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diyAB Amp  The "Honey Badger" build thread
diyAB Amp  The "Honey Badger" build thread
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Old 10th January 2019, 01:18 PM   #3281
rock12 is offline rock12  United States
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Tony thank you I am going to build a hfe tester

thimios I am confused a Zobel is at my speaker crossover? My bias goes crazy without any connections during the original setup when it is turned above +/- 15mv. When it rises up around 60 millivolts r50 on the board gets warm

ostripper thanks for advise. I think we are in the right area. I thought the hb was Class AB
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Old 11th January 2019, 12:50 AM   #3282
TonyTecson is offline TonyTecson  Philippines
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diyAB Amp  The "Honey Badger" build thread
Quote:
Originally Posted by rock12 View Post
ostripper thanks for advise. I think we are in the right area. I thought the hb was Class AB
it is, the thing is to get the output stage bias as low as can be without the crossover distortions..you can listen to the amp at real low volumes and see if you hear grainy sounds, this is if you do not have a scope yet..
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Old 11th January 2019, 02:51 AM   #3283
anatech is offline anatech  Canada
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diyAB Amp  The "Honey Badger" build thread
Hi tony,
Quote:
... and see if you hear grainy sounds, this is if you do not have a scope yet..
Oscillation can also sound like that. To be sure, you really do need an oscilloscope. Thankfully you can buy some extremely good analogue oscilloscopes for a fraction of their original cost. I paid about $500 for a Tektronix 2465B (400 MHz, dual channel) that was thousands when new. You can often get a 100 MHz dual channel 'scope for $200 ~ $250. Philips made some nice scopes like the PM-3070 and PM-3365A. These are excellent scopes with sharp, bright traces. $100 can buy a less expensive scope that is still 100 MHz, dual trace. THey aren't as good, but what do you want in the bargain basement? These are more expensive than some of the USB scopes, but they are far better to have than a cheap USB scope. Tektronix 2235 should be cheap too. They need some work, but like anything else, old equipment needs maintenance.

-Chris
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Old 11th January 2019, 05:53 AM   #3284
TonyTecson is offline TonyTecson  Philippines
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diyAB Amp  The "Honey Badger" build thread
i had my share of output stage oscillations with the Tigersaurus amps of Daniel Meyer, where the output stage had voltage gains of about 4...and is manifested by unexplained heating and current draws that was not supposed to happen...a small pocket AM radio tuned to a station when held very near the amp will show interference....

that was in the 80's then....and now that i build amps only emitter follower amps, i never had that problem...but of course having a scope will reveal those problems for sure..
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Old 13th January 2019, 11:14 AM   #3285
Kay Pirinha is offline Kay Pirinha  Germany
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I think I'm gonna build my HB's within the next weeks. They won't feature a conventional PSU, but a chain of four 24V/5A laptop bricks instead per amp, thus 480 watts maximum DC input power. These bricks feature an active PFC and a power limiter, and I've found out how they can be tweaked for other output voltages. Yes, after disconnecting the PE/negative output terminal link they can be tied and will work in series easily.

The main advantages are the power limiter, the reduced weight, dramatically decreased costs (about € 7 per brick, € 56 for the complete PSU), and that there's no need for big 'lytics.

480 watts DC input relates to about 300 watts output power in an AB amplifier. For 4 ohms loads this would require rails of about 55 Vdc, so 27.5V per brick.


Will three pairs of MJL4281/4302's, bolted on a 300 mm 3U Dissipante heatsink, be up to task for this goal? Or do I have to opt for bigger devices? Which ones?

Best regards!
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Last edited by Kay Pirinha; 13th January 2019 at 11:15 AM. Reason: Removal of unintentional blank lines
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Old 13th January 2019, 02:20 PM   #3286
audiofan is offline audiofan  Canada
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I dont know much about these PC power supply but I would investigate about noise .... they are of course switching type ... and build for battery charging in computers .....
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Old 13th January 2019, 09:03 PM   #3287
Johno is offline Johno  Australia
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diyAB Amp  The "Honey Badger" build thread
....and series connection will not increase the current, only the voltage. So you will have 240W per channel.
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Old 13th January 2019, 09:06 PM   #3288
Kay Pirinha is offline Kay Pirinha  Germany
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...what I'd also consider as sufficient. But how did you calculate this?


Best regards!
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Old 13th January 2019, 09:14 PM   #3289
jwilhelm is offline jwilhelm  Canada
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I'm curious how the computer supplies handle peak currents? Will they allow some short high current pulses or fold back the voltage? Maybe some capacitors on the output may add something?
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Old 13th January 2019, 09:17 PM   #3290
Kay Pirinha is offline Kay Pirinha  Germany
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Will have to try with and without 10.000 F (4 ea) capacitors across the rails and see. Btw, the HB PBC can be populated with 1.800 F/63Vdc 'lytics across each rail.


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