simulator-pay attention!!!!
If you take a line out from any speaker cable as I do with my line out box from CAE
it is a completely hi-fi unshaped sound and can seem very grainy and overly bright.
That signal right there alone has not gone through a speaker and had any highs or lows rolled off like a speaker would do.
All the palmer is really is a lo and hi pass filter that eliminates the extreme highs mostly and some lows. Just like a greenback can only reproduce 75hz-5khz the palmer trims off the excess on each end of the spectrum that we can possibly humanly hear which is 20hz-20khz.
In comparison it would look like this
full frequency [____________________________________________]
shaped by palmer [____________________________]

Note-the palmer does not add resonant cab or bass frequencies at all-just cuts hi and lo frequencies from a hi fi line out signal as if it had passed through real speakers and a tube power amp interacting with those speakers

1.slaving to a guitar tube amp will interact with wet/or 2nd cab guitar speakers and roll off the highs and lows as needed in a very normal way and you WILL NOT need the palmer at all! Here I think is what you guys are doing and seems to be the vh1 tone in spades.

2.Also slaving to a randall rh100 ss amp or titan, or any of those mosfet output sections in those particular amps seems to work without the palmer to. The ss power section design seems to react with the wet cab speakers and you get that roll off like a tube amp will do. amp 1 out to dry cab- lineout-fx-2nd amp fx return-wet cab. Works great for slaved fx. With a line out only thru a boss dd3-perfect mirror repeats!!! identical to the dry cab

3. If you want a PA style power amp for L+R fx-here is what I found

EX A.-1st attempt I simply took the CAE line outsignal robbed from my heads speaker cable going to the dry cab into a t.c. g-force and out to a mackie 1400i stereo power amp and into L+R wet cabs-the fx end sounded very bright and un-natural-horrible!!! the fx sounded like ice picks in your ears!!!

EX B. Next I tried a Yamaha PA power amp that stated mosfet EEE engine blah blah on the front-same results!!!!

EX C. E-mailed Kevin Oconnor from LONDON POWER-he stated most ss amps have crossover distortion in there outputs when trying to react to certain ohm loads and some how I went with this info to a tech at sweetwater music-he pushed me toward a crown CE2000 and stated that would get rid of most of the crossover distortion due to the output design of the amp trying to drive 16ohms.
Hooked up-better but still not there yet-something not quite right yet.
I order palmer pga -05-no load/ speaker filter only!!!
Here it sounds perfect as it gets witht he palmer for no coloration/distortion from the second amp. Just pure uncolored reamplification of dry sound or fx!!
Line out signal goes into palmer-gets rolled off frequencies to my line level signal-shapes it basically like a miked speaker would do-this goes to the fx- fx to crown-crown to L+R wet cabs-
bypass the fx units and it is an identical mirror image tot the original dry cab

Settings for the palmer are-

"Brown" switch engaged-yes it really says brown on it!-puts a midrange green back quality on the signal-more nasal than the alternate setting

Low filter all the way up for full bass

Highs trimmed so the dial is about at 10 or 11 o clock

Filter volume used only- adjusts out level needed

Non filter volume completely off-use this if you want to hear no speaker simulation and how bad that sounds

It has been stated Ed does not use the speaker simulation in his palmer going through the HH v800's -complete hogwash-without the palmer all those fx would sound like ass-also the sheffield 1200 speakers were designed to work with the palmer signal-they are higher powered speakers designed not to break up very much at high volume yet they sound almost identical to my dry cabs re-issue greenbacks.
Basically Ed's Wet side is a glorifed PA for adding fx to his dry tone-its all fed by a direct signal from the palmer

Yet this palmer has nothing to do with anything or albums until 5150 on to present
see ya

[45auto]

sounds kind of like what rob has been doing with his eq.

[dirtycooter]

yes and no

If i understand correctly rob is loading his amp completely, taking a line out from that full load from the original head with no speakers-putting that through an e.q.-sending that to another tube guitar power amp similar to rockstah.

As i have understood-e.q. before distortion will boost gain and response in certain places or frequencies while on the other hand e.q. after distortion simply shapes the distorted signal-not really adding any more overdrive or distortion as much as the first scenario, simply shapes it is all.

The palmer is not an e.q. at all-you cannot get the same results with an e.q. as you can with the palmer period-close but not at all really. The palmer is simply a clever "crossover" that only lets the middle frequencies through. Useful only for sending a direct signal to a ss PA amp. Palmer was not around back in '79 so its not an element to the VH1 tone. Nor will it ever be.

Either you want your line out signal unmolested with no added coloration or distortion [does need to be shaped though by the palmer] and use a solid state amp with 4 X's the power as your dry cab being ran by a 100 watt tube amp-[palmer needed here]
-OR-
you are running one head creating pre and power amp distortion,loading it completely making it a giant distortion pedal in essence and sending that signal into another tube amp with another presence control and more tubes to add even more harmonic richness and additional light power tube distortion-there by juicing up that frumpy stock SL tone that only sounds just "o.k. by itself and taking it a step up. Correct? or was I not quite listening correctly and missed a few details?
i am with Rockstah on the fact he doesn't sound like you want to go into a guitar amp input-that he sounded as if he prefered an fx return or power amp in which would only leave the presence, volume, and additional power tube coloration on that, not all the problems of going through another tone stack and all that preamp section. This is more about simply acheiving the dry kick ass distortion main tone Ed had and not really focusing on fx or fx placement very much

I think Rockstah has the VH1 tone figured out-period-in his last clip.
I just wanted to donate the info on getting WET fx from a ss power amp and why the palmer is really a key to that setup if you are using a SS PA amp. This palmer setup pretty much retro fits any amp tone-fender blues, country twang, metal, etc. The only thing that has to change is the speaker cabs and the main amp head or combo-you'll always have your stereo fx how they are with any tone you're looking for that way. You just have to get your main tone source amp picked out and running like you want it.

you could take Rockstah's preamp, power amp, and 2nd power section idea and still apply the two outside cabs I described above. A 2nd line out on the 2nd power amp -into a dry cab-line out from the speaker line to the dry cab goes to a palmer then to fx then to a crown power amp and then to L+R outside wet cabs.
I know-it sounds complicated. But think about it a little. You could have Rockstah's last clip-add my palmer setup I described and be wet dry wet with Rockstah's exact tone he just got on his last clip coming out of the L+R cabs.
The palmer setup starts from the dry cab speaker line. which would be the speaker line going to the cab he miked up for the clip he posted.