Hello All,
I spend most of my time over on the tube forum, SS just has not been my thing. I am in the process of designing my new reference system.
Details have not been ironed out but the system will rough out like this.
Tube Phono Preamp, CD, PC sound, Tuner into
Tube preamp w/ active 100hz TUBE crossover 12db/octave Linkwitz alignment.
The highpass will be split with another tube active Xover and biamped via tube amps to speakers to be determined.
The low pass is where my question comes in.
Most of my budget is blown on tube amp iron, tubes etc. So I am limited on the budget for the subs and amps. This mean relatively low sensitivity woofers in sealed enclosures. The power needed to drive these will be well beyond SET and even most PP Pentode tube amps so I want to try my hand at a chip amp.
I am looking for about 60WPC with a simple gain control nothing else. I would like to wire it Point to Point in keeping with the theme of the rest of the system.
So what I am looking for is a simple chip amp schematic that would lend itself to P to P wiring and with cost as the major concern.
I spend most of my time over on the tube forum, SS just has not been my thing. I am in the process of designing my new reference system.
Details have not been ironed out but the system will rough out like this.
Tube Phono Preamp, CD, PC sound, Tuner into
Tube preamp w/ active 100hz TUBE crossover 12db/octave Linkwitz alignment.
The highpass will be split with another tube active Xover and biamped via tube amps to speakers to be determined.
The low pass is where my question comes in.
Most of my budget is blown on tube amp iron, tubes etc. So I am limited on the budget for the subs and amps. This mean relatively low sensitivity woofers in sealed enclosures. The power needed to drive these will be well beyond SET and even most PP Pentode tube amps so I want to try my hand at a chip amp.
I am looking for about 60WPC with a simple gain control nothing else. I would like to wire it Point to Point in keeping with the theme of the rest of the system.
So what I am looking for is a simple chip amp schematic that would lend itself to P to P wiring and with cost as the major concern.
http://home.comcast.net/~jhidley/
"$35 each. This product is exempt from the $80 minimum order rule, when shipped to an address in the US, due to the fact that it is already packaged to ship as is..
Foster subwoofer plate amplifier. 115W into 4ohms, 80W into 8ohms. 4th order (24dB/octave) low pass adjustable from 50-200Hz. 0-180 degree phase switch, RCA and speaker level inputs, volume control. Unit has a 3rd order (18dB/octave) high pass filter at 29Hz with a Q of 0.707 built into the subwoofer section. Can easily be modified for any Q and cutoff frequency that you want by changing R615, R617, R618, C607, C608 and C609. The amplifier also has a spectral tilt control that is adjusted to give about 10dB of shelving. It can be manually adjusted with a pot on the PCB. See response curves linked below. A drawing of the amplifier and schematic are both linked below. Two of these amplifiers can be bridged together to produce 220W into 8ohms. See the FAQ below for details of bridging and filter modifications."
NHT drivers and electronics surplus sale
You cannot build anything this powerful for $35.
Ted
"$35 each. This product is exempt from the $80 minimum order rule, when shipped to an address in the US, due to the fact that it is already packaged to ship as is..
Foster subwoofer plate amplifier. 115W into 4ohms, 80W into 8ohms. 4th order (24dB/octave) low pass adjustable from 50-200Hz. 0-180 degree phase switch, RCA and speaker level inputs, volume control. Unit has a 3rd order (18dB/octave) high pass filter at 29Hz with a Q of 0.707 built into the subwoofer section. Can easily be modified for any Q and cutoff frequency that you want by changing R615, R617, R618, C607, C608 and C609. The amplifier also has a spectral tilt control that is adjusted to give about 10dB of shelving. It can be manually adjusted with a pot on the PCB. See response curves linked below. A drawing of the amplifier and schematic are both linked below. Two of these amplifiers can be bridged together to produce 220W into 8ohms. See the FAQ below for details of bridging and filter modifications."
NHT drivers and electronics surplus sale
You cannot build anything this powerful for $35.
Ted
Hi coldcathode, I did a P2P LM3886 using the schematic in BrianGT's Chipamps.com kit. Though you will only get 60W if you are driving a 4 ohm load.. if you are driving 8 Ohms you can safely get 50W.
Tony.
edit: I think I spent around $130 AU on the amp... the Transformer was the most expensive part.
Tony.
edit: I think I spent around $130 AU on the amp... the Transformer was the most expensive part.
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Good instrustions for P to P 3886
http://dogbreath.de/Chipamps/CopperAmp/CopperAmp.html
http://dogbreath.de/Chipamps/ThreeResAmp/ThreeResAmp.html
Mick Feuerbacher Audio Projects has some excellent step by step instructions with pictures of 3886 point to point amplifier. You should look at Linkwitz website for his version of 3886 too which includes safer input circuit.
http://www.linkwitzlab.com/images/graphics/3886pwr.gif
Ted
http://dogbreath.de/Chipamps/CopperAmp/CopperAmp.html
http://dogbreath.de/Chipamps/ThreeResAmp/ThreeResAmp.html
Mick Feuerbacher Audio Projects has some excellent step by step instructions with pictures of 3886 point to point amplifier. You should look at Linkwitz website for his version of 3886 too which includes safer input circuit.
http://www.linkwitzlab.com/images/graphics/3886pwr.gif
Ted
ted,
AWESOME links, EXACTLY what I was looking for!!!
I in no way want to belittle solid state chip amps but I really do not want to spend much time & effort on these amps. Can you or someone else point out for me all the basic info needed to build one of these?
For instance, would 100VA trannys be enough? example 25V @ 4 amp? Bridge rectified I am looking at about 35 Volts?
How can I calculate the power requirements assuming a 4ohm load? I can design tube amps all day long but I need some basics on these amps.
In the schematic for the copperamp I have a couple questions, if you can answer them for me it would be great. (I am willing to assist SS guys looking to get into tubes)
R1 (pot) is used only for volume and sets input inpedance to the source correct? Does it have any effect other than attentuating the signal?
Rg what is Rg use for? some sort of input bias?
Rf gives feedback? how is that value calculated in relation to load power etc.
Rm is a muting resistor and is switch in and out I suppose?
Cs The caps are for smoothing the supply and "headroom" I suppose, doe their value have any significance? ie can I raise the value for more "headroom" considering relatively small trannies?
AWESOME links, EXACTLY what I was looking for!!!
I in no way want to belittle solid state chip amps but I really do not want to spend much time & effort on these amps. Can you or someone else point out for me all the basic info needed to build one of these?
For instance, would 100VA trannys be enough? example 25V @ 4 amp? Bridge rectified I am looking at about 35 Volts?
How can I calculate the power requirements assuming a 4ohm load? I can design tube amps all day long but I need some basics on these amps.
In the schematic for the copperamp I have a couple questions, if you can answer them for me it would be great. (I am willing to assist SS guys looking to get into tubes)
R1 (pot) is used only for volume and sets input inpedance to the source correct? Does it have any effect other than attentuating the signal?
Rg what is Rg use for? some sort of input bias?
Rf gives feedback? how is that value calculated in relation to load power etc.
Rm is a muting resistor and is switch in and out I suppose?
Cs The caps are for smoothing the supply and "headroom" I suppose, doe their value have any significance? ie can I raise the value for more "headroom" considering relatively small trannies?
Use 18-0-18 toroid with at least 160 VA rating. 25 volt AC gives too high DC for 4 ohm speakers and will make too much heat on the 3886. I am looking for link for Antek toroids but it seems to have changed. They were one of the best toroid suppliers.
Sorry I do not have enough time and knowledge to cover all of your questions. Again I will remind you that it is not cost effective to build an amplifier.
Ted
Sorry I do not have enough time and knowledge to cover all of your questions. Again I will remind you that it is not cost effective to build an amplifier.
Ted
Don't overlook class D or T amps for reduced power supply and heat sink cost because of high efficiency. I bought 4 stereo 9 watt per chanel .04% HD at 4 ohm boards that I run from an old ATX power supply. Total deIivered cost was $41. I need several low impedace amplifiers to use for a system using many drivers which I do not want to run in series. Several efficient powered speakers can produce plenty of low distortion sound. I already have two powered subwoofers. Good luck in your adventure. Someday I may go insane and build a high power very low impedance class D amp with digital input.
Ted
Ted
Hi ColdCathode,
I'd highly recommend reading at least pages 18-21 of the LM3886 datasheet
Page 17 might also be helpfull if you are planning on using the smallest heatsink you can get away with.
Rg I'm unsure, I'm even unsure as to whether I had one of these on mine. I mostly used BrianGT's schematic but also took queues off the typical application in the datasheet (which doesn't have this resistor).
The datasheet has the info on calculating the feedback resistors (It is the ratio between rf and ri that sets the gain).
rm provides the necessary current to turn off the muting fuction (ie it will be muted if left out). If you don't want a mute function simply hard wire the resistor in
Cs is a supply bypassing cap. I will quote the following from the datasheet:
You can use bigger caps in the power-supply which I would say would be a good idea if you are using this for bass duty. A lot of people claim that the LM3886 is better with smaller capacitance in the powersuply, but I think usually the reason is because of perceived differences in the midrange and higher freqs, so for bass duty I think would be worth it. Also I would not recommend using ceramics as per the app note quote above, but instead some good quality film capacitors. I used polyester in mine, but I would consider using polypropylene or pps types now.
Tony.
I'd highly recommend reading at least pages 18-21 of the LM3886 datasheet
Page 17 might also be helpfull if you are planning on using the smallest heatsink you can get away with. Rg I'm unsure, I'm even unsure as to whether I had one of these on mine. I mostly used BrianGT's schematic but also took queues off the typical application in the datasheet (which doesn't have this resistor).
The datasheet has the info on calculating the feedback resistors (It is the ratio between rf and ri that sets the gain).
rm provides the necessary current to turn off the muting fuction (ie it will be muted if left out). If you don't want a mute function simply hard wire the resistor in
Cs is a supply bypassing cap. I will quote the following from the datasheet:
You can use bigger caps in the power-supply which I would say would be a good idea if you are using this for bass duty. A lot of people claim that the LM3886 is better with smaller capacitance in the powersuply, but I think usually the reason is because of perceived differences in the midrange and higher freqs, so for bass duty I think would be worth it. Also I would not recommend using ceramics as per the app note quote above, but instead some good quality film capacitors. I used polyester in mine, but I would consider using polypropylene or pps types now.
Tony.
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I would strongly advise against P to P construction of a chip amp. There are numerous PCB deals on Ebay for the LM3886 in fact I recently bought a set (2 amp boards -1 ps board ) for $7.99 plus $4.00 shipping.They are high quality and a proven design. Go to Ebay/Electronics/Amplifiers/and search LM3886. As stated in earlier post the big problem is layout and oscillation. The PCB solves that problem. Apex jr has Avel transformers (toroid) for $22 plus shipping . The plate Amp spoken of earlier is unbeatable in value .
Thanks JB74. Google must have been sleepy when they could not find that from Antek but now I have the correct address.
If I build a chipamp it will use this toroid
Antek - AN-6218
$75 shipped is a good price for 600 VA. That is the largest toroid with 18 volt output and will power about 6 3886 and do a really good job on less plus extra capacity for expansion. Extra capacity will keep the voltage high enough so you do not need regulation. Use a big bridge rectifier to keep things simple as recommended by several designers plus lots of capacitors. Most of Dogbreath's instructions can be followed with good success but make sure your input receives no DC or you must include input capacitor as shown on most chipamp designs. Linkwitz is probably the expert. I downloaded several popular schematics and put them all on a screen so I could compare. You need very big heatsink to keep the 3886 chips cool. Many diy worry about a pretty case more than the needed parts!
Ted
If I build a chipamp it will use this toroid
Antek - AN-6218
$75 shipped is a good price for 600 VA. That is the largest toroid with 18 volt output and will power about 6 3886 and do a really good job on less plus extra capacity for expansion. Extra capacity will keep the voltage high enough so you do not need regulation. Use a big bridge rectifier to keep things simple as recommended by several designers plus lots of capacitors. Most of Dogbreath's instructions can be followed with good success but make sure your input receives no DC or you must include input capacitor as shown on most chipamp designs. Linkwitz is probably the expert. I downloaded several popular schematics and put them all on a screen so I could compare. You need very big heatsink to keep the 3886 chips cool. Many diy worry about a pretty case more than the needed parts!
Ted
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Hi Sandy, yes the risk of it not working is much higher than using if using a proven layout, but if done carefully it works really well
I think coldcathodes decision is mostly a philosopical one The reason I chose to do p2p was twofold one was for exactly the reason of problems caused by layout, the second was that at the time Hardly anyone seemed to be doing p2p 3886's, as it was considered to difficult (red flag to a bull)... Admittedly not everyone will want to make something as compact as what I did, but my way of dealing with layout problems was to make everything as close to the chip as possible
I still kept separate returns fo critical earth return paths as per the data sheet. It is completely stable, and the quietest amp I have ever built! Tony.
Hi Sandy, yes the risk of it not working is much higher than using if using a proven layout, but if done carefully it works really well
Tony.
Wintermute,
Spot ON! Sandy with no disrespect intended, anyone can purchase a PC Board and solder in some components per a datasheet or "proven design".
I come from the world of Vacuum Tube Audio where everything is "risky" and it may seem to most people a LOT of work for little results.
Example. I have a 45 Single Ended Triode amp I designed and built myself from scratch. It took 6 weeks to build, cost me over $350 for parts(not including $250 for tubes). It takes up a 14" x 18" area, weights 55 pounds! and puts out a whopping 1.5 Watts per channel.
The filaments (heaters) for just the 2 output tubes consume 7.5WATTS of power just to heat the tubes.
BUT...This is a BIG BUT, you will NEVER hear anything as smooth as silk and full rich sound as this amp!!
IMHO, 1 Watt of Tube Power = 10 Watts of the highest end Solid State Stuff you could put together.
Again, I mean no disrespect to the Solid State folks here, or else I would not be here looking for info on chip amps. To me everything has its place, and in this case I want to build chip amps for my subwoofers. To get 30-40WPC in a tube design could cost me in excess of $2,000! Not too mention the space it takes up. Since I feel that I would never be able to tell any audible difference in a tube amp or SS in the range of 25 to 100hz I think this is the most reliable, cost effective means for getting that level of power.
I intend for the chassis and overall aesthetics of the chip amps to follow the theme of my tube amps. So I won't be using torroids, EI's look more the part.
I am continuing to research and understand how the chip amps work. I am trying to get some understanding of how the different cap's and resistors affect the output.
I realize I could easily purchase two plate amps and be done with it, but I plan to have a system where every component (besides the sources) has been designed and hand built by myself.
Hi coldcathode, I think the answer to your question on rg is in this thread
Note I assume the rg you are referring to is the one in the second link in Ted's post, as the first one has ri incorrectly labeled as rg (well incorrect from the standpoint of the datasheet )
At this point I'm thinking it would have been really smart to have made some notes about what I did I suspect I went with Brians schematic and used 22K for both rf and rg, I also suspect that I decided to just go with his gain calcs and used the 680 ohm for ri.
The datasheet has a pot on the input for the "typical application" so without it I guess rg is necessary, or you will get the problem Oliphant had
Tony.
Note I assume the rg you are referring to is the one in the second link in Ted's post, as the first one has ri incorrectly labeled as rg (well incorrect from the standpoint of the datasheet
) At this point I'm thinking it would have been really smart to have made some notes about what I did
I suspect I went with Brians schematic and used 22K for both rf and rg, I also suspect that I decided to just go with his gain calcs and used the 680 ohm for ri. The datasheet has a pot on the input for the "typical application" so without it I guess rg is necessary, or you will get the problem Oliphant had
Tony.
All,
A question I have about Power Supply.
I assume that the Positive and Negative supply voltages can be provide via separate EI transformers and bridges, correct?
When calculating current supply needed are we talking in terms of each supply or total.
IE, the calcs on the data sheets indicate a square root of 2xPo/Load is this amperage the peak positive or negative or the total of both?
I ask because I have a quantity of 25VCT 2Amp transformers and am wondering if I could use (2) per channel ?
Hypothetical 32Watts Po would be 64/8 = 8 sqrt = 2.8 amps? So 1.4 from each side or is it peak of 2.8 from either side?
A question I have about Power Supply.
I assume that the Positive and Negative supply voltages can be provide via separate EI transformers and bridges, correct?
When calculating current supply needed are we talking in terms of each supply or total.
IE, the calcs on the data sheets indicate a square root of 2xPo/Load is this amperage the peak positive or negative or the total of both?
I ask because I have a quantity of 25VCT 2Amp transformers and am wondering if I could use (2) per channel ?
Hypothetical 32Watts Po would be 64/8 = 8 sqrt = 2.8 amps? So 1.4 from each side or is it peak of 2.8 from either side?
About 26 watts before the results become unpleasant. This is insufficient for combining LM3886 with the described speakers.
There may be a way to do it. Do you have four identical Dual Bobbin transformers available?
What is confusing to me is this.
In TUBE design we primarily figure output as the power (watts) thru the Primary of an output transformer (OPT) = (the LOAD). This LOAD is based upon the impedance of the speaker reflected to the primary via the ratio of the windings squared.
Example an 8Ohm speaker attached to the secondarys of an OPT with 20:1 turns ratio imposes a load of 3200 ohms. A swing Peak to Peak of 300 Volts and a Current Swing of 50mA would yield a Pout of 15Watts into the load Divide by 8 for RMS and you get about 2 watts.
That is for class A operation where current is flowing all the time in the Primary.
The chip amps I guess operate in Class D this is where I get all confused.
In TUBE design we primarily figure output as the power (watts) thru the Primary of an output transformer (OPT) = (the LOAD). This LOAD is based upon the impedance of the speaker reflected to the primary via the ratio of the windings squared.
Example an 8Ohm speaker attached to the secondarys of an OPT with 20:1 turns ratio imposes a load of 3200 ohms. A swing Peak to Peak of 300 Volts and a Current Swing of 50mA would yield a Pout of 15Watts into the load Divide by 8 for RMS and you get about 2 watts.
That is for class A operation where current is flowing all the time in the Primary.
The chip amps I guess operate in Class D this is where I get all confused.
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