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Old 13th March 2008, 11:53 PM   #1
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Location: killeen, texas.
Question i need help with this LME49810 schematic

Sup! i was going to make the pcb for this schematic but im not sure if it will work the right way.
i was wondering if you guys could look at it and tell me whats wrong and how to fix it.
the out put transistors are not going to be the tip142 and 147 but some thing like tip35CW and tip36cw or the mjl1302ag and mjl3281ag,
do you think i need a predriver for each of the output stage drivers. or just one pair of predrivers to push the 2 pair of output drivers.
for predrivers i have the mje15032g and mje15033g and a set of bdx54c and bdx53c, thanks for the help in advance.
laters all.

i had to change the image type from bmp to jpeg.
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Old 14th March 2008, 04:27 PM   #2
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Looks pretty close to the circuit in the datasheet. Couple things to keep in mind. First is that you will need to optimize values for your particular PCB layout and design. So you should do somethings to have lots of flexibility to work with unless you are experienced enough to kick out a PCB that will work the way you want. Some things to be sure to have:

- 0.1uF capacitor at supply pin of each output device.
- snubber on the output, 0.1uF + 10ohms are good starting values
- Extra driver stage may or may not be needed depending on final output devices, supply voltage and load impedance. You can add places for these and then jumper them out if they are not needed.
- Compensation cap (10pF) will probably need to be higher to start then you can optimize down once you are sure you have stability.
- Add a couple cap footprints across the bias pins, I use a film cap and a small electrolytic. You can play with values and combinations to see what you like.
- Add a cap footprint from the Mute pin to GND depending on if you plan to use the Mute function. A capacitor here will insure no pops going in/out of Mute. If not using Mute mode then don't worry about it.
- You might want to add L+R on the output. Might not be needed.

Good luck.
-SL
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Old 16th March 2008, 08:21 AM   #3
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thanks for the reply SpittinLLama!

My electronics lingo is not so good, so i hope i understood what you where saying. here is what i changed based on your suggestions, plz let me know if the changes i made, was what you suggested.
im new to electronics so i can really use all the info you can help with, thanks again.

Quote:
- 0.1uF capacitor at supply pin of each output device.
*added C8 trough C11 to the collector side of the transistors to ground. I hope thats what you meant, please correct me if i messed up. would 100uF work as well?

Quote:
- snubber on the output, 0.1uF + 10ohms are good starting values
*added R1 and C11 .1uF caps.

Quote:
- Extra driver stage may or may not be needed depending on final output devices, supply voltage and load impedance. You can add places for these and then jumper them out if they are not needed.
*i want this amp to be slightly flexible as far as power rating goes.
so ill add the spaces for a pre driver stage and two more spot for the output drivers. and jumper the unused.

*The power supply i made its a +/-60V unregulated output.
the transformer was pulled from a jvc home 5.1 receiver amp.
the voltage drops to 45v under a 11ohms load at 4.5 amps, so around 200wrms to work with.

*I'm looking to drive from 16ohms to hopefully 4ohms loads.

*The amp will be used for bi amping a pair of 3 way towers.

Quote:
- Compensation cap (10pF) will probably need to be higher to start then you can optimize down once you are sure you have stability.
*would 30pf be too big, what would be a range? if you know.

Quote:
- Add a couple cap footprints across the bias pins, I use a film cap and a small electrolytic. You can play with values and combinations to see what you like.
*Added CC1 its a 30pf from one bias pin to the other. " Not sure if thats how you meant it!" what would be a general value for the film cap?.

Quote:
- Add a cap footprint from the Mute pin to GND depending on if you plan to use the Mute function. A capacitor here will insure no pops going in/out of Mute. If not using Mute mode then don't worry about it.
* i do want to use the mute option. So like you said i added a .1uF from the pin to ground. is that right? what do you mean by footprint?


thanks a bunch.
take care.
l8ter
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Old 16th March 2008, 01:09 PM   #4
AndrewT is online now AndrewT  Scotland
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Hi,
a dual EF output stage requiring drivers is recommended.
The C1=0.47uF input cap will kill the bass performance.
Add an RF filter to the input. C//RS, about 1nF will do.
Why is Rin=243r so low?
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Old 17th March 2008, 03:58 AM   #5
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Hi AndrewT, thanks for the reply.

Quote:
a dual EF output stage requiring drivers is recommended.
i guess ill be using the EF stage to push the output stage. do you know if these devices i have would be worth using as predrivers? mje15032g and mje15033g and a set of bdx54c and bdx53c,
MJE15032G Datasheet
BDX54C Datasheet

they'll have to drive a set of either one of these tip35CW and tip36cw or the mjl1302ag and mjl3281ag,
MJL1302AG Datasheet TIP36CW Datasheet

Quote:
The C1=0.47uF input cap will kill the bass performance.
true thanks. i changed it for a 220uF. is that enough. I cant get the equation formula to work for me.



Quote:
Add an RF filter to the input. C//RS, about 1nF will do.
\
added a 1nF cap in parallel to the rs resistor. is that what you meant?


Quote:
Why is Rin=243r so low?
on the LME application PDF i quote.
" For best Noise performance, lower values of resistors are
used. A value of 243 is commonly used for Ri "
ill play with other values ones the pcb is built, to see how performance changes. any suggestions?


thanks again.
any more help on this will be greatly appreciated.
laters
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Old 17th March 2008, 08:10 AM   #6
AndrewT is online now AndrewT  Scotland
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Hi,
input impedance of 6k8 + 243r~=7k is a bit low.
Ci=220uF is far too large. This cap must define the high pass rolloff.
Use about 1u5F or 1u8F with your original 22k for Rs. These should match <=time constant of the NFB/1.4

You could try Rin between 243r and 750r, any higher and you will probably notice the treble rolling off.
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Old 18th March 2008, 06:40 PM   #7
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Quote:
Originally posted by AndrewT
Hi,
input impedance of 6k8 + 243r~=7k is a bit low.
Ci=220uF is far too large. This cap must define the high pass rolloff.
Use about 1u5F or 1u8F with your original 22k for Rs. These should match <=time constant of the NFB/1.4

You could try Rin between 243r and 750r, any higher and you will probably notice the treble rolling off.

sup!
i think i made the changes you mentioned above, im not sure if they are in the right place though.

for the input stage on the LME would the filtering work the same way as if i was adding a filter to an opamp?

thanks for the help so far.
laters
Click the image to open in full size.
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Old 22nd March 2008, 12:11 AM   #8
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Sup all!
well i guess there is really not much else to change to make it operational.

if you guys have any more tips for the amp, please help me out.

ill play with some of the values once the PCB is done and the amp working.

here is the last schematic and PCB.
Click the image to open in full size.
Click the image to open in full size.

ill provably make the board tomorrow or the next day.
if you see anything i could change to improve, im sure theres allot of room for improvement here, lol, feel free to help

thanks
laters
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Old 23rd March 2008, 10:18 PM   #9
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Sup all!

i came up with a new pcb for the amp, felt this one would be a bit more appropriate, i still have to correct all the traces width according to what ever current they will carry.

Click the image to open in full size.
Click the image to open in full size.

do you think the location of the transistors is better on the previous post PCB or this one?
The Heatsink i have on hand is a 12" x 5 3/8" flat contact surface. i want to use the heat sink to its max,
would it be posible to attach 4 of these amps to this heat sink?
would the 2SC3063 npn transistor work fine for the vbe multiplier?.
here is the 2SC3063 Datasheet

laters
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Old 4th April 2008, 06:30 PM   #10
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Hi Boricuaso,

Any success on your amp? I'm just curios how did it sound, or have you compared it on your existing amps based on the sound quality? What is your trim bias current of your amp? Can you show me know where to point my multimeter leads on measuring the bias?
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