I'm building a Leach Amp version 4.5, and don't know where R51 goes?
R51 is an 82 ohm resistor, shown on the left side of the schematic between Non-Signal Ground and Signal Ground.
If anyone has built one of these amps, can you tell me where R51 is physically located on the amp?
Thanks!
R51 is an 82 ohm resistor, shown on the left side of the schematic between Non-Signal Ground and Signal Ground.
If anyone has built one of these amps, can you tell me where R51 is physically located on the amp?
Thanks!
Desertstorm- Please see link for components. They are not called out with standard BOM, you have to read through the list. R51 is an 82 ohm resistor. I am trying to determine where R51 locates in the amp. First post has the schematic attached:
Leach Amp Plans - Part 3
Thank you all for your time.
Leach Amp Plans - Part 3
Thank you all for your time.
From the FAQs section of the Leach Amp website:
There are two connections for central ground on the board. The one on the input side is on the same trace as the signal ground. What is the purpose of second central ground connection if you are isolating the input jacks from the chassis and have R51 (82ohm) between input ground and central ground? It seems as though you worked on isolating the two grounds from each other and then shorted them with the second central ground connection.
For audio frequency equipment, a central ground is used and all ground wires run in parallel to this point. This prevents what are called "longitudinal voltages" in the ground system from coupling between different stages in the circuit. With parallel ground wires, there is the possibility of what are called "ground loops" if the ground wires connect together at either end. Thus the input cable ground is isolated from the chassis because it is grounded through the circuit board ground. There are 2 ground tracess on the circuit board, one in which signal currents flow and one in which ripple currents from the electrolytic decoupling capacitors flow. Each of these ground traces has its own wire that connects to central ground. A single ground should not be used because the ripple currents could induce hum in the signal part of the circuit. The 2 grounds are connected together with a 82 ohm resistor which is large enough to prevent the current in one ground trace from flowing into the other ground trace, but small enough to keep both traces at approximately the same ac voltage at higher frequencies where the inductance of the ground wires causes the ground system impedance to increase. The theory of this is covered books on electromagnetic compatibility.
There are two connections for central ground on the board. The one on the input side is on the same trace as the signal ground. What is the purpose of second central ground connection if you are isolating the input jacks from the chassis and have R51 (82ohm) between input ground and central ground? It seems as though you worked on isolating the two grounds from each other and then shorted them with the second central ground connection.
For audio frequency equipment, a central ground is used and all ground wires run in parallel to this point. This prevents what are called "longitudinal voltages" in the ground system from coupling between different stages in the circuit. With parallel ground wires, there is the possibility of what are called "ground loops" if the ground wires connect together at either end. Thus the input cable ground is isolated from the chassis because it is grounded through the circuit board ground. There are 2 ground tracess on the circuit board, one in which signal currents flow and one in which ripple currents from the electrolytic decoupling capacitors flow. Each of these ground traces has its own wire that connects to central ground. A single ground should not be used because the ripple currents could induce hum in the signal part of the circuit. The 2 grounds are connected together with a 82 ohm resistor which is large enough to prevent the current in one ground trace from flowing into the other ground trace, but small enough to keep both traces at approximately the same ac voltage at higher frequencies where the inductance of the ground wires causes the ground system impedance to increase. The theory of this is covered books on electromagnetic compatibility.
Hi,
I built my Leach amps according to the original instructions - one thick wire to the "star" and the other thin signal ground wire to the "star" - the R51 is between these two wires on the PCB. Just take into account that the thin signal ground wire is sensitive to interference - it is better to make it shorter and located as far as possible from the transformer...
This can be checked with an oscilloscope, AC millivoltmeter or connect headphones to the output (input must be shorted) - place the wires so that there is no hum in the headphones.
UIt can be done in two ways ( for me 1st one works fine):
I built my Leach amps according to the original instructions - one thick wire to the "star" and the other thin signal ground wire to the "star" - the R51 is between these two wires on the PCB. Just take into account that the thin signal ground wire is sensitive to interference - it is better to make it shorter and located as far as possible from the transformer...
This can be checked with an oscilloscope, AC millivoltmeter or connect headphones to the output (input must be shorted) - place the wires so that there is no hum in the headphones.
UIt can be done in two ways ( for me 1st one works fine):
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