Your readings are not reversed, the offset is just lower. I used 50K pot you are using 25K that one reason it's lower. The offset is almost always lower with volume down.
Also, those values are quite typical and that the amp reacts for volume change may indicate that both chips work fine. It's just connection of the signal is somehow lost, check also power supply connetion.
BTW, check this post for offset measured for a batch of chips: http://www.diyaudio.com/forums/showthread.php?postid=1524877#post1524877
Also, those values are quite typical and that the amp reacts for volume change may indicate that both chips work fine. It's just connection of the signal is somehow lost, check also power supply connetion.
BTW, check this post for offset measured for a batch of chips: http://www.diyaudio.com/forums/showthread.php?postid=1524877#post1524877
found the problem!
seems I put too much heat on the right channel #2 pin on the nobel pot, and melted it inside.
edit: I was able to fix it by mashing some solder wick on the plate, but I'm getting 1.8 ohms of resistance.
I guess I need a new pot. What would you recommend? 50k with a shunt? I have a spare 100k noble, can I use that?
seems I put too much heat on the right channel #2 pin on the nobel pot, and melted it inside.
edit: I was able to fix it by mashing some solder wick on the plate, but I'm getting 1.8 ohms of resistance.
I guess I need a new pot. What would you recommend? 50k with a shunt? I have a spare 100k noble, can I use that?
.Just need to find a nice case.
Master Piece
Superb Tutorial Peter !
A lot Of new things found here
This is out of my expectation
All you give to forum is your commercial amp
Wonderful !
Maybe you will invention a new Class A Amp ?
Who was take the picture when you soldering ?
A great respect from your friend
regards, jeffry
Superb Tutorial Peter !
A lot Of new things found here
This is out of my expectation
All you give to forum is your commercial amp
Wonderful !
Maybe you will invention a new Class A Amp ?
Who was take the picture when you soldering ?
A great respect from your friend
regards, jeffry
Dear Casiomax
You can find standart transformer in Glodok Harco
But hear that hum in transformer
For Better option, order from our neighbour country
http://singapore.rs-online.com/web/...&searchTerm=nuvotem+300va+2x0-25v+sec&x=0&y=0
email me if you need more information
casiomax said:
You can find standart transformer in Glodok Harco
But hear that hum in transformer
For Better option, order from our neighbour country
http://singapore.rs-online.com/web/...&searchTerm=nuvotem+300va+2x0-25v+sec&x=0&y=0
email me if you need more information
Peter,
I’ve had a quick search, and can’t find an answer to my query. I have built an Audiosector LM3875 kit in a dual mono configuration with a separate passive pre amp. I have used 2 identical 120VA, 18-0-18v torroidal transformers. The amp is used to drive 8ohm speakers.
Due to space limitations (new furniture), I have no room for the pre. I now need to turn the amp into a stereo integrated amp. To save me buying another transformer, could I get away with either using 1x 120VA transformer (low power I know, but I don’t listen loud anyway), or could I safely parallel the 2 transformers to give more power? What are the grounding options?
I’ve had a quick search, and can’t find an answer to my query. I have built an Audiosector LM3875 kit in a dual mono configuration with a separate passive pre amp. I have used 2 identical 120VA, 18-0-18v torroidal transformers. The amp is used to drive 8ohm speakers.
Due to space limitations (new furniture), I have no room for the pre. I now need to turn the amp into a stereo integrated amp. To save me buying another transformer, could I get away with either using 1x 120VA transformer (low power I know, but I don’t listen loud anyway), or could I safely parallel the 2 transformers to give more power? What are the grounding options?
zebra100 said:
I understand you want to convert dual mono amp into stereo unit with a potentiometer at the input, hence the integraterd version.
If you connect two transformers in parallel, you will be getting more power only into low impedance loads, when single transformer couldn't before provide more power.
Otherwise there is not much gain in using transformers in parallel, it may actually degrade the sound.
If one 120VA transformer worked fine with a single channel, it might as well work fine with both channels.
Besides, if you are considering using 2 transformers in parallel, why not use them as previously, one per channel?
British Transformers
I was reading Peter's thread with great interest. I noted that several people have asked where to find toroids in England. I have found that rs-online sell a 160VA 2 X 25V for a total of £18-95. A very nice price. I have not tried one but you can find it at www.uk.rs-online.com The manufacturer is Nuvotem and the part no. is 0160P1-2-025. I hope this is of use. Barry
I was reading Peter's thread with great interest. I noted that several people have asked where to find toroids in England. I have found that rs-online sell a 160VA 2 X 25V for a total of £18-95. A very nice price. I have not tried one but you can find it at www.uk.rs-online.com The manufacturer is Nuvotem and the part no. is 0160P1-2-025. I hope this is of use. Barry
There's only schematic, included with each LM4780 kit: http://audiosector.com/lm4780 amp.pdf (the green option for bridged, red for parallel configurations).
I will be soon building more serious LM4780 bridged amps for my personal use, so some guide will be posted here as well.
I will be soon building more serious LM4780 bridged amps for my personal use, so some guide will be posted here as well.
Transformers (UK & Europe)
As per Peter's recommendation for Polish transformers I bought two 22-0-22 300va transformers from Toroidy (http://www.toroidy.pl/index.php?option=com_content&task=view&id=6&Itemid=13) with which I have been very happy. I am just about to order some 25-0-25 300va from them. They are not cheap but they are well made - please see for both the details of the transformers (in Polish!!) and Peter's use of them - http://www.diyaudio.com/forums/showthread.php?s=&postid=930263&highlight=#post930263
As per Peter's recommendation for Polish transformers I bought two 22-0-22 300va transformers from Toroidy (http://www.toroidy.pl/index.php?option=com_content&task=view&id=6&Itemid=13) with which I have been very happy. I am just about to order some 25-0-25 300va from them. They are not cheap but they are well made - please see for both the details of the transformers (in Polish!!) and Peter's use of them - http://www.diyaudio.com/forums/showthread.php?s=&postid=930263&highlight=#post930263
I've been reading around and it seems people recommend increased capacitance on the power rails. I've got some 2200uf caps that i was thinking of trying in the LM4780 kit, would this have any negative effect ?
also how do i rig the inputs for bridge mode ? i.e 2 chips in bridged mode left and right. The diagram provided with the kit shows two inputs for bridge mode. I'm abit confused.
cheers
also how do i rig the inputs for bridge mode ? i.e 2 chips in bridged mode left and right. The diagram provided with the kit shows two inputs for bridge mode. I'm abit confused.
cheers
The diagram included with kits shows 2 options: parts and connections marked in red are for parallel configuration only, those marked in green are for stereo or bridged setup: http://audiosector.com/lm4780 amp.pdf
More info was posted on a forum: http://www.diyaudio.com/forums/showthread.php?postid=636565#post636565
It is no problem to add larger caps; depending on a system they may bring improvement, but not neccessarily.
More info was posted on a forum: http://www.diyaudio.com/forums/showthread.php?postid=636565#post636565
It is no problem to add larger caps; depending on a system they may bring improvement, but not neccessarily.