Thanks for your response Andrew. I know you did mention it, but I'm still not sure it referred to the CMOY or the the LM386 based headbanger the original poster mentioned.
I am uncertain about your statement because the cmoy does not have output caps, at least as originally described. Did you mean output caps, out output side of input caps??? Sorry to be so confused.
If you mean output side of input caps, there is currently a 100k to ground in that position (smaller R2 I know) that sets the input impedence of the whole amp. Changing that to 10k would affect the size needed for the input potentometer, correct. Since the R2 resistor is now 10x larger, the potentometer would have to be 10 smaller, right?
Thanks!
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Mooly, thanks for your reply.
I will not have time today or tonight to work on this but I'll go through your list as soon as I do.
In the meantime, Ill say:
1: Yup, currently no R5
2: I'll use a ~0.1 ceramic here as recommended earlier.
5: Does type matter, can a use a ceramic here also?
I'll get a couple 1uf polyester to try for input.
Finally, I only have a single 9volt battery left and would only be using this with 9v anyway (or I'll change the chip to one that is more stable). IS it OK to base my answers on 9v (+-4.5) or do I need 18v?
Thanks!!!
The 22/47pf can be ceramic or polyester.
Single 9 volts !
Are you using the power supply as shown in the diagram, two 4K7 resistors each bypassed with 220uf caps to create a -/+ 4.5 volt supply ?
It should work, but as to whether it's ultimately loud enough is another matter. The opamp shouldn't drive loads lower than 600 ohm, in practice it will but at a reduced voltage swing at the output. I think getting the series resistor in the output as correct as possible for your phones will be the answer, and that's trial and error.
The 0.1uf cap and the 22 or 47 pf caps will eliminate any possiblity of instability.
Single 9 volts !
Are you using the power supply as shown in the diagram, two 4K7 resistors each bypassed with 220uf caps to create a -/+ 4.5 volt supply ?
It should work, but as to whether it's ultimately loud enough is another matter. The opamp shouldn't drive loads lower than 600 ohm, in practice it will but at a reduced voltage swing at the output. I think getting the series resistor in the output as correct as possible for your phones will be the answer, and that's trial and error.
The 0.1uf cap and the 22 or 47 pf caps will eliminate any possiblity of instability.
Thanks again for the reply.
My first cmoy, based on tangents schematic with a opa2132pa does great at 9v and 5.5 gain. With 66ohm phones I leave source volume ~25% and can't go past ~50% on amp. Sounds great, uses giant 0.1uf polypropylene at input, not blocking caps at ic or extra output R.
Now, not disagreeing with you. I am sure I'm very lucky on the first one. Honestly, how is the second different?
I think said this but the power supply caps are 470uf on the new one 220uf on the original. I have the 470 available and read they might be smoother.
Is that wrong?
My first cmoy, based on tangents schematic with a opa2132pa does great at 9v and 5.5 gain. With 66ohm phones I leave source volume ~25% and can't go past ~50% on amp. Sounds great, uses giant 0.1uf polypropylene at input, not blocking caps at ic or extra output R.
Now, not disagreeing with you. I am sure I'm very lucky on the first one. Honestly, how is the second different?
I think said this but the power supply caps are 470uf on the new one 220uf on the original. I have the 470 available and read they might be smoother.
Is that wrong?
Luck doesn't come into it 🙂
The obvious thing to try (so as to prove to yourself) is just to swap the opamps but make sure you use the same phones.
The 220 or 470uf caps won't make much difference... true that they are used as a "return" for the AC audio but at the impedance we are talking (phones) it really makes little difference.
The obvious thing to try (so as to prove to yourself) is just to swap the opamps but make sure you use the same phones.
The 220 or 470uf caps won't make much difference... true that they are used as a "return" for the AC audio but at the impedance we are talking (phones) it really makes little difference.
DD,
go back and read all of post4.
I give a lot of detailed description.
You seem to have completely overlooked that.
go back and read all of post4.
I give a lot of detailed description.
You seem to have completely overlooked that.
I've reread that several times, and now several more.
I suspect that we are not understanding each other (most likely my inexperience is hindering my understanding of your explination).
BUT, in post 4 of this thead, you distinctly say output caps and then describe the CMOY adding 10k charge/discharge resistors after them to ground. However, the CMOY does NOT have output caps, only input caps which are grounded after with a 100k.
I keep trying to ask if you made a typo and meant input caps, or meant to add output caps to the CMOY, or where referring to the LM386 headbanger chipamp also discussed in the op.
Am I still mis-reading something. My inexperience is keeping me from fully understanding the individual relationships ofthese circuits.
Regardless, Andrew and Mooly, I appreciate all your help (and all the help I've received in your respective posts on other threads) and will attempt to implement those suggestions tomorrow or Saturday.
This might be a lot to ask, but I someone wanted to describe the function and workings of the individual parts of these devices (rc loops, feedback loop, how r2 sets impedance, etc) I'd find it really, really useful in furthering my understanding of electronics circuits. I realize that may be a lot to ask, but it sure would be helpful.
This thread is really confused. There are 2 x 9V batteries in the OP's cmoy PSU diagram. The ground connection should go to the junction of the two batteries and the 4k7 resistors should be omitted.
@dd
It looks to me as though there has been some confusion about the two circuits, one of which (the LM386), as drawn, has output caps and one of which does not. Output caps could be added to the cmoy.
If you want to understand what is going on in these circuits, I suggest you can do 2 things.
1. Buy a copy of Horowitz and Hill's The Art of Electronics (or borrow it from the library) and read the sections dealing with transistor amplifiers and particularly the section on opamps. You won't regret buying this book, I don't know of anybody who owns it who would disagree.
2. Read the LM386 datasheet in detail. Look at the diagrams which show the interior structure of the device and read the text carefully.
You could also download a copy of the Radiotron Designers Handbook (RDH3.pdf or RDH4.pdf) which are old, and contain a lot of information about valves, but also contain a lot of basics about resistor, capacitor and inductor networks and feedback, and both editions (3 & 4) are available free. You need to understand the frequency dependence of capacitive and inductive reactance and how these create voltage divisions at particular frequencies. You also need to understand a bit about AC and DC analysis of circuits.
If you build the cmoy with the optional series output resistor this will help to define the output resistance (dependent on the value you use), which is indeterminate (although low) without it. It's often taken to be ~100R. You can calculate the output resistance by measuring the output voltage unloaded and loaded. You then need to calculate a value for the output cap so that it has a reactance in ohms equal to the output resistance of the amplifier at the lowest frequency required. The formula for determining this is Xc = 1/(2*pi()*f*C).
w
To the OP: could you please post pics of your amp. Troubleshooting from a distance is hard enough, no need to make it harder.
You weren't "lucky" on your first cmoy, it just works as it should. You have a problem with the second though. The schematic from Tangent is well-proven and should work, there is nothing to fix but your implementation. Fix it before "improving" it.
The ATH-M30 is quite easy to drive at 66ohms, 100db/mw. At 40ma (limiting current value of the opa134), we can get 50mw, about 116db, which is very, very loud. Even at loud listening levels, you should have no audible distortion. You need a power supply of at least 12V to achieve max power.
270R 😱 A properly layed out opa134 will happily drive most 32 ohms headphones without any output resistor. In worst cases, a 10r to 22r output resistor is all that's needed.
Let's assume a 30r load and a 300r one and a PS of 18V.
For the 30r load, we're current limited at 40ma (for a opa134). That means a 2.4Vp-p output.
For the 300r load, we're voltage limited at roughly 12Vpp (for the same opa134). That translates into current peaks of 20ma.
If you add a 100r resistor, you limit the voltage swing into high impedance loads and you gain nothing at all for low impedance ones, except possibly messing up the frequency response in the process.
You weren't "lucky" on your first cmoy, it just works as it should. You have a problem with the second though. The schematic from Tangent is well-proven and should work, there is nothing to fix but your implementation. Fix it before "improving" it.
The ATH-M30 is quite easy to drive at 66ohms, 100db/mw. At 40ma (limiting current value of the opa134), we can get 50mw, about 116db, which is very, very loud. Even at loud listening levels, you should have no audible distortion. You need a power supply of at least 12V to achieve max power.
270R 😱 A properly layed out opa134 will happily drive most 32 ohms headphones without any output resistor. In worst cases, a 10r to 22r output resistor is all that's needed.
Let's assume a 30r load and a 300r one and a PS of 18V.
For the 30r load, we're current limited at 40ma (for a opa134). That means a 2.4Vp-p output.
For the 300r load, we're voltage limited at roughly 12Vpp (for the same opa134). That translates into current peaks of 20ma.
If you add a 100r resistor, you limit the voltage swing into high impedance loads and you gain nothing at all for low impedance ones, except possibly messing up the frequency response in the process.
It is actually good as is. If one battery goes bad or empties faster than the other, you won't end up with offset on your phones ; the rail splitter keeps both rails similar.wakibaki said:
IMO these are not good reasons to use a resistive virtual ground. Why do you think they go to the trouble of using an opamp or dedicated IC virtual ground in these circuits?
The only time a virtual ground is required or desirable is when a split supply is not available. This is not true in this case.
The simple answer (and the best in performance terms) is to use 2 fresh batteries from the same batch, this provides the lowest impedance in the ground returns. There is no reason to suppose one battery will 'go bad' or discharge quicker than the other, and even if it does happen, you just replace the batteries if the sound is impaired.
w
That sentence is rather ironic considering that this setup is suggested by Tangent, probably the guy who made amplifiers with buffered virtual grounds really popular. The schematic comes from his website.
I'll let him explain his reasons: HeadWize: DIY Workshop > Virtual Ground
You can make that "they" a "you" btw, I've built a dozen of those "3 channels" amplifiers.
post 4 refers to an earlier schematic.
The only schematics posted earlier than post4 are in post1. Go and look at them.
Now read post4 in conjunction with the post1 schematics.
Now tell me you don't understand the difference between capacitors in the input line and capacitors in the output line.
BTW,
the 386 is not an easy amplifier to analyse as a beginner. It has special features built into it that remove the output offset of a single supply amplifier.
Far easier to start analysis of opamp circuits with a standard opamp.
Download the opamp manual that Jung edited. It has everything in it. From the very simple to the very complicated. You probably would never need another opamp book.
The only schematics posted earlier than post4 are in post1. Go and look at them.
Now read post4 in conjunction with the post1 schematics.
Now tell me you don't understand the difference between capacitors in the input line and capacitors in the output line.
BTW,
the 386 is not an easy amplifier to analyse as a beginner. It has special features built into it that remove the output offset of a single supply amplifier.
Far easier to start analysis of opamp circuits with a standard opamp.
Download the opamp manual that Jung edited. It has everything in it. From the very simple to the very complicated. You probably would never need another opamp book.
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wikibaki and 00940,
Thanks for your comments and I will attempt to understand and apply them when I have a little more time.
Andrew.....
Either I am really stupid and can't understand you, or your not understanding my question. You said:
CMOY has not output caps, so adding a resistor after them is impossible!
The LM386 in the op schematic does have them, and I believe I can understand what adding a resistor to ground after the caps does, it prevents current build-up in those caps - eliminating click when phones added- and allows the circuit to adjust to a new state when the **LM386** is turned on or off. That resistor adds a current path for cap charge/discharge when headphones are not present.
If one added output caps to a cmoy, the same stuff would apply. But the cmoy doe snot have output caps and they seem to be generally considered un-necessary. Apparently, using an appropriately sized INPUT cap (or better cap type with smaller capacitance) will correct my no-bass issue. Higher cap values, 1.0uf, works in conjunction to the resistor to ground after it (R2 on a cmoy schematic and 100k) to dictate the bass roll off and associated phase distortion. f=1/(2piRC) says 0.1uf rolloff sarts ~16hz and phase distortion can affect frequencies up to ~100hz - hence my lack of bass. A 1.0uf cap would set roll-off shoulder at ~ 1.6hz and affected frequencies are generally reduced to much lower frequencies, eliminating most bass cutoff.
At least I believe that is all correct.
The 100K to ground in series with the input capacitor therefore is part of the bass roll-off equation. It also, since it is to ground, dictates the impedance of the amp, as seen by the source. Is it right to say that R2 (the input to ground resistor) not only affects bass roll-off and input cap charge/discharge when source add/removed/cmoy turned on, but the value of this R determines the mA and mV fed to amp from a given source?
A resistor after an output cap, which the CMOY does NOT have, fixes the charge/discharge issues you described in post 4. Since this R is in series with ground, rather than parallel with any possible OUTPUT cap, it does not affect bass response. Is that correct? Adding an output cap across a series output R would boost frequencies. The gain is determined by the size of R and the frequencies affected are determined by the size of C, is that correct? I'll admit I con't fully describe how this works but I believe I almost understand it.
So to answer your question:
What I'm not sure of is if you suggest adding to a CMOY an output C with a 10K R to ground after it.
I am most confused by your talking about adding 10K after the output caps of a CMOY, and "fixing what should not have been printed" when the cmoy has no ouptput cap. Are you advocating adding a C and R, or where you meaning LM386 when you wrote CMOY???
Sorry if I seem so dense!
But thanks to you for your replies!
Thanks for your comments and I will attempt to understand and apply them when I have a little more time.
Andrew.....
Either I am really stupid and can't understand you, or your not understanding my question. You said:
CMOY has not output caps, so adding a resistor after them is impossible!
The LM386 in the op schematic does have them, and I believe I can understand what adding a resistor to ground after the caps does, it prevents current build-up in those caps - eliminating click when phones added- and allows the circuit to adjust to a new state when the **LM386** is turned on or off. That resistor adds a current path for cap charge/discharge when headphones are not present.
If one added output caps to a cmoy, the same stuff would apply. But the cmoy doe snot have output caps and they seem to be generally considered un-necessary. Apparently, using an appropriately sized INPUT cap (or better cap type with smaller capacitance) will correct my no-bass issue. Higher cap values, 1.0uf, works in conjunction to the resistor to ground after it (R2 on a cmoy schematic and 100k) to dictate the bass roll off and associated phase distortion. f=1/(2piRC) says 0.1uf rolloff sarts ~16hz and phase distortion can affect frequencies up to ~100hz - hence my lack of bass. A 1.0uf cap would set roll-off shoulder at ~ 1.6hz and affected frequencies are generally reduced to much lower frequencies, eliminating most bass cutoff.
At least I believe that is all correct.
The 100K to ground in series with the input capacitor therefore is part of the bass roll-off equation. It also, since it is to ground, dictates the impedance of the amp, as seen by the source. Is it right to say that R2 (the input to ground resistor) not only affects bass roll-off and input cap charge/discharge when source add/removed/cmoy turned on, but the value of this R determines the mA and mV fed to amp from a given source?
A resistor after an output cap, which the CMOY does NOT have, fixes the charge/discharge issues you described in post 4. Since this R is in series with ground, rather than parallel with any possible OUTPUT cap, it does not affect bass response. Is that correct? Adding an output cap across a series output R would boost frequencies. The gain is determined by the size of R and the frequencies affected are determined by the size of C, is that correct? I'll admit I con't fully describe how this works but I believe I almost understand it.
So to answer your question:
I think I mostly get it. I'm a little hazy on the relationship between R and C in attenuating or increasing frequency response - but that is not really the question, at the moment.
What I'm not sure of is if you suggest adding to a CMOY an output C with a 10K R to ground after it.
I am most confused by your talking about adding 10K after the output caps of a CMOY, and "fixing what should not have been printed" when the cmoy has no ouptput cap. Are you advocating adding a C and R, or where you meaning LM386 when you wrote CMOY???
Sorry if I seem so dense!
But thanks to you for your replies!
I simply don't agree with him and I consider my expertise to exceed his.
w
Oh, the circuit I'm talking about has a resistive virtual ground. I'll leave it to you to figure out why the performance is better.
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Post1 shows output capacitors.
Post4 refers to those schematics.
There are no other schematics, prior to post4.
Post4 refers to those schematics.
There are no other schematics, prior to post4.
Actually post 1 includes both the cmoy schematic without output caps, see right bottom thumbnail, and the headbanger with output caps. 😕
@wakibaki: if your expertise exceeds his, bring technical arguments then, not an autority one. Tangent has documented cases in which a rail splitter provides additional safety. An obvious factor to take in account is that people cannot be expected to build the cheapest amp possible and then only use fresh alkaline batterise from the same batch; they'll use rechargeable ones.
And what circuit are you "speaking about" ? Aren't we supposed to speak about the OP misbehaving circuit ?
Actually, mine isn't. In the link I gave, Tangent provides sound technical reasons to use a simple rail splitter for very simple and cheap amps rather than using the central points of two batteries. Those reasons are not performance based, they're safety based; the difference in performances is too small to be of concern when discussing such low end amplifiers. Furthermore, it matches my experience of the possibility of uneven discharge of two rechargeable batteries. You have not provided a rebuttal of those points.
To be fully honnest, I did bow to an authority argument on this point before... using the central point of two batteries because Grado did so in their RA1. Then I went back to resistors+caps splitters, with no audible ill effects, at least as far as amps as simple as a cmoy are concerned. The measurable crosstalk went up a little bit, but no big deal.
Obviously, you can go for more advanced designs... but let's fix what should work and doesnt' before moving on.
All the more likely they'll have near identical charge then.
If an offset drawing current does develop, it will be small but it will tend to equalise the batteries as the drain will be differential. Battery discharge is not like a switch being thrown. The likelihood of drawing sufficient current to damage phones is vanishingly small.
You have ignored the performance considerations. Even with an active virtual earth the performance will be poorer than the circuit I have suggested. This is because the input currents disturb the non inverting input more than is the case with the circuit I have described, because the impedance in the 'ground' path is inevitably higher than it otherwise would be.
The circuit about which I originally spoke uses a resistive divider. This is a compromise in terms of the resistance chosen. Lower resistance = better performing virtual ground, more wasted current. Higher resistance = less wasted current, poorer performing virtual ground.
w
No resistive divider or virtual ground = no wasted power.
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