make sure the GC is not a GC.
Add all the components to convert it to a normal AC coupled chipamp, with correct non-inverting gain, a Proper PSU with proper Decoupling, a Zobel or better a Thiele Network on the output and low pass+ high pass filters on the input.
When that is all attended to design/build your buffer/pre-amp.
Add all the components to convert it to a normal AC coupled chipamp, with correct non-inverting gain, a Proper PSU with proper Decoupling, a Zobel or better a Thiele Network on the output and low pass+ high pass filters on the input.
When that is all attended to design/build your buffer/pre-amp.
Thanks for all the input cap advice. I have it in a more permanent home that doesn't involve an ipod 
, so I think I'm going to opt to leave the input cap out for now.
Peter I think you did a fine job getting the point across that the amp is DC coupled. I don't see any reason you should be in the hot seat. I did heed your advice and check the bias before connecting speakers, and the amp was functioning fine with the ipod for several days before Murphy decided to pay a visit.
, so I think I'm going to opt to leave the input cap out for now.Peter I think you did a fine job getting the point across that the amp is DC coupled. I don't see any reason you should be in the hot seat. I did heed your advice and check the bias before connecting speakers, and the amp was functioning fine with the ipod for several days before Murphy decided to pay a visit.
use of LM3875 kit from Audiosector with a 4 ohm loudspeaker
Hi all
I’m very interested in build a LM chip-based amplifier for using it in my secondary system, connected to an old Meridian 206 CD player and a pair of DIY loudspeakers. My doubt is what chip to use. The LM3875 kit from Audiosector is very interesting, because there is a Premium version available (chips selected for very low DC-offset, high quality components), its rectifier PCB is very small (the same size as the amplifier PCB) and Peter Daniel gives very good technical support for builders here. However, I’ve read that this chip is less appropriate for low impedance loudspeakers that the LM3886, so I hope you can give me some advice.
The loudspeaker I’m going to drive with the chipamp is a small DIY loudspeaker from the Intertechnik catalogue, the model called “Kohärenz”, based on the Seas MP14S/H719 4 inch 2-way coaxial driver. My 15x15x30cm enclosure (internal volume= 4.3 litres) is a little taller than the described in the kit.
The loudspeakers are used in a small room (11 sq. metres), placed directly on a desk and against the rear wall. I like its coherent, clear and controlled sound. I listen to them from two different positions (one at 60 cm and other at 2 m distance), mainly classical music at low volume, and I’m not a bass-freak. According to the Intertechnik catalogue, the Kohärenz bass driver is 4 ohms nominal, and the impedance vs frequency curve is as shown in the attached image. It is rather low, with a minimum of 3.5 ohm at 300 Hz.
Do you think the LM3875 is suitable for this specific loudspeaker and my listening habits, or would the LM3886 be a better choice? If so, is it possible to use the Audiosector kit with the LM3886 chip or I need to buy the Chipamp.com kit?
Thanks in advance
Jose
Hi all
I’m very interested in build a LM chip-based amplifier for using it in my secondary system, connected to an old Meridian 206 CD player and a pair of DIY loudspeakers. My doubt is what chip to use. The LM3875 kit from Audiosector is very interesting, because there is a Premium version available (chips selected for very low DC-offset, high quality components), its rectifier PCB is very small (the same size as the amplifier PCB) and Peter Daniel gives very good technical support for builders here. However, I’ve read that this chip is less appropriate for low impedance loudspeakers that the LM3886, so I hope you can give me some advice.
The loudspeaker I’m going to drive with the chipamp is a small DIY loudspeaker from the Intertechnik catalogue, the model called “Kohärenz”, based on the Seas MP14S/H719 4 inch 2-way coaxial driver. My 15x15x30cm enclosure (internal volume= 4.3 litres) is a little taller than the described in the kit.
The loudspeakers are used in a small room (11 sq. metres), placed directly on a desk and against the rear wall. I like its coherent, clear and controlled sound. I listen to them from two different positions (one at 60 cm and other at 2 m distance), mainly classical music at low volume, and I’m not a bass-freak. According to the Intertechnik catalogue, the Kohärenz bass driver is 4 ohms nominal, and the impedance vs frequency curve is as shown in the attached image. It is rather low, with a minimum of 3.5 ohm at 300 Hz.
Do you think the LM3875 is suitable for this specific loudspeaker and my listening habits, or would the LM3886 be a better choice? If so, is it possible to use the Audiosector kit with the LM3886 chip or I need to buy the Chipamp.com kit?
Thanks in advance
Jose
Attachments
just finished building my first gainclone - i'm measuring 23vac out of the transformer, and 30vdc across the binding posts. volume pot seems to have no effect.
any idea where i should start looking - i don't believe this is normal. no shorts/cold joints/etc. that i can find.
thx in advance.
-j.
any idea where i should start looking - i don't believe this is normal. no shorts/cold joints/etc. that i can find.
thx in advance.
-j.
Re: Re: use of LM3875 kit from Audiosector with a 4 ohm loudspeaker
My baffle is cut for an 8 Ohm woofer [16cm] and a 4 Ohm tweeter. I don't know what came over me to do that. To maintain the 8 Ohm load I've decided to add a second tweeter in series, but mounted offset in the rear of the speaker. I had some Infinity Reference Standard 2.5's that did that, though they were four Ohm, and were probably parallel, I can't recall. I have in hand 8 of the little neo tweeters so if I use an extra pair for impedance peace of mind I won't sweat it. The price was right...
Any thoughts on how the rear-firing tweeter would sound? I don't hear much of that these days but Linkwitz modified his Orions for an additional rear -firing tweeter and waxed eloquently about it. I can say that no ears died from my Infinitys either.
I can't quite get my brain around a series hook-up that allows the front tweeter to be L-Padded down to match the woofer but the rear one would be more effective if allowed its full efficiency, about 4 decibals higher, and end up at the desired 8-Ohm nominal.
I guess if I HAD to the rear tweeter could be after the L-Pad for simplicity, but I know it will nag me if I don't at least try some configuration...
Anybody have a quick and dirty schematic?
AndrewT said:
My baffle is cut for an 8 Ohm woofer [16cm] and a 4 Ohm tweeter. I don't know what came over me to do that. To maintain the 8 Ohm load I've decided to add a second tweeter in series, but mounted offset in the rear of the speaker. I had some Infinity Reference Standard 2.5's that did that, though they were four Ohm, and were probably parallel, I can't recall. I have in hand 8 of the little neo tweeters so if I use an extra pair for impedance peace of mind I won't sweat it. The price was right...
Any thoughts on how the rear-firing tweeter would sound? I don't hear much of that these days but Linkwitz modified his Orions for an additional rear -firing tweeter and waxed eloquently about it. I can say that no ears died from my Infinitys either.
I can't quite get my brain around a series hook-up that allows the front tweeter to be L-Padded down to match the woofer but the rear one would be more effective if allowed its full efficiency, about 4 decibals higher, and end up at the desired 8-Ohm nominal.
I guess if I HAD to the rear tweeter could be after the L-Pad for simplicity, but I know it will nag me if I don't at least try some configuration...
Anybody have a quick and dirty schematic?
Hi,
if using a 250VA smps to power one channel of chipamp, then try to explain where the speaker will get it's peak transient current demand.
A few clues to get you towards an answer.
An 8r0 load draws 2.7Aac from a 60W into 8r0 amplifier.
8r0 draws 3.9Apk from the same 60W amplifier.
8ohm speaker draws ~8Apk on longer term transients.
8ohm speaker draws <=12Apk on fast starting or fast stopping transients.
if using a 250VA smps to power one channel of chipamp, then try to explain where the speaker will get it's peak transient current demand.
A few clues to get you towards an answer.
An 8r0 load draws 2.7Aac from a 60W into 8r0 amplifier.
8r0 draws 3.9Apk from the same 60W amplifier.
8ohm speaker draws ~8Apk on longer term transients.
8ohm speaker draws <=12Apk on fast starting or fast stopping transients.
Hi Andrew, thanks.
The SWPS quoted was an example - it will deliver 10.5 amps, all I could glean before I had to dismount from the internet and resume family duties. The question I asked was badly phrased.
The speakers I'm going to be using have a nominal impedance of less than six ohms and have a nasty dip to under three. Is the Gainclone suitable for this type of load?
Given that I could just wire a pair of SMPS from my computer graveyard together, or buy a discrete one with the required -ve amperage required, would a PS as described on this thread be sonically superior? Has anyone tried a SMPS with this amp?
Yours in ignorance,
Jon
The SWPS quoted was an example - it will deliver 10.5 amps, all I could glean before I had to dismount from the internet and resume family duties. The question I asked was badly phrased.
The speakers I'm going to be using have a nominal impedance of less than six ohms and have a nasty dip to under three. Is the Gainclone suitable for this type of load?
Given that I could just wire a pair of SMPS from my computer graveyard together, or buy a discrete one with the required -ve amperage required, would a PS as described on this thread be sonically superior? Has anyone tried a SMPS with this amp?
Yours in ignorance,
Jon
I got the premium kit and put it together the other night. I experimented with shorting R1 and the difference is not subtle! Without R1, everything sounds much more detailed and it took alot of edge off the highs. I am comparing this to ICEPower ASC200 I have and I can say it's more detailed with better mid and highs.
However, I would like to have a little more bass. Would building a dual mono version help on the bass side? Or would I have to look into a bridged version?
However, I would like to have a little more bass. Would building a dual mono version help on the bass side? Or would I have to look into a bridged version?
toufu said:
Yes, indeed, in some setups omitting R1 makes substantial difference. I don't use it in my amps at all: http://www.diyaudio.com/forums/showthread.php?postid=1508778#post1508778
The advantage of dual mono was mentioned here: http://www.diyaudio.com/forums/showthread.php?postid=1517735#post1517735
Bridged version improves bass performance and adds authority, although you will need balanced source and the speakers are not recommended have less than 8 ohm impedance.
Lowering input gain
I've been wanting to build a gainclone for awhile to see what all the fuss is about. It would be my first DIY project. Not having a "bin" of accessories to pull from I found buying many of the misc. pieces like wire, solder, nice input/output connectors, case, heatsinks, power switch, led, ICE connection, torrid, etc., to start to get expensive. I found it easier to buy a lightly used well built unit for 1/2 what I would have paid to buy everything piece meal myself.
I ended up buying a superbly built LM3875 with 300V torrid, Black Gates, Caddock and Riken resistors in a solid well built case with very good heatsinks. Sweet!!!
I am using it in a second system with 6 ohm nominal speakers in a home office. I am using a Dared Sl2000A tube pre-amp and that's where the issue is. The input gain on the amp is way to high for a pre-amp. I need to know if I change the value of R3 (which is a Riken 680R 0.5w) to say something like 1.2K or 2.2K ohm Riken 0.5w if there will be any issues I need to be concerned about, or other areas that need modifying? I'm concerned about leaving the feedback resistor the same value and if the higher value R3 will upset the sound?
Is replacing R3 with a higher value the correct way to lower the input gain of the amp to run with a pre-amp?
I have to say I'm very impressed with the sound of this amp. Lots of bass and very detailed w/o being harsh. I think it's going to be a keeper.
TIA for the help
H9
I've been wanting to build a gainclone for awhile to see what all the fuss is about. It would be my first DIY project. Not having a "bin" of accessories to pull from I found buying many of the misc. pieces like wire, solder, nice input/output connectors, case, heatsinks, power switch, led, ICE connection, torrid, etc., to start to get expensive. I found it easier to buy a lightly used well built unit for 1/2 what I would have paid to buy everything piece meal myself.
I ended up buying a superbly built LM3875 with 300V torrid, Black Gates, Caddock and Riken resistors in a solid well built case with very good heatsinks. Sweet!!!
I am using it in a second system with 6 ohm nominal speakers in a home office. I am using a Dared Sl2000A tube pre-amp and that's where the issue is. The input gain on the amp is way to high for a pre-amp. I need to know if I change the value of R3 (which is a Riken 680R 0.5w) to say something like 1.2K or 2.2K ohm Riken 0.5w if there will be any issues I need to be concerned about, or other areas that need modifying? I'm concerned about leaving the feedback resistor the same value and if the higher value R3 will upset the sound?
Is replacing R3 with a higher value the correct way to lower the input gain of the amp to run with a pre-amp?
I have to say I'm very impressed with the sound of this amp. Lots of bass and very detailed w/o being harsh. I think it's going to be a keeper.
TIA for the help
H9
![URL]](/community/proxy.php?image=http%3A%2F%2F%5BURL%3Dhttp%3A%2F%2Fimg4.imageshack.us%2Fi%2Fampsch.jpg%2F%5D%5BIMGHTTPDEAD%5Dhttp%3A%2F%2Fimg4.imageshack.us%2Fimg4%2F800%2Fampsch.jpg%5B%2FIMGHTTPDEAD%5D%5B%2FURL%5D%5BURL%3Dhttp%3A%2F%2Fg.imageshack.us%2Fimg4%2Fampsch.jpg%2F1%2F%5D%5BIMGHTTPDEAD%5Dhttp%3A%2F%2Fimg4.imageshack.us%2Fimg4%2Fampsch.jpg%2F1%2Fw953.png%5B%2FIMGHTTPDEAD%5D%5B%2FURL%5D&hash=baba1a45273d7d0c9e5b4f7d662733a0)
The schematic seems to be fine, although quite complicated.
With a single transformer you can't really do dual mono. In such case I always recommend a single rectifier board shared between two amp channels: http://www.diyaudio.com/forums/showthread.php?postid=1518369#post1518369
With a single transformer you can't really do dual mono. In such case I always recommend a single rectifier board shared between two amp channels: http://www.diyaudio.com/forums/showthread.php?postid=1518369#post1518369