Hi Guys
Another noob question, I understand the importance of matching.
Question : aside from matching of output transistors, are the rest
of the transistors in the preceding stage very important towards
SQ as well ?
Thks
Another noob question, I understand the importance of matching.
Question : aside from matching of output transistors, are the rest
of the transistors in the preceding stage very important towards
SQ as well ?
Thks
Hi,
if there's a LTP input stage, output DC Offset will benefit from matching the transistor pair(s). No clue if it may affect sound quality also, though.
Best regards!
if there's a LTP input stage, output DC Offset will benefit from matching the transistor pair(s). No clue if it may affect sound quality also, though.
Best regards!
The differential pair that is used as the front end of many amplifiers must be matched, either with two near identical transistors or a method of balancing the Hfe with a pre set pot. As long as the rest of the transistors have at least the Hfe required to produce the current required to drive the loudspeaker, as per the design, there is no need for matching as the feedback loop takes care of any errors and reduces the errors to near zero.
For an example in theory, if you require 10A drive on the output stage, the output transistors have an Hfe of a minimum 20 then the drivers need an Hfe of say 100 if there is 5mA available from the voltage amplifier. 5mA X 100 = 500mA X 20 = 10A available from the output.
Early designs used the maximum Hfe as a current limit.
For an example in theory, if you require 10A drive on the output stage, the output transistors have an Hfe of a minimum 20 then the drivers need an Hfe of say 100 if there is 5mA available from the voltage amplifier. 5mA X 100 = 500mA X 20 = 10A available from the output.
Early designs used the maximum Hfe as a current limit.
In general, what KP, Jon said.
The Diff pair is the most important circuit to ensure they are matched
including thermally (T/C coefficient) matching/sharing if possible.
If you amp/unit already has a dual transistor that is a diff pair in one
devise (multi pins) or came with them, unless they are damaged, etc
it will be hard to beat and maybe not worth the effort as you could
easily make it worse.
Output matching is important if you are looking for lowest distortion.
Motorola, and on some data sheets will advise that matched output
devices can lower distortion 10 times.
Cheers,
The Diff pair is the most important circuit to ensure they are matched
including thermally (T/C coefficient) matching/sharing if possible.
If you amp/unit already has a dual transistor that is a diff pair in one
devise (multi pins) or came with them, unless they are damaged, etc
it will be hard to beat and maybe not worth the effort as you could
easily make it worse.
Output matching is important if you are looking for lowest distortion.
Motorola, and on some data sheets will advise that matched output
devices can lower distortion 10 times.
Cheers,
Thank you SynTronx
Well I had to replace a a pair of 2n5401 on one module
of my amp but they aren't match so I have a much higher
off set on this module.
Oh may I ask, it seems that input differential pair is almost
the defacto standard in SS amps. Is there a reason why &
can they not be replaced by other input stage design like
example SE.
Thank you kindly
Well I had to replace a a pair of 2n5401 on one module
of my amp but they aren't match so I have a much higher
off set on this module.
Oh may I ask, it seems that input differential pair is almost
the defacto standard in SS amps. Is there a reason why &
can they not be replaced by other input stage design like
example SE.
Thank you kindly
Sumotan,
It is that way for a reason. It gets rid of all the common mode noise.
Everything we do now days is bombarded by signals at various
frequencies, cell phones, wi fi, spurious electrical noise, TVs,
radio broadcasts, LEDs, transformers, toasters, refrigerators,
automobiles, motor cycles, etc.
Anything we plug into the amp will cause noise, but, if we have a
differential pair input devise, all this crap get blocked/filtered/canceled
because the signal is then split 180 degrees out of phase and this cancels out
all the noise it picked up, called common mode noise.
Hope that helps,
Cheers,
It is that way for a reason. It gets rid of all the common mode noise.
Everything we do now days is bombarded by signals at various
frequencies, cell phones, wi fi, spurious electrical noise, TVs,
radio broadcasts, LEDs, transformers, toasters, refrigerators,
automobiles, motor cycles, etc.
Anything we plug into the amp will cause noise, but, if we have a
differential pair input devise, all this crap get blocked/filtered/canceled
because the signal is then split 180 degrees out of phase and this cancels out
all the noise it picked up, called common mode noise.
Hope that helps,
Cheers,
The diff pair needs to be matched in order for the subtraction to be accurate. This can be accomplished by either matching the transistors themselves or by local degeneration (if the drop in open loop gain can be afforded). One reason singleton input stages often sound really nice is that there is no critical matching of a pair for the feedback to work as it is supposed to. A badly unbalanced diff pair will sound terrible, even with high feedback factors. To get to the theoretical distortion levels you can get to with most designs you need a decent match for vbe and hfe at ic. D.C. Offset is often quoted as the reason but that is the least of your worries.
Matching outputs is needed within a parallel bank - the lower the emitter resistor value the more critical for current sharing.
Matching outputs is needed within a parallel bank - the lower the emitter resistor value the more critical for current sharing.
Differential inputs make it easy to get close to zero volts dc on the output.
Single ended input amplifiers eg the Quad 303 usually end up with output capacitors
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