Just a quick note to say I've figured out the volume issue. I'm just going to use the Schiit SYS passive pre that I already have + their MODI 3 DAC for Optical, instead of using the MiniDSP for optical processing. That way I'll just have a single stereo RCA pair going into the DSP and nothing else, and I can use the SYS for my master volume control (I only have 2 inputs, vinyl via a MANI and digital tunes via AirPlay). I know there are probably more elegant solutions but this fits with what I already have.
Good that you found a solution to the volume control. Your solution should work just fine.
My solution is to use the volume control in the MiniDSP. I did that with the 4x10HD and am doing it now with the SHD. They're rock solid.
I do share your concern with relying on the media player to control the volume. I'd be worried about some software update setting the volume to max. There are times where I just throw myself into the listening chair and turn on the music. I guarantee you that I will not be checking the volume control setting under those circumstances. It just needs to be set to whatever it was set to yesterday. I wouldn't want to be surprised by incredibly loud music caused by a software update.
Now, about the speakON connectors: As someone pointed out, there is an 8-pole version. I would probably use multiple 4-pole ones, though. In fact, I have standardized on 4-pole speakON connectors. So even if I only need two poles, I'll still mount 4-pole connector. It saves on BOM cost and makes life easier as you only have to build one type of cables.
The 8-pole connector can be nice if you're building an amp for the LX521.4.
Tom
My solution is to use the volume control in the MiniDSP. I did that with the 4x10HD and am doing it now with the SHD. They're rock solid.
I do share your concern with relying on the media player to control the volume. I'd be worried about some software update setting the volume to max. There are times where I just throw myself into the listening chair and turn on the music. I guarantee you that I will not be checking the volume control setting under those circumstances. It just needs to be set to whatever it was set to yesterday. I wouldn't want to be surprised by incredibly loud music caused by a software update.
Now, about the speakON connectors: As someone pointed out, there is an 8-pole version. I would probably use multiple 4-pole ones, though. In fact, I have standardized on 4-pole speakON connectors. So even if I only need two poles, I'll still mount 4-pole connector. It saves on BOM cost and makes life easier as you only have to build one type of cables.
The 8-pole connector can be nice if you're building an amp for the LX521.4.
Tom
Well I finally finished my build!
Tom did a fantastic job with this amplifier design and DIYers who build and discover this amp are getting an end game build as long as it is powerful enough for their needs. What is surprising is how when the volume is increased, it does not start sounding compressed and "loud" due to distortion mechanisms. That will be the undoing of this amp because it sounds so good the desire to crank it up a little more is there.
Thank You Tom, best wishes in your future endeavours!
Tom did a fantastic job with this amplifier design and DIYers who build and discover this amp are getting an end game build as long as it is powerful enough for their needs. What is surprising is how when the volume is increased, it does not start sounding compressed and "loud" due to distortion mechanisms. That will be the undoing of this amp because it sounds so good the desire to crank it up a little more is there.
Thank You Tom, best wishes in your future endeavours!
Attachments
Connection as per Tom
Modulus-86: Composite amplifier achieving <0.0004 % THD+N.
What I did was connect the RCA signal to the + on the XLR on the rear.
Then you connect RCA ground to the - on the XLR.
Then you place a switch connecting the Ground and - as the selection. I believe this is the way most commercial offering do it as well.
NOTE the caveat is that you MUST only connect one input connection at any given time.
Right now, they are driving some Polk Audio LSIM707s. A speaker that is known to dip into 3 ohms. I also turned down the SMPS300ReH to output 27.6 volts, the lowest available. That should minimize the SPIKE kicking in at low impedances.
I hope for DIYers that the LM3886 is not EOL soon so that other DIYers can enjoy this quality of design.
Modulus-86: Composite amplifier achieving <0.0004 % THD+N.
What I did was connect the RCA signal to the + on the XLR on the rear.
Then you connect RCA ground to the - on the XLR.
Then you place a switch connecting the Ground and - as the selection. I believe this is the way most commercial offering do it as well.
NOTE the caveat is that you MUST only connect one input connection at any given time.
Right now, they are driving some Polk Audio LSIM707s. A speaker that is known to dip into 3 ohms. I also turned down the SMPS300ReH to output 27.6 volts, the lowest available. That should minimize the SPIKE kicking in at low impedances.
I hope for DIYers that the LM3886 is not EOL soon so that other DIYers can enjoy this quality of design.
Thank you. You did a fantastic job of building it. That's a nice looking build there!
I have no insider knowledge - and if I did I wouldn't be allowed to share it anyway - but I think if TI wanted to kill the LM3886, they would have done so when they killed many of the other members in the Overture series. I would think that the LM3886 is a pretty strong seller, so it is unlikely to die. Similarly, TI would probably never get rid of the LM317 regulator IC, even though it must be over 40 years old by now.
I do share your concern though. If TI were to get rid of the LM3886, I would be looking at buying a lifetime supply of them.
Tom
Quick question, which I assume the answer is "Yes, duh, no problem!"
Is there any reason that the Power-86 boards can't be mounted vertically? I'm struggling to figure out how to cram 3 of those, plus a huge transformer, plus 6 of the Modulus-86 boards into a 3U Dissipante that's only 300mm deep. I think it'll all fit with enough room to spare if I mount the Power-86 boards vertically to a custom bracket.
Is there any reason that the Power-86 boards can't be mounted vertically? I'm struggling to figure out how to cram 3 of those, plus a huge transformer, plus 6 of the Modulus-86 boards into a 3U Dissipante that's only 300mm deep. I think it'll all fit with enough room to spare if I mount the Power-86 boards vertically to a custom bracket.
Good question about the horizontal mounting of capacitors. I had this idea too at first, it is possible, but for me there were too many buts and ifs. So I choose the safe route and bought a bigger enclosure.
In page 20 of the attached document you will find some more details. The main issue seems to be lifetime reduction. Hope this documents helps
In page 20 of the attached document you will find some more details. The main issue seems to be lifetime reduction. Hope this documents helps
In page 20 of the attached document you will find some more details. The main issue seems to be lifetime reduction. Hope this documents helps
Thank you for attaching that document. It's always good with data. The recommendations for the mounting direction only apply to capacitors with screw terminals, however. There is some mention about how the electrolyte can pool along the side of the cap, which seems to apply to other capacitor types as well. However, the document also describes how this can be mitigated by the cap manufacturer.
The section on mounting direction has been cleaned up in the latest revision of the document. Now it basically reads: Most capacitors can be mounted in any direction. The exception is the screw terminal caps. The rest of their recommendations deal mainly with how to allow the electrolyte to escape the cap safely when it eventually does fail.
Fascinating read, though. In the new version of the doc, you'll find some SEM images of cap innards and EM simulations of the ESL of a capacitors. Very cool stuff!
Not really. I suspect you'll get a bit better reliability if you mount the boards horizontally as this puts less strain on the capacitor pins. You'll also have an easier time wiring to them.
I would make a mezzanine (shelf) in the middle of the chassis. You can probably fit it above the transformer. Just make sure not to create a shorted turn through the transformer (i.e. don't let the mezzanine touch the mounting bolt of the transformer).
Yep. Long standoffs would make that possible. Or threaded rod. That breathing room is worth gold when you try to assemble the amp.
Tom
What kind of wires are recommended for connecting the transformer inputs and outputs, the power module and the amplifier modules?
I sourced some AWG20 and AWG18 cables from an old tower PC but I don't know if the gauge is big enough and if solid core is preferred over stranded.
Also, from what I understand the transformer input and output should be twisted and preferably shielded.
Thanks!
I sourced some AWG20 and AWG18 cables from an old tower PC but I don't know if the gauge is big enough and if solid core is preferred over stranded.
Also, from what I understand the transformer input and output should be twisted and preferably shielded.
Thanks!
Stranded vs solid: Meh. The electrons won't care, so use what you have handy. I prefer stranded because I find it easier to work with.
20 AWG would be perfect for the input, but is a bit skinny for the power supply and speaker connections. Some (me included) would prefer shielded cable on the input, though. I generally use microphone cable for this, though in my most recent build I used star quad cable.
I generally use AWG 16 for the speaker connections. Some may prefer heavier gauges. You can always use 2-3 18 AWG in parallel and just zip tie them together.
The wires on the transformer itself are generally long enough to reach. They need to be tightly coupled. I run them parallel and zip tie them together. I doubt you'd be able to get a tighter coupling if you twisted or braided them together.
Tom
20 AWG would be perfect for the input, but is a bit skinny for the power supply and speaker connections. Some (me included) would prefer shielded cable on the input, though. I generally use microphone cable for this, though in my most recent build I used star quad cable.
I generally use AWG 16 for the speaker connections. Some may prefer heavier gauges. You can always use 2-3 18 AWG in parallel and just zip tie them together.
The wires on the transformer itself are generally long enough to reach. They need to be tightly coupled. I run them parallel and zip tie them together. I doubt you'd be able to get a tighter coupling if you twisted or braided them together.
Tom
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Sorry push .. its black friday and smps240qr is currently on sale .. i need two
Originaly, i was planning on two smps300eeh @85 euro each .. so 170 boths ..
Smps240qr now sale for 45 each until sunday .. so thats a nice saving over my original plan
But i just dont know if they ok since i read on this thread that smps300reh was suitable
Originaly, i was planning on two smps300eeh @85 euro each .. so 170 boths ..
Smps240qr now sale for 45 each until sunday .. so thats a nice saving over my original plan
But i just dont know if they ok since i read on this thread that smps300reh was suitable