Am i Passing the Correct Voltages for my Amp Circuit?

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Al1B

Member
Joined 2010
Hello to DIY community...:cool::cool:


i have built a parallel 100w amp using two Lm3886tf chips. in the schematics that i attach it says the circuit needs +30 and -30 Volts plus gnd to function.



i have two issues here.....



dipr_lm3886t_pa100.gif




1) i am going to connect this Amp to a Guitar Pre-Amp i've built... and for that use case , do i need to change the value of C1 (1uf) in the input section? i can also share the the pre-amp's schematics







2) my Transformer is giving me output about 32 Volts, and at the end of Filerting capacitors in PSU something near 40 volts.
so what are my options? can i use a bigger heat-sink on the chips and hope that they will handle more voltage withouth getting fried?


or should i use a symmetrical PSU circuit and fix it on 30 Volts?




Thanks in Advance..
 
rayma

rayma

Moderator
Joined 2011
Al1B said:
i have built a parallel 100w amp using two Lm3886tf chips. in the schematics that i
attach it says the circuit needs +30 and -30 Volts plus gnd to function.
Click to expand...

The C1 is ok with the specified value.

To get +/- 30VDC supplies, the transformer needs to be either a
center-tapped 44VAC (22VAC-0-22VAC), or else two 22VAC secondary windings.

The absolute maximum is +/- 42VDC, so there is little safety margin.
 
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A

Al1B

Member
Joined 2010
abraxalito said:
Ballast resistors can work fine though I'd recommend higher than 0.1ohm, say 0R22. The problem with the schematic I can see is gain matching is going to suffer at LF due to the tolerances of the 100uF caps. Best make those at least 470uF.
Click to expand...


for R10+11 , i couldnt find that exact resistor (0R1 3w) so i used three 0R47 1w in parallel. i think im a bit close to what u suggest.


and about 100uf capacitors. i've already made the PCB . are they gonna make some problem? by LF you mean Low Frequency or i am mistaking?
 
JMFahey

JMFahey

Member
Joined 2009
Paralleling voltage sources is bad engineering.
Notice that to (barely) succeed they *demand* 0.1% matched resistors , so both independent "brains", the amplifiers, think more or less the same and difference can be handled (more or less) by the very crude kludge of adding series resistors at each output so they are not perfect voltage sources any more.
An accident waiting to happen.

Sadly they *look* simple (they are not) and so are a DIYer magnet.

Commercial designers avoid this and design proper amplifiers instead, one commercial Guitar amplifier company, Marshall, started using them , including the 4 chip parallel bridged circuit in the MF450 ... which became the most unreliable amplifier in their history.

They (sort of) tried to tame the problem by installing chipamps in their own miniboards, each connected to the main board with individual flat cable connectors, so when they fail (notice I didn´t say "if"), the Musician can replace the chipamps all by himself ... a mess.

I suggest you clone any commercial *guitar* power amp instead, "regular" circuits of course, any Randall/Peavey/Marshall/Laney/H&K/Crate you like.
In particular 80´s 90´s Laney are very solid, sensible and easy to replicate ones, just avoid the couple using 5 leg Power Transistors which included biasing diodes inside the same package.

In the 100W range many used TIP142/147 power transistors, very robust, easy to find, and thanks God have not been faked , so any circuit in the above suggested brands is recommended.

Go with the experienced guys who make tens of thousands amplifiers; Audiophile thinking is fine for their own ends but belongs in a different world; Musical Instrument stage amplification world is brutal and you need robust simple time tested designs.
 
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A

Al1B

Member
Joined 2010
JMFahey said:
Paralleling voltage sources is bad engineering.
Notice that to (barely) succeed they *demand* 0.1% matched resistors , so both independent "brains", the amplifiers, think more or less the same and difference can be handled (more or less) by the very crude kludge of adding series resistors at each output so they are not perfect voltage sources any more.
An accident waiting to happen.

Sadly they *look* simple (they are not) and so are a DIYer magnet.

Commercial designers avoid this and design proper amplifiers instead, one commercial Guitar amplifier company, Marshall, started using them , including the 4 chip parallel bridged circuit in the MF450 ... which became the most unreliable amplifier in their history.

They (sort of) tried to tame the problem by installing chipamps in their own miniboards, each connected to the main board with individual flat cable connectors, so when they fail (notice I didn´t say "if"), the Musician can replace the chipamps all by himself ... a mess.

I suggest you clone any commercial *guitar* power amp instead, "regular" circuits of course, any Randall/Peavey/Marshall/Laney/H&K/Crate you like.
In particular 80´s 90´s Laney are very solid, sensible and easy to replicate ones, just avoid the couple using 5 leg Power Transistors which included biasing diodes inside the same package.

In the 100W range many used TIP142/147 power transistors, very robust, easy to find, and thanks God have not been faked , so any circuit in the above suggested brands is recommended.

Go with the experienced guys who make tens of thousands amplifiers; Audiophile thinking is fine for their own ends but belongs in a different world; Musical Instrument stage amplification world is brutal and you need robust simple time tested designs.
Click to expand...




thanks for your useful information
 
A

Al1B

Member
Joined 2010
thanks to the useful information all of you shared here, i came to a conclusion that maybe this amp wont be the perfect fit for my guitar amp. just because i used chips in parallel .


does this mean that using a single LM3886 at nearly (68W) , will give me better results? or should i just abandon this part and find better alternatives ?
 
JMFahey

JMFahey

Member
Joined 2009
Oh, using *one* and driving an 8 ohm guitar speaker (or a 4 ohm one but at somewhat reduced voltage, just follow what the datasheet suggests) will give you an excellent and very reliable amplifier.

Paralleling chipamps only gives you the capability of driving half the impedance, so 4 ohm if using +/-35V or 2 ohm if using +/-28V (whatever the datasheet suggests) ... and that if the paralleling is successful, which depends on both "thinking the same at the same time" as dictated by ultra precision NFB resistors.
In my book, not worth it.

From experience, a 50/60W amplifier driving a good (Eminence/Celestion/Jensen/WGS/Weber/Scumback) speaker is able to cope with any rehearsal or Club date.

You play in a Stadium? ... even easier, they will mike you through a huge PA system :)

FWIW, guess what is inside this respected very well designed amplifier, meant to reproduce all kinds of sounds thrown at it by complex pedalboards ;) :

ou9mbm7fcn95beuj3nrp.jpg


71LpYS1SYbL._SX679_.jpg


Yup, an LM3886 and a Celestion speaker :)

Versatile?

Dunno,YOU tell me ;)

YouTube
 
A

Al1B

Member
Joined 2010
JMFahey said:
Paralleling voltage sources is bad engineering.
Notice that to (barely) succeed they *demand* 0.1% matched resistors , so both independent "brains", the amplifiers, think more or less the same and difference can be handled (more or less) by the very crude kludge of adding series resistors at each output so they are not perfect voltage sources any more.
An accident waiting to happen.

Sadly they *look* simple (they are not) and so are a DIYer magnet.

Commercial designers avoid this and design proper amplifiers instead, one commercial Guitar amplifier company, Marshall, started using them , including the 4 chip parallel bridged circuit in the MF450 ... which became the most unreliable amplifier in their history.

They (sort of) tried to tame the problem by installing chipamps in their own miniboards, each connected to the main board with individual flat cable connectors, so when they fail (notice I didn´t say "if"), the Musician can replace the chipamps all by himself ... a mess.

I suggest you clone any commercial *guitar* power amp instead, "regular" circuits of course, any Randall/Peavey/Marshall/Laney/H&K/Crate you like.
In particular 80´s 90´s Laney are very solid, sensible and easy to replicate ones, just avoid the couple using 5 leg Power Transistors which included biasing diodes inside the same package.

In the 100W range many used TIP142/147 power transistors, very robust, easy to find, and thanks God have not been faked , so any circuit in the above suggested brands is recommended.

Go with the experienced guys who make tens of thousands amplifiers; Audiophile thinking is fine for their own ends but belongs in a different world; Musical Instrument stage amplification world is brutal and you need robust simple time tested designs.
Click to expand...






regarding your suggestion, ive been looking for transistor amps circuits. and i found this one:
150 Watt Power Amplifier Circuit Board


is this Amp a better solution for me ?
thanx again
 
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