That is what I am thinking and hoping.
I did recently pick up an oscilloscope, any idea how to use one to measure PS noise?
Or any other parameters I could measure?That is what I am thinking and hoping.
I did recently pick up an oscilloscope, any idea how to use one to measure PS noise?
attention
please check at the SMPS what is GND and /or main earth!
an oszilloskop is always main earth !!!! so your ground clip = BNC connector is main earth.
EEVblog #279 - How NOT To Blow Up Your Oscilloscope! - YouTube
EEVblog #594 - How To Measure Power Supply Ripple & Noise - YouTube
I finished up the Ebay LM1875 amp today, and it is NOT working correctly!
At full blast, there is a very low volume sound coming from the speakers, both channels have the same problem.
PSU is producing correct +-24v, 48v at amp from +-, ground continuity is there.
Any ideas on what I should be checking?
Thank you,
David.
At full blast, there is a very low volume sound coming from the speakers, both channels have the same problem.
PSU is producing correct +-24v, 48v at amp from +-, ground continuity is there.
Any ideas on what I should be checking?
Thank you,
David.
Hi David
sorry to read that.
Did the amps working in a other configuration?
power off and wait 10mins.
then disconnect every wire and check if you had contact to the chassis where should not have it !!! -
RCA connectors,
speaker terminals,
chip to heat sink (maybe you forgot the isolated screw)
knob volume
check potentiometer connection diagram, maybe you do a wrong solder and you do not have a variable resistor...
smps seams ok - voltage is ok
chris
sorry to read that.
Did the amps working in a other configuration?
power off and wait 10mins.
then disconnect every wire and check if you had contact to the chassis where should not have it !!! -
RCA connectors,
speaker terminals,
chip to heat sink (maybe you forgot the isolated screw)
knob volume
check potentiometer connection diagram, maybe you do a wrong solder and you do not have a variable resistor...
smps seams ok - voltage is ok
chris
Could be incorrect wiring of the pot shunting the signal to ground. The other possibility is reversing 22K/1K feedback resistors on the amp PCB which would give almost no gain. Check all your resistors are in the correct locations.
With power amp building you should do 3 basic checks with a DMM.
1. Make sure the chip is isolated from the heatsink.
2. Check the supply voltage on the PCB, +ve to ground and -ve to ground to ensure correct rail voltages. Don't measure from +ve to -ve as it is not referenced to ground and gives no idea of the symmetry of the supply.
3. Check the DC offset on the speaker output and should be < 10mVDC and all mine have been < 2mVDC.
After doing those basic checks, I suggest you run a source with volume capabilities (such as an iPod) directly to the amp PCB inputs one amp at a time. This will tell you if the amp has gain and is working correctly.
I've added a pic for reference of one I threw together this month.
With power amp building you should do 3 basic checks with a DMM.
1. Make sure the chip is isolated from the heatsink.
2. Check the supply voltage on the PCB, +ve to ground and -ve to ground to ensure correct rail voltages. Don't measure from +ve to -ve as it is not referenced to ground and gives no idea of the symmetry of the supply.
3. Check the DC offset on the speaker output and should be < 10mVDC and all mine have been < 2mVDC.
After doing those basic checks, I suggest you run a source with volume capabilities (such as an iPod) directly to the amp PCB inputs one amp at a time. This will tell you if the amp has gain and is working correctly.
I've added a pic for reference of one I threw together this month.
Attachments
Do Not assume the SMPS is working well... despite what your meter may read.
I've had 2 ! 24v Dual rail SMPSs' Fail... intended as Dual mono supplies. I test metered Both of them prior to fitting.. they metered "fine'.
One Died in the first few minutes.. taking out the matched and fairly Pricey output transistors in process. The other died a day or so later.. it at least didn't fry anything on it's way out.
These were Not bargain priced units either.
Not surprisingly, there proved to be NO response let alone recourse, from their Chinese vendor.
IMO.. Unless buying a long proven decent Chinese brand SMPS... Meanwell for example, it's a complete crapshoot.
I've had 2 ! 24v Dual rail SMPSs' Fail... intended as Dual mono supplies. I test metered Both of them prior to fitting.. they metered "fine'.
One Died in the first few minutes.. taking out the matched and fairly Pricey output transistors in process. The other died a day or so later.. it at least didn't fry anything on it's way out.
These were Not bargain priced units either.
Not surprisingly, there proved to be NO response let alone recourse, from their Chinese vendor.
IMO.. Unless buying a long proven decent Chinese brand SMPS... Meanwell for example, it's a complete crapshoot.
Hello, I bought few years ago 4 LM1875 kits on ebay like yours.
I would like to build a power amp for my 4 in ceiling speakers.
the thing that i did not found yet is:
- what kind of power supply should i need to setup for such configuration, do i need to have multiple or one unique is sufficient, and how do i connect the 4 of them to it?
- is RCA the only input i can use? i would like to have XLR instead
- is there a need for speaker protection or the LM1875 has it internally as it seems?
I would like to build a power amp for my 4 in ceiling speakers.
the thing that i did not found yet is:
- what kind of power supply should i need to setup for such configuration, do i need to have multiple or one unique is sufficient, and how do i connect the 4 of them to it?
- is RCA the only input i can use? i would like to have XLR instead
- is there a need for speaker protection or the LM1875 has it internally as it seems?
Hello, I bought few years ago 4 LM1875 kits on ebay like yours.
I would like to build a power amp for my 4 in ceiling speakers.
the thing that i did not found yet is:
first please buy original LM1875 up to 28V at 8 ohm speakers.
with 4R speakers i would set the max voltage supply at about max 25V.
- what kind of power supply should i need to setup for such configuration, do i need to have multiple or one unique is sufficient, and how do i connect the 4 of them to it?
fred use a SMPS with dual rail ..like thisdual group output +-24V and DC12V 300W power board MX50 L20 audio amplifier board power supply instead toroidal transformer|AC/DC Adapters| - AliExpress
i personally used a 120VA 18-0-18VAC transformer and rectifier and about 14000µF rail caps. but i bought this smps too...i think its a vernice idea and the PSRR of the chip amp is sufficient.
- is RCA the only input i can use? i would like to have XLR instead
with RCA that amp runs very good.
the amp is single ended design and XLR means extra effort = a buffer board like this:
Universal Buffer – Neurochrome
or
BTSB Buffer SE/Bal to SE/Bal Buffer | Etsy
- is there a need for speaker protection or the LM1875 has it internally as it seems?
if you use original parts =1875 chip then the short cut test is working very well and a speakers protection is not needed.
in principle its a good idea to use for every chassis a separate amp = bi amping, bi wiring. its still on my to do list
chris
I would like to build a power amp for my 4 in ceiling speakers.
the thing that i did not found yet is:
first please buy original LM1875 up to 28V at 8 ohm speakers.
with 4R speakers i would set the max voltage supply at about max 25V.
- what kind of power supply should i need to setup for such configuration, do i need to have multiple or one unique is sufficient, and how do i connect the 4 of them to it?
fred use a SMPS with dual rail ..like thisdual group output +-24V and DC12V 300W power board MX50 L20 audio amplifier board power supply instead toroidal transformer|AC/DC Adapters| - AliExpress
i personally used a 120VA 18-0-18VAC transformer and rectifier and about 14000µF rail caps. but i bought this smps too...i think its a vernice idea and the PSRR of the chip amp is sufficient.
- is RCA the only input i can use? i would like to have XLR instead
with RCA that amp runs very good.
the amp is single ended design and XLR means extra effort = a buffer board like this:
Universal Buffer – Neurochrome
or
BTSB Buffer SE/Bal to SE/Bal Buffer | Etsy
- is there a need for speaker protection or the LM1875 has it internally as it seems?
if you use original parts =1875 chip then the short cut test is working very well and a speakers protection is not needed.
in principle its a good idea to use for every chassis a separate amp = bi amping, bi wiring. its still on my to do list
chris
Like Chris said, do use a genuine LM1875 as the ones in the kit appear to be fakes. I ended up throwing out all the components supplied and used my own of known quality.
For 4 channels a single power supply is ample. I'd go with around 200VA 15-0-15 to give around ±21VDC which will handle lower impedance like 4 ohm. If your speakers are 8 ohm then you can use 18-0-18. 10000uF caps per rail would work fine for 4 channels. Just connect all the amps to the same power supply +ve, ground, -ve.
These are SE so RCA is the way to go but you can use XLR connectors but wired for SE.
The LM1875 caters for speaker shorts but it does have a small pop at shutdown which is the nature of the chip as it has no muting but it's not a problem.
For 4 channels a single power supply is ample. I'd go with around 200VA 15-0-15 to give around ±21VDC which will handle lower impedance like 4 ohm. If your speakers are 8 ohm then you can use 18-0-18. 10000uF caps per rail would work fine for 4 channels. Just connect all the amps to the same power supply +ve, ground, -ve.
These are SE so RCA is the way to go but you can use XLR connectors but wired for SE.
The LM1875 caters for speaker shorts but it does have a small pop at shutdown which is the nature of the chip as it has no muting but it's not a problem.
Have a look at the ESP P72 as a guide on the linear power supply.
Single Chip 25W Amplifier (Project 72)
Single Chip 25W Amplifier (Project 72)
I just tested a "genuine" LM1875, and a so-called "fake" one that came with this kit from China:
20W HIFI Mono Channel LM1875T Stereo Audio Amplifier Board Module DIY Kit | eBay
The distortion spectra were identical. The "fake" actually had a cleaner leading/trailing edge on square wave testing. I see no benefit whatsoever to replacing it.
You think I am lying? For what purpose? Measurements don't lie.
My recommendation is not wrong, it is the truth. The chip I got with the kit I linked above is a good one. I was expecting junk, but it wasn't. It measures the same, and sounds the same, as the ones from Digikey. Photos and measurements are in other thread:
Complete chip amp kit with enclosure, etc ?
Is it a "genuine" LM1875? I can't say yes or no. But it is a good chip. It measures the same (not only distortion), in two different boards, and sounds the same too.
I don't like the LM1875, so I have no invested interest.
My recommendation is not wrong, it is the truth. The chip I got with the kit I linked above is a good one. I was expecting junk, but it wasn't. It measures the same, and sounds the same, as the ones from Digikey. Photos and measurements are in other thread:
Complete chip amp kit with enclosure, etc ?
Is it a "genuine" LM1875? I can't say yes or no. But it is a good chip. It measures the same (not only distortion), in two different boards, and sounds the same too.
I don't like the LM1875, so I have no invested interest.