Hi,
I am new and this is my first post here. Thank you in advance for your indulgence, because I am also new to audio (not to electronics though) and English is not my mother tongue.
In short, I need some help in order to design an amplifier.
Here is the context. I am building an virtual pipe organ, using a ~50 year old electronic church organ. I have removed all the original (analog !) electronics to build my own one. I have done infrared barrier sensors for the keys, managed by an Arduino board. Another Arduino takes the sensors signals as input and outputs a MIDI signal to a Raspberry Pi, the latter containing a virtual organ software (GrandOrgue). The Raspberry Pi is also connected to a DAC board (a HifiBerry DAC+). Finally, I have build a DIY headphone amp based on the CMoy design, with 2 improvements : an op-amp based virtual ground, and a LM317 to further stabilize the voltage provided by an already regulated SMPS. While I can't compare it to any reference (not even a physical pipe organ, because the purpose of my project is precisely to start learning organ), I feel that it "sounds good", with no obvious noise nor distortion. Note: building a CMoy is not in contradiction with being an audio newbie. Two weeks ago, I didn't know anything about headphone amps! I just learnt using Internet resources.
Now to my topic: my organ is working with headphones, I would like to make it work with loudspeakers too.
The orginal organ had four loudspeakers, which I have kept, of course. A quick test with an amplifier I have but that I don't want to reuse for this project (a Yamaha A-S301, too bulky + I suspect it is not in good working condition) showed that the loudspeakers are working well. Plus they probably still have a significant value. All speakers have a resistance of around 7.5 Ohm (from 7.2 to 7.8). I have tested each of them and measured the RMS voltage at the same time. I got quite consistent results: at 5 V, they are very loud, and at 7-8 V it became to be painful. So, in order to have a safety margin, if I design an amplifier capable of 10 V RMS, I will need 10*10/7,5 = 13.3W per speaker.
I think that the orginal organ had a mono output, because the loudspeakers are arranged this way inside: (see attachment).
So I intend to do the following:
[CMoy] -> [Convert stereo to mono] -> [Amplifier] -----> low-pass filter -> two large loudspeakers in parallelSince the same amplifier would drive all speakers at the same time I would need 13.3x4 = 53.3 ~ 50W.
Then I would have to choose the class. I hesitate between class A and class D, but I think that the power is still low enough for a class A amplifier, which would provide the sound quality and simplicity I am looking for. For example, the LM3886 seems to be up for the task, since its datasheet says "68W cont. avg. output power into 4 Ohms at VCC = +/- 28V". Still, I have to read the datasheet in details to check if this is true, because my configuration is somewhat different : ~2 Ohms at VCC = +/- 10V, i.e. less voltage but more current.
I have had a look at a few designs and it seems that many of them include a pre-amp stage. In my case, I feel I don't need it, thank to the CMoy.
For the stereo to mono conversion, I intend to do this : https://www.instructables.com/id/Simple-Way-to-Convert-Stereo-to-Mono/, while I am not 100% sure if it the right way (it seems too simple to be true).
For the filters, I have no knowledge, but I guess that I will have to go through the following steps: 1) determine the response curve of each loudspeaker 2) design the filters accordingly 3) adjust for overall balance. I am not sure what I will do if one speaker is significantly louder or weaker than the others.
The final word: I am not after the highest sound quality using complex refinements, just a good sound for a reasonable amount of money (say less than 100 € of components). I have posted in the "Chip amps" section of the forum, because I guess this is the best path for simplicity, but I may be wrong.
So any advice is appreciated. In addition, a link to a successful project in this forum with similar specifications would be extremely helpful.
I am new and this is my first post here. Thank you in advance for your indulgence, because I am also new to audio (not to electronics though) and English is not my mother tongue.
In short, I need some help in order to design an amplifier.
Here is the context. I am building an virtual pipe organ, using a ~50 year old electronic church organ. I have removed all the original (analog !) electronics to build my own one. I have done infrared barrier sensors for the keys, managed by an Arduino board. Another Arduino takes the sensors signals as input and outputs a MIDI signal to a Raspberry Pi, the latter containing a virtual organ software (GrandOrgue). The Raspberry Pi is also connected to a DAC board (a HifiBerry DAC+). Finally, I have build a DIY headphone amp based on the CMoy design, with 2 improvements : an op-amp based virtual ground, and a LM317 to further stabilize the voltage provided by an already regulated SMPS. While I can't compare it to any reference (not even a physical pipe organ, because the purpose of my project is precisely to start learning organ), I feel that it "sounds good", with no obvious noise nor distortion. Note: building a CMoy is not in contradiction with being an audio newbie. Two weeks ago, I didn't know anything about headphone amps! I just learnt using Internet resources.
Now to my topic: my organ is working with headphones, I would like to make it work with loudspeakers too.
The orginal organ had four loudspeakers, which I have kept, of course. A quick test with an amplifier I have but that I don't want to reuse for this project (a Yamaha A-S301, too bulky + I suspect it is not in good working condition) showed that the loudspeakers are working well. Plus they probably still have a significant value. All speakers have a resistance of around 7.5 Ohm (from 7.2 to 7.8). I have tested each of them and measured the RMS voltage at the same time. I got quite consistent results: at 5 V, they are very loud, and at 7-8 V it became to be painful. So, in order to have a safety margin, if I design an amplifier capable of 10 V RMS, I will need 10*10/7,5 = 13.3W per speaker.
I think that the orginal organ had a mono output, because the loudspeakers are arranged this way inside: (see attachment).
So I intend to do the following:
[CMoy] -> [Convert stereo to mono] -> [Amplifier] -----> low-pass filter -> two large loudspeakers in parallel
--> band-pass filter -> medium-sized loudspeaker
--> high-pass filter -> small loudspeaker
Then I would have to choose the class. I hesitate between class A and class D, but I think that the power is still low enough for a class A amplifier, which would provide the sound quality and simplicity I am looking for. For example, the LM3886 seems to be up for the task, since its datasheet says "68W cont. avg. output power into 4 Ohms at VCC = +/- 28V". Still, I have to read the datasheet in details to check if this is true, because my configuration is somewhat different : ~2 Ohms at VCC = +/- 10V, i.e. less voltage but more current.
I have had a look at a few designs and it seems that many of them include a pre-amp stage. In my case, I feel I don't need it, thank to the CMoy.
For the stereo to mono conversion, I intend to do this : https://www.instructables.com/id/Simple-Way-to-Convert-Stereo-to-Mono/, while I am not 100% sure if it the right way (it seems too simple to be true).
For the filters, I have no knowledge, but I guess that I will have to go through the following steps: 1) determine the response curve of each loudspeaker 2) design the filters accordingly 3) adjust for overall balance. I am not sure what I will do if one speaker is significantly louder or weaker than the others.
The final word: I am not after the highest sound quality using complex refinements, just a good sound for a reasonable amount of money (say less than 100 € of components). I have posted in the "Chip amps" section of the forum, because I guess this is the best path for simplicity, but I may be wrong.
So any advice is appreciated. In addition, a link to a successful project in this forum with similar specifications would be extremely helpful.
Attachments
The original organ drives all speaker drivers in parallel. However there will be a "crossover" network of passive components (inductors, capacitors and resistors) which directs power according to the frequency bands appropriate to each of the 4 speaker drivers. There will also be an appropriate mono amplifier and power supply feeding that crossover network. The load seen by the amp will be benign and around 6 ohms or so.
Why not re-use these components? It will give you the best fidelity with the least cost and effort.
Why not re-use these components? It will give you the best fidelity with the least cost and effort.
Ah this is a good point - and good news! The amplifier will not see a ~2 Ohm load (four ~8 Ohm loads in parallel) as I wrote. If I use the two woofers in parallel, it will be rather 4 than 6 Ohms, though.
OK, so my new spec is: 25-30W. Do we agree on that? This gives me an even stronger argument in favor of class A.
Lastly, why not reusing the original components? Because I am stupid and thrown them away to give place to my new design :-(
I started with the sensors and the Arduino stuff I was more familiar with, telling me that I would do the audio part at the end, and also that I would never reuse anything from the original electronics...
OK, so my new spec is: 25-30W. Do we agree on that? This gives me an even stronger argument in favor of class A.
Lastly, why not reusing the original components? Because I am stupid and thrown them away to give place to my new design :-(
I started with the sensors and the Arduino stuff I was more familiar with, telling me that I would do the audio part at the end, and also that I would never reuse anything from the original electronics...
Don't over-think. "Class" of amplification should not be a critical issue. (and whether 50W or 20W, this is big class A.)
The amplifier is NOT a permanent part. Bach replaced bellows as needed and you can replace amplifier every few years, because the old one is cracked and leaky or because you get bigger gigs and need bigger puffer for your bigger audiences.
Sight unseen, that Yamaha was probably a fine starter amp. I've known Yamas to serve well for many years, in PA in Rock and in HiFi. If it is truly ill, go to the rock shop and get the smallest pre-owned stereo PA amp they got, save it from a life of polka and beer.
You really should have kept the speaker *filters* (crossover). I know what two 15"s do, and what one 5" does, but blending both with that 12" opens many possibilities, once solved but now lost. You might even ask Rock Shop if they have a "Keyboard Amp"; modern stage amps are some better than semi-affordable 1950s stuff.
The amplifier is NOT a permanent part. Bach replaced bellows as needed and you can replace amplifier every few years, because the old one is cracked and leaky or because you get bigger gigs and need bigger puffer for your bigger audiences.
Sight unseen, that Yamaha was probably a fine starter amp. I've known Yamas to serve well for many years, in PA in Rock and in HiFi. If it is truly ill, go to the rock shop and get the smallest pre-owned stereo PA amp they got, save it from a life of polka and beer.
You really should have kept the speaker *filters* (crossover). I know what two 15"s do, and what one 5" does, but blending both with that 12" opens many possibilities, once solved but now lost. You might even ask Rock Shop if they have a "Keyboard Amp"; modern stage amps are some better than semi-affordable 1950s stuff.
I always thought it’d be great to use one of these;
https://www.organsupply.com/assets/Help-Center-Instructions/Spencer-Orgoblo-For-Pipe-Organs.pdf
But really, the majority of stage amps will handle 4 ohms just fine. Maybe just a tpa3116 board for very little investment.
https://www.organsupply.com/assets/Help-Center-Instructions/Spencer-Orgoblo-For-Pipe-Organs.pdf
But really, the majority of stage amps will handle 4 ohms just fine. Maybe just a tpa3116 board for very little investment.
I started discussing with my wife about installing an orgoblo in our garage, but I got a somewhat cold feedback...
Anyway, back to electronics! I have good and bad news.
The good news is that I kept one board, to use as a stock of components, and it was the one to keep. After a closer inspection, I have identified that the amplifier and the filters of the 4 loudspeakers are located in the upper right part of the board. The amplifiers are the 2 black boxes mounted vertically on the right. I removed the metallic part on one of them to be able to read the component reference: SI1125HD. This is a 25W Dual Channel Amp.There are 2 of them for a total of 4 channels. The filtering is obtained with a network of resistors and capacitors (I don't see any inductance). There are also potentiometers which allow probably to do some adjustements on the filters. One the back of the board, you can see the letters "LS", identifying the loudspeakers outputs. The whole circuit is powered by a 7815 (on the left of the huge 2N3055 transistor) which is a 15 V voltage regulator. The rest of the board manages the keyboards and the (analog) sound generation for each organ pipe.
The bad news is that there are a lot of capacitors involved, and the performance of the SI1125HD is probably outdated.
So I am not really motivated in reusing this electronics, unless somebody explains me why I am wrong.
Anyway, back to electronics! I have good and bad news.
The good news is that I kept one board, to use as a stock of components, and it was the one to keep. After a closer inspection, I have identified that the amplifier and the filters of the 4 loudspeakers are located in the upper right part of the board. The amplifiers are the 2 black boxes mounted vertically on the right. I removed the metallic part on one of them to be able to read the component reference: SI1125HD. This is a 25W Dual Channel Amp.There are 2 of them for a total of 4 channels. The filtering is obtained with a network of resistors and capacitors (I don't see any inductance). There are also potentiometers which allow probably to do some adjustements on the filters. One the back of the board, you can see the letters "LS", identifying the loudspeakers outputs. The whole circuit is powered by a 7815 (on the left of the huge 2N3055 transistor) which is a 15 V voltage regulator. The rest of the board manages the keyboards and the (analog) sound generation for each organ pipe.
The bad news is that there are a lot of capacitors involved, and the performance of the SI1125HD is probably outdated.
So I am not really motivated in reusing this electronics, unless somebody explains me why I am wrong.
Attachments
So, as PRR suggests, let's concentrate on the crossover filters first.
What if I buy a 3-way crossover filter? Like this one, for example. I also found a model for 4 speakers (2 bass, 1 mediant, 1 trebble) which is exactly my configuration. There are even models with some adjustments, which would allow me to try various settings and determine the best one.
In a first step, I could try one of these with my Yamaha amplifier.
What if I buy a 3-way crossover filter? Like this one, for example. I also found a model for 4 speakers (2 bass, 1 mediant, 1 trebble) which is exactly my configuration. There are even models with some adjustments, which would allow me to try various settings and determine the best one.
In a first step, I could try one of these with my Yamaha amplifier.
No.
I was going to make a comparison to, say, JS Bach's "outdated" organ(s), which is(are) avidly played today... but it seems over 300 years they have in fact been heavily rebuilt due to wear and change of fashion.
I don't know where you are going. You seem to have nearly all of the end-stages, very clean. They all worked when made, and are not too likely to be "worn out" now. You want "to start learning organ". Use the parts you have and start playing.
I have used the organ when it was in its original condition. Some stops were working properly others had issues. There was constant background noise (hiss), more or less hidden while playing, but clearly audible at rest. I would not qualify this as "clean" and I would like to have something better. I have a much cleaner signal with my headphone amplifier, for example.
This hiss could be caused by either the sound generation circuits or the filtering + amplifying circuits. Or both. At this stage, I don't know.
Now regarding your recommendation of using the parts I have: this makes sense at first sight of course, but there is also a significant work of retro engineering. This is not going to be plug and play. First, there are wires soldered on the board coming from another board I have thrown away, so I have to figure out what they were for. Then the logic was completely different: the pipes were assembled in groups, and each group was sent to one speaker. So I have no idea whether sending the same signal to the 4 channels would produce the result I want. And I will have to feed all this with a good and stable 15V, but that's the easiest part.
Anyway this is worth a try.
Regarding "starting playing": I have not be waiting for you to give me this (wise) recommendation ;-) I can already enjoy a fully functional instrument on headphones!
PS: Bach would be probably excited to play on a modern organ which can do many things former instruments couldn't.
This hiss could be caused by either the sound generation circuits or the filtering + amplifying circuits. Or both. At this stage, I don't know.
Now regarding your recommendation of using the parts I have: this makes sense at first sight of course, but there is also a significant work of retro engineering. This is not going to be plug and play. First, there are wires soldered on the board coming from another board I have thrown away, so I have to figure out what they were for. Then the logic was completely different: the pipes were assembled in groups, and each group was sent to one speaker. So I have no idea whether sending the same signal to the 4 channels would produce the result I want. And I will have to feed all this with a good and stable 15V, but that's the easiest part.
Anyway this is worth a try.
Regarding "starting playing": I have not be waiting for you to give me this (wise) recommendation ;-) I can already enjoy a fully functional instrument on headphones!
PS: Bach would be probably excited to play on a modern organ which can do many things former instruments couldn't.
I've never seen a strong argument for class A(!), its very inefficient indeed, 30W of class A is a large room heater, completely unnecessary.
Go for class B or D, keep it simple. D runs coolest, is simplest to build too, a TPA3116 module might be appropriate as it can drive 2 channels at 4 ohms and they are readily available.
For class B there are various chip amp options if you want a simple approach, although a lot of them are being phased out of production. The LM3886 is very highly regarded example that can drive 4 ohms.
Thank you for your recommendation! I have had a look at the datasheet and the typical application circuit looks very simple. So simple that I wonder if I could change my original plan (1 amplifier + 3 way crossover filter), buy 3 of those (they are cheap) and use one amplifier per speaker. This would allow me to filter the signal before amplification, thus avoiding bulky and more expensive components, and also to be able to adjust the amplification level for each speaker. What do you think?
Something like an LM3886 would provide plenty of power and sound quality for your needs. I'm obviously partial to my LM3886DR, but there are many other incarnations of the LM3886, including a free layout should you want an all-DIY route. If you choose the DIY route, I recommend that you read my Taming the LM3886 article series.
Can the organ software handle crossover duty as well? If so, you can implement the crossover digitally. That'll save you a bunch of trouble. The drawback is that you'll then need three DAC channels and three amplifiers.
Tom
Can the organ software handle crossover duty as well? If so, you can implement the crossover digitally. That'll save you a bunch of trouble. The drawback is that you'll then need three DAC channels and three amplifiers.
Tom
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There you are.
I was just thinkin' , this sounds like a job for a well implemented, bullet-proof 3886 ...
I was just thinkin' , this sounds like a job for a well implemented, bullet-proof 3886 ...
... actually you don't even need to read Tom's excellent articles [you should], just study the PCB for 5-10 min.
You can see good EMC/EMI control [~his job] on the inputs and outputs, the "toight"-as-possible PS caps snuggled right up to the chip. The proper, well-thought-out, efficiently executed extra/ancillary components/circuits as per all recommendations from the creators.
And then the uniquely HUGE interconnection between the top and bottom ground planes [and in a ... surprising place], and ... oh, what else?
Oh, that "Made In Canada" labels carries some gravitas! if I so say so myself.
;p
You can see good EMC/EMI control [~his job] on the inputs and outputs, the "toight"-as-possible PS caps snuggled right up to the chip. The proper, well-thought-out, efficiently executed extra/ancillary components/circuits as per all recommendations from the creators.
And then the uniquely HUGE interconnection between the top and bottom ground planes [and in a ... surprising place], and ... oh, what else?
Oh, that "Made In Canada" labels carries some gravitas! if I so say so myself.
;p
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No, it can't. There are other softwares for that, I actually tried one, but it messed up my audio configuration. With Linux there is potentially a solution to any problem, but it takes time to select the right piece of software and then set it up, especially for semi-beginner like me.
I agree and that's the reason I'm not looking into this direction now. The only DAC solution I know with more than 2 outputs for Raspberry pi is the Octo sound card and but its performance doesn't seem to be outstanding.
Fun thread! Nice project . I don't have much to add other than the LM3886 would be the ticket. You should go with it.
Also, I just love the look of those PCBs in post #6. They don't make 'em like that any more. 🙂
Also, I just love the look of those PCBs in post #6. They don't make 'em like that any more. 🙂
... actually you don't even need to read Tom's excellent articles [you should], just study the PCB for 5-10 min.
View attachment 874338
You can see good EMC/EMI control [~his job] on the inputs and outputs, the "toight"-as-possible PS caps snuggled right up to the chip. The proper, well-thought-out, efficiently executed extra/ancillary components/circuits as per all recommendations from the creators.
And then the uniquely HUGE interconnection between the top and bottom ground planes [and in a ... surprising place], and ... oh, what else?
Oh, that "Made In Canada" labels carries some gravitas! if I so say so myself.
;p
Thank you for this information!
I have done a test last weekend with my current amplifier and a rather cheap (~30€) 3-way crossover filter. At first, I was missing high frequencies (which are critical to get the specific organ brilliance). My amplifier has knob to adjust treble fortunately. At the maximum setting, I got an acceptable sound. At least way better than all tests I did before without the crossover filter.
Now I have a new problem to solve: if I use the LM3886DR circuit (I like the "DR"!), with a crossover filter, I won't have any mean to balance my 3 loudspeakers... I would like to avoid a software equalizer, to be able to switch quickly from headphones to loudspeakers without the need to adjust the equalizer settings in the Raspberry, because my goal is to run it headless.
Thank you!
You're right. While disassembling all these old parts, I could not help but think of the operator(s) who have soldered, wired and assembled all this manually... For example, each key had 3 wires to connect it to an electronic board. Since the organ has two 61 key manuals plus a 30 key pedalboard, this gives a total of (61+61+30)*3 = 456 wires! I have kept them, of course, and I think I now have enough wire for the rest of my life 🙂
I would suggest an individual volume control pot on each channel of your LM3886 amp.
That's the easy way to adjust levels between the speakers. Once set, you leave it.
Active setups with amp volume control are hardly practical.
That's the easy way to adjust levels between the speakers. Once set, you leave it.
Active setups with amp volume control are hardly practical.
After a month of silence, I'm back! Silence, but not inactivity: I worked on other aspects of my project.
Today I eventually managed to install a software equalizer on my Raspberry Pi. In addition, I found how to define two different profiles (for headphones and loudspeakers) and change them on the fly. I will build a small electronic boards detecting if the headphones are connected and informing the Pi through one I/O pin.
This is good news, because I will only need 1 amplifier, instead of 3. The scheme will be:
Raspberry Pi -> equalizer -> DAC -> stereo to mono converter -> amplifier -> crossover filter -> loudspeakers.
I already have the 3 way crossover filter, and 2 resistors will do the stereo to mono conversion.
I now have to study the LM3886 more closely.
I also need a PSU. I know that the PSU has an impact on sound quality. Any advice?
Today I eventually managed to install a software equalizer on my Raspberry Pi. In addition, I found how to define two different profiles (for headphones and loudspeakers) and change them on the fly. I will build a small electronic boards detecting if the headphones are connected and informing the Pi through one I/O pin.
This is good news, because I will only need 1 amplifier, instead of 3. The scheme will be:
Raspberry Pi -> equalizer -> DAC -> stereo to mono converter -> amplifier -> crossover filter -> loudspeakers.
I already have the 3 way crossover filter, and 2 resistors will do the stereo to mono conversion.
I now have to study the LM3886 more closely.
I also need a PSU. I know that the PSU has an impact on sound quality. Any advice?