My F5 Lives!!!!!!!

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Russellc

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Andersonix said:
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....!)
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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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Russellc

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fab said:
This shows also an increase of gain
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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
 
Nelson Pass

Nelson Pass

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alazira said:
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)
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That's the ticket.

:cool:
 
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dantwomey

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6L6 said:
Hold your hand on them for 5+ seconds?
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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)

Regards,
Dan :)
 
Andersonix

Andersonix

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dantwomey said:
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.
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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."
 
Andersonix

Andersonix

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Russellc said:
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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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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dantwomey

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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.

Fans.jpg


Regards,
Dan :(
 
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dantwomey

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Andersonix said:
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."
Click to expand...

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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dantwomey

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If these fans wouldn't melt I think it would be kind of interesting to mount them internally with an auto-temp switch. This of course would include generous venting of the top panel. Although it makes the most thermal sense IMHO the bottom panel is too occupied for any effective venting.

Regards,
Dan :)
 
Andersonix

Andersonix

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What are your plans for a cover? Maybe you could put in an array of 1/4 inch holes through both top and bottom at the same time (by clamping them together) at a later time -- after you've had some time to think about the amp as a whole?

(motto: Don't do today what can be put off until tomorrow.)
 
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dantwomey

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Andersonix said:
What are your plans for a cover? Maybe you could put in an array of 1/4 inch holes through both top and bottom at the same time (by clamping them together) at a later time -- after you've had some time to think about the amp as a whole?

(motto: Don't do today what can be put off until tomorrow.)
Click to expand...

I'm not too concerned about the aesthetics of the bottom plate. It'll probably be three 3/4" (19mm) holes in a line under the mosfets. For the top plate I intend to get very artistic and cut a series (of yet to be decided size and shape) openings and fill them with the perforated aluminum plate I linked in a previous post.

Regards,
Dan :)
 
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ottopilot

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alazira said:
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)
Click to expand...
Forgive me for I am a noob, but I did a double-take when I read this. If the goal is 50 ohms, how does replacing two 100 ohm in parallel with a single 50 ohm produce a different feedback result or measurably (or even perceptibly) change the sound? Does this have something to do with the differences between the physical construction of resistors of different power dissipation ratings? If so, anyone care to enlighten me as to what exactly is going on here?
 
fab

fab

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dantwomey said:
If these fans wouldn't melt I think it would be kind of interesting to mount them internally with an auto-temp switch. This of course would include generous venting of the top panel. Although it makes the most thermal sense IMHO the bottom panel is too occupied for any effective venting.

Regards,
Dan :)
Click to expand...

Why an auto-temp switch? this is a class A amp, the fans would run all the time anyway.. To avoid noise injection by the fans, you would benefit to power them from a separate power supply... I also run the fans at lower speed b/c they make a lot of mechanical noise otherwise...
 
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