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L'Amp: A simple SIT Amp
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Old 6th October 2019, 09:35 PM   #3071
Rodeodave is offline Rodeodave  Austria
hates ground loops
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L'Amp: A simple SIT Amp
L'Amp PSU sneak peek.

Do you even star ground, bro?
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Old 7th October 2019, 12:39 PM   #3072
plasnu is online now plasnu  United States
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Star ground has any advantage here? I was told series ground is better...
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Old 7th October 2019, 01:15 PM   #3073
Rodeodave is offline Rodeodave  Austria
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L'Amp: A simple SIT Amp
Advantage...hm. I believe that with the given architecture - involving screw terminal caps, point-to-point wiring, voltage regulators and significant distances between building blocks - it is actually easier to implement star grounding. And with quiescent currents of up to 3A, I'd rather have a separate current return path for each PSU cap.

Almost done
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Old 7th October 2019, 03:24 PM   #3074
twitchie is offline twitchie  Canada
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L'Amp: A simple SIT Amp
Looks so warm and cool at the same time!!! Great job @Rodeodave!
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Old 7th October 2019, 09:53 PM   #3075
Rodeodave is offline Rodeodave  Austria
hates ground loops
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Alright, I finished the amp tonight and fired it up. Biasing went without a hitch, no smoke, no drama. Or so I thought. After hooking up some headphones I discovered that there's an awful lot of hum/buzz present. The scope showed a similar picture.

I'm suspecting the ground layout really. Currently all grounds meet at the star ground. I think I'll try and have the signal grounds and the bias supply ground meet at the VFET, and route it to the star ground from there.

Once I get the amp working quietly I'll pull some numbers from the circuit and mess around with finding the sweet spot.
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Old 7th October 2019, 10:07 PM   #3076
Rush is offline Rush  United States
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Quote:
Originally Posted by Rodeodave View Post
Alright, I finished the amp tonight and fired it up. Biasing went without a hitch, no smoke, no drama. Or so I thought. After hooking up some headphones I discovered that there's an awful lot of hum/buzz present. The scope showed a similar picture.

I'm suspecting the ground layout really. Currently all grounds meet at the star ground. I think I'll try and have the signal grounds and the bias supply ground meet at the VFET, and route it to the star ground from there.

Once I get the amp working quietly I'll pull some numbers from the circuit and mess around with finding the sweet spot.
Those light bulbs are awfully close to the V-Fets. Could they be inducing your hum/buzz?

Rush
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Old 7th October 2019, 11:11 PM   #3077
res07njc is offline res07njc  United States
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also, might be helpful to have two star grounds... main one for PSU at chassis, and another star as floating amp circuit(s) ground, connected to PSU ground with/series a CL-60 thermistor. The resistance of the thermistor helps block any loops.
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Old 8th October 2019, 03:40 PM   #3078
Rodeodave is offline Rodeodave  Austria
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I did some light probing, and it looks like the output is mirroring whatever is coming out of the bias supply, and that ain't clean DC. At least I think I know where to start cleaning up.
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Old 14th October 2019, 10:43 AM   #3079
maxlorenz is offline maxlorenz  Chile
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All Stars are connected.

M.
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Old 14th October 2019, 08:40 PM   #3080
Rodeodave is offline Rodeodave  Austria
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I couldn't get the negative supply generator to work like intended, so I'm converting it to a proper negative bias supply with a dedicated transformer. I have this small-ish 12VA 40Vac (230V primary) transformer that I'll be running off the 44Vac secondary of the main transformer, which should give me something like 11Vac or about -14Vdc to work with. I have also found a cozy place for the little fella:
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