Intrest Check: 120w @ 8ohm Tube Buffered LM3875 Amplifier - Page 3 - diyAudio
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Old 25th November 2008, 01:02 PM   #21
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are you still entertaining the idea of a 3886 version?
B
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Old 25th November 2008, 01:07 PM   #22
rhysh is offline rhysh  United Kingdom
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Quote:
Originally posted by mantisory
are you still entertaining the idea of a 3886 version?
B
Maybe at a later date yes. I have put a lot of work into this amplifier so i don't want to throw it down the drain just yet. I will probably get a 3386 version in the works once i have ordered this set of pcb's.
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Old 25th November 2008, 02:24 PM   #23
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that'd be great. I would order these ones, but have several 3886's kicking around gathering dust...maybe i should just build a PTP clone, i dunno...
thanks,
Byron
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Old 25th November 2008, 02:29 PM   #24
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I have a pair of 3875's on the spare that i can give you if you wish.
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Old 25th November 2008, 03:13 PM   #25
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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?
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Old 25th November 2008, 03:56 PM   #26
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Quote:
Originally posted by danielwritesbac
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?
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Old 25th November 2008, 04:07 PM   #27
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Here is my implementation of this.

Click the image to open in full size.

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.
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Old 25th November 2008, 05:12 PM   #28
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Ok, this is the FINAL board design. I dont plan to change anything else.

Click the image to open in full size.

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.
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Old 25th November 2008, 05:32 PM   #29
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Quote:
Originally posted by rhysh
Ok, this is the FINAL board design. I dont plan to change anything else.

Click the image to open in full size.

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
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Old 25th November 2008, 05:45 PM   #30
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Quote:
Originally posted by Tripmaster



This sounds fab

Thankyou
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