LM3886 based amp with sub output
I want to build a LM3686 gainclone based amp with sub output.
Im beginning to find parts – mainly the mechanical parts, but plan to begin making the pcb´s in late October.
I have come across a sew problems, so I hope you can help me out.
The Sub
Im planning to make the sub signal just like the left and right. But should I add extra electrolytic capacitors for the sub channel?
My plan is to use the sub, just as a supliment to my normal speakers(Old Rauna Njord), that might need a little extra in the lower frequencies.
How do I “Make” the sub signal? I would like to merge the left and right signal, and cut off the frequencies above lets say 500Hz. But I would like to be able to adjust the cutoff frequency with a digital potentiometer, so I can control the cutoff frequency with a micro.
Tone Control
I want a tonecontrol. But I want to be able to control it from my microprocesser and not by buttons. So it can be controlled with a digital potentiometer. This way I can make my amp really minimalistic, but still have the features that an integrated amp has.
So Im looking for a good 3 channel tonecontrol solution with bass, mid and treble and volume control.
Any links og suggestions is highly appreciated.
Peter
I want to build a LM3686 gainclone based amp with sub output.
Im beginning to find parts – mainly the mechanical parts, but plan to begin making the pcb´s in late October.
I have come across a sew problems, so I hope you can help me out.
The Sub
Im planning to make the sub signal just like the left and right. But should I add extra electrolytic capacitors for the sub channel?
My plan is to use the sub, just as a supliment to my normal speakers(Old Rauna Njord), that might need a little extra in the lower frequencies.
How do I “Make” the sub signal? I would like to merge the left and right signal, and cut off the frequencies above lets say 500Hz. But I would like to be able to adjust the cutoff frequency with a digital potentiometer, so I can control the cutoff frequency with a micro.
Tone Control
I want a tonecontrol. But I want to be able to control it from my microprocesser and not by buttons. So it can be controlled with a digital potentiometer. This way I can make my amp really minimalistic, but still have the features that an integrated amp has.
So Im looking for a good 3 channel tonecontrol solution with bass, mid and treble and volume control.
Any links og suggestions is highly appreciated.
Peter
Hi Peter,
That’s quiet the skill set in order to accomplish your needs considering you are asking some rather fundamental questions on analog design but also wanting digital control as well. Sure it’s possible to do but also a learning curve. I question your assertion that it’s minimalist, does not sound that way to me unless you purchase something with those capabilities and not something that you are able to design yourself.
Anyways it’s easy to sum the left and right channels, a simple resistor network can do that for you. Not sure why you are asking about the requirement for an ecap as that depends on the design
Many references to refer to, check out Rod Elliot’s web site it’s full of examples in the analog domain, for the digital side of the design you have to determine what hardware you want to use such as an arduino or similar
Good luck
Rick
That’s quiet the skill set in order to accomplish your needs considering you are asking some rather fundamental questions on analog design but also wanting digital control as well. Sure it’s possible to do but also a learning curve. I question your assertion that it’s minimalist, does not sound that way to me unless you purchase something with those capabilities and not something that you are able to design yourself.
Anyways it’s easy to sum the left and right channels, a simple resistor network can do that for you. Not sure why you are asking about the requirement for an ecap as that depends on the design
Many references to refer to, check out Rod Elliot’s web site it’s full of examples in the analog domain, for the digital side of the design you have to determine what hardware you want to use such as an arduino or similar
Good luck
Rick
With a passive circuit, it would be difficult to adjust the LF sub pole without affecting the gain at the same time.
You could do it actively with a couple of op amps. The pot can be a digitally controlled pot.
You could do it actively with a couple of op amps. The pot can be a digitally controlled pot.
Last edited:
I would split this into three "projects" and then tackle each one in turn - that way you can more easily find designs to work from:
This way I think you get a better chance of success and of course verifying if what you are planning is actually going to work. And yes, Rod Elliot's site is a super place to start.
- LM3886 power amps (as many channels as you need).
- Preamp with tonecontrol and sub filter + controls.
- Digital controls with uC and buttons.
This way I think you get a better chance of success and of course verifying if what you are planning is actually going to work. And yes, Rod Elliot's site is a super place to start.
For the digitally controlled tone control you may have a look to the TDA7439 or 49. those are obsolete parts but can still be found.
Some kind of library exists too :
https://github.com/ahuxtable/TDA7439
LM1036 or LMC1982 should be usable too.
Some kind of library exists too :
https://github.com/ahuxtable/TDA7439
LM1036 or LMC1982 should be usable too.
Thank you for your replies
Nisbeth: I already split the project up in many parts. Some of them has many sub-projects included.
Pre amp
Most likely based on NE5534. Design is close to project#88 from Rod Elliot.
I will include tone control and gain separately on each channel.
Also merging left right channel to a sub with variable gain and lowpass cutoff
All pots will be replaced with digital potentiometers, so they can be set with a micro.
Power Amp(s)
Amp will be mor or less a standard (if such thing exists) SuperGainclone. There are many different versions, and im making a prototype before making final decision un that.
I think I will include 4 identical channels for speakers, and one for sub. The sub may have a slightly larger capacitor behind it, but I will decide when I got it running and can put a scope and some ears on it.
Microprocessor
This is the least difficult part, and im not going to give it much attention until I got the other parts testing and running on a bench.
I would like both a VU meter(or 2), and perhaps a graphical equalizer. So an OLED screen is under consideration.
The micro will not take any part of the signal path except controlling relays, and setting the digital potentiometers.
Control will be a rotary encoder with push function. Apart this the only other thing on the front plate will be the on/off button.
Im still in the process of figuring out if the input selector should be completely digital, og based on relays. I tend to like the relays more. Any advice
Chassis/PSU
This is where im gathering parts. A bit of a no brainer, and for the last 5 years I have been collecting ideas. Deciding what not to include is the thing. But it is going to be extremely minimalistic, heavy and a lot of laser-cut stainless steel and some old teak planks I came across years back.
Still got to calculate the size of the torrid transformer. This is not really easy. I don’t want it to small, but knowing that I seldom play loud it is hard to dimension it right.
Any input on a good input selector solution. What are the advantages on quality relays vs. digital?
Peter
Nisbeth: I already split the project up in many parts. Some of them has many sub-projects included.
Pre amp
Most likely based on NE5534. Design is close to project#88 from Rod Elliot.
I will include tone control and gain separately on each channel.
Also merging left right channel to a sub with variable gain and lowpass cutoff
All pots will be replaced with digital potentiometers, so they can be set with a micro.
Power Amp(s)
Amp will be mor or less a standard (if such thing exists) SuperGainclone. There are many different versions, and im making a prototype before making final decision un that.
I think I will include 4 identical channels for speakers, and one for sub. The sub may have a slightly larger capacitor behind it, but I will decide when I got it running and can put a scope and some ears on it.
Microprocessor
This is the least difficult part, and im not going to give it much attention until I got the other parts testing and running on a bench.
I would like both a VU meter(or 2), and perhaps a graphical equalizer. So an OLED screen is under consideration.
The micro will not take any part of the signal path except controlling relays, and setting the digital potentiometers.
Control will be a rotary encoder with push function. Apart this the only other thing on the front plate will be the on/off button.
Im still in the process of figuring out if the input selector should be completely digital, og based on relays. I tend to like the relays more. Any advice
Chassis/PSU
This is where im gathering parts. A bit of a no brainer, and for the last 5 years I have been collecting ideas. Deciding what not to include is the thing. But it is going to be extremely minimalistic, heavy and a lot of laser-cut stainless steel and some old teak planks I came across years back.
Still got to calculate the size of the torrid transformer. This is not really easy. I don’t want it to small, but knowing that I seldom play loud it is hard to dimension it right.
Any input on a good input selector solution. What are the advantages on quality relays vs. digital?
Peter
You'll probably want to add another inverting stage so the output remains in phase with the input.
Tom