Pros/Cons Of Neurochrome 686 vs Purifi EVAL1 Builds

[fluid]

Assuming Antek 8425, or Hammond 1182U24 are suitable (second one definitely is), what might be some more local (RS Online etc etc) alternatives? <----------- my country. Thanks.

As Tom said the best transformer will depend on what you plan to do with the rest of the power supply. It could work out to be not that much more expensive to go with a dual mono setup depending on the shipped price for the transformer.

800VA transformers are not that common as a commodity part RS does not list any with the right secondary voltages as far as I can see.

The Hammond is available from Mouser who will usually ship for free over a certain amount which I think would be covered by the cost of the transformer. That may be the cheapest option it is listed as a 48V centre tapped one.

https://au.mouser.com/ProductDetail/Hammond-Manufacturing/1182U24?qs=qPaGMJUC%2BStLB26dZ4ZZHg==

 

[tomchr]

Appendix A-3 of the design doc attached. Note that this isn't an exhaustive list.

The Toroidy Audio Grade or Supreme Audio Grade 2x25 V, 800 VA would work well also. Each transformer is custom wound, so you can request it with 4x25 V windings as well.

Tom

 

[concorde1]

Wow those Toroidy ones sure look flash; I'll see how much they would charge to send to my country, I doubt it will be affordable.

@fluid Unfortunately Mouser charges 70 NZD for shipping the transformer; heavy things like that break the rules of free shipping.

Thanks for the answers.

 

[tomchr]

70 NZD (50 USD) is not bad actually. Antek might be able to do a bit better on the cost of the transformer and shipping combined.

Tom

 

[tomchr]

Try Newark/Farnell and RS Components. They tend to have more global inventory than Mouser.

You need 2x24 VAC to 2x25 VAC @ 175 VA per channel for 8 Ω and 330 VA per channel for 4 Ω.

Tom

 

[concorde1]

Only one I found at Newark or RS that meets 750W+ and 2x25 was: https://nz.element14.com/triad-magn.../toroidal-transformer-medical-1kva/dp/2611183

But it's pretty expensive. However, it will deliver FREE for me. Not available in stock till 2022 lol

I will go for Antek 8425 or Hammond 1182U24 or one of these Toroidy ones.

Regarding Toroidy, there are Standard Grade, Audio Grade and Supreme Audio Grade V2 for 800VA transformers. I notice the Antek and Hammond ones are not vacuum sealed or shielded unlike the Supreme Audio Grade V2 from Toroidy. Is this fancy stuff necessary for higher fidelity? The Supreme Audio Grade V2 is the most expensive of all the ones in this post.

 

[tomchr]

The Toroidy Standard Grade is a plain Jane transformer. 1-2 primary windings, two secondary windings. Nothing fancy. The Audio Grade adds an electrostatic shield between primary and secondary and some black tape on the outside. I suspect there's also a belly band or GOSS band. The Audio Supreme Grade adds a polished steel bell and epoxy potting.

Aside from looks and possibly slight attenuation of the already low leakage fields from the transformer, I don't see a technical advantage of the Supreme Grade. They look good though. Note that they're pretty tall. The mounting plate adds 2 mm and the standoffs 10-15 mm, so even the 200 VA model will need 82 mm of chassis height.

If you're looking to cut cost, going with a Standard Grade will be fine. The extra shielding of the Audio Grade attenuates RF fields and reduces the RF coupling between the primary and secondary, but it's not really until within the last 10-or-so years that such shields have become more commonplace - at least in the affordable end of the price spectrum. That said, the Audio Grade is still pretty darn affordable.

If I was building the amp, I'd go with the Audio Grade. At the very least the added shielding buys peace of mind. It also looks more "high end" than the Standard Grade. And, yes. Looks are important.

Tom

 

[Murrayp]

I'd really like to hear your thoughts on the Purifi EVAL1, once you get it up and running and put in some listening time, especially when sonically compared to the 686. I wouldn't be surprised if the 686 sounded subjectively better.

I'll also chime in and say that I'm happy with my two NC400 mono blocks, but only after some extensive modding. It was the only way I could get them to sound satisfactory to me, as there was always this harshness/graininess in the sound which gets annoying over time and which Bruno himself acknowledged was an audible problem that affected all Ncores due to hysteresis caused by the iron core inductor used in the LC output filter. Without the mods to fix this, I would have sold mine.

Interesting about the NC400 mods - are these documented somewhere please? thanks

 

[concorde1]

Well unfortunately Toroidy is out of the question, because shipping would be 87 EURO.

Antek AN-8425 shipping 73.50 USD. [1.21 ratio of product price to shipping price]
Total 227 NZD.

Hammond 1182U24 (from Mouser) shipping 68 NZD, but product itself is 202 NZD. [2.97]
Total 272 NZD.

So I'm tempted to go for Hammond 1182U24 just because the ratio of product price (2.97) to shipping price is highest. Although the Hammond has a lower wattage (750VA).

--

EDIT: I found Hammond 1182U24 for only 180 NZD (22 less) at Digikey. Also interested in Hammond 1182V24. The 'V'24 is 1000VA instead of the 750VA 'U'24. It says free shipping to me for either but I'm not convinced.

 

[fluid]

Interesting about the NC400 mods - are these documented somewhere please? thanks

https://www.audiosciencereview.com/forum/index.php?threads/hypex-nc400-diy-mods.22588/

 

[concorde1]

I got the Hammond 1182U24 for 197 NZD with free shipping

I almost got the 1182V24 (1000VA) but decided it's probably unnecessary.

 

[concorde1]

I have used Conrad Heatsinks before and they are very well made, certainly better than the modushop ones, I don't know what they cost to ship to NZ but they were pretty reasonable in AUS. The thermal ratings are helpful to decide on the right size.

http://www.conradheatsinks.com/products/flat100_350.html

The MF35-151.5 from Conrad looks ideal if I want to use the heat sink AS the side of the chassis - it's 350mm deep, which is near 400mm of the Modushop Dissipante 4U depth, and it's almost high enough at 151.5mm.

However, is it truly 0.21K/W? According to a post on diyaudio, "For class A I'd strongly recommend the MF35-151.5. When corrected for ambient room temperature, this model has a c/w rating of .29." (From topic called "Conrad heatsinks group buy" (page 1).)

Then there's the Wakefield-Vette 127737 (0.19 C/W), but that has the fins mounted incorrectly if I were to use the 12" depth as the depth of the chassis. (Horizontal instead of vertical.)

Then there's the ABL Components 177AB1000B (0.12 C/W), but that costs a lot (170 USD for two). Also it's only 300mm long, so I'd have to make up 100mm instead of just 50mm for the Conrad.

 

[fluid]

In comparison to the Modushop values the 0.21 C/W is valid, the point being made in that thread is that the ambient temperature has to be considered in any calculations as the higher the ambient temp is the less thermal headroom the heatsink has.

https://sound-au.com/articles/heatsink-amp.htm#s3

Tom lists the 400/4U Dissipante as being enough which is 0.23 C/W the biggest Conrad is slightly better. I don't think you can really have too much heatsink if you can deal with the size and cost. I have mine in a 5U 400 Dissipante (0.14 C/W) with a 10mm front panel of some size and aluminium top and bottom covers and it still gets warm.

 

[tomchr]

The MF35-151.5 from Conrad looks ideal [...]

I agree.

However, is it truly 0.21K/W?

Great question. I typed the dimensions into this online heatsink calculator: https://www.heatsinkcalculator.com/heat-sink-size-calculator.html
I chose 80/0.21 = 380.95 W dissipated as the Conrad heat sink is specified for 80 ºC temperature rise and 0.21 K/W. The calculator says the heat sink should be 419 mm wide and have 52 fins. In reality it's 350 mm wide with 35 fins.
I tried with the dimensions of a 0.4 K/W heat sink that I have on hand and the calculator spits out results that are ~10-15% higher than reality. So I'm thinking the Conrad specs are probably pretty close to reality.

However, where Conrad's specs do diverge from reality is on the 80 ºC temperature rise. That would mean that the heat sink reaches 105 ºC in a warm living room (25 ºC). Thats way too hot. Heat sinks get more efficient as the delta-T rises, so Conrad's specs are optimistic there. Normally heat sinks are specified for a delta-T of 70 ºC so Conrad is cooking the books a little, though not overwhelmingly so.

I recommend staying below 60-65 ºC heat sink temperature so you don't burn your fingers if you touch the heat sink. For a 65 ºC heat sink temperature at 25 ºC ambient, you're looking at a delta-T of 65-25 = 40 ºC. The heat sink will be less efficient there, so you need to multiply the 0.21 K/W specified by Conrad by a correction factor.

I've attached a table I grabbed from Aavid's website before they were bought out and the information vanished. Note that the correction factors are for 75 ºC, not 80 ºC. Close enough! The correction factor is 1.170, so your nice 0.21 K/W heat sink (specified) is actually 1.170 * 0.21 = 0.25 K/W.

Assuming you're designing for max power and run the Modulus-686 on ±36 V, you're looking at 100 W dissipated in the heat sink for an 8 Ω load driven to clipping with a music signal (14 dB crest factor). 186 W dissipated when used with a 4 Ω load driven to clipping with a music signal. So you'll need a thermal resistance of 40/100 = 0.4 K/W for the 8 Ω case and 40/186 = 0.22 K/W for the 4 Ω case.

This math assumes that the amp is driven continuously with a signal that has 14 dB CF and the peaks at clipping. Most music doesn't look like that. And few - very few - run the amp at clipping for any length of time. So I would say that your 0.25 K/W Conrad heat sink would be fine for music reproduction into 4 Ω. You could probably even get away with 0.40 K/W for that use case, but I would then definitely fit the heat sink with a thermal switch that turns the amp off once the heat sink temperature exceeds 60-65 ºC.

In case you're wondering where the 60-65 ºC comes from: I'm not aware of any standards that dictate how hot audio gear is allowed to get. But there are standards for appliances, so I use that as a guide. The controls (knobs) on the stove in your kitchen are allowed to reach 55 ºC during normal operation. Any surface that is not a control but can be touched by the user during normal operation is allowed to reach 65 ºC. So that's what I aim for.

Those further interested in the math behind this should have a look here: https://neurochrome.com/pages/thermal-design and here: https://neurochrome.com/pages/power-supply-design

Then there's the Wakefield-Vette 127737 (0.19 C/W), but that has the fins mounted incorrectly if I were to use the 12" depth as the depth of the chassis. (Horizontal instead of vertical.)

Yeah. You definitely want the fins vertical. Unless you're doing forced air cooling.

Tom

 

[concorde1]

Quick update, I have almost finished my Neurochrome Modulus-686 amplifier!! It has taken ages for various reasons but it is going to be great!!

I plan to post some pictures of it in another ASR thread if I may (I will link here to it).

I just need to powder coat my aluminium panels then it is ready for final assembly.

I designed and hand assembled my own chassis for it. It is very solid.

And with a bit of luck it will, well, work first time.

It has been a fun challenge to build this and the chassis - and thanks to @tomchr for the support along the way.

 

[groovybassist]

Based on the Mod-286 Tom built for me, I’m sure you’ll dig the 686!

 

[sq225917]

All Tom's amps are great, I've build half a dozen 286, a 686 and use a pair of bridged dual mono 86p myself.

 

[tomchr]

The "86p" is actually the Parallel-86. It originally used the LM4780, which TI discontinued. The modern-day equivalent is the Modulus-286, which offers quite a few improvements over the Parallel-86.

Tom

 

[sq225917]

Having tried the 286, 686 and 4x 86p as a pair of bridged monos, I'd say audibly there's nothing in them until it gets louder than I listen to. Then you can sense the 286 lose grip on the bass begin to get a touch congested.

The 286 and 686 are an easier build.

I have 4 spare lm4780, just in case...

 

[tomchr]

That's been my experience as well. With my KEF R700 (8 Ω, high-80s sensitivity) I do find that the sound quality improves with the Modulus-686 when I turn up the volume.

Tom