But seriously people,
This hype has gone far enough I think. The gainclone represents everthing I have learned to disdain: complex, diodes for biasing, IC, class AB, high open loop, high feedback ,etc, etc.
So how about a serious discussion about the equivalent circuits as published in the LM3875, LM3886 (and LM1875) datasheets.
Things like: Output stage, biasing arangment, input followers, Diff pair (1K resistors?), Dominating pole at 1KHz?...
And can somebody explain what a 1.5K resistor from output to V+ has for effect, besides the claim of much improve sound quality...
What would the LM3885 do compared to the LM3875 circuit.. more bias current? Simpler circuit (no muting)?
well I hope some serious post can end this hype..
Greetings,
Thijs
http://www.national.com/ds/LM/LM1875.pdf
http://www.national.com/ds/LM/LM3875.pdf
http://www.national.com/ds/LM/LM3886.pdf
This hype has gone far enough I think. The gainclone represents everthing I have learned to disdain: complex, diodes for biasing, IC, class AB, high open loop, high feedback ,etc, etc.
So how about a serious discussion about the equivalent circuits as published in the LM3875, LM3886 (and LM1875) datasheets.
Things like: Output stage, biasing arangment, input followers, Diff pair (1K resistors?), Dominating pole at 1KHz?...
And can somebody explain what a 1.5K resistor from output to V+ has for effect, besides the claim of much improve sound quality...
What would the LM3885 do compared to the LM3875 circuit.. more bias current? Simpler circuit (no muting)?
well I hope some serious post can end this hype..
Greetings,
Thijs
http://www.national.com/ds/LM/LM1875.pdf
http://www.national.com/ds/LM/LM3875.pdf
http://www.national.com/ds/LM/LM3886.pdf
Hi,
Yup. And it proves (again) that it is not so much WHAT you do that matters but HOW you do it. Back in the very old days (1980's) I build an active speaker based originally around a TDA2030 Application note circuit. I used a 55.25" Wideband Midrange, a 1" Dome Tweeter and two 8" Woofers in a slim tower.
This was later modified using a discrete active X-Over and using "current mode" drive on Midrange and Tweeter plus negative feedback on the Woofers. It sounded very good in the end, probably quite close in essential qualities to my "normal" setup which was either a DIY Speaker based on an EVI15 with an 8HD/1824M Midrange Horn and T35 Tweeter or East German Studio 8" Fullrange Drivers with studio Class A Push-Pull Pentode Amplifiers (EL34, very similar to V69).
Looking at the (simplified) equivalent circuits I notice a few things.
First, there is very very close thermal coupling and the output stage is quasi complementary, meaning a lot of the thermal issues found in discrete circuits (that is the much hyped "memory distortion" Lavardin goes on about) are surpressed by extremely close matching.
Also I suspect (can't be sure without seeing the Die) the output transistors are not single large power structures but arrays of parallel lower power on die structures which will be precision matched and much faster than normal "big" types.
Further, many emitter followers buffer critical nodes (BJT's draw a signal dependent input current, Buffering the base can drastically linearise the open loop behavious), something rarely seen in discrete circuits. Equally a lot of cascoding and active loading goes on |(again this improves linearity), again thing rarely seen in discrete circuits.
One of the reasons consequent buffering, cascoding and active loading is not much found in discrete circuitry is the space issue. Using consequently SMD components I suspect most of this would be easily implemented, but it makes DIY basically near impossible.
So, given the need for Class AB Operation and a "conventional" structure I feel that these chip amplifiers are better than MANY well respected discrete circuits. Also, keeping current loops short does help. Also, inverting the circuit helps, but that is equally applicable to discrete amplifiers.
Where I do agree to take exception is to declare the "gainclone" to be "the best amp ever". Nothing is ever THAT good that it gives all people all they want.
Sayonara
tschrama said:
Yup. And it proves (again) that it is not so much WHAT you do that matters but HOW you do it. Back in the very old days (1980's) I build an active speaker based originally around a TDA2030 Application note circuit. I used a 55.25" Wideband Midrange, a 1" Dome Tweeter and two 8" Woofers in a slim tower.
This was later modified using a discrete active X-Over and using "current mode" drive on Midrange and Tweeter plus negative feedback on the Woofers. It sounded very good in the end, probably quite close in essential qualities to my "normal" setup which was either a DIY Speaker based on an EVI15 with an 8HD/1824M Midrange Horn and T35 Tweeter or East German Studio 8" Fullrange Drivers with studio Class A Push-Pull Pentode Amplifiers (EL34, very similar to V69).
Looking at the (simplified) equivalent circuits I notice a few things.
First, there is very very close thermal coupling and the output stage is quasi complementary, meaning a lot of the thermal issues found in discrete circuits (that is the much hyped "memory distortion" Lavardin goes on about) are surpressed by extremely close matching.
Also I suspect (can't be sure without seeing the Die) the output transistors are not single large power structures but arrays of parallel lower power on die structures which will be precision matched and much faster than normal "big" types.
Further, many emitter followers buffer critical nodes (BJT's draw a signal dependent input current, Buffering the base can drastically linearise the open loop behavious), something rarely seen in discrete circuits. Equally a lot of cascoding and active loading goes on |(again this improves linearity), again thing rarely seen in discrete circuits.
One of the reasons consequent buffering, cascoding and active loading is not much found in discrete circuitry is the space issue. Using consequently SMD components I suspect most of this would be easily implemented, but it makes DIY basically near impossible.
So, given the need for Class AB Operation and a "conventional" structure I feel that these chip amplifiers are better than MANY well respected discrete circuits. Also, keeping current loops short does help. Also, inverting the circuit helps, but that is equally applicable to discrete amplifiers.
Where I do agree to take exception is to declare the "gainclone" to be "the best amp ever". Nothing is ever THAT good that it gives all people all they want.
Sayonara
This is a good link http://home.student.utwente.nl/f.s.bouwman/audio/thor-amp.html
Check Gaincard by 47 Labs.
Check Gaincard by 47 Labs.
I think I have to take exception tschrama. I'm not saying that the gainclone is the be-all-end-all of amplifiers, but it is quite possibly a very good one.
1. It measures quite well
2. Many respected people (DIY people, not Stereophile people) have commented favorably on the sound
3. The design is good enough to be commercially successful at an astronomical price
Now, if it "represents all you have come to disdain" with respect to topology, where is the error? Possibly it sounds bad due to a flawed topology. Possibly your disdain for the topology is flawed.
Kuei Yang Wang seems to have made the important point: perhaps the flaw was not in the topology, but in our ability to implement it with the sophistication allowed by modern manufacturing technology. Food for thought.
1. It measures quite well
2. Many respected people (DIY people, not Stereophile people) have commented favorably on the sound
3. The design is good enough to be commercially successful at an astronomical price
Now, if it "represents all you have come to disdain" with respect to topology, where is the error? Possibly it sounds bad due to a flawed topology. Possibly your disdain for the topology is flawed.
Kuei Yang Wang seems to have made the important point: perhaps the flaw was not in the topology, but in our ability to implement it with the sophistication allowed by modern manufacturing technology. Food for thought.
Alright alright...I'll give this amp a try (since it is so simple).
I guess this is the place to start:
http://www.geocities.com/rjm003.geo/rjmaudio/diy_gc.html
however, I would like to build the 50W version...should be similar, any schematics around here?
btw, does someone have pictures of the inside of the original gaincard?
any additional info appreciated.
I guess this is the place to start:
http://www.geocities.com/rjm003.geo/rjmaudio/diy_gc.html
however, I would like to build the 50W version...should be similar, any schematics around here?
btw, does someone have pictures of the inside of the original gaincard?
any additional info appreciated.
I found good info at the Amp Chip board:
http://pub4.ezboard.com/ffakeidsfrm1
If you click on the circuit "banner" at the top of the page, it will take you to the Thorsten inverted design that is so popular. I built a 2 channel amp based on this circuit with LM3875's, except I did not include the cap between V- and V+ or the 0.22ohm resistor on the output. I have had zero stability problems, and noise is barely audible at full volume with my ear at the speaker.
For a project this easy and cheap, I am VERY pleased. I've been enjoying it for several months now.
-f4
http://pub4.ezboard.com/ffakeidsfrm1
If you click on the circuit "banner" at the top of the page, it will take you to the Thorsten inverted design that is so popular. I built a 2 channel amp based on this circuit with LM3875's, except I did not include the cap between V- and V+ or the 0.22ohm resistor on the output. I have had zero stability problems, and noise is barely audible at full volume with my ear at the speaker.
For a project this easy and cheap, I am VERY pleased. I've been enjoying it for several months now.
-f4
I'm building a 4 channel gainclone amp that will drive two sets of Tangband (w3-871s) based speakers, and I was wondering about potentiometer choices. I'd like to have a master volume control, and then a volume knob for each channel. I guess that would mean a 50k logarithmic stereo pot, and 4 mono 50k log pots.
Being of frugal-phile disposition, I'd prefer not to spend Black Beauty prices for my attenuators.. Any suggestions?
--Jordan
Being of frugal-phile disposition, I'd prefer not to spend Black Beauty prices for my attenuators.. Any suggestions?
--Jordan
This is the part that I have yet to understand. Even exotic Gaincloen implementations are very affordable. One would be hard pressed to spend $400 on the parts, even at full pop retail mail order prices. To spend $3000+ for the amp seems...well at least questionable to someone who has built more complex devices from scratch.
I have a stack of LM3886T as well as some of the Alesis modules from Apex Jr on my desk this week. I hope to have a 6 channel power amp by the end of the month. This I will use to drive in-ceiling speakers in several zones throughout my home.
Michael
Grataku;
I am the first to admit that I know nothing about the current cutting edge of technology in regard to DIY amps. You may have built IC amps in the 70's and they sounded dreadful, fair enough, I am not arguing.
But, I have listened to my iterations of inverted gainclones in comparison to commercial amps, not mass market, but up to the £4000 high end price range, and although they don't have everything they are a fair comparison.
I too am confused, it goes against everything I ever thought about Hi Fi, but I built some, and I listened, and I was blown away...
I am the first to admit that I know nothing about the current cutting edge of technology in regard to DIY amps. You may have built IC amps in the 70's and they sounded dreadful, fair enough, I am not arguing.
But, I have listened to my iterations of inverted gainclones in comparison to commercial amps, not mass market, but up to the £4000 high end price range, and although they don't have everything they are a fair comparison.
I too am confused, it goes against everything I ever thought about Hi Fi, but I built some, and I listened, and I was blown away...
pinkmouse said:
I had the same experience when i slid my BD-Pipes with the $50 USD worth of Radio Shack drivers in where the big-buck ESLs had stood -- it was only supposed to be temporary. I'm not saying the pipes were better sounding than the ESLs but at least as musical and allowed me to start playing with SE tube amps....
dave
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