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.
hi, any progress on the manual for this amp.? I got the kits and transformer in the mail, and am a bit confused about how to hook up the transformer to the AC and volume control. The boards and transformer seem straightforward.
This will be used to drive some JBL speakers, (http://www.jblpro.com/pub/obsolete/4301.pdf) I've had since the early 80's (rebuilt many times)
Peter
Mark Audio CHP-70's and LM1875
Hi all,
I have an LM3875 Gainclone with [very] standard components and a pair of 160VA 25v toroids.
Having heard a pair of Frugel Horn MK3's with the new Mark Audio CHP-70's driven by a pair of 300B's, [which I can't afford to make] I am going to make a pair of speakers myself.
I tried my GC with them and it was not in the same street as the 300B, CHP-70's are 4 Ohm 18 Watt drive units and I wondered if the LM1875 would be suitable for them.
Looking through the chipamp threads I came a cross a post from Dave [Planet 10] who said he prefered the LM1875 over the LM3875 and the LM3886. Looking at the LM1875 data sheet and if the complexity of the internal components is anything to go by then it wins hands down. It looks to me like a little National Semiconductor mistake, I am into photography and Canon make a cheap plastic 50mm lens that is up there with the £700 all metal ones with edge to edge definition over a full 35mm full frame sensor.
I wondered if anyone has made any side by side comparisons and if indeed the LM1875 would mate with the CHP-70's.
Any opinions would be very welcome.
Jim
Hi all,
I have an LM3875 Gainclone with [very] standard components and a pair of 160VA 25v toroids.
Having heard a pair of Frugel Horn MK3's with the new Mark Audio CHP-70's driven by a pair of 300B's, [which I can't afford to make] I am going to make a pair of speakers myself.
I tried my GC with them and it was not in the same street as the 300B, CHP-70's are 4 Ohm 18 Watt drive units and I wondered if the LM1875 would be suitable for them.
Looking through the chipamp threads I came a cross a post from Dave [Planet 10] who said he prefered the LM1875 over the LM3875 and the LM3886. Looking at the LM1875 data sheet and if the complexity of the internal components is anything to go by then it wins hands down. It looks to me like a little National Semiconductor mistake, I am into photography and Canon make a cheap plastic 50mm lens that is up there with the £700 all metal ones with edge to edge definition over a full 35mm full frame sensor.
I wondered if anyone has made any side by side comparisons and if indeed the LM1875 would mate with the CHP-70's.
Any opinions would be very welcome.
Jim
Dear Andrew,
When I listened to Colin's [toppsy] CHP-70's in his FH3's he was using a pair of 300B's, max 8 Watts. I did try my LM3875 GC and though it didn't sound as good as the 300B's it wasn't having any problems that I could hear.
I did hear some Fostex FE126en's in the FH3's as well they are 8 Ohm 95 db but the CHP-70's sounded much better to my my ears.
Warmest wishes - Jim
When I listened to Colin's [toppsy] CHP-70's in his FH3's he was using a pair of 300B's, max 8 Watts. I did try my LM3875 GC and though it didn't sound as good as the 300B's it wasn't having any problems that I could hear.
I did hear some Fostex FE126en's in the FH3's as well they are 8 Ohm 95 db but the CHP-70's sounded much better to my my ears.
Warmest wishes - Jim
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Is it just me?
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.
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.
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.
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.
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?
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.
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).
Its pretty easy to test the transistors with a multimeter, just google it...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
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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