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Old 28th March 2006, 11:32 PM   #211
fab is offline fab  Canada
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gp4Jesus,

Dick has good arguments there. Although I do not know what is a "plate amp". I suppose that the XL-280 has impressive characteristics like frequency bandwidth so its use for only sub frequency will not take advantage of its full potential. I suppose that you have verified that your mid/hi freq amps are better than your XL-280?

In my DH-200 amps I have not change the transformer due to space limitation. I saw one implementation using a big toroidal where the chassis had to be cut to install it. However, I have changed to power caps from (2x) 10000 uF to (2x) 30000 uf while keeping the same size factor. In my other DH-200 I used (4x) 14000 uF and 2x 35A diode bridge. AS Dick said, the XL-280 uses a pcb on top of the power caps so you better stay with same form factor. I had this caps setup for several years with no problem. Increasing the transfo VA rating may require an "in-rush" limiter. Also, from the user manual the XL-280 has 2 separate windings for 2 available voltages (driver stage with a slight highest voltage and power stage voltage). You may have problem to find the same output voltages unless you use 2 transformers but again space limitation inside the chassis is again a problem.

"How high a VA rating and how much capacitance will bring me to the point of diminishing returns?"

I would put the highest value caps that fit into the XL-280 and make sure you use the same voltage ratings.
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Old 29th March 2006, 12:22 AM   #212
fab is offline fab  Canada
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Quote:
Originally posted by mlloyd1
fab:
...
the servo 50 driver board that i purchased from borbely years ago has onboard discrete regulators. very simple - not as elaborate as the millenium. ...
mlloyd1
Hi mlloyd1

The servo 50 is discontinuited at Borbely Audio and it last sold at 205 Euro / pair. When you bought the kit, did it include the pcb layout?

Thanks

Fabien
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Old 29th March 2006, 06:00 AM   #213
mlloyd1 is offline mlloyd1  United States
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that was a long time ago- i don't think so, but i'm not sure. i think i just got a parts placement diagram in addition to the article on the website.

the PCBs had more jumpers than i would prefer to have. i always thought about redoing them but that has obviously gotten VERY low on my priority list.

Quote:
Originally posted by fab


Hi mlloyd1

The servo 50 is discontinuited at Borbely Audio and it last sold at 205 Euro / pair. When you bought the kit, did it include the pcb layout?

Thanks

Fabien
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Old 29th March 2006, 03:17 PM   #214
ilardi is offline ilardi  United States
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I have modelled the DH-200 on Switchercad SPICE but cannot find models for the 2SK134 or 2SJ49 output MOSFETS. I was able to find models for 2SK1058 and 2SJ162 MOSFETS and used these as substitutions. Even with these substitued parts the model seems pretty accurate (I also substituted 1N4740A diodes for the 1N5240B zeners and estimated coil L1 at 1.5uH). I modelled the amp in the hope of getting a better idea about the various parts substitutions recommended. Besides it was an easy exercise and kind of fun.

It has been instructive to see how changing various caps and resistors changes (not much admittedly) the frequency response of the unit. I am still a SPICE novice so haven't run distortion simulations yet.

Right now the model runs "hot"-- that is, at the middle of P1's adjustment range bias is running around 450 mA. Since this does not accurately simulate the actual circuit I am trying to figure out why but my guess is that this is due to the use of the wrong output devices.

If anyone has models for the 2SJ49 and 2SK134 MOSFETS I would much appeciate it.

I'd also be happy to share the DH-200 model with anyone else who is interested.

Terry Ilardi
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Old 29th March 2006, 04:30 PM   #215
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Hey all. Some of you remember me with the DH-200 switch that went bad. You all helped me out GREATLY. Thanks!!

I have read though this WHOLE thread. WOW, what great info.

I want to change out my inputs and outputs on the amp. I want to go with maybe gold plated. Better than what the originals are. What do you all recomend? The originals are starting to corode.

I deal alot with www.partsexpress.com . Do you all know if anything from there would work? Somehting that would be a "drop in" fit?


Jake
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Old 29th March 2006, 05:51 PM   #216
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Or www.mouser.com or ww.radioshack.com . Thay all seem to carry one type or another. Just wondering which one was the best fit. Also about the speaker output, I would like to go with the same style, just maybe gold plated. Something that would also accept bananna plugs.
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Old 29th March 2006, 06:08 PM   #217
mlloyd1 is offline mlloyd1  United States
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ilardi:
if you have good models for the 2SK1058/2SJ162, then you have good models for the 2SK135/2SJ50 (the 2SK134/2SJ49 are the lower voltage siblings).

hitachi used the same die in different physical packages.

it is indeed a fun circuit to simulate. some years ago, a person i met in the high end audio newsgroup sent some notes he prepared because he taught about the hafler design in an electronics class. i've got to find it and see if he'll let me share it.

mlloyd1

Quote:
Originally posted by ilardi
I have modelled the DH-200 on Switchercad SPICE but cannot find models for the 2SK134 or 2SJ49 output MOSFETS. I was able to find models for 2SK1058 and 2SJ162 MOSFETS and used these as substitutions. Even with these substitued parts the model seems pretty accurate
...

Terry Ilardi
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Old 30th March 2006, 11:45 AM   #218
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to Dick West:

Quote:
You might be better off getting a big plate amp specifically designed to drive subwoofers.
What's a plate amp?

Quote:
These plate amps might be cheaper, run cooler, take less space, etc.
this part I get.

Quote:
If you beef up the XL-280 with too much PS capacitance and a toroidal transformer you risk blowing the power switch and the bridge diode in the power supply unless you also incorporate a soft start circuit.
I think this will fill the soft start need. http://www.sound.westhost.com/project39.htm Upgrading the bridge diode is easy and low $. If I have to mount add'l caps out side the case...

Yeah I'm crazy

tony
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Old 30th March 2006, 02:28 PM   #219
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Go here for an example of a Plate Amp:

http://www.partsexpress.com/pe/showd...number=300-794

For a subwoofer you don't need to be quite so concerned about purity of sound. Most of the value of the XL-280 is wasted if it only drives a subwoofer.

Parts Express has a variety of plate amps. Go to the discussion board at Parts Express and read the mail, check the searches and archives, and ask a question. The guys who hang there are very expert in subs and with plate amps.

http://www.pesupport.com/cgi-bin/config.pl

Many plate amps provide features to enhance the use of a subwoofer that your XL-280 lacks -- such as a variable phase control to help the sub better blend with your other speakers.

Sell your XL-280 amps, buy a couple of plate amps, and smile all the way to the bank plus enjoy better sound with less fuss and worry.
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Old 31st March 2006, 11:44 AM   #220
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Just glanced @ your reply. Will spend time on the PE forum.

I won't sell them; I'll use them elsewhere in my home theatre system.

Thanks

tony
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