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Informative questions before starting β24 build

beta24

Re: Informative questions before starting β24 build

Postby Pieterh » May 22nd, 2017, 10:50 am

I was looking for a 'connecting strip' on e.g. mouser that can used to make a star ground, i.e. connect all the grounds to each other, something like the photo here. But looking at the photo I assume this is a barrier strip where the connectors were 'interconnected 'on the bottom DIY. So, isn't there a connector where the metal strip goes over the entire lenght of such a strip?
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Re: Informative questions before starting β24 build

Postby amb » May 22nd, 2017, 11:09 am

You can make yourself a "buss" to interconnect all of the positions together below. A cut piece of heavy copper clad blank PCB would be a good candidate, drilled with holes to accommodate the barrier strip pins.

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Re: Informative questions before starting β24 build

Postby Pieterh » May 24th, 2017, 9:29 am

I am looking for the four big caps. It seems that the Kemet PEH200 series is a good choice according to recommendations here, low impedance, high ripple current. But I wonder about how to mount these caps? The technical sheet states that these should be mounted upright or horizontally (this means with the terminal screws and safety vent on top). However, I wanted to mount these caps in just the other way, like in Ti's reference build, terminals downwards and with the clamps. Can i do that with these Kemets?

Then if one can mount these caps downwards, we have the issue of the big single mounting screw on the other side of this cap. Can we use a heavy piece of rectangular copper and bolts here to connect two caps (per channel). Would that work ?

http://nl.mouser.com/Search/ProductDeta ... 0MD5100MB2

Your thoughts are welcome? Or tips for other types for the big Caps?
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Re: Informative questions before starting β24 build

Postby amb » May 24th, 2017, 11:56 am

Are you building the class A or low-power variant of β24? Because the Kemet you linked is rated only 63V. Instead of screw-mount capacitors, how about ones with solder pins? For example United Chemi-con ESMH101VND103MA63T or EKMH101VRT103MB80T? These are 10000uF 100V.
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Re: Informative questions before starting β24 build

Postby mpa2 » May 24th, 2017, 12:53 pm

Well, Ti, the Elna caps you've used in your build are rated 50V :)
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Re: Informative questions before starting β24 build

Postby amb » May 24th, 2017, 1:19 pm

mpa2 wrote:Well, Ti, the Elna caps you've used in your build are rated 50V :)

Duh. I was thinking "across the rails". Here are some 10000uF 50V capacitors to look at: Nichicon LGU1H103MELC or LGY1H103MELC40, Cornell Dubilier 381LX103M050A042.
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Re: Informative questions before starting β24 build

Postby Pieterh » May 24th, 2017, 11:24 pm

amb wrote: Here are some 10000uF 50V capacitors to look at: Nichicon LGU1H103MELC or LGY1H103MELC40, Cornell Dubilier 381LX103M050A042.


Thanks for the recommendations! I am building the A/B version like you did :) For my understanding, looking at these nichicons and Cornells, these have lifetimes of 3000-5000hrs, max ripple currents of 3- 4A, no impendance stated. The Kemets and similar more expensive caps have higher lifetimes of over 10.000hrs and ripple currents of over 13A, and relatively low impendance. How about the importance of these specific specs?

how about the size of your ELNA Caps, they are around 70 mm (2.75 inch) height? The Kemets height and other similar more expensive Caps is up to 95mm which may be a bit too much in the 4U chassis.
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Re: Informative questions before starting β24 build

Postby amb » May 25th, 2017, 12:41 am

I believe both Nichicons have an ESR rating of 30mΩ. Under quiescent or low output power scenarios, the current demand on the main bulk capacitors is low and negligible. At full power output (class AB high power version) into 8Ω, with a worst case sine wave signal, the current supplied by the capacitors is about 4.6A. This might seem to exceed the capacitor ratings, but the β24 also has eight 2200µF local capacitors onboard, which has a combined riplpe current rating of about 10A per channel. These onboard capacitors dampen the flow of current from the main bulk caps, so that it should not exceed the capacitor's rating except under artificial lab conditions which you'll never encounter under real use. Music is much more transient in nature and has a much lower "crest factor" than sine waves, so the pratical demand on the power supply is also transient, making the average current much lower.

As for the life time rating, it assumes the capacitor is operating at maximum rated temperature (85°C or 105°C), and at maximum ripple current the whole time. Note that the capacitor will heat up due to the current flowing through its ESR, so lower ESR will cause less internal heating. In actual operation on the β24, the capacitor is never operated in that kind of environment. The lower the heat, the life span of the capacitor will be dramatically extended. So much so that you don't have to worry about it. If anything, it's more important to turn the amp on periodically even if you're not using it, to allow the capacitors to power up and prevent them from degrading.

The big screw terminal caps are indeed rated for higher current and long life time, but the Nichicon LGU or LGY series is more than sufficient for the job. The Elnas I used are 35x70mm (diam/height). The aforementioned Nichicons are 35x40mm. Since they are so compact, you may want to "upgrade" to 15000µF in the same series, which are 35x50mm. Or, go with Nichicon LLS1H153MELC which is 18000µF in 35x50mm, and higher ripple current rating too.

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Re: Informative questions before starting β24 build

Postby daniele86 » May 25th, 2017, 11:22 am

amb wrote:I believe both Nichicons have an ESR rating of 30mΩ. Under quiescent or low output power scenarios, the current demand on the main bulk capacitors is low and negligible. At full power output (class AB high power version) into 8Ω, with a worst case sine wave signal, the current supplied by the capacitors is about 4.6A. This might seem to exceed the capacitor ratings, but the β24 also has eight 2200µF local capacitors onboard, which has a combined riplpe current rating of about 10A per channel. These onboard capacitors dampen the flow of current from the main bulk caps, so that it should not exceed the capacitor's rating except under artificial lab conditions which you'll never encounter under real use. Music is much more transient in nature and has a much lower "crest factor" than sine waves, so the pratical demand on the power supply is also transient, making the average current much lower.


What about ripple current rating on Class A version at 4Ω load?

Thanks

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Re: Informative questions before starting β24 build

Postby amb » May 25th, 2017, 1:09 pm

A pure class A amp will draw a relatively constant amount of current from the power supply, at any output power level. When no audio is playing, most of the current flows right through the N and P output MOSFETs. When audio is playing, depending on power level, a proportion of that current is diverted into the load instead. In this case, the instruction says to bias the output stage to idle at 1.4A per channel. So that's the amount of current the bulk cap will need to provide. This is not a problem at all with the specified capacitors.

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