Okay, as a stopgap measure, and for the purpose of supporting a wider variety of speakers, can you document the means to use this as a LM3875 parallel amplifier. That, (I think) would remove any objections from the owners of 4to8, MTM, 4 ohm, and "hard to drive" speakers--because it would, in effect, avoid setting off NatSemi's Spike system.
So, a simple means to parallel would be nice.
This being a stereo board, we'd want to add a "jumper" or something in order to insure that the input is exactly the same for both chips--an option to switch on for whenever its used in parallel operation.
Then you can get approximately 60w, no matter what speakers, and also avoid the spike screech (related to load).
Prediction: Parallel operation would have a "darker" sound, a bit less midrange, and the slightest loss of resolution (any parallel mismatch is cancellation). For my use, a "less distracting" frequency response and saying "goodbye" to Spike, is a higher fidelity at end result. I'm very interested in this!
I think all it takes is a "mod document" to provide this option. What do you think?
So, a simple means to parallel would be nice.
This being a stereo board, we'd want to add a "jumper" or something in order to insure that the input is exactly the same for both chips--an option to switch on for whenever its used in parallel operation.
Then you can get approximately 60w, no matter what speakers, and also avoid the spike screech (related to load).
Prediction: Parallel operation would have a "darker" sound, a bit less midrange, and the slightest loss of resolution (any parallel mismatch is cancellation). For my use, a "less distracting" frequency response and saying "goodbye" to Spike, is a higher fidelity at end result. I'm very interested in this!
I think all it takes is a "mod document" to provide this option. What do you think?
danielwritesbac said:Okay, as a stopgap measure, and for the purpose of supporting a wider variety of speakers, can you document the means to use this as a LM3875 parallel amplifier. That, (I think) would remove any objections from the owners of 4to8, MTM, 4 ohm, and "hard to drive" speakers--because it would, in effect, avoid setting off NatSemi's Spike system.
So, a simple means to parallel would be nice.
This being a stereo board, we'd want to add a "jumper" or something in order to insure that the input is exactly the same for both chips--an option to switch on for whenever its used in parallel operation.
Then you can get approximately 60w, no matter what speakers, and also avoid the spike screech (related to load).
Prediction: Parallel operation would have a "darker" sound, a bit less midrange, and the slightest loss of resolution (any parallel mismatch is cancellation). For my use, a "less distracting" frequency response and saying "goodbye" to Spike, is a higher fidelity at end result. I'm very interested in this!
I think all it takes is a "mod document" to provide this option. What do you think?
This is a very good idea. I was thinking a relay to switch between parallel and normal modes, but then i realized that the relay could be accidentally switched. I believe a jumper is the best option for this like you said. I will play around with the schematics and the board, and post a update later.
I understand you are basically saying you would like to use a single board per channel into 4ohm speakers?
Here is my implementation of this.
Basically, either both or just one channel inputs are used.
To drive a 4 ohm speaker, simply move the jumper cap down one place. You will also need to place a 0.1-0.2R 5w resistor on the outputs. Simply use some veroboard with the correct pair of resistors if you want to use a 4ohm load with a pair of jumpers to bypass. I was thinking about relay driving the whole thing but it is not possible without redesigning the board.
An externally hosted image should be here but it was not working when we last tested it.
Basically, either both or just one channel inputs are used.
To drive a 4 ohm speaker, simply move the jumper cap down one place. You will also need to place a 0.1-0.2R 5w resistor on the outputs. Simply use some veroboard with the correct pair of resistors if you want to use a 4ohm load with a pair of jumpers to bypass. I was thinking about relay driving the whole thing but it is not possible without redesigning the board.
Ok, this is the FINAL board design. I dont plan to change anything else.
Click for v. High Res
This board can now output 110W into 4ohms, (one speaker that is).
Please note, you will need 0.2R resistors on the output to avoid the chips cancelling eachother out.
An externally hosted image should be here but it was not working when we last tested it.
Click for v. High Res
This board can now output 110W into 4ohms, (one speaker that is).
Please note, you will need 0.2R resistors on the output to avoid the chips cancelling eachother out.
rhysh said:Ok, this is the FINAL board design. I dont plan to change anything else.
An externally hosted image should be here but it was not working when we last tested it.
Click for v. High Res
This board can now output 110W into 4ohms, (one speaker that is).
Please note, you will need 0.2R resistors on the output to avoid the chips cancelling eachother out.
This sounds fab
20 Boards Remaining...
Can everyone wanting boards for definate, please contact me via email so i can get you down on a spreadsheet (even if you have allready posted in the thread). My email address is rhys@pressure-drop.org. Thanks.
Can everyone wanting boards for definate, please contact me via email so i can get you down on a spreadsheet (even if you have allready posted in the thread). My email address is rhys@pressure-drop.org. Thanks.
Hello everyone,
BOM Is HERE!.
Total cost for everything apart from transformers is only $107.78!
I have tried to use high quality parts in the BOM, please make your own decisions on the coupling caps R105 L + R if you wish!
EDIT: Forgot the tube socket, you need a 9 pin PCB mount socket.
Rhys
BOM Is HERE!.
Total cost for everything apart from transformers is only $107.78!
I have tried to use high quality parts in the BOM, please make your own decisions on the coupling caps R105 L + R if you wish!
EDIT: Forgot the tube socket, you need a 9 pin PCB mount socket.
Rhys
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