Slaving a Plexi Project

[erigm]

Does anyone know, in theory, if you could you run a low to high impedance matching microphone transformer out of your amp/attenuator's lineout and achieve the desired result

http://accessories.musiciansfriend.com/ ... sku=330710" onclick="window.open(this.href);return false;

http://store.a2zcable.com/audio-audio-a ... --xlr.html" onclick="window.open(this.href);return false;

This is what I was talking about using a DI box backwards. Haven't tried it yet, but may get to it next week. Maybe a DI box forwards it the way to go, I don't know. I'll have to try both ways. That's all a passive DI really is anyway, a matching tranny. I have the Groove Tubes Passive DI.

[erigm]

Rockstah,

I thought the first clip "slaved project" sounds more like VH1 and "slaved 24" sounds more like VHII. That is on my computer speakers anyway.

Also, what I was suggesting before about the two stock plexi's was not due to the incorrectness of your tone. The tone your getting is there. I was just considering what is most likely that Ed used back in the day. It seems most likely to me that he was just using stock amps, and doing something between them. On some of the bootleg clips it sounds like he's driving the poop out of one of the amps. Can't tell if its the first amp or the second.

[psychodave]

First clip better. 2nd sounded a "little" thin and "crisp".

[IloveMyMarshall]

not that i have heard yet. when u go through the front end of a stock plexi you lose all that headroom that u hear it eds sound. thats what we have been doing by adding a 330u cap to a stock plexi - trying to create that headroom - when you run in the front of another amp it doesn't have that quality that eds sound has - show me clip - lets talk about it.

http://soundclick.com/share?songid=5609241" onclick="window.open(this.href);return false;

i used a stomp box Boss EQ in between the 2 amps. plexi ->EQ-> JTM.

does running the signal through a stomp box EQ have the same effect as far as impedance matching goes?
does the stomp box act as a converter of sorts?

Rob! That was bad ass!!! hang em high is so NAILED brother! As well as the other stuff!! I am at the same stage of the game impedance matching. I'm using the Boss Ge7 Eq as rob suggested to knock the signal down and eq. However, I'm still having a problem. I'm using that damn pod xt live cab sim, and I know its a no no not it however, it seems to eq it very well. Now when I turn that effect off it doesn't sound that bad buts its brash and way to harsh= back to the impedance issue???
Awesome clip and tone!!

[psychodave]

[quote="IloveMyMarshall"][quote="rgalpin"][quote="rockstah"]not that i have heard yet. when u go through the front end of a stock plexi you lose all that headroom that u hear it eds sound. thats what we have been doing by adding a 330u cap to a stock plexi - trying to create that headroom - when you run in the front of another amp it doesn't have that quality that eds sound has - show me clip - lets talk about it.[/quote]
http://soundclick.com/share?songid=5609241" onclick="window.open(this.href);return false;

i used a stomp box Boss EQ in between the 2 amps. plexi ->EQ-> JTM.

does running the signal through a stomp box EQ have the same effect as far as impedance matching goes?
does the stomp box act as a converter of sorts?[/quote]


Rob! That was bad ass!!! hang em high is so NAILED brother! As well as the other stuff!! I am at the same stage of the game impedance matching. I'm using the Boss Ge7 Eq as rob suggested to knock the signal down and eq. However, I'm still having a problem. I'm using that damn pod xt live cab sim, and I know its a no no not it however, it seems to eq it very well. Now when I turn that effect off it doesn't sound that bad buts its brash and way to harsh= back to the impedance issue???
Awesome clip and tone!![/quote]

I wish this video camera didnt clip... The Chimera tone was VERY close to VH... I could only play VH riffs and hang em high came easily.

Rob is the first person I have heard play Hang em high.

http://s17.photobucket.com/albums/b83/S ... imera2.flv" onclick="window.open(this.href);return false;

[leadguy]

Things that need impedance matching are power devices like speakers, some microphones and radio transmitter aerials and some other things. A speaker is a current and voltage driven device and current multiplied by voltage equals power so that's why the speakers impedance has to be the same as the amps output impedance, so that maximum current and voltage (power) can be transferred from the amp to the speaker.

A Marshall input is not a power driven input, it is a high impedance voltage driven input and does not require impedance matching and it operates best with impedance mis matching in one direction. It is designed so that medium to high impedance devices like pickups can transfer their maximum voltage to the Marshalls input. The main requirement of the Marshall input is that the Marshall input impedance has to be a fair bit higher than the guitar pickup impedance so that input voltage losses don't happen. If the guitar pickups impedance was higher than the Marshall input impedance then a weak input signal would happen.

If you take amp 1's low impedance 8 ohm speaker output and step it up to a 10k or more impedance to simulate the impedance of a guitar pickup and then input it to amp 2, then you hav'nt done anything. The signal voltage hitting the Marshall input is about the same for a 8 ohm or 10k source impedance. (For the 10k source impedance the Marshall input voltage would be a bit smaller then from the 8 ohm source).

Effects like guitar pedals are designed like a Marshalls input, to be high input impedance voltage driven devices and not power driven devices.

Transformers have no impedance by themselves. Transformers only have a reflected impedance. Whatever impedance is connected to the transformers primary gets reflected back to the transformers secondary and this reflected secondary impedance is determined by the impedance connected to the transformers primary and the transformers turns ratio,

[StuntDouble]

I'm sorry if this is a dumb question. I'm trying to keep up with the technical aspect of this without getting too befuzzled, and I thing I understand it somewhat. Not a matter of impedance matching...got it.
My question is, could I mod an existing lineout, from an attenuator or from the amp itself, to reduce the voltage 1/4 and achieve the proper signal strength...as I understand that is what the Jose Load Box effectively does to the signal in addition to providing a load for the amp?

Thanks,

Ben

[leadguy]

It's not essential for the Jose load box to step down the Marshalls voltage by a 1/4 but it's not a bad idea as it limits the max line out output voltage and it gives finer level control when using the pot for level control.

The Jose load box has around 28 volts on amp 1's side of the transformer (the 10k or secondary side) and this 28 volts gets stepped down to around 7 volts on amp 2's side of the transformer (the 600 ohm or primary side) and then the 7 volts goes to a voltage divider made up of a pot and a resistor or just a pot and the pot divides the 7 volts down to a useable level that amp 2's input can handle like 1 volt or 1/2 volt or something like that. With the 4:1 stepdown transformer the max line out output voltage is limited to around 7 volts.

If a stepdown transformer isn't used and a 1:1 transformer is used (600 ohm secondary 600 ohm primary), then there will be around 28 volts on amp 2's side of the transformer and 28 volts will be going to the voltage divider pot and there will be around 28 volts max line out output voltage and less finer pot control to bring the 28 volts down to a useable 1 or 1/2 volts.

You can use a dummy load like a high wattage 8 or so ohm resistor and then have the voltage divider pot in parallel with it but you will have 28 or so volts going to the pot voltage divider like the 1:1 transformer above.
You can use a voltage dropping resistor which drops the voltage down by a 1/4 and then a pot voltage divider which will get 7 or so volts like the Jose stepdown transformer load box above.

http://en.wikipedia.org/wiki/Voltage_divider" onclick="window.open(this.href);return false;

This is a simple dummy load and voltage divider circuit with a 1k voltage dropping resistor (that drops the voltage similar to a stepdown transformer) before the 20k voltage divider pot and the capacacitor in the circuit can be left out.

[leadguy]

Pretty basic drawing of a Jose load box with no transformer



R1 is a voltage dropping resistor that will drop the voltage going to the P1 voltage divider pot by around 1/4

R1 is around 750k
R2 is around 680 ohms and is optional to stop the pot going to 0 ohms
P1 is a 250k voltage divider pot (from Jose load box)

If you use a lower pot value then R1 can be lower as well.

[leadguy]

Pretty basic drawing

Jose load box as I understand it.



Transformer is a 4:1 step down transformer. 10k secondary on amp 1's side and 600 ohms primary on amp 2's side
P1 is a 250k voltage divider pot (from Jose load box)
R1 is optional and is supposed to be 68k (from Jose load box) although 68k is way too high IMO and should be more like 680 ohms
R1 stops the P1 pot value ever going to 0 ohms.

[leadguy]

Here is the same sort of thing as the Jose load box but with basic speaker simulation and a 1:1 transformer. If you leave the speaker simulation capacitors out it's very similar to the Jose load box http://scopeboy.com/ssim.html" onclick="window.open(this.href);return false;

and another http://www.storm-software.co.yu/diy/ind ... ect=zogzog" onclick="window.open(this.href);return false; but leave out the light bulb.

[rockstah]

so whats the deal one has a 1:1 and one has 4:1 - whats it all mean?

so the transformer one needs for jose is spec: 10k secondary 600 ohms primary ? how do we know this?

[IloveMyMarshall]

Here is the same sort of thing as the Jose load box but with basic speaker simulation and a 1:1 transformer. If you leave the speaker simulation capacitors out it's very similar to the Jose load box http://scopeboy.com/ssim.html" onclick="window.open(this.href);return false;

and another http://www.storm-software.co.yu/diy/ind ... ect=zogzog" onclick="window.open(this.href);return false; but leave out the light bulb.

Thanks for posting this information. Makes me wonder with my line out built inside my amp I did myself can I add a cap to cut the harsh and or britle tone to that??

[rockstah]

the power brake has a lineout - i wondered what the transformer was for inside it... i wonder if this will?work the same as this line out/load box?

[SoZo]

I get hum when I hook up a transformer ... And I loose bottom.