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;
- although your merc ot is not selflead.
I can't wait to let a couple buddies hear that clip. I will make sure the cardiac paddles are handy!
