Here are my suggestions for setting up the LM1875.
First schematic shows how I like it.
Gives like 27 Watt into 8 Ohm. 32 Watt into 4 Ohm.
The potentiometer is to adjust DC offset on the output.
Second image is the Fourier Analysis.
Third image is the AC Analysis. Upper frequency is like 400kHz.
For 4 Ohm speakers I recommend transformer 2x15VAC.
First schematic shows how I like it.
Gives like 27 Watt into 8 Ohm. 32 Watt into 4 Ohm.
The potentiometer is to adjust DC offset on the output.
Second image is the Fourier Analysis.
Third image is the AC Analysis. Upper frequency is like 400kHz.
For 4 Ohm speakers I recommend transformer 2x15VAC.
Attachments
What's the purpose of the potentiometer, R6? If you're trying to adjust offset, that's not a good way to go about that. Also, as pointed out above, you don't need offset adjustment with the LM1875. If you want lower offset than the LM1875 has to offer add a DC servo.
0.000 % THD. That's impressive... Or not... 🙂 I'm willing to bet money that distortion is not included in the LM1875 simulation model.
That said, I'm sure the circuit will work fine. Should be a fun project.
Tom
0.000 % THD. That's impressive... Or not... 🙂 I'm willing to bet money that distortion is not included in the LM1875 simulation model.
That said, I'm sure the circuit will work fine. Should be a fun project.
Tom
I agree. Best offset cancelling is to insert a very small voltage at the bottom of R2 with say, +/- 200mV range.
The offset voltage of an LM1875 is ±1 mV typical and ±15 mV worst case. That's perfectly fine for a speaker amp. If you're planning to use the LM1875 for a headphone amp I'd add an offset adjustment or DC servo.
From the LM1875 data sheet (page 3):
Tom
From the LM1875 data sheet (page 3):
Tom
That circuit is not much different from the datasheet and it wouldn't sound better.
Does "definitive" mean that?
The BIG power limit is LM1875 peak current: 4 A
Perfect for 8 ohm loads, not enough on 4 ohm.
Remember it is good practice to have at least some 20% margin and to boot, a 4 ohm speaker can easily drop to 3 ohm (sometimes even 2.5 ohm) at mid-low mid frequencies (between 250 and 4Hz where there is a lot of program energy.
Yes, as mentioned above, if you significantly lower power rail voltages, so load does not pull 4A, then you can use it ... but not at 30-32W RMS.
As much as I´d love to, it is not a TDA2050 🙁
Perfect for 8 ohm loads, not enough on 4 ohm.
Remember it is good practice to have at least some 20% margin and to boot, a 4 ohm speaker can easily drop to 3 ohm (sometimes even 2.5 ohm) at mid-low mid frequencies (between 250 and 4Hz where there is a lot of program energy.
Yes, as mentioned above, if you significantly lower power rail voltages, so load does not pull 4A, then you can use it ... but not at 30-32W RMS.
As much as I´d love to, it is not a TDA2050 🙁
What about the LM1875 single-supply thump?
Thump occurs because the big DC blocking cap C6 must charge through the speaker while the LM1875 is settling. The thump can be reduced or eliminated by limiting the initial charge rate of that cap.TBD2: This problem occurs because of race conditions during power-up. The power supply has a certain settling time to charge it's circuits and the LM1875, at the same time, is charging the input caps. Eventually, the output pin 4 will track input pin1 exactly. However, this does not occur until pin 1 has several volts. The exact voltage is non-deterministic so far. I found that if C1 is increased to 220uf (arbitrarily), no start-up thump occurs. I would like to have a model that explains a good design of the input circuits.
TBD1: This is a simple option to use instead of TBD1. Open SW1, then apply power. Wait a second, then close SW1 for normal operation. This option works because the initial surge to C6 is reduced. C6 does not need to be completely charged before SW1 is closed.
Why not make SW1 a changeover switch instead? Then connect the normally closed side of the switch to a 4R resistor to GND. That way C6 charges through a resistor rather than the speaker. Close the switch to listen or your 4R resistor will get hot.
What Thump ? I have a wee 1875 DIY amp built exactly to the Data sheet circuit. Toroid dual rail PS, also a diy cobble up..
No turn on thump whatsoever. Am I missing something ?
Daily use on a pair of 4" Full rangers. A pleasingly good amp and sounds.. for what it is.
Although it does produce a small squawk at turn off, But not enough for me to bother 'fixin' .
No turn on thump whatsoever. Am I missing something ?
Daily use on a pair of 4" Full rangers. A pleasingly good amp and sounds.. for what it is.
Although it does produce a small squawk at turn off, But not enough for me to bother 'fixin' .
Why not make SW1 a changeover switch instead? Then connect the normally closed side of the switch to a 4R resistor to GND. That way C6 charges through a resistor rather than the speaker. Close the switch to listen or your 4R resistor will get hot.
That would work but must wait until the volt drop across C6 = VCC/2
That would work but must wait until the volt drop across C6 = VCC/2
Perhaps yours ...
Yes, yours runs on a dual supply, which is much less susceptible to a power-on thump.
I had to look at the datasheet to be sure, the first "Typical Applications" schematic shows it powered from a dual supply. There's a "Figure 1" on the first page showing the pinout, then a "Figure 2" on the third page showing a single-supply circuit, but the dual-supply schematic on page 2 has no "Figure" number.
Bare said: What Thump ? I have a wee 1875 DIY amp built exactly to the Data sheet circuit. Toroid dual rail PS, also a diy cobble up..
No turn on thump whatsoever. Am I missing something ?
Good that you have the dual rail amp working. Now try the the single supply version. Be ready for the surprise.
No turn on thump whatsoever. Am I missing something ?
Good that you have the dual rail amp working. Now try the the single supply version. Be ready for the surprise.
Built heaps of LM1875 amps and only had slight turn off noise. Used 21VDC rails so could be used with lower impedance speakers but also did some with 25VDC rails.
Some examples https://www.diyaudio.com/community/threads/ebay-mono-lm1875-kit.341675/
Why use a single supply when dual rails works well and what surprise?
Some examples https://www.diyaudio.com/community/threads/ebay-mono-lm1875-kit.341675/
Why use a single supply when dual rails works well and what surprise?
Rabbitz said: Why use a single supply when dual rails works well and what surprise?
It has a DC block cap so I won't ruin a spkr with an accident or mistake. I used 19vdc laptop brick for power. A small heatsink is sufficient in this LM1875 configuration. It can drive a KEF Q100 bookshelf spkr for say backgroud music. Next I will try a dual-rail version.
This thread is intended to be definitive so it should include the single-supply which has pros and cons.
Surprise for @Bare .. the spec does not discuss the single-supply thump.
It has a DC block cap so I won't ruin a spkr with an accident or mistake. I used 19vdc laptop brick for power. A small heatsink is sufficient in this LM1875 configuration. It can drive a KEF Q100 bookshelf spkr for say backgroud music. Next I will try a dual-rail version.
This thread is intended to be definitive so it should include the single-supply which has pros and cons.
Surprise for @Bare .. the spec does not discuss the single-supply thump.
If you select opa with ten times lower THD than lm1875 in nested loop, than you can approach definitive.
Have you checked the open loop gain frequency response ?
Or distortion at 1kHz compared to say 10kHz ?
Cheers,
Patrick