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Old 8th March 2005, 07:34 AM   #21
AndrewT is offline AndrewT  Scotland
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Hi Dan
what is mandatory?
An open loop bandwidth wider than audio?
Or open loop bandwidth beyond the audible range is unecessary?
If beyond then how far beyond?
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Old 8th March 2005, 08:49 AM   #22
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Well ideally you should have closed loop FR an order of magnitude outside of the band you intend on using. So if you want 20Hz - 20kHz, you should be thinking something around 2Hz - 200kHz.
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Old 8th March 2005, 10:12 AM   #23
MikeB is offline MikeB  Germany
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Hi Tom !

Have you tried the resistorload in vas ? It's a very simple change,
just add a resistor in vas to gnd, or symetrical, two, one on each
side of vbe-multiplier.

Mike
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Old 8th March 2005, 10:21 AM   #24
MikeB is offline MikeB  Germany
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Quote:
Originally posted by AudioFreak

Well if you want decent phase response anywhere near the edges of the audible range then it's pretty much manditory.
My experience is, phasehifts within closedloop are evil, the less
phaseshift the better dynamics and details. Sadly i was not able
to get below 20° at 10khz with the amp beeing stable.
(the 20° with opened loop,phasedifference from input to output)
But, with "normal" designs, you easily reach values above 50°.
(like ccs-loaded vas, driven from currentmirrored LTP)

Do you mean -3db at 200khz ?

Mike
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Old 8th March 2005, 12:35 PM   #25
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Quote:
But in every single amp i've constructed it was absolutely necessary to keep it flat, or sound was "trash".
There are two possibilities: either having flat open loop phase within the audio band is important, or the thing you changed to achieve this changed the sound for an entirely different reason.

Quote:
Well ideally you should have closed loop FR an order of magnitude outside of the band you intend on using.
Ideally there should be no distortion whatsoever. In practice the O.L. bandwidth is not very important of itself. If you are using feedback then you want as much as possible: typical designs use Miller compensation to create a first pole at only a few hundred Hz, causing the O.L. phase to drop to near 90 deg during most of the audio band. But this doesn't really matter. I'd say you want to aim for a C.L. bandwidth of 40kHz and any more isn't important. What can happen is that when a designer alters the circuit to create a 200kHz bandwidth they also alter other factors and it is these other factors that dominate the sound.
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Old 8th March 2005, 01:18 PM   #26
MikeB is offline MikeB  Germany
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Quote:
Originally posted by traderbam

There are two possibilities: either having flat open loop phase within the audio band is important, or the thing you changed to achieve this changed the sound for an entirely different reason.
Yes, i was thinking about that too, adding these resistors lowers
Z-out of the vas, making it less sensitive to reactive loads.
But my latest amp did not need these resistors for reasonable flat
OLBW, and it sounds as it should, like the others with resistors.

Mike
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Old 8th March 2005, 09:31 PM   #27
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Quote:
Originally posted by MikeB

Do you mean -3db at 200khz ?
Yes. Although commercially -3dB at 100kHz is more practical there are a few situations where you can really benefit from -3dB @ 200kHz if you pay close attention to stability etc.
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Old 9th March 2005, 02:41 AM   #28
thanh is offline thanh  Viet Nam
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Quote:
My LM3886 chip amp sounds extremely harsh
Have you ever listened the sound of TDA7295?
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Old 9th March 2005, 05:15 AM   #29
tmblack is offline tmblack  United Kingdom
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I haven't tried the TDA7295.
Is that a smooth sounding one?

The current mirror seems to make the sound unnaturally crystallized.

Could this be the transistors used(2SA1015)?

Using resistor loads in LTP and current source sounds very natural.

Tom
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Old 9th March 2005, 12:06 PM   #30
MikeB is offline MikeB  Germany
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Hi Tom !

Can you show schematic of your amp ?

Mike
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