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
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
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..
Hi tony,
-Chris
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
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..
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..
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!
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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SMPS actively monitors current draw/voltage and will increase on time for the flyback
switcher as the voltage falls.
High current protection occurs when increased on time can no longer regulate output
voltage. Too large of a capacitance at the output can actually degrade regulation.
Most 4-500w audio SMPS's just have a few Kuf at output , even a Lab Gruppen
"monster" SMPS at 10Kw has <20Kuf .... but it's controller is fine tuned for this
greater output capacitance plus it has the "horsepower" to make microsecond corrections with the larger capacitance.
SMPS capacitor ESR quality is the main factor. PC supplies will use high end
Panasonic FM/EEU-FS series low ESR models at 5/12V outputs .
A different realm than analog. (more refined - and controllable !)
Edit - protection depends on capacitance in a minor way. Shut down is determined
by the controller IC settings. Some controller IC's have a "peak current" mode that can
make them behave more like a high capacitance analog supply.
OS
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Hi Tony,
I've not yet tried it with these 24V 5A SMPS bricks, but I've well tried it with smaller (24V 2.5A) open frames. A chain of four, connected as described above and supplied with one reverse diode at each units' output, works well when loaded by two 10mF 'lytics in series and an ohmic load that represents the HB at idle. I didn't try it at full power, though.
Best regards!
I've not yet tried it with these 24V 5A SMPS bricks, but I've well tried it with smaller (24V 2.5A) open frames. A chain of four, connected as described above and supplied with one reverse diode at each units' output, works well when loaded by two 10mF 'lytics in series and an ohmic load that represents the HB at idle. I didn't try it at full power, though.
Best regards!
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Smaller caps , better ESR quality ... like panasonic eeu-fs.
This is not 50/60hz.
Edit - Consider , an SMPS controller can see a huge capacitance as a overcurrent event.
OS
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I'm talking about these SMPS's. Sorry, this shop doesn't feature an English spoken site 
. Actually I don't know what these bricks are dedicated to. The laptop use was not more than an assumption of mine.
Best regards!
. Actually I don't know what these bricks are dedicated to. The laptop use was not more than an assumption of mine.Best regards!
A Battery charging curve is different than the instant inrush of an aluminum
electrolytic. An SMPS for charging batteries would most likely incorporate
the intended battery's charging curve into the circuit.
Example - a lead acid cell with a dead short (at start) or too much draw
at the end of the curve would be treated as a protection event.
No charge , no smoke , no boom!
PS - the COMP input on most (8pin) smps controller IC's connected to the opto
have a capacitance , this determines the RC of the feedback. A larger output
capacitance (bank) would require a larger RC. One could still kill the mosfet
or saturate the flyback with a small unit.
More advanced IC's also have a separate winding in the flyback to monitor saturation , as well.
OS
I'm talking about these SMPS's. Sorry, this shop doesn't feature an English spoken site
Best regards!
Laptop SMPS = Li-ion charging curve is in the battery pack. So , the linked unit
is just a simple 8 pin (opto FB) unit. At 6.95 euro , I doubt if it has as many advanced
features as advertised.
I modify these type cheap units (add real PFC , change for peak current).
As purchased , they have planned obsolescence.
This SMPS500R +-60V (dual voltage) 230V Power Supply is ideal.
I tried this one - 500W +/-70V Amplifier PSU Audio Amp Switching Power Supply Board High-power 648738894272 | eBay plus added panasonics - (new electro's).
Not bad for 34USD.
OS
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