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Old 11th January 2019, 08:51 AM   #1721
marconi118 is offline marconi118  Germany
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output could be taken at the primary or secondary of transformer.

Sugested stantard EI transformer
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Old 11th January 2019, 10:11 AM   #1722
indra1 is offline indra1  Indonesia
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Originally Posted by marconi118 View Post
what do you think about the "balanced MoFo" presented here? ...
You are reinventing Sue Parker's Zeus Amp. Read up and learn the finer points she and others have shared over the years.
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Old 11th January 2019, 11:49 AM   #1723
leftovers53 is offline leftovers53  United States
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Can someone please comment on post 1662 in which a Tubecad variation is shown using an order of magnitude smaller inductor? Here is the relevant commentary from Broskie's blog entry re the circuit.

"Don't you mean 2-Henry inductor? No, 2mH is enough, as the 8-ohm load is in parallel with the MOSFET's fantastically-low output impedance. The choke's own DCR, however, is in series with its inductance, which undermines the MOSFET's low output impedance. Thus, an air-core inductor isn't the slam dunk easy option that it might seem at first, in spite of offering such benefits as no saturation and no core hysteresis. For example, a typical 2mH air-core inductor might present a DCR of 0.3 ohms, even with 16-gauge wire, four times more than an IRFP250's 0.073 ohm Rds. In other words, a larger-valued air-core inductor will be needed, say 10mH, but then it must incur a larger DCR. In addition, the inductor's DCR will create a sizable DC offset at the output; for example, 3A against 0.8 ohms creates a 2.4Vdc offset. Thus, with an air-core inductor, an output coupling capacitor will be needed, say a 1kF/10V capacitor." Cathode-Follower Power
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Old 12th January 2019, 12:52 AM   #1724
xrk971 is offline xrk971  United States
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Default The MOAMOFO

I am currently running the Mother of All MOFO’s and it’s putting an ear to ear grin on my face. 4.65 amp bias current at 37v supply rail with big fat IXYS MOSFET putting out 160w per channel, microwave oven transformer and Melbourne Preamp driving it. My Melbourne was running on +/-24.5v rails so max output was limited by Preamp at 42.4Vpp into 8ohms. I will boost preamp rails and should be able to hit 50wrms into 8ohms. Here is recent O-scope shot at onset of clipping.

Cooling is of course provided with a heatpipe CPU cooler and PWM fan. MOSFET body temp is only 50C so not even hot.

Build This MoFo!-45502640-20b4-42ed-8572-a43a374d4f7d-jpeg
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Last edited by xrk971; 12th January 2019 at 12:55 AM.
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Old 12th January 2019, 01:17 AM   #1725
kp93300 is offline kp93300  Malaysia
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XRK 971 .
I am interested to see how you set up the Mother of MOFO esp the heat sink etc
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Old 12th January 2019, 01:27 AM   #1726
vdi_nenna is offline vdi_nenna  United States
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That's wild.
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Old 12th January 2019, 01:48 AM   #1727
xrk971 is offline xrk971  United States
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Here is how the CPU coolers are mounted to the MOSFETs. I am using ceramic spacers and heatsink compound (2x better than keratherm pads). CPU coolers are surplus Dell units with the big copper pad. I recently got these 15mm T rails from Maker Beam. Nice stuff.
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Old 12th January 2019, 01:58 AM   #1728
kp93300 is offline kp93300  Malaysia
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XRK971.
You are a super diyer.
Skilled in electronic and mechanical aspect . I take my hat off .
Is this the ' best ' sound to your ears ???
cheers
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Old 12th January 2019, 02:04 AM   #1729
xrk971 is offline xrk971  United States
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Thanks for the kind words KP, but it’s no big deal to use tinker toys to assemble heatsinks.
I am still assembling the cap Mx and second power trafo, will have stereo soon and will describe sound once I hear in stereo. In mono, it sounds like a MoFo for the smoothness and transparency but with the grunt of what feels like a 100w Class AB when driving a low sensitivity speaker.
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Last edited by xrk971; 12th January 2019 at 02:06 AM.
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Old 12th January 2019, 02:18 AM   #1730
kp93300 is offline kp93300  Malaysia
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XRK,
what is the part no for the mosfet ?
I have placed an order for the 17 amp Dell computer smps and heatsink like the one used by ERic.
I will borrow your ideas when the parts arrived .
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