Hi,
I just built the inverted gainclone using LM3876. The changes were as follows
1> I used a 15-0-15 5 Amp transformer for the supplyand
2> I used 4700 uf capacitors as power supply buffers.
3> I even tried to paralleling 47uf at input making it 94uf but to no avail. Even my TDA2009 amp gives more bass.
Pls help.
I just built the inverted gainclone using LM3876. The changes were as follows
1> I used a 15-0-15 5 Amp transformer for the supplyand
2> I used 4700 uf capacitors as power supply buffers.
3> I even tried to paralleling 47uf at input making it 94uf but to no avail. Even my TDA2009 amp gives more bass.
Pls help.
Link provided
I used the design found at
http://www.decdun.fsnet.co.uk/gainclone.html
Please go to 'Building the amp' section for the circuit.
Regards,
Goldy
I used the design found at
http://www.decdun.fsnet.co.uk/gainclone.html
Please go to 'Building the amp' section for the circuit.
Regards,
Goldy
Don't forget that chip amps need a few days to 'break in' and all areas of performance, expecially bass, will improve a great deal within the first 100-or-so hours of use. Also, have you got a big enough heatsink attached as a bigger sink means more bass 
BTW, Nuuk's site (Decibel Dungeon) has schematics for amps based on the LM3875 chip - I presume this is what you mean...
BTW, Nuuk's site (Decibel Dungeon) has schematics for amps based on the LM3875 chip - I presume this is what you mean...
I am surprised
"You did adjust for the different pinout of the LM3876 from LM3875? You did use a suitable resistor in your mute enable/disable wiring?"
Yes I did.
"Don't forget that chip amps need a few days to 'break in' and all areas of performance, expecially bass, will improve a great deal within the first 100-or-so hours of use. Also, have you got a big enough heatsink attached as a bigger sink means more bass"
Does 'break-in' really have such a huge difference? Let me admit that I did not have a huge heatsink (I am running off a 15-0-15 supply). But how can heatsink affect bass. The heatsink were not too hot to justify a bigger one.
"You did adjust for the different pinout of the LM3876 from LM3875? You did use a suitable resistor in your mute enable/disable wiring?"
Yes I did.
"Don't forget that chip amps need a few days to 'break in' and all areas of performance, expecially bass, will improve a great deal within the first 100-or-so hours of use. Also, have you got a big enough heatsink attached as a bigger sink means more bass"
Does 'break-in' really have such a huge difference? Let me admit that I did not have a huge heatsink (I am running off a 15-0-15 supply). But how can heatsink affect bass. The heatsink were not too hot to justify a bigger one.
Yes, breaking in new components, solder joints, wiring, etc always takes time. On my first IGC I noticed a very big improvement in sound from one day to the next (leaving it on overnight) for about three days.
A big heatsink really does give a different sound - this is one of those things I have tried and can say worked for me. Using just a couple of small pc chip heatsinks the igc ran fine (not too warm) but changing just the heatsinks for larger 6mm thick aluminium L-sections gave a much more solid sound. Some people have done quite a lot of work into this - those that agree seem to think that it is to do with the lower resonance of more massive heatsinks having less of an influence on the chip (making it more stable).
A big heatsink really does give a different sound - this is one of those things I have tried and can say worked for me. Using just a couple of small pc chip heatsinks the igc ran fine (not too warm) but changing just the heatsinks for larger 6mm thick aluminium L-sections gave a much more solid sound. Some people have done quite a lot of work into this - those that agree seem to think that it is to do with the lower resonance of more massive heatsinks having less of an influence on the chip (making it more stable).
Hi goldyrathore;
I'm with Pink Mouse on this.
Check out the spec sheets on both chips - the LM3876 is pretty much dedicated to 8r loads (pg 9, "output power vs load resistance"), while the TDA2009 actually does better with 4r loads than 8r loads (pg 5, "output power vs supply voltage" - check out the 4r vs 8r curves!!). Thus if you're using 4r speakers, or if there's a big dip in the impedence somewhere in the midbass, it's going to suck the life right out of the system.
Good luck on it and all the best!
Morse
PS Yes, breakin CAN make a big improvement in the sound of some components IME, but the differences between those two chips performance into low z loads is eye-opening!
I'm with Pink Mouse on this.
Check out the spec sheets on both chips - the LM3876 is pretty much dedicated to 8r loads (pg 9, "output power vs load resistance"), while the TDA2009 actually does better with 4r loads than 8r loads (pg 5, "output power vs supply voltage" - check out the 4r vs 8r curves!!). Thus if you're using 4r speakers, or if there's a big dip in the impedence somewhere in the midbass, it's going to suck the life right out of the system.
Good luck on it and all the best!
Morse
PS Yes, breakin CAN make a big improvement in the sound of some components IME, but the differences between those two chips performance into low z loads is eye-opening!
Breakin and heatsinks.
Hi Goldyrathore,
Can we just call you Goldy ?
Break in of components was something that I was very skeptical about a few years ago. I have a CD67SE that was 'awful' and a Denon amp that sounded flat when I got them . As a result I hardly used them since I have other alternatives. Then the 'alternatives' went out of service due to upgrades and broken parts. So these units came back into service. Both went through opamp changes - obviously - but did not improve as much as desired. However they had to be used till the others came back on line. That was about 9 weeks or so. The transformation has been quite dramatic. I am sure more tweaks will improve this further , but it DID make a difference. So sit back and relax. Pass judgement after at least two weeks of use.
About the heatsink. Bass transients occur fast and if the heat sink is not adequate it will raise the junction temperature dramatically causing all kinds of problems. However when the transient is gone the temp falls. The duration is so short that it will not raise the temp of the heat sink significantly and you might hardly see any long term effect on the heatsink.
So use as big a heatsink as you can accomodate - within reason of course.
In addition , if you are using a 1000uF power supply cap as some people do , you probably will hardly get any bass due to power supply drop. Especially if the speaker impedance is low. Use at least 4700uf or preferably 10,000uF. I can hear lots of protests , but it is up to you to determine what sounds best in your system.
I am still working on my LM3886 gainclone with 4700uF supply caps per channel ( 4700+4700).
Cheers.
Ashok
Don't forget that the load on your preamp is 10K ohms. So check the output cap on your preamp. The one on the power amp is big enough but the one on the preamp output may be not big enough- if there is one over there.
Hi Goldyrathore,
Can we just call you Goldy ?
Break in of components was something that I was very skeptical about a few years ago. I have a CD67SE that was 'awful' and a Denon amp that sounded flat when I got them . As a result I hardly used them since I have other alternatives. Then the 'alternatives' went out of service due to upgrades and broken parts. So these units came back into service. Both went through opamp changes - obviously - but did not improve as much as desired. However they had to be used till the others came back on line. That was about 9 weeks or so. The transformation has been quite dramatic. I am sure more tweaks will improve this further , but it DID make a difference. So sit back and relax. Pass judgement after at least two weeks of use.
About the heatsink. Bass transients occur fast and if the heat sink is not adequate it will raise the junction temperature dramatically causing all kinds of problems. However when the transient is gone the temp falls. The duration is so short that it will not raise the temp of the heat sink significantly and you might hardly see any long term effect on the heatsink.
So use as big a heatsink as you can accomodate - within reason of course.
In addition , if you are using a 1000uF power supply cap as some people do , you probably will hardly get any bass due to power supply drop. Especially if the speaker impedance is low. Use at least 4700uf or preferably 10,000uF. I can hear lots of protests , but it is up to you to determine what sounds best in your system.
I am still working on my LM3886 gainclone with 4700uF supply caps per channel ( 4700+4700).
Cheers.
Ashok
Don't forget that the load on your preamp is 10K ohms. So check the output cap on your preamp. The one on the power amp is big enough but the one on the preamp output may be not big enough- if there is one over there.
Re: Breakin and heatsinks.
As I have been away from this Forum for some time, what I am going to say may have already been discussed.
The question on the capacitance being small if you want more bass can be solved by bi-amplifying. These chip amps are simple enough to use two of them with separate pots at the input to balance the levels of both sections.
Such a setup would work better if you are using a subwoofer, that is a 2-way for highs + mid/mid-low and a sub for the low.
Then you can use just 1000uF for the 2-way amp and 10,000uF or more for the sub amp.
A simple 2nd order filter at the input might do the cross (besides the passive xover inside the 2-way) or you may try an active one. My preference is for the former, to keep things simple.
Then you would have the best of both worlds.
Carlos
ashok said:
As I have been away from this Forum for some time, what I am going to say may have already been discussed.
The question on the capacitance being small if you want more bass can be solved by bi-amplifying. These chip amps are simple enough to use two of them with separate pots at the input to balance the levels of both sections.
Such a setup would work better if you are using a subwoofer, that is a 2-way for highs + mid/mid-low and a sub for the low.
Then you can use just 1000uF for the 2-way amp and 10,000uF or more for the sub amp.
A simple 2nd order filter at the input might do the cross (besides the passive xover inside the 2-way) or you may try an active one. My preference is for the former, to keep things simple.
Then you would have the best of both worlds.
Carlos
Hi there
May I add one more suggestion. In your first post you wrote:
If I am correct that translates to a 150VA trannie. Have you considered upgrading the trannie to a 220VA or better? I wuld go as far as suggesting you go as big as you can get. It is known that a 700VA trannie for a PRE-amp makes a HUGE difference over a 300VA, so my suggestion is not totally mad.
I would also suggest upping the total capacitance of the PSU. Adding some larger caps could just be beneficial to the low-end.
One last suggestion is this- if you're going to stay at low voltages, try experimenting with battery power. Find a shop that sells 2nd hand car batteries, and use that as the basis for your PSU. I would still suggest bridging the battery with a handful of small caps (1000uF down to 4.7uF) as this will just improve the 'speed'.
I hope this helps.
Enjoy,
Deon (who is far out there)
May I add one more suggestion. In your first post you wrote:
If I am correct that translates to a 150VA trannie. Have you considered upgrading the trannie to a 220VA or better? I wuld go as far as suggesting you go as big as you can get. It is known that a 700VA trannie for a PRE-amp makes a HUGE difference over a 300VA, so my suggestion is not totally mad.
I would also suggest upping the total capacitance of the PSU. Adding some larger caps could just be beneficial to the low-end.
One last suggestion is this- if you're going to stay at low voltages, try experimenting with battery power. Find a shop that sells 2nd hand car batteries, and use that as the basis for your PSU. I would still suggest bridging the battery with a handful of small caps (1000uF down to 4.7uF) as this will just improve the 'speed'.
I hope this helps.
Enjoy,
Deon (who is far out there
)
The amp that I built based on the same circuit that Goldy uses (but with the 3875 chip) produced almost too much bass. It had a single 120VA transformer!
I am sure that 700VA for a preamp makes a difference over a 300VA - but an improvement?
As others here, I suspect that the problem may lie with the speaker matching.
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