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Chip Amps Amplifiers based on integrated circuits

Modulus-86  build thread
Modulus-86  build thread
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Old 26th May 2020, 11:08 PM   #5161
asuslover is offline asuslover  Romania
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Similar project here, mod86 rev2.1 , instead of r7(100ohm) I would like to use a coupling cap, what would be correct value of this cap in this situation? And for the tweeter , I am going to use a crossover cap, is the servo necessary ?
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Old 27th May 2020, 04:22 AM   #5162
tomchr is online now tomchr  Canada
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If you want to implement AC coupling and single-ended input, connect pin 3 to pin 6 on the THAT1200 footprint as described above. Then connect 47 kΩ from the input connector pin 1 (GND) to pin 2 (IN+). Connect the AC coupling cap from your input signal to pin 2 of the MOD86 input connector. I'd use 10 uF for the AC coupling cap.

If you AC couple on the output, as you describe for your tweeter amp, you technically don't need the DC servo. That said, you can expect about 200 mV of DC offset at the output of the amp, plus 10x whatever DC your source puts out (unless you AC couple there as well).
I'd leave the DC servo in place, but that's me.

Tom
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Modulus-86, 186, 286, & 686: 40-240W (8Ω), <-120dB THD. HP-2 Headphone Amp: 660mW, <-130dB THD. Taming the LM3886.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 27th May 2020, 08:25 PM   #5163
asuslover is offline asuslover  Romania
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Great , thanks Tom!
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Old 28th May 2020, 05:24 AM   #5164
thejohn is offline thejohn  South Africa
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Thanks Tom,

My theory of there being enough power is I am using my Mod86 monobocks to run a passive pair of Proac studio 3 (which are ATC SCM50 drivers) to louder than I could want levels without getting anywhere near Spike!

The tweeters and woofers are 8ohm and the mid dome is 16ohm. Sensitivies of the drivers are in the mid 90's more or less...

So why would I need bigger amps on any of the drivers in an active config?

I did consider doing a class d of some type on the bass driver but when you actually look at specs on most of them, they're 1% distortion into 4ohms... at the end of the day continuous, low distortion output into 8 ends up being much lower than advertised...
Then I'd need a different power supply and everything would just get infinitely more complicated...

The ATC active monitors sound amazing and use amps that are beyond simple - an opamp driving a pair of lateral fets on each driver.
I'm hoping that soundwise I should be able to improve upon that... or at worst equal it and have some fun doing it.

John
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Old 29th May 2020, 04:34 AM   #5165
tomchr is online now tomchr  Canada
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Quote:
Originally Posted by thejohn View Post
The tweeters and woofers are 8ohm and the mid dome is 16ohm. Sensitivies of the drivers are in the mid 90's more or less...

So why would I need bigger amps on any of the drivers in an active config?
Thank you for the added context. You don't need bigger amps. In fact, with 8 Ω and above, you can run the Modulus-86 on ±35-36 V rails. That'll give you 60 W into 8 Ω and probably 30-35 W (says math) into 16 Ω.
The LM3886 can provide slightly higher output swing into a lighter load, so that's why I'm estimating the output power to be a bit higher than 30 W.

A Power-86 with a 2x25 VAC transformer would be perfect. You should be able to run all three channels from a 200 VA transformer.

The only drawback is that with that rail voltage, the amp is optimized for 8 Ω or above, so if you later change to 4 Ω speakers, the amp won't operate optimally. At the higher rail voltage with 4 Ω loads, the SPiKe protection in the LM3886 will engage sooner so you "only" get 55-60 W into 4 Ω with ±35 V rails, instead of the full 68 W that you'd get with ±30 V rails. I know it's counter-intuitive. The LM3886 works in mysterious ways...

Tom
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Modulus-86, 186, 286, & 686: 40-240W (8Ω), <-120dB THD. HP-2 Headphone Amp: 660mW, <-130dB THD. Taming the LM3886.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 2nd June 2020, 03:56 PM   #5166
erozsolt is offline erozsolt  Hungary
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Hi,

Would this layout work for 2 x Mod86 + SMPS300RAh? This Mini Dissipante costs the same as the "big" 300 Dissipante, but if possible I'd prefer the smaller case. This has 150x300 mm internal dimensions.

Click the image to open in full size.

Mini Dissipante 2U 300mm frontale 10mm NERO coperchi in alluminio 2mm e retro 3mm

What would be the advantages of going with the big Dissipante?
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Old 3rd June 2020, 04:40 AM   #5167
tomchr is online now tomchr  Canada
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What you have will work, but I think it can be improved. Specifically, I would avoid dragging the mains voltage all the way through the chassis. So I'd put the SMPS300RAh towards the back and slide the Modulus-86 modules forward.
I do realize that doing so will put the Modulus-86 off-centre on the heat sink. With only one module per heat sink, that should be fine.

I also recommend keeping the mains rectifier section of the SMPS (so the upper right corner of it in your drawing) away from the input of the amp. That rectifier emits quite a bit of switching noise, so give a good 30-40 mm of separation from anything sensitive (such as the amp inputs).

Tom
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Modulus-86, 186, 286, & 686: 40-240W (8Ω), <-120dB THD. HP-2 Headphone Amp: 660mW, <-130dB THD. Taming the LM3886.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 12th June 2020, 09:56 PM   #5168
shlauff is offline shlauff  United Kingdom
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A little while ago I acquired some (as it turns out) fairly rare 70’s cottage industry HiFi kit from Monogram, a Pre-amp and a power amp. Little is documented about this stuff yet reportedly pretty pricey in it’s day it appears well made. The power amp doesn’t work and I’m slowly working on getting that resolved, part of the problem is getting over the claim that Monogram Professional Audio made in their blurb- a “New” and “Exciting” circuit due to its ‘Class A+’ operation, it says it on the front- so it must be true! I gather this is reportedly Class A operation up to a given threshold then AB after that. Bless. …rubbish of course but not understanding the thing or indeed how to bias it, it’s a project for another time…

What surprised me was how well built, and good sounding the preamp was; looking inside there’s lots of quality components, big stepped Alps pots and Philips 015 caps- the phono stages (MM and MC) aren’t half bad either. (…is this a Modulus amp build thread? –Ed.) Endearingly we also have fruity text on the front, “Coherent Sound System” “Handcrafted in England” and in italics on the power amp “Studio Reference”… I didn’t just want to leave it at the back of the cupboard somewhere.

Furthermore, and here might be where the astute reader might see where this is going, they come packaged in (nearly) 2U rack enclosures in black- much like the Dissipante line favoured by many of those on this now epic thread.
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File Type: jpg DIYA2.jpg (616.0 KB, 155 views)
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Old 12th June 2020, 10:02 PM   #5169
shlauff is offline shlauff  United Kingdom
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It’s the lockdown in the UK and I fancied a little handcrafting of my own and wanted to build something to match the pre- amp and keep this thing alive- so I’ve re-created the Monogram power amp with Modulus 86 innards after having followed this forum for a while. Front panel layout was to be as similar as possible, though I couldn’t bring myself to write “Studio Reference” on the front… I kept it whimsical and opted for an in-joke with my friends instead, “Signature Style” and “Handcrafted in Kent” where we live.

I’ve had great fun doing it- first amplifier build- and credit should be given (of course) to Tom at Neurochrome and also Gianluca at Modushop for quality products, reasonably priced and speedily dispatched, thank you both. Followed Tom’s excellent documentation exactly and everything thankfully went very smoothly. Should also mention I stole the idea for the amp board brackets from a recent build from user Klas- neat…
Sounds great… Thanks again Tom!
Attached Images
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File Type: jpg IMG_0739 (1).jpg (761.9 KB, 157 views)
File Type: jpg IMG_0783 (1).jpg (937.8 KB, 87 views)
File Type: jpg IMG_0779 (1).jpg (598.3 KB, 109 views)
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Old 13th June 2020, 04:43 AM   #5170
tomchr is online now tomchr  Canada
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You're welcome. I'm glad it came together nicely for you. Nice work with the front panel. You matched the Monogram style nicely.

I don't envy the task of poking holes in that steel rear panel. I did that once. That steel is rather hard... It looks like the hole punch worked nicely, though.

That preamp is insane. It looks like the switches are connected to the levers on the front panel by a flexible mechanical link. That's pretty darn cool!

Tom
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Modulus-86, 186, 286, & 686: 40-240W (8Ω), <-120dB THD. HP-2 Headphone Amp: 660mW, <-130dB THD. Taming the LM3886.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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