Brian:
Those dimensions are based upon locating his new brackets relative to the PCB to provide adequate lead length above and below the PCB, as shown in the photo I have attached. It really is a moot point what the numbers are if you use the template as intended...Tom has taken the measuring out of the procedure.
For those who may worry about the center punch maybe slipping or just being off a bit when aligning it to the center cross-hairs, here is tip/trick I use. Before center punching, tape the pattern to a piece of card box and then use a straight pin to pierce a little hole on each center point. I do this using one of those goofy looking headband magnifiers (aging eyes). Now you have a self-aligning template for the center punch. If you mess it up a bit, just print a few extra templates.
Attachments
All you need to do is to print the .pdf at 1:1 and tape the template to your heat sink. Centre punch at the ten crosshairs. Drill, tap, done.
If you'd rather do the measuring work yourself, you're more than welcome to. You can always slide the LM3886es up. It'll give you a bit more lead length, but that should be OK. The additional 0.05" shouldn't be a big deal even for hand measurements, though. If you have access to a height gauge, you can make it even easier.
You could argue that I should have placed the holes in the bracket 0.05" lower. I do need to provide enough space that you can get a screwdriver in above the PEM nuts (and any components in the way on the PCB). Those considerations drove the hole placement in the face of the bracket that faces the heat sink. I could drop the top hole down 0.05", but that makes the hole spacing 0.450", which is harder to find on a ruler than 0.5".
Tom
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Thanks Tom.
This is something you can consider to add to your documentation. Should someone need this in the future ...
Done. I added the input impedance spec to my Modulus-686 page. If you don't see it, please hit Reload in your browser.
It'll make it into the design doc at the next update.
Tom
based on performance for HP-1 
which happen have same father : ) as those nice looking power amps there guess there will be some good quality rock'n roll and a room full of visitors.Tom,
I was thinking about using a Modulus setup for an lxMini build -- the usual miniDSP to amp then speakers. The 86 can easily power the full range mid-tweeters, but the woofers look like they can run all day on 80w into 8 with up to 250w peaks. Do you think 686's are needed for the woofers are could you get away with 86s? Maybe run the woofers on class Ds? (yuck, but at those frequencies?)
Im a big fan of holography, so I also want to make sure everything in the signal chain maintains proper phase.
looking forward to the build.
I was thinking about using a Modulus setup for an lxMini build -- the usual miniDSP to amp then speakers. The 86 can easily power the full range mid-tweeters, but the woofers look like they can run all day on 80w into 8 with up to 250w peaks. Do you think 686's are needed for the woofers are could you get away with 86s? Maybe run the woofers on class Ds? (yuck, but at those frequencies?)
Im a big fan of holography, so I also want to make sure everything in the signal chain maintains proper phase.
looking forward to the build.
Keep in mind that the LXmini crosses from the woofer to the tweeter smack in the middle of the midrange. I forget the exact crossover frequency, but it's in the 1-2 kHz range as I recall. You'll have quite a bit of energy emitted by the woofer well into the kHz range. Thus, I would not consider a Class D for that.
I used to think that "40 W aught to be enough for everybody" (to borrow a mis-quote) and recommended 4xMOD86 as result. I was rather surprised when I got the first pair of MOD686es running on the LXmini and found a significant improvement in sound quality and imaging. I run my MOD686 on ±27 V for 130 W into 8 Ω as doing so allows me to use a 3U ModuShop Mini Dissipante chassis.
Can you get away with 4xMOD86? Sure! I ran that way for years. I did find that I got some strain/harshness at louder SPLs, though. I took that as an indication that I should turn the volume down. With the MOD686, that strain/harshness is gone. So I'd definitely go with the MOD686 on the woofers if you can.
Tom
Thanks Tom. So do you run 4 x mod686 or 2xmod86 + 2xmod686?
BTW: How did it go at BurningAmp?
I ran 4xMOD86 for three years. I've run 4xMOD686 and 2xMOD686+2xMOD86 for about three weeks each. I prefer 4xMOD686. 2xMOD686+2xMOD86 is a close second. I suspect 2xMOD686+2xMOD186 (to be released in November/December) would be between the 4xMOD686 and the MOD686/86 combo.
If I leave San Francisco with as many amps as I arrived with, I'll continue with the 4xMOD686 setup. Yes. That's a hint.
Just a moment. Let me enter my time machine.
Burning Amp is this weekend.Tom
4xMOD686 and WAF
Hehe. Like Dr Who, sometimes I get ahead of myself.
I'm trying to imagine 4xMOD686 and the WAF. Normally I'd take the miniDSP output, convert it to balanced and run it to remote amps by the speakers. I'm a little concerned that a MOD686 and PS wouldn't exactly hide behind an LXmini tower. Could you save space using a switching PS? Is the PSRR good enough? The Lxminis themselves look like they're not too imposing.
BTW: I live in Denver. If you're going to RMAF maybe I could audition your setup. I looked at the exhibitors and I didn't see Linkwitz Labs, although I imagine they are going through a lot of heartache and transition right now.
I ran 4xMOD86 for three years. I've run 4xMOD686 and 2xMOD686+2xMOD86 for about three weeks each. I prefer 4xMOD686.
Just a moment. Let me enter my time machine.
Tom
Hehe. Like Dr Who, sometimes I get ahead of myself.
I'm trying to imagine 4xMOD686 and the WAF. Normally I'd take the miniDSP output, convert it to balanced and run it to remote amps by the speakers. I'm a little concerned that a MOD686 and PS wouldn't exactly hide behind an LXmini tower. Could you save space using a switching PS? Is the PSRR good enough? The Lxminis themselves look like they're not too imposing.
BTW: I live in Denver. If you're going to RMAF maybe I could audition your setup. I looked at the exhibitors and I didn't see Linkwitz Labs, although I imagine they are going through a lot of heartache and transition right now.
Eris,
4xMod686 in a single enclosure makes for a very large enclosure.
Tom built a pair of stereo Mod686 in matching 3Ux300 mini dissipante enclosures with SMPS.
I was originally planning on building two stereo Mod86's for Lx-minis. I decided to pivot and build the Mod686/Mod86 combo amps. I already have the Mod86's and parts. I will try to fit them in a 3Ux300 mini disspante enclosure with a linear PS. It should just fit. I plan to put the analog crossovers in enclosures under the amp. So from my DAC/preamp I run a single XLR cable to analog crossover than 2 XLRs from the crossover into the amp. Then a single speakon connection into the Lx-mini. The amp and crossover will be sitting on the floor somewhat behind the Lx-mini.
4xMod686 in a single enclosure makes for a very large enclosure.
Tom built a pair of stereo Mod686 in matching 3Ux300 mini dissipante enclosures with SMPS.
I was originally planning on building two stereo Mod86's for Lx-minis. I decided to pivot and build the Mod686/Mod86 combo amps. I already have the Mod86's and parts. I will try to fit them in a 3Ux300 mini disspante enclosure with a linear PS. It should just fit. I plan to put the analog crossovers in enclosures under the amp. So from my DAC/preamp I run a single XLR cable to analog crossover than 2 XLRs from the crossover into the amp. Then a single speakon connection into the Lx-mini. The amp and crossover will be sitting on the floor somewhat behind the Lx-mini.
Yes I suppose 4xMOD686 in a single enclosure would be huge and counter productive. I never really entertained that idea.
I'm more interested in them as monoblocks or the closest thing to a monoblock. It sounds like you have a pretty good idea. Combine each channel into a single enclosure for a pseudo active speaker system.
If it were me I'd use a miniDSP as a DAC / active crossover, convert each output channel to balanced and run XLR cables to the amp/speakers for amplification and a very short length of speaker cable. At that point your combined channel chassis idea should work very well. Do you think there would be any space improvements if you moved the power supply into an external chassis?
One last thing. A friend of mine who has a masters in EE and used to design
radar and laser control systems (and is a patent attorney grrr) looked at the Modulus design and thought it looked pretty damn good. He asked about phase noise and even though I know what that is I haven't seen that spec anywhere for Modulus 86 or 686. Maybe TomC can comment. I imagine excessive phase noise would ruin the holographics on the LXminis and would have been found by now.
eris
This EE with a master's degree also thinks it's pretty nifty.
You're MSEE friend should know that phase noise is not really applicable to audio amplifiers. Phase noise is a frequency domain expression of deviations of a single-frequency signal from it nominal frequency. In an RF system, running a signal through an amplifier will add some noise which when clocked into a receiver will add to the phase noise of the signal. However, that is not really applicable to a audio power amplifier. Phase shift through the amplifier which is a function of low-frequency and high-frequency rolloff might have an effect, but with response as extended and flat as the Modulus amps, that is not an issue.
You're MSEE friend should know that phase noise is not really applicable to audio amplifiers. Phase noise is a frequency domain expression of deviations of a single-frequency signal from it nominal frequency. In an RF system, running a signal through an amplifier will add some noise which when clocked into a receiver will add to the phase noise of the signal. However, that is not really applicable to a audio power amplifier. Phase shift through the amplifier which is a function of low-frequency and high-frequency rolloff might have an effect, but with response as extended and flat as the Modulus amps, that is not an issue.
Eris,
I have a hypex DLCP that I could use also. I intend to use it for my subs, but I will probably try it with the lx-minis at some point. I was getting hung up on the ADC step for my phono input to apply DSP to run the lx-minis. Moving the PS to a separate enclosure would most likely end up taking up more space.
I have a hypex DLCP that I could use also. I intend to use it for my subs, but I will probably try it with the lx-minis at some point. I was getting hung up on the ADC step for my phono input to apply DSP to run the lx-minis. Moving the PS to a separate enclosure would most likely end up taking up more space.
Yeah, hiding the amp (any amp but an itty-bitty class D really) behind the LXmini's 6" vertical tube ain't gonna happen. I "hide" my amp by putting it on a central table that also hosts my media player (2010 MacBook Pro) and running a 4-conductor speakON cable to the speaker.
The Lxminis themselves look like they're not too imposing.
I guarantee that I will not make it to RMAF this year. Maybe next year. I've blown my travel budget several times over this year already.
Linkwitz died three weeks ago, so I guarantee you that going to a trade show will not be a priority. I'm pleasantly surprised to see that his widow will make it to Burning Amp.
That it would. The enclosure would likely also need to be water cooled if all the channels were to be run at clipping levels into a 4 Ω load.
Make that a quad of stereo MOD686es.
I built a pair for the Vancouver Island DIY Fest. One will head to San Francisco with me on Saturday. The other is on its way to Quebec for a test drive. I need to bring a total of three amps to BAF, so I built two more. All four are 2x MOD686 with 2x Mean Well RPS-400-27-C.Yep. It's for oscillators. Not amps.
Awesome! I'm glad you like them. I just took delivery of 20 pairs of brackets today. Have 16 left...
Tom