I am paralleling 2 LM4780 chips per channel fo my amp.
I have the power wired, but I am unsure of how to wire the signal paths. Both IN AND OUT.
I have ideas but thought I better ask before I see that magic black smoke!!LOL
Do I just run the + signal to one chip and the - to the other and then the corresponding polarity to the output jack?
*A diagram would be nice*
I am using the kits from audiosector.com.
Thanks a ton,
Dominick
I have the power wired, but I am unsure of how to wire the signal paths. Both IN AND OUT.
I have ideas but thought I better ask before I see that magic black smoke!!LOL
Do I just run the + signal to one chip and the - to the other and then the corresponding polarity to the output jack?
*A diagram would be nice*
I am using the kits from audiosector.com.
Thanks a ton,
Dominick
Read LM4780's datasheet.There is a schematic of paralell config.
If the power supply is wired correctly,you shouldn't smoke LMs that easy.
A common problem is when there is no insulation washer between chip and heat sink(chip has -Vs connected to its case). If the sink is grounded , the power supply is usually powerful enough to blow IC in chunks.I have done it by myself once 🙂.
Regards ,
Lukas.
If the power supply is wired correctly,you shouldn't smoke LMs that easy.
A common problem is when there is no insulation washer between chip and heat sink(chip has -Vs connected to its case). If the sink is grounded , the power supply is usually powerful enough to blow IC in chunks.I have done it by myself once 🙂.
Regards ,
Lukas.
I dont think that my question was understood.
I have 2 chips already wired in parallel. Now I need to know how to parallel the paralelled chips!!
Dominick
I have 2 chips already wired in parallel. Now I need to know how to parallel the paralelled chips!!
Dominick
Good observation.
That is exactly why I am doing it.
I intend on using this amp on my Martin Logan Ascent i speakers.
I called the company direct and they said that the speakers run at 2.5 ohms @ 20k.
Dominick
That is exactly why I am doing it.
I intend on using this amp on my Martin Logan Ascent i speakers.
I called the company direct and they said that the speakers run at 2.5 ohms @ 20k.
Dominick
2.5 ohms...that would run fine just with a parallel lm4780. 1 x 4780 parallel should give you about 120w @ 2 ohms I'm pretty sure.
Did you have a heatsink on it? It shouldn't be a problem at all. People use the paralleled lm4780 setup from brian at chipamp.com for 2 ohms.
**edit**
Here is the schematic they use:
http://chipamp.com/lm4780.pdf
**edit**
Here is the schematic they use:
http://chipamp.com/lm4780.pdf
LM3886s can stand continous short circuit and has lots of protection.
Adding more in parallel may even worsen results , if ICs have DC offsets greater than a few mV.
Adding more in parallel may even worsen results , if ICs have DC offsets greater than a few mV.
I found it necessary to add the optional Ci capacitors (shown on the datasheet) for unity gain at DC on my parallel 4780. Without it the amp got quite warm before even hooking it up to speakers. Perhaps this is what happened to you?
I appreciate all of the suggestions, but I am sure that the amop cannot handle the ML speakers with one ship per channel. Before running the ML's, I used the amp for about 5 hours STRAIGHT on an 8 ohm load. Then, the next day, it blew with the logans in 1 minute.
I have since ONLY replaced the 1 chip and have probably used the amp on an 8 ohm load for about 50 more hours with no problems what so ever.
I already have the 2 chips per channel comleted....
I just need to no how to run the input/output signals.
UPDATE:
Last night I ran the sig in and sig g to both chips and ran the out from one chip and the out g from the other.
Funny thing is I could here a light distorted sound from the 8 ohm speaker.
When I turned the amp on, it was blaring so loud that I couldnt tell if the distortion was from the amp or if it was just too loud for the speaker.
I rolled the pot to the other side and the same thing occurs although this time I didnt get any light distorted sound prior to kicking on the amp???
Obviously I am doing something wrong but I think I am close.
HELP ME PLEASE,
Dominick
I have since ONLY replaced the 1 chip and have probably used the amp on an 8 ohm load for about 50 more hours with no problems what so ever.
I already have the 2 chips per channel comleted....
I just need to no how to run the input/output signals.
UPDATE:
Last night I ran the sig in and sig g to both chips and ran the out from one chip and the out g from the other.
Funny thing is I could here a light distorted sound from the 8 ohm speaker.
When I turned the amp on, it was blaring so loud that I couldnt tell if the distortion was from the amp or if it was just too loud for the speaker.
I rolled the pot to the other side and the same thing occurs although this time I didnt get any light distorted sound prior to kicking on the amp???
Obviously I am doing something wrong but I think I am close.
HELP ME PLEASE,
Dominick
I think that the main problem is NOT related with low drive capability.
2.5 ohms is not so low.
I have had some experience with shorting outputs of LMs , and they stand this easy , even in bridged configs.
In your place , i would try just a single LM3886 and see what happens.
With paralelling , the chips may start to fight in some cases(especially if they oscillate).
Oscillation could be your problem.
Try placing ~0.5 ohm resistor at ouput of your amp.
Also , check if chips don't get hot while not playing sound.
Have you wired everyting to a single ground poit ?
2.5 ohms is not so low.
I have had some experience with shorting outputs of LMs , and they stand this easy , even in bridged configs.
In your place , i would try just a single LM3886 and see what happens.
With paralelling , the chips may start to fight in some cases(especially if they oscillate).
Oscillation could be your problem.
Try placing ~0.5 ohm resistor at ouput of your amp.
Also , check if chips don't get hot while not playing sound.
Have you wired everyting to a single ground poit ?
I did notice that one of the two chips didn't get warm when I turned the amp on for a few secs.
But I still got a loud distorted sound.
Does this mean that one chip is not turning on?
I don't know what this means?
Dominick
But I still got a loud distorted sound.
Does this mean that one chip is not turning on?
I don't know what this means?
Dominick
I only need to use the out on one chip and the out ground on the other, right?
or,
Do I need to connect the out and ou ground of both chips to the speaker terminals?
Dominick
or,
Do I need to connect the out and ou ground of both chips to the speaker terminals?
Dominick
In order to parallel two parallel configured LM4780 chips, the best way it to position the boards back to back. This will simplify ground connections.
For both boards, you connect together: OG, SG, //OUT and IN. It's better to use two R4 resistors (one per board), however they will be in parallel and this will lower input impedance to 10K (this will also produce much less DC offset). Alternatively, you can substitude 22K resistors with 40K resistors, for 20K total shunt input impedance.
Everything else is configured the same as per schematic for parallel setup here: http://www.audiosector.com/lm4780 amp.pdf
PS wires cannot be connected with short jumpers (between two boards) as their access pads are not symetrical , you need to use longer pieces of wire. Both grounds connections (for two boards) can be as short as space between the boards ( as the pads are symetrical here).
For both boards, you connect together: OG, SG, //OUT and IN. It's better to use two R4 resistors (one per board), however they will be in parallel and this will lower input impedance to 10K (this will also produce much less DC offset). Alternatively, you can substitude 22K resistors with 40K resistors, for 20K total shunt input impedance.
Everything else is configured the same as per schematic for parallel setup here: http://www.audiosector.com/lm4780 amp.pdf
PS wires cannot be connected with short jumpers (between two boards) as their access pads are not symetrical , you need to use longer pieces of wire. Both grounds connections (for two boards) can be as short as space between the boards ( as the pads are symetrical here).
Attachments
Sorry I didnt understand what you were doing originally.
If one chip isnt functioning, Im sure you are going to have problems. I researched paralleling four LM3886 a while back and was told that the resistors used on the outputs should be 1% or better. Im guessing that the ones used on Peters boards (R8,9) are such. It was also suggested that I use 4700uf caps on each output, after the resistors, and then combine the outputs. This is suppose to prevent any DC interaction between the amplifiers.
It appears that this may be what was done on the Meier power amp:
http://www.meier-audio.homepage.t-online.de/index.htm
I havent gotten mine completed, so I cant comment on the success of this arrangement. Hope this is of some help.
amt
If one chip isnt functioning, Im sure you are going to have problems. I researched paralleling four LM3886 a while back and was told that the resistors used on the outputs should be 1% or better. Im guessing that the ones used on Peters boards (R8,9) are such. It was also suggested that I use 4700uf caps on each output, after the resistors, and then combine the outputs. This is suppose to prevent any DC interaction between the amplifiers.
It appears that this may be what was done on the Meier power amp:
http://www.meier-audio.homepage.t-online.de/index.htm
I havent gotten mine completed, so I cant comment on the success of this arrangement. Hope this is of some help.
amt
I just tested each board seperatly and they are producing an audio signal to the speaker although with a very slight hum.
The wierd thing is that on one board, the chip never even warms up??
But both boards play?? The other chip gets warm regardless of the board with the audi signal??
Wierd huh?
IDEAS?
Dominick
Peter, I will try to understand you post!lol And execute!
The wierd thing is that on one board, the chip never even warms up??
But both boards play?? The other chip gets warm regardless of the board with the audi signal??
Wierd huh?
IDEAS?
Dominick
Peter, I will try to understand you post!lol And execute!
In combining 2 parallel LM4780 chips (4 x LM3886), it may be a good idea to increase output resistors to 0.22R or even a bit more.
I also have some chips that are measured for DC offset. Paralleling chips with similar DC offset could be advantegous here.
I also have some chips that are measured for DC offset. Paralleling chips with similar DC offset could be advantegous here.
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