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Old 14th March 2011, 08:24 AM   #111
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Default Is it just me?

Quote:
Originally Posted by danielwritesbac View Post
Speakers are the output. The difference between a 25 watt amplifier and a 100 watt amplifier can be made up by a 6db difference in speaker efficiency.

Possibly, those would be slightly larger speakers, but this isn't larger than any other speakers that could make a similar output (that 25w is a big head start). Only the design is somewhat different, but its not less powerful.

An example:
Per each channel this example is 2 of 7" Dayton RS 4 ohm speakers, four of LM1875's arranged as a pair of parallel amplifiers. Each parallel amplifier (2 chips each amplifier) drives 1 woofer. The cabinet size of this speaker is modest, given that the output resistors have reduced the cabinet size requirement a bit. Now, that's just one channel. Twice that much would be sufficient to crack up plaster or drywall. Its physically about 100 watts per channel, except that the speakers mentioned are extremely efficient, and the example mentioned produces 400 watt equivalency (200w equivalency per channel).
In other words, this can make for some fiercely loud audio, more than sufficient for most home use needs.

You can scale to 4 or 5 woofers per cabinet and still have a nice light active speaker that's about the size of a footlocker. Just remember that it takes 2 of LM1875 (as a parallel amplifier) per each four ohm woofer.

This simple equipment can run nonstop without straining (no straining = still hi-fi when cranked up loud) and is scalable to much higher figures, which would destroy some part of your house because of too much force.

So, I can't imagine why anyone would think its powerless.
Daniel your posts are just utter nonsense. Where are you getting this from? its utterly ridiculas and also very misleading / confusing for a thread aimed as a "newbie" build guide. Plese do us a favour nd think before you type and back up your ideas with some logically deduced figures and theories not just inaccuracies padded out with waffle. Sorry if this offends but people are starting out here if you read the posts and mains electricity coupled with bizare and incorrect advice can KILL. No ifs, no buts Gameover.
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Old 24th March 2011, 10:21 AM   #112
madman is offline madman  Norway
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Hi All !
I just finnished my LM1875 amp kit and it sounds good but when I removed cap C2 (shorting it) from gain-resistor to ground the amps make a loud buzz in the speakers.
This caps should be optional but I have to leave them in. Why ?

Last edited by madman; 24th March 2011 at 10:39 AM.
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Old 24th March 2011, 04:52 PM   #113
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Quote:
Originally Posted by guaxian View Post
Nice!
but I don't like 1875 & 2030A,
powerless @-@
Powerless? nah, 20 watts can be loud. Depends on what You have as speaker. High sensitivity ones require only a few watts to be loud and powerfull.

this ic is verry nice performer, and specialy good as first DIY project.
Choose proper speakers and i bet YOu will not need more than 10 watts to make it louder than You need in a medicore room.
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Old 27th March 2011, 08:37 AM   #114
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Quote:
Originally Posted by tom wesley View Post
Daniel your posts are just utter nonsense. Where are you getting this from? its utterly ridiculas and also very misleading / confusing for a thread aimed as a "newbie" build guide. Plese do us a favour nd think before you type and back up your ideas with some logically deduced figures and theories not just inaccuracies padded out with waffle. Sorry if this offends but people are starting out here if you read the posts and mains electricity coupled with bizare and incorrect advice can KILL. No ifs, no buts Gameover.
Here are the figures you requested in your post (#111):

Remember, every time you double the amplifier power output, you get only +3db more from the speaker.

If a given speaker is 91db at 1 watt then:
94db at 2 watts
97db at 4 watts
100db at 8 watts
103db at 16 watts

104db with LM1875
107db with parallel LM1875 to a 4 ohm speaker, like an MTM

P.S.
Inferring from the alarm in your post, here's a transformer voltage figure:
The transformer for the majority of LM1875 designs is the common 18,0,18 volt transformer. And, in that case, four ohm speakers would need parallel LM1875 amplifiers.
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Old 4th May 2011, 04:37 PM   #115
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Default DC offset way too high

I'm building my first chipamp with this kit. I have completed the PSU and one amp. Everything checks out until I get to measure the DC offset between OUT to OG which is 24'2 V (I get ~25V from the PSU).

Something I obviously wrong but I cannot figure out what. Any suggestions?
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Old 4th May 2011, 09:47 PM   #116
johnr66 is offline johnr66  United States
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Quote:
Originally Posted by turminder View Post
I'm building my first chipamp with this kit. I have completed the PSU and one amp. Everything checks out until I get to measure the DC offset between OUT to OG which is 24'2 V (I get ~25V from the PSU).

Something I obviously wrong but I cannot figure out what. Any suggestions?
Put your negative test lead on ground and measure voltage at Pin 3 (should be negative supply voltage (say, -25v)) and on Pin 5 (should be positive supply voltage (say, +25v)). Also check for unintended shorts from solder bridges. Double check your wiring and components.

I recommend building a battery powered bulb tester before putting full power to the amp (or use a current limited power supply). Use two 9 volt batteries with a 6 to 8 volt 300ma bulbs in series. One battery provides + rail, the other, the - rail. If there is a problem, the bulb(s) will light up brightly. This prevents potential destruction of the IC from heavy currents if there is a problem when the real PS is connected.

Some will test with a line operated dim bulb tester. Use a low wattage bulb when testing amps with these ICs.
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Old 5th May 2011, 09:34 PM   #117
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Quote:
Originally Posted by johnr66 View Post
Put your negative test lead on ground and measure voltage at Pin 3 (should be negative supply voltage (say, -25v)) and on Pin 5 (should be positive supply voltage (say, +25v)). Also check for unintended shorts from solder bridges. Double check your wiring and components.

I recommend building a battery powered bulb tester before putting full power to the amp (or use a current limited power supply). Use two 9 volt batteries with a 6 to 8 volt 300ma bulbs in series. One battery provides + rail, the other, the - rail. If there is a problem, the bulb(s) will light up brightly. This prevents potential destruction of the IC from heavy currents if there is a problem when the real PS is connected.

Some will test with a line operated dim bulb tester. Use a low wattage bulb when testing amps with these ICs.
Thanks for the reply. I have checked the connections and components, I cant see whats wrong. I've must have blown the chips. I'm using a bulb tester with a 60W bulb but my toroid is 300VA (18-0-18), is it too big?
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Old 6th May 2011, 02:54 PM   #118
johnr66 is offline johnr66  United States
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Quote:
Originally Posted by turminder View Post
Thanks for the reply. I have checked the connections and components, I cant see whats wrong. I've must have blown the chips. I'm using a bulb tester with a 60W bulb but my toroid is 300VA (18-0-18), is it too big?
18-0-18 is fine as long as the amp is used with no less than 8 ohm loads. 300VA is overkill IMO, but works. If everything checks out, then you may have bad chips. Since the chips were not likely this way new, something killed them so you will have to figure that out.

I'd use a 25 watt bulb. power up with everything connected so the filter caps don't get a chance to build up full potential. The bulb should flash bright on power up and settle to very dim (almost no light) if all is well (no signal).
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Old 6th May 2011, 05:32 PM   #119
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Quote:
Originally Posted by jemraid View Post
Dear Andrew,

Blast!! :-)

I will have to make another JLH 10 Watt class A. My first one packed up after 10 years use, I can identify the components but when something goes wrong ......... I'm b0110xed

Thanks - Jim
Its pretty easy to test the transistors with a multimeter, just google it...
I'd replace all the elctrolytics, as they get their lifespan reduced heavily by the temperatures, and then it shoudl start right up again.
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Old 2nd December 2011, 07:07 AM   #120
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Hi all!
I have a question about this amplifier: Do you can feedback in this amplifier can be performed with a resistor of 180k and 10k [(180/10) +1]?
Which is better feedback 22k​​/0.68k and 180k/10k?
Thank you for your response
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