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Old 5th May 2011, 11:19 PM   #1111
AKSA is offline AKSA  Australia
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Kurt,

Each output, Q3 and Q4, dissipates (0.12A x 15V) = 1.8W of heat. If the heatsink is 16C/W, you could expect it to run at around 29C above ambient. If ambient is 25C, that's 54C, which is pretty damn hot. At 65C you cannot keep you fingers on a heatsink for more than about three seconds, depending a bit on your tolerance for pain.

You can consider reducing the quiescent current, depending on what headphone impedance you will be using. For 24R cans, then 120mA is preferred, but for 75R cans or higher, you could reduce the output quiescent to around 50mA (R11 at 22R), which would greatly lower dissipation in the heatsinks.

These changes should be acceptable to the design without additional modifications.

Cheers,

Hugh
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Old 8th May 2011, 05:28 PM   #1112
Bigun is offline Bigun  Canada
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KnoghtOfAwesome,

I think your design is looking very nice indeed.

If heat is a worry - I think you'll have more flexibility for assigning heatsinks if you don't mount them on the pcb but allow the power devices to hang off the pcb and be mounted to a larger heatsink, or even the amplifier casework.
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Old 8th May 2011, 06:24 PM   #1113
peranders is offline peranders  Sweden
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It's a big advantage to have a pcb mounted heatsink. Less can go wrong.
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Old 10th May 2011, 10:13 PM   #1114
KnightofAwesome is offline KnightofAwesome  Canada
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I complete my very crude breadboard of the ASPEN, I hadn't installed C1,C2,C3 or C4... None the less, but it was stable! I took the off/on offest measurements and found no massive offsets. Was there a reason as to why there was suspicion of such a large offset? My rather simplistic multimeter measured none.

Good news?
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Old 11th May 2011, 04:14 AM   #1115
peranders is offline peranders  Sweden
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You must have had something. Did you set the multimeter at the 200 mV range and got 0.0 mV?... DC range?
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Old 11th May 2011, 04:29 AM   #1116
KnightofAwesome is offline KnightofAwesome  Canada
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I used two bench PSU's too, On thursday I'll use the scope, because clearly the multimeter didn't show any massive offset at the mV's range.

Can I get a reason for suspicion?

Edit: Yes, I managed to get the offset down to about 0.0mV
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Old 12th May 2011, 10:53 PM   #1117
KnightofAwesome is offline KnightofAwesome  Canada
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Due to time constraints dealing with things other then breadboarding, R6 and C4 are the only parts not installed at the moment.
Although this massive initial offset is no where to be seen, I've seen maybe ~200mV from not turning the two PSU's on at exactly the same time. It's also possible that this is from adding the 100uF capacitor, mostly turn on offset starts at ~30mV and moves down to a rather "normal" offset value.
When I get a chance I'll add R6 and C4
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Old 16th May 2011, 11:34 PM   #1118
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All components installed, a maximum of 1 volt offset from turn on, those measurements were also taken by throwing two separate switches to turn on the PSU.
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Old 17th May 2011, 04:56 AM   #1119
AKSA is offline AKSA  Australia
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Good news, KoA, this is marvellous.

Have you had a good listen?

Should sound very nice indeed, since it's all single ended......

Hugh
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Old 18th May 2011, 10:29 PM   #1120
KnightofAwesome is offline KnightofAwesome  Canada
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I find breadboarded amps are a little to unsafe for listening. If anything touches, It's going to throw the offset way off. and on top of that, these bench supplies are quite noisy... Not the greatest for impressions.

Anything else that should be worked on?
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