Krell KSA 50 PCB

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#4,842
Sort of, still waiting for Mark's ThermAlloy insulators before i can mount output devices.
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Yes, I am back again and I finally have gotten caught back up on shipping again just today. These sudden road trips are getting to get old thats for sure. So all of you that ordered ceramic insulators should get them very soon and I appologize for the delay....... or should I blame it on Harry Potter again. He has been getting in my way too much the last few years about this time. Any of you have a magic potient so I can get rid of him once and for all?????

Mark
 
#4,844
Mark A. Gulbrandsen said:
Any of you have a magic potient so I can get rid of him once and for all?????
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Easy,
send me the adress of the Rowlin writer woman and i'll dispatch Jacco the Ripper to pay her a visit.

Most of us figured long ago you are a busy bee, Mark.
But thanks for posting.

Off Topic:
placing a number of CRC's in parallel is a smart idea, imo.
Getting 50 watts in full class A from 2 Sanken output devices on the Zaps looks impossible, 10 to 30 watts max is more realistic. For a Krell running on full class A bias putting a number of smaller capacitors in parallel with a big cap, as K-amps posted a couple of times, seems the better choice.
 
#4,847
Nice neat design. How much?
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50€ ex.VAT

BTW, I'm still waiting for a consensus opinion to the questions I asked on the other thread!
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I don't think you can DIY that circuit for the same amount of money as the Hypex module. Ok, Algar's design is not exactly the same.
I already have a very small PS for my fans (read ventilators) so something like the Hypex module is in fact all I need.

Regards
 
#4,848
I've got a question about fans. I'm trying to get the case for my second KSA50 put together today. I got side-tracked with an Aleph-X thanks to LGreen. 😀

Anyway. I am using two flat type heatsinks mounted together with the fins facing each other to form a tunnel. I plan to use two 3" fans to cool it. When I selected the fans I was at the electronics store and had the salesman plug in a bunch of then and picked the quietest ones. While holding these fans in your hand when they are running they are almose completely silent.

Yet, when I bolt them to the heatsinks there is an audible sound. Seems they have some physical vibration that is transfered to the heatsinks. So I need to insulate them from the heatsinks. What do you guys use for this purpose? What ever it is, it needs to be able to take heat of course.

Thanks, Terry
 
#4,849
Hi Terry

I'm gonna use a silicone gasket and rubber fasteners. My fan will be mounted on a separate plate.

Regards
 

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#4,853
Re: Power supply caps

Harry3 said:
I�m still not sure if I should use one large cap or many small caps in parallel for the power supply. Both have advantages and disadvantages.

This site (http://www.lcaudio.com/index.php?page=29) describes a different method for using paralleled caps in their Class A 50 Watt amp.

Quote:
�Our novelty Virtual 4 pole Capacitor bank is one example. In this bank 10 high speed low impedance power electrolytic capacitors are connected together to form 2 big caps for the amplifier rails. None of these caps are connected in parallel, as this would pose problems with current transfer woppling. This is when several low impedance caps are connected directly in parallel; they tend to compete for the power. The first cap gets current first, then the next tries to take some of the charge from the first, and so on. In terms of sound performance, you get a loss of precision in the high frequencies and a cold midrange at larger power outputs - where the woppling is more severe. One alternative is to use only large can capacitors. This to some extent also will solve the two problems described, however almost any large can capacitor will work very slowly, and play with a slow and out-of-beat bass. The V4P setup however solves both problems! Bass is fast and in sync, while precision in mid and high ranges are intact at all levels. Due to the special V4P network, power is charged and discharged to each cap at exactly the same time and rate. At the output of the V4P network no electrolytic caps are present, so here we found a perfect opportunity to place a huge Polyprop (22uF) which this way will be the only capacitor the amplifier can 'see' above 1 kHz.�

And

�Current is fed to each capacitor simultaneously through a low-inductive Power Resistor. �

I assume that each cap has a series resistor from the bridge and another one leading off to the power amp?
Is this assumption correct? If yes, what would be the value for the resistors?
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Discussion here:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=26045&perpage=10&pagenumber=1
 
#4,854
oopsie!

On turning off the krell, i waited few seconds and then measured the V- rail with my DMM, to see how fast the volts were falling. On touching the probes, a massive bang and spark occurred.....turns out that someone (me?) had swapped leads on the DMM so I rather than being inserted in the volt probe locations, it was set up for current measurement! All the current must have gone through it and shorted V- to ground, which is weird because I tried current measurement months ago on something else, did it badly, and blew out the current measurement fuse in the DMM.

Other than a nice big black mark at the point of contact, did anything get permenantly damaged? I fired it up again and the rails do charge up correctly with no dc on the output, but have not tried it with speakers yet.
 
#4,855
Hi Lgreen,
The current peak may have damaged the Capacitor bank (-V only?) but you could be lucky. I blew the end off a screwdriver (only once) and the three // caps survived.

The DMM current fuse is often only to protect the lower ranges. The highest range is probably unprotected. This is due to trying to minimise the voltage drop across the DMM when using high current scale. DMM high current resistor may be blown out (I guess uneconomic to replace, unless it's a piece of HEAVY gauge wire)
 
#4,856
Re: Soft Sart

GeWa said:
I'm thinking to give one of these a try.
Hypex datasheet

Not to expensive and the PCB isn't all that big.

An externally hosted image should be here but it was not working when we last tested it.


Any comments?

Cheers
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The reason I was looking forward to the other unit was for the remote on / off switch and accessory controls.

This unit has a standby function and the amp can be "toggled" on with a momentary contact. Also it has provisions for "high temp" shut down which is perfect for these home brew Class A amps..

It bites that I am building 4 mono block amps instead of 2 stereo. Ouch it's gonna cost... :xeye:

EDIT:

Anyone want to split shipping on a few? Hypex charges something like ~ $50 to ship to the US whether it is a single unit or 10 units.

EDIT 2:

"the amp can be "toggled" on with a momentary contact." Reads remote triggered from preamp so one switch turns on all the equipment.. VERY HIGH and important WAF. She hates the "no this one first, then this one...."
 
#4,857
Re: oopsie!

lgreen said:
On turning off the krell, i waited few seconds and then measured the V- rail with my DMM, to see how fast the volts were falling. On touching the probes, a massive bang and spark occurred.....turns out that someone (me?) had swapped leads on the DMM so I rather than being inserted in the volt probe locations, it was set up for current measurement! All the current must have gone through it and shorted V- to ground, which is weird because I tried current measurement months ago on something else, did it badly, and blew out the current measurement fuse in the DMM.

Other than a nice big black mark at the point of contact, did anything get permenantly damaged? I fired it up again and the rails do charge up correctly with no dc on the output, but have not tried it with speakers yet.
Click to expand...

Sometimes the arc caused by such a short will create a non-contact situation and save both the caps and the DMM. The probes may need resurfacing..., Though possible, I doubt you damaged the amp, I say this because the current of the caps would be so great that you would not mantain a connection with the probe long enough to do real damage.

If the discharge rate of the +v and -v caps is about the same, I'd say the caps are fine. Connect speakers with a 10-20ohm resistance in series with the speakers to test out before connecting them directly.

Things do go wrong, but sometimes its not as bad as one thinks.


😉
 
#4,859
Re: Soft Start

Bud Barnez said:
USA,

If that Hypex module looks suitable, an identical looking soft start is available in your homeland from DIYcables, located in Port Angels.

http://www.diycable.com/main/product_info.php?products_id=586

...but it's $69.50
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Yep, that IS the Hypex soft start module. It is slightly more than ordering from Hypex, but shipping is ALOT less.

I will see if I can get a discount on 4 of them... Thanks for the pointer / URL.
 
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