AFAIK replace always means "instead of"... You would never "replace" a headlight by jamming a second one in would you? Or replace a coffee filter by putting another filter on top of it?
There is only a single D1 and a single Q2 on the schematic, so I don't see how anyone could get confused there either.
There is only a single D1 and a single Q2 on the schematic, so I don't see how anyone could get confused there either.
For your transformer,
I suggest a quick trip to Decibel Dungeon to have a look at the larger chips that would just love to run at that voltage, And a nice stable inverting design that facilitates a practical and pleasant experience with the LM3875TF, LM3876TF, LM3886TF. The Decibel Dungeon Gainclone index page with links to all chip amp articles. <--link
You won't need a kit for this--Decibel Dungeon shows how to build easier and better, without a board. Your transformer will work nicely with those projects.
For your power board,
At that transformer voltage you need 50v (or higher) rated caps (the 35v caps wouldn't last a long time if run near max). But, if you've got the 50v caps, then your power supply can work nicely with many projects (including the Decibel Dungeon power amplifiers).
P.S.
The above was a most cost effective solution with good practical results; however, many other options do exist. For example, look at Decibel Dungeon's regulated power supply, which will work with LM1875's (regulated supply lets you control the voltage).
I suggest a quick trip to Decibel Dungeon to have a look at the larger chips that would just love to run at that voltage, And a nice stable inverting design that facilitates a practical and pleasant experience with the LM3875TF, LM3876TF, LM3886TF. The Decibel Dungeon Gainclone index page with links to all chip amp articles. <--link
You won't need a kit for this--Decibel Dungeon shows how to build easier and better, without a board. Your transformer will work nicely with those projects.
For your power board,
At that transformer voltage you need 50v (or higher) rated caps (the 35v caps wouldn't last a long time if run near max). But, if you've got the 50v caps, then your power supply can work nicely with many projects (including the Decibel Dungeon power amplifiers).
P.S.
The above was a most cost effective solution with good practical results; however, many other options do exist. For example, look at Decibel Dungeon's regulated power supply, which will work with LM1875's (regulated supply lets you control the voltage).
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Hi all!
Back after some time and interested in continuing my LM1875 journey. Need some advices here.
My amp is powered by 12-0-12 vac, 5 amps transformer and the voltage rails are approximately +/- 16 vdc to drive a bookshelf 8 ohm speakers. I install 1 M resistor parallel to the RCA inputs for both channel, and a potentiometer (2x100 k). I then connect to an input cap of 2.2 uF then a shunt 22 k resistor to +in. I don't use 100 nF at +/- pin of the LM1875, instead, I only use 220 uF electrolytic caps. My NFB is 22k / 1 k with 220 uF shunt cap to ground. I previously installed the zobel of 1R and 0.22 uF but removed them already. Kind of standard configuration from the original datasheet only the difference is the shunt NFB cap and no zobel.
1. I need to know the passband of this amp and whether all the values are suitable. In the datasheet, NFB shunt cap is 22 uF and mine is 220 uF. Can anybody tell me how to calculate/check this pass band? I am eager to learn.
2. I notice bad sound if I use a Transcend MP860 (it only has headphone output), however, the amp sounds better when I connect to FiiO E-10 from its line out not the headphone out. What is the source/cause of this difference in sound?
5. Do you think a pre amp will help? I kind of observe that as the value of the potentiometer changes (as it turns up and down), so does the sound (not the volume, you know what I mean). So, I think that adding a pre amp in front of the amp will help.
Thanks.
Back after some time and interested in continuing my LM1875 journey. Need some advices here.
My amp is powered by 12-0-12 vac, 5 amps transformer and the voltage rails are approximately +/- 16 vdc to drive a bookshelf 8 ohm speakers. I install 1 M resistor parallel to the RCA inputs for both channel, and a potentiometer (2x100 k). I then connect to an input cap of 2.2 uF then a shunt 22 k resistor to +in. I don't use 100 nF at +/- pin of the LM1875, instead, I only use 220 uF electrolytic caps. My NFB is 22k / 1 k with 220 uF shunt cap to ground. I previously installed the zobel of 1R and 0.22 uF but removed them already. Kind of standard configuration from the original datasheet only the difference is the shunt NFB cap and no zobel.
1. I need to know the passband of this amp and whether all the values are suitable. In the datasheet, NFB shunt cap is 22 uF and mine is 220 uF. Can anybody tell me how to calculate/check this pass band? I am eager to learn.
2. I notice bad sound if I use a Transcend MP860 (it only has headphone output), however, the amp sounds better when I connect to FiiO E-10 from its line out not the headphone out. What is the source/cause of this difference in sound?
5. Do you think a pre amp will help? I kind of observe that as the value of the potentiometer changes (as it turns up and down), so does the sound (not the volume, you know what I mean). So, I think that adding a pre amp in front of the amp will help.
Thanks.
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So, at that voltage, you're fairly close to perfect, except for the missing zobel. Natsemi/Ti's zobel figures depend on a lossy cap, and you've probably used something better, as in more efficient, which makes the resistor value wrong (that happens A LOT!). Also, the lower voltage has the amp running more stably, so the need of stabilizing components changes. For your zobel, try using a resistor with a value really close to the DCR (use ohmmeter) of your speaker, and a polyester dip (not box) cap in the range of 22n~68n.
That particular cap you're curious about:
If too small, bad overly warm boomy muddy bass
If too big (that's hard to do!) thud-only cold bass
*An even amount of both distortions will cancel bass distortion, so DO aim for the middle ground.
If the treble is not satisfactory in the "airy" department try a 10n or 22n polyester dip (not box) cap added parallel to your NFB-Shunt cap (the in- coupler).
Oh, yes, by that description, it is likely that you'll be wanting a constant input impedance instead of having the input impedance vary off the beam every time you turn the volume knob.
Likely candidates for preamp are Classic Valve Design's Moosefet preamp or Decibel Dungeon's NE5534 Building a Gainclone chip amp with various active buffers using opamps and discrete components. (authentic NE5534 haven't been made since 1996 and are Signetics, Raytheon and Philips, so if you've got a TI, don't bias it but rather just build it more simply without the transistor mess at output). And there are many other preamps to use.
Hi Daniel,
So this Zobel idea is about matching the Zobel impedance with the speaker impedance at certain frequency?
If this is true, then I may determine my Zobel network like this:
1. I measure dc resistance of my 8-ohm speaker, it says 10 ohm (resistance, I just measured this). This dc resistance will be my Zobel resistor value.
2. Then my capacitive reactance --> Xc = sqrt(Zspeaker^2 - Rzobel^2)
This gives me Xc = j6 ohm --> j = sqrt(-1)
3. I define the frequency at which the impedance should be the same (right?). In this case, I choose 100 kHz
4. I calculate my cap value
C = 1 / (2*pi*100000*6)
C = 0.26 uF --> approx. 0.22 uF
5. So my Zobel is 10 ohm resistor in series with 0.22 uF.
Is this correct? Can anybody verify this?
Thanks
So this Zobel idea is about matching the Zobel impedance with the speaker impedance at certain frequency?
If this is true, then I may determine my Zobel network like this:
1. I measure dc resistance of my 8-ohm speaker, it says 10 ohm (resistance, I just measured this). This dc resistance will be my Zobel resistor value.
2. Then my capacitive reactance --> Xc = sqrt(Zspeaker^2 - Rzobel^2)
This gives me Xc = j6 ohm --> j = sqrt(-1)
3. I define the frequency at which the impedance should be the same (right?). In this case, I choose 100 kHz
4. I calculate my cap value
C = 1 / (2*pi*100000*6)
C = 0.26 uF --> approx. 0.22 uF
5. So my Zobel is 10 ohm resistor in series with 0.22 uF.
Is this correct? Can anybody verify this?
Thanks
And for the NFB cap, I should follow AndrewT's suggestion on http://www.diyaudio.com/forums/chip-amps/260251-lm1875-gainclone-input-cap-size.html#post4017486
1. My input cap size is 2.2 uF and the parallel resistor is 22 k which form the HPF with frequency 1/(2*pi*r*c) = 3.29 Hz
2. NFB frequency < HPF/sqrt(2) which results in 2.33 Hz
3. With my NFB shunt resistor of 1 k, so my NFB cap size > 1/(2*pi*2.33*1000) which results in 68 uF --> so putting a 220 uF is fine, I suppose.
However, I have not understood about the PSU part. He mentioned
".. Then the PSU is set to < actual NFB freq/sqrt(2).."
Does this mean a SNUBBER ?
Thanks.
1. My input cap size is 2.2 uF and the parallel resistor is 22 k which form the HPF with frequency 1/(2*pi*r*c) = 3.29 Hz
2. NFB frequency < HPF/sqrt(2) which results in 2.33 Hz
3. With my NFB shunt resistor of 1 k, so my NFB cap size > 1/(2*pi*2.33*1000) which results in 68 uF --> so putting a 220 uF is fine, I suppose.
However, I have not understood about the PSU part. He mentioned
".. Then the PSU is set to < actual NFB freq/sqrt(2).."
Does this mean a SNUBBER ?
Thanks.
the PSU has a capacitor that supplies speaker current during one halfwave of the AC signal.
The speaker capacitor combination is another RC.
For minimal reaction to LF signals I place this RC below the NFB frequency.
I saw it suggested about 6 or 7years ago, using the sqrt(2) ratio and experimented with that and found it met all my requirements for very low bass.
The speaker capacitor combination is another RC.
For minimal reaction to LF signals I place this RC below the NFB frequency.
I saw it suggested about 6 or 7years ago, using the sqrt(2) ratio and experimented with that and found it met all my requirements for very low bass.
Either that's not an 8 ohm speaker or the meter might need a new battery.
Let's try a few things. . .
Firstly, I would like to assume that an 8 ohm speaker would be somewhere in-between 0 and 10 ohms.
Measure zero: What is the ohmmeter readout with its leads crossed (should be zero; however, the screen will probably show a non-zero figure)?
Measure 10: Measure a 10 ohm resistor as close as possible to the resistor's body (no excessive pin length), and then how much higher than 10 is the meter readout?
Measure the speaker, as closely to the speaker as possible (not from the opposite end of the wire), subtract the meter error (those excess figures that showed up in the prior two steps need subtracted), and is the result more like 6.8 ohms?
If the result, after subtracting for meter error, is still 10R then you've got a "12 ohm" speaker, which is not commonplace.
That is proven by real active service and by arriving at similar figures by alternate means. I endorse this post. That is valuable, accurate, information.
Hi Daniel,
Thanks. I just checked my previous meter, when I cross the probes, it showed 1 ohm. And I connect the probes to speaker terminals again, meter showed 9 ohm. I am seeking for another meter now.
About the speaker capacitor mentioned by AndrewT, does this mean the large electrolytic capacitor at the power supply? Or is it the output electrolytic capacitor in series with the speaker? Could you elaborate more on this? Or point me to a link about this.
Thanks.
Thanks. I just checked my previous meter, when I cross the probes, it showed 1 ohm. And I connect the probes to speaker terminals again, meter showed 9 ohm. I am seeking for another meter now.
About the speaker capacitor mentioned by AndrewT, does this mean the large electrolytic capacitor at the power supply? Or is it the output electrolytic capacitor in series with the speaker? Could you elaborate more on this? Or point me to a link about this.
Thanks.
Hi Andrew,
Thanks for the reply.
And Daniel, I have re-measured my speaker with other multimeter, the reading is 7.5 ohm. What do you think? This new multimeter seems to read correctly, it shows zero if I cross its probes.
So, what would you suggest the R-C value for my Zobel?
Thanks for the reply.
And Daniel, I have re-measured my speaker with other multimeter, the reading is 7.5 ohm. What do you think? This new multimeter seems to read correctly, it shows zero if I cross its probes.
So, what would you suggest the R-C value for my Zobel?
Values near the datasheet's frequency, except at lower current, include
3.9R with 56n
5.6R with 39n
6.8R with 33n
I have no idea why or if that rather high frequency was important; however, those Resistor values aren't low enough to make your RC act like a bad cap instead of an RC; and, those resistor values aren't high enough for insufficient current. At least the resistor values are probably practical.
It may not be necessary to have the pitch that high if the inductor||resistor series element were added to the amplifier output so that the filter could work more reasonably.
In theory, it should be possible to use 4.7R~7.5R with 68n, which is a range of RC values all lower pitched than AM radio interference along with a cap value that is probably too small to irritate the amp. However, if you wanted to use a larger cap, the datasheet sort of slightly infers that you'll be wanting the inductor||resistor input filter parts. See the section on stability. http://www.ti.com/lit/ds/symlink/lm1875.pdf LM1875 datasheet makes specific mention of a 10Ω resistor in parallel with a 5 μH inductor.
It is very unusual for the low resistance scale of a normal DMM to read 0.0r for the resistance of the probes+leads+internal wiring.
I have 4 DMM that offer a low resistance scale.
They read 0.1r, 0.3r, 0.2r and 0.14r(this is the 50000count bench meter).
I have an old car/auto multimeter that has a low resistance scale. It has an adjustment knob to zero out the leads/probes error. But it's operation is quite different. This operational method is generally only found on dedicated resistance meters. It is on my broken AVO8 meter and on my broken 20k/V analogue meter.
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Whoops! not input filter parts. I had meant to type: output filter parts.
The datasheet schematic has half of them missing.
The trouble that will cause along with too much capacitive load for such an omission, is all mentioned in that Stability section in the datasheet. It seems unlikely that the datasheet schematic and the chapter on stability were written by one person.
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