Hello all and congrats on a wonderful site. First I will introduce myself im 28 and live in the USA and work as an automotive tech. I Have some electronic experience.
With that said on to the topic. I have some samples from TI 3xlm3886 and 3xlm4780 thanks TI. Now I have been reading over all the info on these gainclones and the like.
The more I dive in the more questions arise. So here is, I am after a 2 chanel Amp with 2 bridged lm4780s, my questions are.
How would I go about adding gain control to the standard bridged lm4780 stereo gainclone
As i undersrand how you would on inverting or non but on the bridged is both?
Second im not 100% on my PSU needs my mains voltage is 119 from the wall how big of a xformer is needed?
Then there's the heat sink would 2 standerd PC CPU coolers work
Or if there is a beter option with the opamps I have on hand
This amp is intended to be used with 8ohm speakers an as a home theater amp
Thanks in advance for any help
With that said on to the topic. I have some samples from TI 3xlm3886 and 3xlm4780 thanks TI. Now I have been reading over all the info on these gainclones and the like.
The more I dive in the more questions arise. So here is, I am after a 2 chanel Amp with 2 bridged lm4780s, my questions are.
How would I go about adding gain control to the standard bridged lm4780 stereo gainclone
As i undersrand how you would on inverting or non but on the bridged is both?
Second im not 100% on my PSU needs my mains voltage is 119 from the wall how big of a xformer is needed?
Then there's the heat sink would 2 standerd PC CPU coolers work
Or if there is a beter option with the opamps I have on hand
This amp is intended to be used with 8ohm speakers an as a home theater amp
Thanks in advance for any help
Most designs for power amplifiers are for a fixed gain where the amp will work best. Typically gain control is done at the preamp. Almost everything is set for the preamp to output 1-1.5V and the amp to accept this to drive it to maximum power output. If you are going to run it from a fixed preamp, a 10k variable resistor/pot between the preamp and the power amp is about right.
I'm guessing you want about 120 Watts per channel or 240 Watts total from your description. Good guess would be transformer that will be ~70% of its max at full power output or 340 Watts to keep things from burning up. Coffee hasn't taken effect yet this morning, you sometimes can't find the exact transformer you need. You could get something in the range of 30VAC at 12 amps to 45VAC at 8 amps. Looking at the specs, you are not to exceed 84V<94?> for the device. To do the conversion from AC to DC for a rectified power supple you just multiply times 1.4 so it implies your drop dead burn up the device number would be a 60VAC transformer. Of course if all you can find are 34VAC at 5 amps, you can use two, one for each channel.
Heat sink, biggest piece of finned aluminum you can get your hands on. Yes a fan would help. Mild nag here, ~5 Watts per channel is a comfortable listening level. George Thorougood and the Destroyers have been known to use 600 Watts for some venues. You are building a couple of hundred Watts of amp. If you miss on a few parts, for example transformers that only have 16VAC, it will limit the output such that it would be hard to burn anything out with 8 Ohm speakers and still produce a lot of sound.
I'm guessing you want about 120 Watts per channel or 240 Watts total from your description. Good guess would be transformer that will be ~70% of its max at full power output or 340 Watts to keep things from burning up. Coffee hasn't taken effect yet this morning, you sometimes can't find the exact transformer you need. You could get something in the range of 30VAC at 12 amps to 45VAC at 8 amps. Looking at the specs, you are not to exceed 84V<94?> for the device. To do the conversion from AC to DC for a rectified power supple you just multiply times 1.4 so it implies your drop dead burn up the device number would be a 60VAC transformer. Of course if all you can find are 34VAC at 5 amps, you can use two, one for each channel.
Heat sink, biggest piece of finned aluminum you can get your hands on. Yes a fan would help. Mild nag here, ~5 Watts per channel is a comfortable listening level. George Thorougood and the Destroyers have been known to use 600 Watts for some venues. You are building a couple of hundred Watts of amp. If you miss on a few parts, for example transformers that only have 16VAC, it will limit the output such that it would be hard to burn anything out with 8 Ohm speakers and still produce a lot of sound.
72 views no replies am i thrown to the wolves.
this is the diagram i am looking at A 120 Watt Bridged
if i have read correctly it wants +/-26v, to my understanding the transformers output depends on the voltage input, plus losses in rectifier and caps
how would one calculate for that?
second the gain is a sum of the resistors used on the input signal and feedback like explained here Shavano Music Online - Introduction to Op-Amps - Part 1
so on the bridged lm4780 would i put a liner pot at r2 and r7 of the diagram linked above
as for the heat sink well lets tackle one thing at a time
ok again thanks for any help (pls dont throw this audio noob to the wolves)
this is the diagram i am looking at A 120 Watt Bridged
if i have read correctly it wants +/-26v, to my understanding the transformers output depends on the voltage input, plus losses in rectifier and caps
how would one calculate for that?
second the gain is a sum of the resistors used on the input signal and feedback like explained here Shavano Music Online - Introduction to Op-Amps - Part 1
so on the bridged lm4780 would i put a liner pot at r2 and r7 of the diagram linked above
as for the heat sink well lets tackle one thing at a time
ok again thanks for any help (pls dont throw this audio noob to the wolves)
you slipped that reply in there on me now!
any how, so its not to important to get the power dead on and as long as its not over or under specs for the opamp i will be ok?
would something along the lines of this work to power 2 lm4780's Avel Y236652 250VA 25V+25V Toroidal Transformer | 122-625
as for the gain i do not have a preamp not in the budget at the moment to buy/build one
the plan was to build the amp with 3-5 selectable inputs and control the gain of the amp with a liner pot or maybe a stepped atun.
any how, so its not to important to get the power dead on and as long as its not over or under specs for the opamp i will be ok?
would something along the lines of this work to power 2 lm4780's Avel Y236652 250VA 25V+25V Toroidal Transformer | 122-625
as for the gain i do not have a preamp not in the budget at the moment to buy/build one
the plan was to build the amp with 3-5 selectable inputs and control the gain of the amp with a liner pot or maybe a stepped atun.
use one 3886 and build a temporary single channel amplifier.
Add a potentiometer volume control.
Find out about your build, why it works, what bits don't work as expected, how much room it takes up, how you solved the hum and buzz issues.
Then you are ready to look at what is required to build a stereo amplifier.
Those two builds may just about give you enough information to decide if a bridged amplifier is within your capabilities and resources.
Add a potentiometer volume control.
Find out about your build, why it works, what bits don't work as expected, how much room it takes up, how you solved the hum and buzz issues.
Then you are ready to look at what is required to build a stereo amplifier.
Those two builds may just about give you enough information to decide if a bridged amplifier is within your capabilities and resources.
Don't adjust the gain of a build that is already successful and recommended.
The stability margins are tied very closely with the gain.
Change the gain and you could end up with a far worse performing amplifier and at worst an oscillator.
Select equipment with just sufficient output that at maximum volume control the very loudest (0dBfs in digital) just reach clipping.
Then your volume control is all you need to adjust to your listening mood.
Have you read:
http://www.diyaudio.com/forums/diyaudio-com-articles/186018-what-gain-structure.html
The stability margins are tied very closely with the gain.
Change the gain and you could end up with a far worse performing amplifier and at worst an oscillator.
Select equipment with just sufficient output that at maximum volume control the very loudest (0dBfs in digital) just reach clipping.
Then your volume control is all you need to adjust to your listening mood.
Have you read:
http://www.diyaudio.com/forums/diyaudio-com-articles/186018-what-gain-structure.html
Check out Peter's site: DIY Chip Amplifier Kits, PCB's, Components and Information.
I built one of his LM3875 premium kits in dual mono and could not be happier.
Best
Michael
I built one of his LM3875 premium kits in dual mono and could not be happier.
Best
Michael
+1 to the build a stereo from two separate boards if you have the time and energy to do it. The economics doing it that way can be much better in the long run. Easier to find transformers for one, easier to have a 3rd backup channel in case something goes wrong, ...
Off topic a bit, DON'T worry about how many views your message has. The situation with data miners and robots is beyond ridiculous right now. I had a small web site forum for myself and a few friends. Over 7,000 phony members signed up in less then a year! They just use names like 'cheap viagra' and links to their web sites. When google or whatever search engine is looking at your site, it automatically includes them in their data base. 72 views probably means [you, me, 70 robots]. Terrible situation if you are paying for bandwidth.
Off topic a bit, DON'T worry about how many views your message has. The situation with data miners and robots is beyond ridiculous right now. I had a small web site forum for myself and a few friends. Over 7,000 phony members signed up in less then a year! They just use names like 'cheap viagra' and links to their web sites. When google or whatever search engine is looking at your site, it automatically includes them in their data base. 72 views probably means [you, me, 70 robots]. Terrible situation if you are paying for bandwidth.
Thank you all for the advice, I am going to take it slow and start with just one lm3886. Build and test it learn what everything dose and then go from there. Maybe some pic's of the build along the way when I get ready to go forward with it. For now more reading and research are in order.
again thanks and keep the good info flowing.
again thanks and keep the good info flowing.
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