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Old 7th April 2012, 03:12 PM   #41
AndrewT is offline AndrewT  Scotland
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Originally Posted by 6L6 View Post
Hold your hand on them for 5+ seconds?
Are "them" the output devices?
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Old 7th April 2012, 03:30 PM   #42
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Originally Posted by Andersonix View Post
IME sparkle, shimmer, sizzle, etc are undesirable and suggest distortion or noise. The cleaner my top end has become, the 'darker' and 'richer' overall the sound has become, while the treble is smoother and more delicate and revealing than ever, and the sound also has better micro dynamics, making it sound louder and more explosive at the same volume setting as previously -- like live sounds.

(A couple of weeks ago, I went from CRC to CLC on my class AB amp and cannot believe the improvement everywhere....!)
I think that depends on you definition of sparkle and shimmer....in my definition, these are GOOD things, as long as they are not exaggerated....Cymbals shimmer to me when live or in a recording....sizzle? not so much. That descriptor belongs with frying bacon!

Russellc
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Old 7th April 2012, 03:35 PM   #43
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Originally Posted by fab View Post
This shows also an increase of gain
That's interesting to note, my current F-5 build will be sans limiting circuitry, plus I am going to use 220 instead of the 100 ohm feedback resistors. The resistor change is said to increase gain from 15 dB to 22dB.

Do you know how much gain is increased with the elimination of the limiting circuits?

Thanks,

Russellc
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Old 7th April 2012, 04:23 PM   #44
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Originally Posted by alazira View Post
R5 & R7 are paralleled so they are equal to a single 50 ohm resistor. If using a single resistor, use 5W. A single 100 ohm resistor as in the schematic Peter Daniel shows would reduce feedback/increase gain and have a little warmer sound (probably the opposite of what you want if you are looking for a shinier top end)
That's the ticket.

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Old 7th April 2012, 04:29 PM   #45
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Very nicely wired, I wish my F-5's internal wiring was that neat!

Russellc
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Old 7th April 2012, 04:31 PM   #46
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Originally Posted by 6L6 View Post
Hold your hand on them for 5+ seconds?
I 'adjusted' the input level on the CD source so I'm not running at full power anymore and the heatsinks are only getting 'warm'. Yesterday when I was running full power for an hour or more they were getting pretty toasty then.

I do have a plan for excess heat. I plan on cutting some openings in the top cover and installing some perforated aluminum.

Order Aluminum 3003 Perforated Sheet in Small Quantities at OnlineMetals.com

After that I'm considering installing a thermostatic switch that turns on a couple of 2 inch CPU fans that I'll mount to the underside of the perforated aluminum.

The switch I'm going mount to one heatsink that'll turn the fans on/off automatically.
Digi-Key - 317-1502-ND (Manufacturer - CS703515Z)

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Dan
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Old 7th April 2012, 05:08 PM   #47
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Originally Posted by dantwomey View Post
I 'adjusted' the input level on the CD source so I'm not running at full power anymore and the heatsinks are only getting 'warm'. Yesterday when I was running full power for an hour or more they were getting pretty toasty then.
The heat on the hs you describe doesn't sound quite right, so I've included a snippet from an old post by AndrewT (hope you don't mind) to see if you agree, Dan:

"A ClassA amplifier dissipates maximum power in the quiescent state, if it is never asked to exceed the ClassA current limit.
As the output current increases from zero to maximum ClassA output current the dissipation in the output stage progressively falls.
If our 27W into 8r0 amplifier is biased @ 1.3A and runs on +-24V supply rails, then during quiescent state the output stage dissipation is 1.3 * [24+24] = 62.4W.
When the sine wave output to a resistive load is 1W the dissipation drops to 62.4 - 1 = 61.4W
When 10W is output the dissipation is down to 52.4W.
When 27W is output the dissipation is down to 35.4W.

If that same amplifier goes into ClassAB then dissipation starts to increase again from that 35.4W minima.
At 100W output the dissipation has increased to approximately 60W.
Much the same as it dissipates at the quiescent state.

The F5 can operate all day at any power output from zero to 100W all day long. That is what is really nice about a properly designed push-pull ClassA amplifier."
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Old 7th April 2012, 05:20 PM   #48
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Originally Posted by Russellc View Post
I think that depends on you definition of sparkle and shimmer....in my definition, these are GOOD things, as long as they are not exaggerated....Cymbals shimmer to me when live or in a recording....sizzle? not so much. That descriptor belongs with frying bacon!

Russellc
I agree. I brought it up because it's easy for an inexperienced listener to form a first impression that a new, better piece of equipment sounds dry or dark and that the 'sparkle' has gone, when in fact it is the result of hearing less distortion or noise...
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Old 7th April 2012, 05:29 PM   #49
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All power numbers aside I'm guessing that after extended use I'm running too hot. I can put my hand on the heatsinks for 5+ seconds but that's pushing it a bit. I'm now contemplating where to mount these fans. As mentioned previously there are about 2 inches square. I'm thinking of either mounting them inside the case right on the heatsinks or remove the mini-sink they come with and mount the fans directing on the back fins just outboard of the speaker connectors.

Click the image to open in full size.

Regards,
Dan
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Old 7th April 2012, 05:33 PM   #50
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Originally Posted by Andersonix View Post
The heat on the hs you describe doesn't sound quite right, so I've included a snippet from an old post by AndrewT (hope you don't mind) to see if you agree, Dan:

"A ClassA amplifier dissipates maximum power in the quiescent state, if it is never asked to exceed the ClassA current limit.
As the output current increases from zero to maximum ClassA output current the dissipation in the output stage progressively falls.
If our 27W into 8r0 amplifier is biased @ 1.3A and runs on +-24V supply rails, then during quiescent state the output stage dissipation is 1.3 * [24+24] = 62.4W.
When the sine wave output to a resistive load is 1W the dissipation drops to 62.4 - 1 = 61.4W
When 10W is output the dissipation is down to 52.4W.
When 27W is output the dissipation is down to 35.4W.

If that same amplifier goes into ClassAB then dissipation starts to increase again from that 35.4W minima.
At 100W output the dissipation has increased to approximately 60W.
Much the same as it dissipates at the quiescent state.

The F5 can operate all day at any power output from zero to 100W all day long. That is what is really nice about a properly designed push-pull ClassA amplifier."
You're right. It's my second experience with a class and my first one was oversinked so I never reached this point. I'm starting to learn now that maximum temperature is a function of how long the amp is turned on. Not what work it has been doing.

Regards,
Dan
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