LM1875 Project
May 6th, 2018, 9:53 am
I'm working on a project based on the LM1875 and would enjoy running some ideas by someone local who has experience working with this chip or others in the gainclone family.
Semi-related: a picture of a little amp I made with some $3 LM1875 modules from Aliexpress.
Semi-related: a picture of a little amp I made with some $3 LM1875 modules from Aliexpress.
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Re: LM1875 Project
May 6th, 2018, 11:42 am
Re: LM1875 Project
May 6th, 2018, 2:03 pm
Thanks for the links. Roscoe, what determined your minimal parts count?
I've built a few kits and have built up several point to point/proto board versions using essentially the schematic from the datasheet. I'm really looking for someone to have a conversation with regarding effect of changing certain values, some stability additions, different power supply ideas. I suppose I'm wanting to gain a bit more understanding now that I've become familiar with the circuit and some variations, and I usually understand better in a less specific situation like this by having a discussion with one person versus the forum format.
I've built a few kits and have built up several point to point/proto board versions using essentially the schematic from the datasheet. I'm really looking for someone to have a conversation with regarding effect of changing certain values, some stability additions, different power supply ideas. I suppose I'm wanting to gain a bit more understanding now that I've become familiar with the circuit and some variations, and I usually understand better in a less specific situation like this by having a discussion with one person versus the forum format.
Re: LM1875 Project
May 6th, 2018, 7:17 pm
The data sheet on this device warns about procedures that should be followed to prevent oscillations. This is common with all high bandwidth devices.
STABILITY
The LM1875 is designed to be stable when operated at a closed-loop gain of 10 or greater, but, as with any
other high-current amplifier, the LM1875 can be made to oscillate under certain conditions. These usually involve
printed circuit board layout or output/input coupling.
Proper layout of the printed circuit board is very important. While the LM1875 will be stable when installed in a
board similar to the ones shown in this data sheet, it is sometimes necessary to modify the layout somewhat to
suit the physical requirements of a particular application. When designing a different layout, it is important to
return the load ground, the output compensation ground, and the low level (feedback and input) grounds to the
circuit board ground point through separate paths. Otherwise, large currents flowing along a ground conductor
will generate voltages on the conductor which can effectively act as signals at the input, resulting in high
frequency oscillation or excessive distortion. It is advisable to keep the output compensation components and the
0.1 μF supply decoupling capacitors as close as possible to the LM1875 to reduce the effects of PCB trace
resistance and inductance. For the same reason, the ground return paths for these components should be as
short as possible.
STABILITY
The LM1875 is designed to be stable when operated at a closed-loop gain of 10 or greater, but, as with any
other high-current amplifier, the LM1875 can be made to oscillate under certain conditions. These usually involve
printed circuit board layout or output/input coupling.
Proper layout of the printed circuit board is very important. While the LM1875 will be stable when installed in a
board similar to the ones shown in this data sheet, it is sometimes necessary to modify the layout somewhat to
suit the physical requirements of a particular application. When designing a different layout, it is important to
return the load ground, the output compensation ground, and the low level (feedback and input) grounds to the
circuit board ground point through separate paths. Otherwise, large currents flowing along a ground conductor
will generate voltages on the conductor which can effectively act as signals at the input, resulting in high
frequency oscillation or excessive distortion. It is advisable to keep the output compensation components and the
0.1 μF supply decoupling capacitors as close as possible to the LM1875 to reduce the effects of PCB trace
resistance and inductance. For the same reason, the ground return paths for these components should be as
short as possible.