Yes yes, sorry, I know I want the Guardians (more on this at the end), but I think I was unclear mixing things up:
I was asking about the ISS main use, not the Guardians. I understand it doesn't protect the amp from overvoltage/current, PSU failure, etc? ("only" pops protection).
Also, from HarmonicTHD answer, is it true that for a stereo Mod86 I will not need the ISS as you don’t need such large transformers?
Makes sense, thank you
Good
Can you please confirm this? I understood from the product page that a stereo Mod86 (2 boards) need 2xGuardian-86 OR 1xGuardian-686 (that it can even be split in two boards). Cost for the latter is 13$ cheaper
Thank you again
Sorry for the confusion. I knew the Guardian 86 was not to be used for the Mod686 and wrongly concluded the opposite might also be true. Reading Toms description more thoroughly I believe my initial statement to be wrong. At least that’s how I would interpret the description on his webpage „The Guardian-686 is intended for use in bridged/balanced/BTL amplifiers, such as the Modulus-686. As the Guardian-686 is a stereo version of the Guardian-86 circuit, it is equally useful in single-ended stereo amplifiers, such as the Modulus-86, Modulus-286, and LM3886 Done Right.“.
I will keep quite next time I am not 100% sure. Again sorry.
I will keep quite next time I am not 100% sure. Again sorry.
hey no prob! i thought i’d better double check, english is not my native language, audio engineering even less xD
The ISS does not protect the amp. The ISS protects the mains transformer by limiting the inrush current at startup, thereby minimizing the mechanical stress on the transformer on startup. This makes the transformer last longer. The ISS also makes it possible to use a more reasonably sized mains fuse, which in turn protects your house should something catastrophic happen within the amp chassis.
All transformers and power supplies draw large current when they're first turned on. The larger the transformer and supply, the larger the current. With, say, a 200 VA transformer you can get around this by slightly over-sizing the fuse. With, say, 400-500 VA transformers the required fuse will probably exceed the ampacity of your household wiring. So then you have a situation where you're using a 10-15 A slow-blow fuse to ensure the fuse survives startup in a circuit that draws a 2-3 A when running at full blast. Attached image touches on the silliness of that idea. Using a grossly oversized fuse is not a good design. It's also not a safe design. The ISS allows you to size the fuse much closer to the actual max power draw of your circuit, thereby increasing the amount of protection the fuse provides.
I'd say if your transformer is beyond 200-250 VA, you should consider using a soft start circuit. Certainly by 400-500 VA, I'd strongly encourage you to use a soft start.
Even if you don't need the soft start feature, the 12V trigger, support for momentary power switch, bi-colour power LED, etc. are nice to have.
You cannot split the Guardian-686 into two boards. At least I don't think you can. I certainly didn't design it so you could just saw the board down the middle and have two circuits.
The Guardian-686 is two Guardian-86es on one board with some connections between the two halves to make it work well if you use it in a balanced amp, such as the Modulus-686.
The Guardian-686 is intended for use with balanced/BTL/bridged amps, such as the Modulus-686. It can also be used with stereo single-ended amps, such as the Modulus-86.[/QUOTE]
For a Modulus-686, you will need one Guardian-686 per channel. For the Modulus-86, -186, and -286, you'll need one Guardian-86 per channel (or one Guardian-686 per stereo amp).
Yes. The Modulus-686 is free of turn on/off thumps.
The Guardian-86 and -686 are not exclusively for use with the Modulus-686. The Guardian-86 and -686 provide the anti-thump feature, which some amps need. Check the Pass ACA thread for examples.
The Guardian-86 and -686 also provide protection against DC on the output of the amp, which gives some people more peace of mind. I personally don't use speaker protection in my DIY builds, but would most certainly include it in a commercial amp.
Tom
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OK got it. I had it wrong. Is there anything to protect the amp?
I see. And this by itself is a very important feature. I contracted an electrician to re-wire all my flat, and he added a line only for my audio stuff (DAC, turntable and amp). Still pending the protection switch on the entrance box (for that line), but I guess it'll be either 10A or 16A. So, if I get a power-86 for the 2xMod86, which needs 2x36V I'd be below the 200-250 VA threshold you mentioned above, right?
Ah, sorry I had misinterpreted your "Furthermore, the two halves of the Guardian-686 can be electrically separated for use in dual-mono builds of single-ended amplifiers." in the product page.
I think I changed my mind and will probably get 2x-86 in order to place them one in each side in the back of the enclosure.
OK I think I'm lost here as well with 2&3. Do the Guardians need a DC input? If so, does it ned to be from the same secondary powering the amp?
Thank you again, as always
That's all in the amp already. The LM3886 is protected against over-current, over-temperature, and SOA (safe operating area) violation. It's not impossible to destroy an LM3886, but you have to work pretty hard at it. If you want additional over-temperature protection, you could fit each heat sink with a thermal switch and take the output of this switch to the 6-pin connector of the ISS and make the amp turn off when the heat sinks get too hot.
A stereo MOD86 amp can run comfortably from a 2x22 VAC @ 100 VA transformer and a Power-86. In that case, you won't need a soft start.
I recommend using ±28-30 V with the MOD86 for reasons outlined here: Taming the LM3886 - Output Power. 2x22 VAC will result in ±28-30 V DC.
Also note that this is the Modulus-686 thread. For questions related to the Modulus-86, the build thread (Modulus-86 build thread) or vendor thread (Modulus-86: Composite amplifier achieving <0.0004 % THD+N.) would be more appropriate places to ask. You're also always welcome to contact me directly through email, which you can do through the Contact Us form on my website.
Electrically separated = no connections between them.
Physically separated = located in separate places.
Yep. The Guardian-86 and -686 run from the same power supply as the amp. It's all described in the design doc.
Tom
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Tom,
Is there a layout where the 686 board can mount parallel to the heatsink? LM3886 devices underneath the board and mounted on to the heatsink. I understand this is definitely harder, but wondering if such layout can allow 4 of these modules+heatsinks to be placed inside a single enclosure for a 4 CH amp.
p.s. couldnt make it to BAF. Was hoping to ask some of these questions face to face.
thanks
Is there a layout where the 686 board can mount parallel to the heatsink? LM3886 devices underneath the board and mounted on to the heatsink. I understand this is definitely harder, but wondering if such layout can allow 4 of these modules+heatsinks to be placed inside a single enclosure for a 4 CH amp.
p.s. couldnt make it to BAF. Was hoping to ask some of these questions face to face.
thanks
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Not really. The LM3886 sits perpendicular to the board. I do know of one build where the builder bent all the leads to allow the PCB to be mounted parallel to the heat sink, but that's not something I'd recommend.
It's not a matter of physically fitting the boards in the box. Two MOD686es will physically fit on a 4U heat sink. They'll just overheat as a 4U heat sink doesn't have a low enough thermal resistance to get rid of the heat.
If you really-really want four MOD686 channels in one box, I suggest using the ModuShop Dissipante 5U size (300 or 400 mm depth - doesn't matter). You'll still need to lower the supply voltage to ±28 V to prevent the amps from overheating when driven with music at clipping levels with a 4 Ω load. If you want the full 240/360 W (8/4 Ω), you'll need ±36 V and one 4U chassis per stereo amp.
Sorry. Physics and math made me do it...
Tom
Just as info, I've spotted one build with an interesting trick to mount the lm3886 // to the pcb without any leg bending: JLM Audio Shop (you have to cut the leads though).
It's a pretty trick because, looking at the package, the leads from the back row are indeed flat with the body. So no need for bending.
You're underestimating me
Clever
Good, I think I really do not need the ISS in that case.
Yes, sorry for hijacking your Mod686 thread but I didn't spot any ISS/Guardian threads, I thought these Qs fitted better here. In a way, due to power demand, ISS is clearly focused to Mod686 but the Guardians could easily have their own place. IMO. No critizism
All I need to know for now then
PCB power!
A typical Modulus-686 board draws about 350-360 mA, so you're looking at ~20 W at ±28 V and ~25 W at ±36 V.
Yes, sorry for hijacking your Mod686 thread but I didn't spot any ISS/Guardian threads, I thought these Qs fitted better here. In a way, due to power demand, ISS is clearly focused to Mod686 but the Guardians could easily have their own place. IMO. No critizism
No worries. I do need to start a separate thread for the ISS and the Guardians. I also need to add a section in the Resources part of my website about the design of soft starts. Sort of a "Taming Your Soft Start".
That is a neat trick. I also like how they use the back row of holes both for the horizontal mount and the vertical mount. Very neat.
I don't like that they require you to cut pins off of the LM3886, though. That's expensive in production!
Look again! The back row of pins are bent close to the IC package and hit the holes in the regular PCB footprint. Then the front row of pins are bent flat against the board to hit the oblong pads.
Cool! Thanks for mentioning this. It's definitely possible in the DIY world. I tend to design circuits that can be mass produced, so my considerations are a bit different.
Yeah, I don't think they did the math on that one.
Also note that they miss the local decoupling (2x10 uF minimum) by the LM3886es. It may be that the bulk caps are close enough to the LM3886 that they don't need the 10 uF, but I've seen LM3886es break into oscillation if you leave the 2x10 uF. The oscillations happen if you draw lots of output current (think >30 V peak output swing and low-impedance loads). I generally recommend 2x22 uF and use 2x33 uF in the MOD686. The can size is the same for 22 uF vs 33 uF, so I opted to get the extra capacitance.Tom
Mmm we might label back and front differently... To be clearer, it looks to me that pins 1-3-5-7-9-11 are just cut and stuck in their normal row of holes. Then the pins 4-8-10 naturally fall on the oblong pads. There might be a tiny bit of bending needed so that the odd numbered pins are hitting the holes with the proper 90° angle.
This being said, you're right. It's labor intensive and I wouldn't suggest it in a production amp. Just a little bit of lm3886 trivia.
