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Mod-286 build thread
Mod-286 build thread
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Old 17th July 2017, 01:38 PM   #61
HarmonicTHD is offline HarmonicTHD  Switzerland
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Just found some more detailed Infos on the heat dissipating capabilities of the Modushop Dissipante casings.

http://www.modu.it/CARATTERISICHE_TERMICHE_DISS.pdf

For the 3U / 300mm deep model it says 0.41K/W and claiming to dissipate 230W (4 x TO3-P) in total, that is ca 115W per side.

Is it a good guesstimate that for example a 200W chip amp e.g. based on LM3886 would emmit in the worst case roughy half its power in heat, that is ca. 100W?

Last edited by HarmonicTHD; 17th July 2017 at 01:44 PM.
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Old 17th July 2017, 04:41 PM   #62
tomchr is offline tomchr  Canada
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Data! Fantastic! Thank you.

0.41 K/W @ 230 W -> 0.41*230 = 94.3 C rise in temperature, so with a 25 C ambient (probably a bit optimistic) you're looking at a heat sink temperature of about 120 C. That may be safe for the transistors but it's certainly not safe for the user.

I recommend a heat sink temperature of 60 C max. This number is a bit arbitrary, I admit. It's about the highest temperature I can keep my hand on for a few seconds before the pain sets in. For reference, appliance makers are required to maintain 55 C or lower on controls and 65 C or lower on all other surfaces so my 60 C is in the right ballpark.
I use 25 C for the ambient temperature. That's a pretty warm living room. 60-25 = 35. The heat sink is specified for delta-T of 70 C and is less efficient (25.7 % less to be specific) at delta-T of 35 C. Thus, the max power I'd dissipate in each of the Dissipante 3U heat sinks is:

(60-25)/(0.41*1.257) = 68 W

You have two heat sinks on each side of the chassis, so 136 W total per chassis side. For the full math and explanation see the Thermal Design section of my Taming the LM3886 series.

For the calculation of the power dissipated in the LM3886, see the Thermal Design page I linked to above. For a quick estimate, use 40 W per LM3886 (assuming worst case dissipation - sine wave at Pout = Pmax/2).

Some quick back-of-the-envelope math suggests about 175 W dissipated with a Class AB output stage running at 70 V at 14 dB crest factor in to a 4 Ω load. That would result in a heat sink temperature of 70 C. That's pretty damn hot. Lower the supply voltage to 60 V and you can shoehorn it in at a dissipated power of 130 W.
So yeah... It'll work (-ish). Definitely don't make the heat sink any smaller.

The Modulus-S will be a discrete output stage with an error correction circuit on it. I expect it to deliver Modulus-level performance. I hope to get 200 W (8 Ω) as that would make a nice marketing blurb. One could build it with, say, 56 V supply and get 150 W or 45 V and get 100 W. Right now the design exists in the simulator but not in reality. It needs to meet with reality but that meeting keeps being postponed as other projects pop up on the priority list. It's a constant juggle between "do I want money now" or "do I want the possibility of money later". Sometimes I do need money now so I can keep the lights on.

Tom
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Modulus-86: 40W/8Ω @ 0.000061% THD. HP-1: 3W/20Ω, 450mW/300Ω @ 0.000032% THD. DG300B and Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right

Last edited by tomchr; 17th July 2017 at 04:44 PM.
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Old 17th July 2017, 05:57 PM   #63
HarmonicTHD is offline HarmonicTHD  Switzerland
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Tom. Wonderful summary. Thanks so much and for correcting the Modushop data. Yes I don't wanna cook on my amps nor heat my house, although it can get cold in Switzerland sometimes.
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Old 18th July 2017, 06:01 PM   #64
tomchr is offline tomchr  Canada
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BTW: The Modulus-S will be a pre-assembled or partially assembled module. I'll keep the schematic and BOM to myself. So it'll be a bit of a culture shift - and a wise business move. More plug-n-play than DIY.

Speaking of heat sinks... I was conducting a heat sink experiment for a prospective client last night. My lab was a cool 18 C ambient. I ran two of the channels of my 4xMOD86 amp at 1/3 the rated output power into a 4 Ω load. This is a common test. The two channels were on the same heat sink (12x3.5x1.5 inches - eBay 'BZ4309' chassis; similar to the 2U Modushop Dissipante) and the heat sink reached 45 C after an hour. I could actually feel the thermal gradient walking into the room after that hour.
I also ran the 32-tone test signal (14 dB crest factor) at just below clipping into a 4 Ω load on two channels. Under this condition the heat sink reached 40 C.
A lot of heat is actually conducted away by the 10 mm thick front panel and the 3 mm top, bottom, and rear panels. The Modushop chassis has powder coated steel panels (except for the front which is either 4 mm or 10 mm aluminum) so I'd expect it to run a bit hotter than the 'BZ4309'.

Tom
__________________
Modulus-86: 40W/8Ω @ 0.000061% THD. HP-1: 3W/20Ω, 450mW/300Ω @ 0.000032% THD. DG300B and Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right

Last edited by tomchr; 18th July 2017 at 06:07 PM.
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Old 18th July 2017, 06:35 PM   #65
HarmonicTHD is offline HarmonicTHD  Switzerland
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... nothing really exciting happening today as I am laying out the details of the housings ..therefore let's recap some of the experiences over that past week for those how are also new to the diy audio field and want to follow a similar path to a Mod286.

Equipment:
You only need a voltmeter.
No need for an LC-Meter to test the inductors. Just follow the instructions in the from Tom provided description. Also as Andrew and Tom pointed out earlier the values aren't super critical.
Also no need for a function generator either, as the manual give you a link to generate and download a 400Hz test tone, which you then can play from a MP3 player connected to the input. (It might have been a different story if I had run in trouble and would have had to do some error finding).

Soldering:
A decent preferably temp controlled solder iron. I used a 1.6mm chisel tip for the smd work (correction from an earlier post where I mistakenly wrote 0.6mm) and a pencil tip for the diodes and opamps.

LM3886 mounting & heat sinks:
As pointed out above the heatsinks in the pics are too small and for testing only.
Before soldering the two LM3886, I bolted the Mod286 pcb to the heat sink, loosely dropped in the LM3886 (without soldering yet) and also bolted them to the heat sink. Use metal screws (e.g. M4 will work for the metrics guys among you, don't use nylon screws - Tom thanks for the hint). Now the everything is tightened, solder the LM3886s.

Power Supply.
Please find attached a pic of my test setup. It uses both trafo and power supplies from a previous audio project of mine. I also got two boards of the matching Power86, which I will complete later. The manual and Tom describes the selection of power supplies and trafo in detail.
Because it's from an earlier project I'm using a 2x22V, 160VA trafo. Ideal would be a 2x25V, >200VA trafo, which I will get as soon as the amp tests out ok. I am using the Amplimo trafos (from NL) which generally ship cheaper within the EU as the Antek trafos.

Softstart and DC protection:
As you see there is a trafo start up board connector between mains in and trafo. It's most likely not needed for the Trafos of this size. This particular model also serves as a DC protection circuit. However I don't really like it because of the possibly sound affecting two relays and the DC sensing wire running back from the speaker ground. Tom if you can ever design a good circuit for DC protection, I would appreciate the additional insurance for my valuable speakers.

Ah before I forget... use the light bulb as a safety device and current limiter when hooking up everything the first time ... Google if you don't know how to rig it.

... now on with the cabinet selection....
Attached Images
File Type: jpg IMG_2065.jpg (966.3 KB, 194 views)

Last edited by HarmonicTHD; 18th July 2017 at 06:37 PM.
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Old 18th July 2017, 06:52 PM   #66
HarmonicTHD is offline HarmonicTHD  Switzerland
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Quote:
Originally Posted by tomchr View Post
BTW: The Modulus-S will be a pre-assembled or partially assembled module. I'll keep the schematic and BOM to myself. So it'll be a bit of a culture shift - and a wise business move. More plug-n-play than DIY.
....

Tom
Although I personally regrett it, I can perfectly understand such a decision. E.g. better IP protection, wider customer group i.e. larger market, and probably more efficient from a support/ troubleshooting point of view and more volume... and hopefully somewhat more margin (although sometimes I get the impression, that one is not to make any profit in the diy sector and everything if it's not free it's already too expensive.
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Old 18th July 2017, 07:59 PM   #67
tomchr is offline tomchr  Canada
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I enjoy "playing" in the DIY market. I've made many friends that way. I will keep that going and will add circuits as I go along. Some will be DIY and some will be DIy. Yet others may be IDIFY (I Do It For You). Time will tell.

Output protection board: That's a common request. It'll likely happen. Same for a transformer soft-start. I'll probably combine the two on the same board.

Tom
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Modulus-86: 40W/8Ω @ 0.000061% THD. HP-1: 3W/20Ω, 450mW/300Ω @ 0.000032% THD. DG300B and Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 19th July 2017, 12:01 PM   #68
ukhopeful is offline ukhopeful  United Kingdom
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Quote:
Originally Posted by tomchr View Post
A lot of heat is actually conducted away by the 10 mm thick front panel and the 3 mm top, bottom, and rear panels. The Modushop chassis has powder coated steel panels (except for the front which is either 4 mm or 10 mm aluminum) so I'd expect it to run a bit hotter than the 'BZ4309'.

Tom
The Modushop Dissipante chassis is also available with 3mm aluminium top, bottom and rear panels.
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Old 19th July 2017, 05:02 PM   #69
tomchr is offline tomchr  Canada
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Oh. You're so absolutely right. Thanks. I much prefer the aluminum panels. Whatever steel Modushop uses is hard stuff. Aluminum is so much easier to work with - easier on the tools too.

I've worked with both the eBay 'BZ4309' chassis and the Modushop Dissipante 2U and 4U versions. The Modushop are quite a bit better in terms of build quality. Last I checked the Modushop chassis with steel panels was less expensive than the eBay chassis once shipping charges were included. You can get the Modushop chassis through the DIY Audio Store and through Modushop directly. The latter is especially attractive for those within the EU as Modushop is in Italy.
Modushop will also poke holes in the panels according to your specifications for a very reasonable fee. $35 I think it is.

Tom
__________________
Modulus-86: 40W/8Ω @ 0.000061% THD. HP-1: 3W/20Ω, 450mW/300Ω @ 0.000032% THD. DG300B and Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right

Last edited by tomchr; 19th July 2017 at 05:05 PM.
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Old 19th July 2017, 08:25 PM   #70
HarmonicTHD is offline HarmonicTHD  Switzerland
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Yes they are. The steel panels are 1mm and the alu are 3mm.

I am just brushing up my CAD skills to send them a DWG file for the hole cutting and the engravings.
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