Hi guys, I just finnished building a Guitar amp that uses the LM3886 as the Power amp and a simple Dual opamp preamp circuit...The LM3886 circuit was the basic circuit from the Datasheet.... I have it powered from a 100Va 18v,0v,18v, Torroid with 8000uF of filtering on each Rail or 16000uF total....
It has 2 speakers with an adjustable JBL crossover , One speaker is a 6in 20w speaker and the other is a 12in of unknown wattage....
The problem (it has a few) is that it just doesn"t go as loud as it should ,My 15w Practice amp goes louder......
I think there might be a few things that Could possibly be causeing this , But I don"t know if any of these reasons are valid or not so I figured I would throw them out there and maybe someone could tell me if any of these things could be causeing the problem....
1) Maybe the Inductor I used on the output is too big ,The schematic called for to use 22 gauge wire and wrap it arround a 10R 2w resistor about 12 times, all I had was 18 gauge and I might have mistakenly put 12 or maybe more wraps arround it...
Could that cause low power output??
2) Maybe my Torroid isn"t powerfull enough to push the full 50w or so?? It is also a rather small in size torroid ,about half as small as my other 100vA torroid but the torroid was custom made for me and it says that is is 100vA at 2.38A.....
Could that cause low power output??
3) I made the PCB myself useing a 1oz copper board and the Traces are about 3mm wide at there smallest and about 10mm wide at there widest....
Could it be possible that the 1oz board isn"t thick enough to carry the power needed to run the chip at full volume??
4) I don"t know if this makes a differance but I used a 10K pot as the Volume knob for the power amp, would a Larger value like a 50K be better?? also Some of the Pots do not have a connection to ground and I do get a bit of a Hum , Should I solder a wire to the back of these pots to ground??
All of the Pots are wired off board and some of the leads are a bit long ,would this make the signal weaker??
5) The last thing I can think of is maybe the Crossover is makeing the signal weak?? or the fact that I am useing 2 speakers and the power is being distributed to 2 speakers makeing it half as loud??
Is there an easy way of adding another LM3886 chip to the circuit without haveing to mod the PCB? ,like wireing the Chip in paralell to the board useing P2P wireing and just wireing the leads of the first LM3886 to the leads of the second Lm3886?? would that work for increaseing the ouput power?? if so would I have to change any of the values of the resistors and caps on the board??
Sorry for all of the Stupid questions but there are so many things that seem like they could be a possible cause for the low output problem and I didn"t know if any of these were valid and didn"t really know were to start in finding the problem....
Thanx Guys....
It has 2 speakers with an adjustable JBL crossover , One speaker is a 6in 20w speaker and the other is a 12in of unknown wattage....
The problem (it has a few) is that it just doesn"t go as loud as it should ,My 15w Practice amp goes louder......
I think there might be a few things that Could possibly be causeing this , But I don"t know if any of these reasons are valid or not so I figured I would throw them out there and maybe someone could tell me if any of these things could be causeing the problem....
1) Maybe the Inductor I used on the output is too big ,The schematic called for to use 22 gauge wire and wrap it arround a 10R 2w resistor about 12 times, all I had was 18 gauge and I might have mistakenly put 12 or maybe more wraps arround it...
Could that cause low power output??
2) Maybe my Torroid isn"t powerfull enough to push the full 50w or so?? It is also a rather small in size torroid ,about half as small as my other 100vA torroid but the torroid was custom made for me and it says that is is 100vA at 2.38A.....
Could that cause low power output??
3) I made the PCB myself useing a 1oz copper board and the Traces are about 3mm wide at there smallest and about 10mm wide at there widest....
Could it be possible that the 1oz board isn"t thick enough to carry the power needed to run the chip at full volume??
4) I don"t know if this makes a differance but I used a 10K pot as the Volume knob for the power amp, would a Larger value like a 50K be better?? also Some of the Pots do not have a connection to ground and I do get a bit of a Hum , Should I solder a wire to the back of these pots to ground??
All of the Pots are wired off board and some of the leads are a bit long ,would this make the signal weaker??
5) The last thing I can think of is maybe the Crossover is makeing the signal weak?? or the fact that I am useing 2 speakers and the power is being distributed to 2 speakers makeing it half as loud??
Is there an easy way of adding another LM3886 chip to the circuit without haveing to mod the PCB? ,like wireing the Chip in paralell to the board useing P2P wireing and just wireing the leads of the first LM3886 to the leads of the second Lm3886?? would that work for increaseing the ouput power?? if so would I have to change any of the values of the resistors and caps on the board??
Sorry for all of the Stupid questions but there are so many things that seem like they could be a possible cause for the low output problem and I didn"t know if any of these were valid and didn"t really know were to start in finding the problem....
Thanx Guys....
I believe the Gain on the Preamp is about 50dB or higher but I have no idea what it is on the Power amp...Whatever the Gain is on the Basic implemtation of the LM3886 chip is what the gain is as I used the design directly from the Data sheet....
If I hook up a Distortion pedal and crank it up the Volume does get quite a bit louder .....
Cheers
I just checked the specs of the Preamp stage and it says that the Power amp stage has to have a Minimum Input sencitivity of at least 750mV to properly power the preamp stage and from looking through the LM3886 datasheet it says that the LM3886 has an input sencitivity of 894mV at a gain of 20 and 84mV at a gain of 200...What does this mean??....
Do you think the problem is that the Preamp isn"t putting out enough Signal for the Power amp??
If so do you know of a Guitar Preamp that would put out a very strong signal and also have a Good Crunchy Overdrive??
I built the PCB so I could easilly seperate the preamp and Power amp stages if one of them didn"t work out by simply cutting the PCB.....
Thanx
If I hook up a Distortion pedal and crank it up the Volume does get quite a bit louder .....
Cheers
I just checked the specs of the Preamp stage and it says that the Power amp stage has to have a Minimum Input sencitivity of at least 750mV to properly power the preamp stage and from looking through the LM3886 datasheet it says that the LM3886 has an input sencitivity of 894mV at a gain of 20 and 84mV at a gain of 200...What does this mean??....
Do you think the problem is that the Preamp isn"t putting out enough Signal for the Power amp??
If so do you know of a Guitar Preamp that would put out a very strong signal and also have a Good Crunchy Overdrive??
I built the PCB so I could easilly seperate the preamp and Power amp stages if one of them didn"t work out by simply cutting the PCB.....
Thanx
low output
If you built the chip amp via LM circuit the gain should be 27db giveing you an input senstivity around 700mv, IMHO I would drive the chip a little harder add a buffer with about 2 to 3db of gain, because when you add the distortion pedal you probably add some more overall gain.
driveing the chip harder, more output.
If you built the chip amp via LM circuit the gain should be 27db giveing you an input senstivity around 700mv, IMHO I would drive the chip a little harder add a buffer with about 2 to 3db of gain, because when you add the distortion pedal you probably add some more overall gain.
driveing the chip harder, more output.
Hi, Ok ,Actually there is a 4.7k resistor I can change in the preamp to Boost the gain so I"ll try changeing it to a 2.2k and see if that helps but If I don"t get enough gain I will add a Booster stage either after or before the preamp or maybe both....
Maybe some sort of multiple cascadeing fet gain stages with a NPN buffer on the output to lower output impedance??
I"ll give it a shot...Thanx
Maybe some sort of multiple cascadeing fet gain stages with a NPN buffer on the output to lower output impedance??
I"ll give it a shot...Thanx
Well the Transformer is a 18v,0v,18v AC transformer(it reads 21v AC without a Load) so after rectification and diode Voltage drop it is something like 24v DC....
So from going from the data sheet is should probably get a bit over 30w output power.....
Well I know for sure that I am not even getting 10w in loudness as my 15w Practice amp goes what seems twice as loud and my 15w Garnet tube amp (which is on the fritz right now) goes what seems like 4 times as loud.....
There are a couple things I am going to try to get more output power....
The first is changeing the gain set resistor from a 4.7k to a 2.2k which should increase the available gain....
I am also going to put a better opamp in the Preamp...I was going to use some OPA2134 that i had be I realized that I didn"t have them and only had some opa134 so I designed a small adapter PCB that converts two single opamps into a Dual opamp so I will make one and try a few Higher end Opamps that I have that are only singles like some OPA627 ,OPA602 and OPA134 and see how they sound in the circuit.....
I have also got a design for a Super Gain Booster/Overdrive circuit(It is basicly a high output distortion pedal) that Im going to install before the Preamp which should add that real crunchy loud distortion sound, It uses 4 Cascadeing low noise NPN transistor gain stages each with a Diode cliper which should add considerably to the signal the preamp gets and also have a low output impedance which means I get to use a bigger variety of Opamps for the preamp stage.....
Hopefully this will make it loud enough to at least jam and have a good crunchy distortion sound.....
I"ll let you know how it turns out.....
Cheers
So from going from the data sheet is should probably get a bit over 30w output power.....
Well I know for sure that I am not even getting 10w in loudness as my 15w Practice amp goes what seems twice as loud and my 15w Garnet tube amp (which is on the fritz right now) goes what seems like 4 times as loud.....
There are a couple things I am going to try to get more output power....
The first is changeing the gain set resistor from a 4.7k to a 2.2k which should increase the available gain....
I am also going to put a better opamp in the Preamp...I was going to use some OPA2134 that i had be I realized that I didn"t have them and only had some opa134 so I designed a small adapter PCB that converts two single opamps into a Dual opamp so I will make one and try a few Higher end Opamps that I have that are only singles like some OPA627 ,OPA602 and OPA134 and see how they sound in the circuit.....
I have also got a design for a Super Gain Booster/Overdrive circuit(It is basicly a high output distortion pedal) that Im going to install before the Preamp which should add that real crunchy loud distortion sound, It uses 4 Cascadeing low noise NPN transistor gain stages each with a Diode cliper which should add considerably to the signal the preamp gets and also have a low output impedance which means I get to use a bigger variety of Opamps for the preamp stage.....
Hopefully this will make it loud enough to at least jam and have a good crunchy distortion sound.....
I"ll let you know how it turns out.....
Cheers
Well I have the Speakers Connected to an adjustable JBL crossover which keeps the Impedance at a steady 8 Ohms and each of the 2 speakers are 8 ohms (the 6 in is rated at 20w and the 12 in power handleing is unknown)....
I guess the Crossover achieves this useing audio transformers as the crossover network has 2 transformers on it which I guess are for Impedance matching and it has a knob for adjusting the crossover frequency.....
I am about to start building the Booster circuit so I should hopefully be finnished tonight or tomorow...
Cheers
I guess the Crossover achieves this useing audio transformers as the crossover network has 2 transformers on it which I guess are for Impedance matching and it has a knob for adjusting the crossover frequency.....
I am about to start building the Booster circuit so I should hopefully be finnished tonight or tomorow...
Cheers
UPDATE: Well I finnished building the Booster circuit and installed it and made some other Mods and it is WAY LOUDER!! and it sounds FREAKIN AWESOME!! Compared to what it sounded like before and the crunchy overdrive this circuit produces is up there with some of the best Overdrive/Distortion pedals I have tried....
It still isn"t as Loud as I thought it would be but it is at least twice as loud or even 3 times as loud as before.... I still have some Hum problems and the scratchy Pots but it is a 300% improvement.....
This circuit is so simple also and only has maybe 25 parts and uses common transistors ,Resistors and diodes and a few small Polly Caps.....
If anyone is interested in this circuit I can post it for you....
Cheers
It still isn"t as Loud as I thought it would be but it is at least twice as loud or even 3 times as loud as before.... I still have some Hum problems and the scratchy Pots but it is a 300% improvement.....
This circuit is so simple also and only has maybe 25 parts and uses common transistors ,Resistors and diodes and a few small Polly Caps.....
If anyone is interested in this circuit I can post it for you....
Cheers
Actually after I finnished the Mods i tried the amp while it was still on my bench and it sounded awesome and worked great but after i put it back into it"s case and tried it it suddenly doesn"t work at all anymore and I can"t get it to work at all now and I am Quite pissed off....
all I get now is a VERY Loud Hum and it seems to be comeeing from the power amp....
I am about to Junk this version of my amp and Just start from scratch again useing a different preamp design...I found a schematic for a very simple Preamp curcuit that uses 4 Fets and is supposed to be a solid state version of a fender tube preamp accept I will Throw an opamp at the end of it with some extra gain, I will also throw in the Overdrive Booster curcuit and This time I think i might try useing 2 bridged or paralelled LM3886 Chips with a 200vA EI transformer I have......
Thanx for the Help guys But for some reason My amp is F*kt and I am to frustrated right now and Can"t find the problem so i am Back to the drawing board....
Cheers
all I get now is a VERY Loud Hum and it seems to be comeeing from the power amp....
I am about to Junk this version of my amp and Just start from scratch again useing a different preamp design...I found a schematic for a very simple Preamp curcuit that uses 4 Fets and is supposed to be a solid state version of a fender tube preamp accept I will Throw an opamp at the end of it with some extra gain, I will also throw in the Overdrive Booster curcuit and This time I think i might try useing 2 bridged or paralelled LM3886 Chips with a 200vA EI transformer I have......
Thanx for the Help guys But for some reason My amp is F*kt and I am to frustrated right now and Can"t find the problem so i am Back to the drawing board....
Cheers
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