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Old 25th July 2011, 03:49 AM   #321
Salas is offline Salas  Greece
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The DiyA author Variac informed me that he will be adding the Mezmerize DiyA production board in the site's Store in some time by the way, when exactly I am not sure. Just to inform that this fully 6 input relay switched buffer pre-amp will be future secured. For now, better seek a spare.
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Old 25th July 2011, 03:55 AM   #322
Frosteh is offline Frosteh  United States
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Originally Posted by Ed LaFontaine View Post
I'd be glad to assist if I may...

Omron G6H-2 12VDC relays

If a set of "matched" devices varies 0.08/8.00, that is 1%. I have never sent out a set with more than 0.04 variance. I have sent out quad sets above the 7-8 mA range... I do give the greater emphasis to channel-channel matches.

I may find a Mesmerize board as well.
I like it! Thanks for replying! Let me know if you're able to find a PCB; they are a bit difficult to find. I'll send you a pm in a day or so if I need those FET's; I'm waiting for an eBay auction to finish that could end up cheaper than this build.
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Old 26th July 2011, 09:44 AM   #323
Frosteh is offline Frosteh  United States
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Originally Posted by particleman14 View Post
hey all, I'm about to put in my order for some mez parts but have 1 question. I intend to hotrod mine a little bit, so I'm going to get some 6.2R wirewound resistors (for a little over 300ma current) but will the 120 diodes be ok? I was going to order some mur860 or stealths but I would have to bend the pins to make them fit the mez board since they are to-220 trying to fit into a do-41. Should I do this? or can I safely hotrod the mez with the 120s? does the "ultrafast" recovery time make that much of a dif?
Has anyone successfully completed a hot rod like this to 300mA? It seems all the other components should be able to handle this if I use 6.2R resistors.
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Old 26th July 2011, 10:23 AM   #324
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you can fit on To-220 diodes without too much trouble.
You just need to keep them on on part from touching each other. I've used electricians tape for that. Not elegant, but works.
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Old 26th July 2011, 09:09 PM   #325
Frosteh is offline Frosteh  United States
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you can fit on To-220 diodes without too much trouble.
You just need to keep them on on part from touching each other. I've used electricians tape for that. Not elegant, but works.
That I understand. I'm wondering if I have my parts correct, though. In order to hot rod, do I need to replace all the diodes with the upgraded ones?
Here's the list of parts I'm planning to order:
4 mur820 rectifiers from mouser (MUR820 Taiwan Semiconductor Rectifiers)
2 6.2R Wireround resistors (280-CR10-6.2-RC Xicon Wirewound Resistors - Through Hole)

To hit 300mA would I need 2 or 4 of the 6.2R resistors? I'll be installing some small fans in the case to aid cooling since I'm thinking it will get quite toasty at that current. I'll probably use a fan like This.

Last edited by Frosteh; 26th July 2011 at 09:19 PM.
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Old 26th July 2011, 10:00 PM   #326
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What diodes are in there now? I would get 6.2 pair and 10R pair, and add both if it is too low on the current. Need IRF's attached to casing at this point.
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Old 26th July 2011, 10:22 PM   #327
Frosteh is offline Frosteh  United States
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What diodes are in there now? I would get 6.2 pair and 10R pair, and add both if it is too low on the current. Need IRF's attached to casing at this point.
I just bought the board and it has the stock 120's on it. Why would it be low on current? 6.2R is way lower than the original 34R with the 68R resistors. But that's a good idea. I'll keep both on hand. And yes, they will definitely be attached to the case w some TIC underneath to increase thermal transfer.
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Old 27th July 2011, 11:26 PM   #328
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Are these an acceptable replacement for the MUR120's? They're MUR820's made by Taiwan Semiconductor instead of ON Semiconductor. Only difference is it has a faster recovery time (25ns vs 35ns). MUR820 Taiwan Semiconductor Rectifiers
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Old 28th July 2011, 12:59 AM   #329
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I would them or my preference is for the cheaper IXYS TO-220's.
There may be in fact differences in the sound of these diodes.
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Old 28th July 2011, 01:14 AM   #330
Salas is offline Salas  Greece
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Originally Posted by Frosteh View Post
That I understand. I'm wondering if I have my parts correct, though. In order to hot rod, do I need to replace all the diodes with the upgraded ones?
Here's the list of parts I'm planning to order:
4 mur820 rectifiers from mouser (MUR820 Taiwan Semiconductor Rectifiers)
2 6.2R Wireround resistors (280-CR10-6.2-RC Xicon Wirewound Resistors - Through Hole)

To hit 300mA would I need 2 or 4 of the 6.2R resistors? I'll be installing some small fans in the case to aid cooling since I'm thinking it will get quite toasty at that current. I'll probably use a fan like This.
Many Mez averaged at about 1.75V drop across the setting resistors, some went near 2V. The negative side was lower some times. Mosfets differ, and N polarity ones seemed happier for Vgs. LEDS can differ too. If we assume the commonly reported 1.75V drop then you are getting ~280mA and ~0.5W dissipation on that resistor. But it can go ~320mA & 0.64W if with 2V drop. Experience has shown that in constant current dissipation and where we put those resistors, 3-5W types are comfortable after long. 2W ones get unhappy. But 10W you will not need, and they are bulky. Imagine that you must use 80C per W rule of thumb thermal climb when parallel and very near to the board for DO-41 cased diodes like 120s. So if they drop say 0.9V*0.3A=0.27W*80=+22C above ambient. MUR820 or IXYS TO-220 are fine and more reliable in the long term than 120s for 300mA because big and upright. But you got to watch they don't rub shoulders, the Mez PCB wasn't conceived for hot rod really, so it will be a bit awkward but doable. For long term you would like your semiconductors at lower than 50C. Ambient in a box can go 40C with several dissipation sources radiating around. Use one of those cheap supersonic laser point thermal meter guns to spot check the build before deciding on noisy fans. Point at the Mosfets, point at the diodes, point at the setting resistors after half an hour. If you will not find 50C+ somewhere don't bother with fans. Good luck.
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