Big dynamics meets low gain? How?
I'm curious for more information on your method to make the unusual combination of good dynamics and low gain. Somehow you've resolved that conflict, and I'd sure like to know how.
Both please.Me or Walt Jung?
I'm curious for more information on your method to make the unusual combination of good dynamics and low gain. Somehow you've resolved that conflict, and I'd sure like to know how.
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Both please.
Why thank you.
It's funny that I never felt like I sacrificed "dynamics" for more loop gain. To be fair I have never dealt in depth with the 1875 (breadboarded one a long time ago and thought it was pretty good but I wasn't excited about it at the time). So in all fairness I could try a couple different gains and see what it's worth. I arrived on a gain of 12 as a contrived comprimise after scrutinising the data sheet for a while.
And I am a person that is very sensitive to the dynamic nature of reproduced music too. I can hear compression right away and if it's speaker compression it fatigues me in short order.
Many subtle distortions are caused by circuits that are not optimised, or to look at it objectively, contain errors. Knowing which errors are worth going the extra mile to correct for your particular application is the ace up your sleeve. Walt Jung goes into extreme detail on reducing or eliminating errors in circuits.
My personal experience is that dynamic deficiencies in an amplifier are power supply or headroom issues. A sagging power supply will help protect marginal devices with a smaller heatsink, but it will modulate the amplifier circuitry and introduce a source of distortion that could be subjectively described as "loss of dynamics" and objectively observed as actual distortion introduced by the modulating effect of the power supply.Devices with marginal thermal integrity (like a power chip or op amp in a headphone circuit) will be subject to instantaneous thermal modulation at a high frequency that produces a distortion profile that Walt Jung describes as "complex"in nature.
There are a million caveats and knowing which ones are relevant to your particular situation is a matter of knowledge, experience, and judgement. The internet makes it a million times easier because chances are that if you're having an issue so has somebody else.
If you think I always get a hole in one, you are mistaken. But I am tenacious at attacking issues and sometimes I am lucky enough to have that ace up my sleeve.
Well, I thought up a question.
Is it a good idea to have the feedback-shunt resistors meet up just one nfb-shunt cap, and a really similar scheme for using just one input cap as well? I was thinking about this because capacitors can vary by up to 20% which may be further magnified by the gain factor. It looks like my idea removes the cap differences at the expense of not removing the chip differences. Anyway, I was curious how its going with the Parallel LM1875?
Is it a good idea to have the feedback-shunt resistors meet up just one nfb-shunt cap, and a really similar scheme for using just one input cap as well? I was thinking about this because capacitors can vary by up to 20% which may be further magnified by the gain factor. It looks like my idea removes the cap differences at the expense of not removing the chip differences. Anyway, I was curious how its going with the Parallel LM1875?
First I will address your question.
Yes, there are advantages to utilising one feedback capacitor for the triple parallel amp. First, it will help with matching the amplifiers (although it should be a moot point if you placed your poles properly). Second it will reduce parts count, which is important for my application.
The caveat is that the "swamping" effect of the oversize capacitor will be reduced by a third. So, a 660 uF cap will provide the same performance as a 220 uF cap in a single amplifier application. The rule of thumb is to make the feedback pole one tenth the input pole. That way, there will be virtually no interaction of the poles and there will be virtually zero AC voltage across the feedback cap at any time. This means that you can use an electrolytic for the feedback cap with "virtually zero" distortion added by the cap. You should then choose the input cap for low distortion with AC voltages; in other words, not an electrolytic (ideally). There are many discussions of capacitor distortion with links to relevant articles right here on this website.
I have been working on layout of parts on my (small) circuit board. 3 amplifiers must fit on a 40x60 cm (approximately) board with input buffers and RF filters on a small separate board. Output RF chokes and output relays are on a seperate board (along with the output terminals). I have had a sudden influx of parts, chassis, etc (lots of good stuff ) as well as some decent vintage electronics with more to come. (Some of it even worked with little to no work, including a nice CD player and surprisingly decent preamplifier.) I will repair a couple of recievers and use them for a while while I revamp my beloved Nakamichi reciever and build my "ultimate" system.
So I've been sorting parts, working on layout, triaging my growing collection of vintage junk; as well as many activities not related to hi-fi/electronics. But I do have to build a couple of fairly original designs "from scratch" to meet a specific objective.
Yes, there are advantages to utilising one feedback capacitor for the triple parallel amp. First, it will help with matching the amplifiers (although it should be a moot point if you placed your poles properly
). Second it will reduce parts count, which is important for my application.The caveat is that the "swamping" effect of the oversize capacitor will be reduced by a third. So, a 660 uF cap will provide the same performance as a 220 uF cap in a single amplifier application. The rule of thumb is to make the feedback pole one tenth the input pole. That way, there will be virtually no interaction of the poles and there will be virtually zero AC voltage across the feedback cap at any time. This means that you can use an electrolytic for the feedback cap with "virtually zero" distortion added by the cap. You should then choose the input cap for low distortion with AC voltages; in other words, not an electrolytic (ideally). There are many discussions of capacitor distortion with links to relevant articles right here on this website.
I have been working on layout of parts on my (small) circuit board. 3 amplifiers must fit on a 40x60 cm (approximately) board with input buffers and RF filters on a small separate board. Output RF chokes and output relays are on a seperate board (along with the output terminals). I have had a sudden influx of parts, chassis, etc (lots of good stuff
) as well as some decent vintage electronics with more to come. (Some of it even worked with little to no work, including a nice CD player and surprisingly decent preamplifier.) I will repair a couple of recievers and use them for a while while I revamp my beloved Nakamichi reciever and build my "ultimate" system.So I've been sorting parts, working on layout, triaging my growing collection of vintage junk
; as well as many activities not related to hi-fi/electronics. But I do have to build a couple of fairly original designs "from scratch" to meet a specific objective.
nice solution. wondering though if the resistors at the non-inverting inputs should be larger value--a bit over 3k?
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