Hi,
I'm new to the world of chipamps.
I'm a guitarist and was wondering whether a chipamp such as the kit available here <http://chipamp.com/product/non-inverting-lm3886-mono-kit/> would be suitable for use as a clean guitar amplifier. My plan is to use effects pedals for all distortion, tone shaping, etc. and use the chipamp purely as a clean amplifier.
Also, would the chipamp require a preamp or could the pedals' output be sent straight the chipamp input?
Cheers,
Chris
I'm new to the world of chipamps.
I'm a guitarist and was wondering whether a chipamp such as the kit available here <http://chipamp.com/product/non-inverting-lm3886-mono-kit/> would be suitable for use as a clean guitar amplifier. My plan is to use effects pedals for all distortion, tone shaping, etc. and use the chipamp purely as a clean amplifier.
Also, would the chipamp require a preamp or could the pedals' output be sent straight the chipamp input?
Cheers,
Chris
Yes you certainly can use a chip amp. As long as the amp has the required power output you need. You would need a preamp if the pedal has no line level out.
To Play electric music you NEED a "player's" preamp.
That is very different from reproducing someone's music.
That is very different from reproducing someone's music.
What's the output from the pedals?
You could always piggyback a preamp into one of the pedals, borrowing its power supply.
You could always piggyback a preamp into one of the pedals, borrowing its power supply.
The later model Marshall Valavestate amplifiers use Two TDA7293's in parallel.
You might like to take a look at this nice module,
Yuan-Jing 3 x TDA7293 Parallel 250W Mono Power Amp Board
I am currently helping a friend with putting 4 of these in a case for his line array's.
So I can't tell you yet as to how they perform, but I have used the Valvestate amp's with these chips and they sound quiet and nice and clean as well.
FWIW
jer 🙂
P.S. These 3xTDA7293's may be better suited for 4 ohm loads and heavy use as a guitar amplifier than what a single LM3886 would be.
A 30Vac-0-30Vac transformer for +/- 42.5Vdc would allow you 112.5 watts into 8 ohms and 225 watts into 4 ohms.
These same boards can be found on Ebay for the same price of $19.99 and $10 for shipping. 🙂
You might like to take a look at this nice module,
Yuan-Jing 3 x TDA7293 Parallel 250W Mono Power Amp Board
I am currently helping a friend with putting 4 of these in a case for his line array's.
So I can't tell you yet as to how they perform, but I have used the Valvestate amp's with these chips and they sound quiet and nice and clean as well.
FWIW
jer 🙂
P.S. These 3xTDA7293's may be better suited for 4 ohm loads and heavy use as a guitar amplifier than what a single LM3886 would be.
A 30Vac-0-30Vac transformer for +/- 42.5Vdc would allow you 112.5 watts into 8 ohms and 225 watts into 4 ohms.
These same boards can be found on Ebay for the same price of $19.99 and $10 for shipping. 🙂
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Could you expand on this a bit please, I'm not sure what you mean.
I plan to create the "tone" using pedals (EQ, distortion, etc.). I want to use the power amp only for volume. There are several examples of guitarists using this approach - David Gilmour, Eddie Van Halen.
I'm not sure what you mean by "better suited" - is the issue related to performance (i.e. is there something about amplifying a guitar that is different to other sources?) or are you referring to something like reliability?
Cheers,
Chris
Better suited as to the type of abuse the amp will endure and speaker loads, namely 4 ohms.
Yes, Performance and especially Reliability!!
As far as Preamps are concerned any of your favorite flavors can be used.
My two personal favorites happens to be the Valvstate front end as it is very easy to duplicate and I love the sound of it, and, the Peavey Renown front end.
Or you can make a very simple tube preamp as well with one or two 12AX7's.
jer 🙂
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The speakers I intend to use are both 8 ohms - a Celestion G12H - 100 and a Jensen P10Q. Remember too that I want this amp to be clean and not have any preamp distortion.
Any suggestion for schematics or kits?
Do you have a heat sink? How about a transformer? Both can be had with savvy and lucky dumpster diving.
Chipamps.com has everything from individual parts (including mono boards and power supply boards) to partial kits to turnkey kits for the 3886. For cheap you could get their board and order the parts from Mouser or Digikey. Chipamps has some good prices on some of their parts too. They offer the TF version of the 3886 at a great price; but the TF version isn't the best choice when going for maximum power or for 4 ohm loads.
Have you assembled a kit before?
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"Chip amp" is a slang term, it has no special electronic significance. In fact, these days all non-valve instrument amps are chip amps, you can't buy anything else. So the answer to your question is yes, and lots of people are already doing it, look on YouTube.
The factory circuit would do you proud ( http://www.ti.com/lit/gpn/lm3886 ), and so would any of various modifications. It's a matter of opinion whether any given modification is better than the factory's circuit, which was developed by the same engineers who created the LM3886 in the first place.
For working live you want to remember two things. a) No compression, as is done to recorded music, and: b) The keyboard player is going to want to plug in. These mean serous demands on the power supply, which doesn't mean complexity, it just means pure honkin' size, meaning watts (VA).
Now speaking of that power supply:
The LM3886 will put out some 50 watts with a +/- 35 volt power suppy (per the data sheet linked above), but it will aso put out "135W Instantaneous Peak Output Power." Peak power as in you're hitting some hard licks, or the keyboard player suddenly comes in with s/his left hand at full volume. But the amp can only put out as much power as you put in. It all comes down to the power supply.
To give you just some general information, the rule of thumb for any serious use is that the power supply is twice as big as the amp's full output. That is, a 50-watt amp would need a 100-watt power supply. But for your use it might be a good idea to go a step beyond that, to something like a 150-watt power supply.
Unfortunately, power doesn't come cheap. Power supplies are of a muchness, basically you just plug them into the amp. The variable is how much power they can put out, which comes down to the transformer's capacity. Transformers are rated in VA, not watts, but the rule of thumb is watts = volts x amps = VA, which means a 150-watt power supply would need a 150VA transformer.
Such a beast runs a few bucks. But slow down, remember I'm just giving you some general information. You don't have to go the full distance, in fact, theoretically you could just plug in a wall wart and run the thing. As long as you provide around +/- 20 volts (per the instructions for your kit) the amp will run. It's just that if you hook it to a 5-watt power supply (5VA transformer), well, the amp will put out 5 watts and that's all you get. (Actually you also get a lot of distortion as the power supply is overloaded, but that's beside the point.)
Look on page 14 of the data sheet linked above, at figure 37 labeled "Output Power vs Supply Voltage." Remember that the voltages indicated are +/-, and this tells the tale. In the auto parts store they'll ask you, "Speed costs money, how fast do you want to go?" The same applies to power.
None of which is intended to scare you off. Remember those guys on YouTube, their amps are working fine. Just to make you aware of the situation.
PS just to put a bug in your ear, eBay computer heat sinks are very effective used in chip amps, you can run them with or without the fan.
.
"Chip amp" is a slang term, it has no special electronic significance. In fact, these days all non-valve instrument amps are chip amps, you can't buy anything else. So the answer to your question is yes, and lots of people are already doing it, look on YouTube.
The factory circuit would do you proud ( http://www.ti.com/lit/gpn/lm3886 ), and so would any of various modifications. It's a matter of opinion whether any given modification is better than the factory's circuit, which was developed by the same engineers who created the LM3886 in the first place.
For working live you want to remember two things. a) No compression, as is done to recorded music, and: b) The keyboard player is going to want to plug in. These mean serous demands on the power supply, which doesn't mean complexity, it just means pure honkin' size, meaning watts (VA).
Now speaking of that power supply:
The LM3886 will put out some 50 watts with a +/- 35 volt power suppy (per the data sheet linked above), but it will aso put out "135W Instantaneous Peak Output Power." Peak power as in you're hitting some hard licks, or the keyboard player suddenly comes in with s/his left hand at full volume. But the amp can only put out as much power as you put in. It all comes down to the power supply.
To give you just some general information, the rule of thumb for any serious use is that the power supply is twice as big as the amp's full output. That is, a 50-watt amp would need a 100-watt power supply. But for your use it might be a good idea to go a step beyond that, to something like a 150-watt power supply.
Unfortunately, power doesn't come cheap. Power supplies are of a muchness, basically you just plug them into the amp. The variable is how much power they can put out, which comes down to the transformer's capacity. Transformers are rated in VA, not watts, but the rule of thumb is watts = volts x amps = VA, which means a 150-watt power supply would need a 150VA transformer.
Such a beast runs a few bucks. But slow down, remember I'm just giving you some general information. You don't have to go the full distance, in fact, theoretically you could just plug in a wall wart and run the thing. As long as you provide around +/- 20 volts (per the instructions for your kit) the amp will run. It's just that if you hook it to a 5-watt power supply (5VA transformer), well, the amp will put out 5 watts and that's all you get. (Actually you also get a lot of distortion as the power supply is overloaded, but that's beside the point.)
Look on page 14 of the data sheet linked above, at figure 37 labeled "Output Power vs Supply Voltage." Remember that the voltages indicated are +/-, and this tells the tale. In the auto parts store they'll ask you, "Speed costs money, how fast do you want to go?" The same applies to power.
None of which is intended to scare you off. Remember those guys on YouTube, their amps are working fine. Just to make you aware of the situation.
PS just to put a bug in your ear, eBay computer heat sinks are very effective used in chip amps, you can run them with or without the fan.
.
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Unless otherwise stated, you can assume that any amp (as opposed to a preamp, mixer, pedal, whatever) requires a line level input to output its full rated power.
Unfortunately, in these international times there are several definitions of "line level." But you won't go far wrong by using the classic line level value of one volt.
So it depends on the output level of the pedal, which might or might not be known to you...look in the specs? But anything with a battery will probably drive an amp to a more or less satisfactory level.
Be aware that a guitar or other instrument with a magnetic (standard for guitars) or piezo pickup is a special beast due to its high impedance output (high Zout). These should be plugged into a high impedance input (high Zin). Such inputs are standard on guitar amps, but to plug a guitar into anything else you have to specify that you need high Zin. (which is in the 1/2 to one megohm region)
This might or might not not apply to acoustic guitars with onboard electronics (volume, tone, whatever). You'd have to look at the specs to see exactly what they require, but obviously it's a safe bet that they'll plug into a guitar amp.
None of this apples to headphone outputs, or line outputs. These are always low Zout and can be plugged directly into any standard amp, or into a guitar amp. They can be expected to have enough output to drive the amp, but this is not certain, they might need a preamp.
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Many thanks for the detailed explanation.
Could you suggest a suitable power supply/transformer so I can get an idea of the sort of thing that's required.
Cheers!
What kind of output power do you want and what is the load impedance you are expecting?
Typically your Transformers Vac^2/ohm will tell what the amp should produce providing that it is rated for the power level.
For instance I am building a 4 channel amp using the 3xTDA7293 module I had posted. I selected a 30v-0-30v transformer at 800VA.
For that voltage I expect about +/-42Vdc for the amps and this comes out to 30v*30v/8ohms=112.5 watts for 8 ohms and 225watts for 4 ohms at the edge of clipping (approx1% THD).
Now I should have selected a 1000VA transoformer since my load for these amps will be 4 ohms but they will never see more than 150 to 200 watts of power use.
Not only that it is for a bi-amped speaker system and the tweeters will never need more that about 120 watts leaving ample power leftover should the other two amps for the woofers use the full 225 watts that they are capable of.
It has been shown that chipamps need an ample amount of heatsink in order to keep them cool.
This is especially important if you are running a higher voltage on them for an 8 ohm load and decide to hook it to a 4 ohm load, it is advisable to run to chips in parallel and is why Marshall does so with the Valvestate.
Can't go wrong with A 3x chipamp even if you never intend to use all of the power it produces especially for the price of $30 or so.
You can't populate that board for that price with but just the chips alone!!
The other thing is that the TDA7293's don't have the annoying Spike protection should the amp start to reach clipping or get a bit warm due to heavy use.
If you do choose to go with the LM3886's I would seriously consider using two of them in a PA100 configuration.
See this App. note,
http://www.ti.com/lit/an/snaa021b/snaa021b.pdf
FWIW
jer 🙂
Typically your Transformers Vac^2/ohm will tell what the amp should produce providing that it is rated for the power level.
For instance I am building a 4 channel amp using the 3xTDA7293 module I had posted. I selected a 30v-0-30v transformer at 800VA.
For that voltage I expect about +/-42Vdc for the amps and this comes out to 30v*30v/8ohms=112.5 watts for 8 ohms and 225watts for 4 ohms at the edge of clipping (approx1% THD).
Now I should have selected a 1000VA transoformer since my load for these amps will be 4 ohms but they will never see more than 150 to 200 watts of power use.
Not only that it is for a bi-amped speaker system and the tweeters will never need more that about 120 watts leaving ample power leftover should the other two amps for the woofers use the full 225 watts that they are capable of.
It has been shown that chipamps need an ample amount of heatsink in order to keep them cool.
This is especially important if you are running a higher voltage on them for an 8 ohm load and decide to hook it to a 4 ohm load, it is advisable to run to chips in parallel and is why Marshall does so with the Valvestate.
Can't go wrong with A 3x chipamp even if you never intend to use all of the power it produces especially for the price of $30 or so.
You can't populate that board for that price with but just the chips alone!!
The other thing is that the TDA7293's don't have the annoying Spike protection should the amp start to reach clipping or get a bit warm due to heavy use.
If you do choose to go with the LM3886's I would seriously consider using two of them in a PA100 configuration.
See this App. note,
http://www.ti.com/lit/an/snaa021b/snaa021b.pdf
FWIW
jer 🙂
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Could you point to a suitable tranny/power supply for 100W output into 8 Ohms for use with a 3xTDA7293 board.
ATM, I'm a bit confused about what I'm actually looking for!
One thing I want is for the amp to have plenty of headroom and to stay clean at all times.
This one would be suitable and allow you some extra power should you use a 4 ohm load as well,
AN-2230 - 200VA 30V Transformer - AnTek Products Corp
The board only has 50V caps on it so you are limited to high of a voltage you can go with out modding it or replacing the caps.
If you want just a little more at 125watts into 8 ohms you could use a 32V transformer,
AS-2232 - 200VA 32V Transformer - AnTek Products Corp
I had considered using a 34Vac transformer for 144.5 watts but it doesn't leave much headroom for line fluctuations and the caps could pop like dynamite!!!
Apex Jr. has some 33,000uf 50V caps for about $3-$4, we got four of them for our build.
You will need at least two of them or something suitable.
Radial Capacitors
They are about $9 from jameco,
U32D50LG333M35X117HP: NIPPON CHEMI-CON CORP.: Passive Components
You may be able to get by with something smaller for a single amp if cost is an issue.
They also have a 600PIC 25amp bridge rectifier for $2.50 as well or this,
400V 25A Bridge Rectifier
P.E also has a heatsink that is reasonable it is small but should be okay for 100watts,
Aluminum Heat Sink Kit 218.44 x 58.42 x 18mm
I have seen rectifier+cap boards for a reasonable price but it is still cheaper by far to make your own.
But just in case P.E.'s board looks nice but it is way overpriced at $69 if you ask me,
75V 20A 18800uF Rectifier Board for Amplifiers
I found this one on EBay for $25 and would be suitable only it was to small for my 4-channel build,
68X220UF 63V AC DC Power Supply Board DIY Kit for Power Amplifier D3 | eBay
Here is a Ripple voltage calculator to help you determine what size capacitors is big enough for your application.
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/rectct.html#c4
The 66,000uf I am using (per rail) for 4 amp boards will give me a maximum of only about .7Vdc of ripple with each amp at a full 200watts of power.
jer 🙂
P.S Below is a wiring diagram I found that may help you if this is unfamiliar territory for you. 🙂
http://sound.westhost.com/psw-f2.png
Found here,
http://sound.westhost.com/psu-wiring.htm#s2.2
AN-2230 - 200VA 30V Transformer - AnTek Products Corp
The board only has 50V caps on it so you are limited to high of a voltage you can go with out modding it or replacing the caps.
If you want just a little more at 125watts into 8 ohms you could use a 32V transformer,
AS-2232 - 200VA 32V Transformer - AnTek Products Corp
I had considered using a 34Vac transformer for 144.5 watts but it doesn't leave much headroom for line fluctuations and the caps could pop like dynamite!!!
Apex Jr. has some 33,000uf 50V caps for about $3-$4, we got four of them for our build.
You will need at least two of them or something suitable.
Radial Capacitors
They are about $9 from jameco,
U32D50LG333M35X117HP: NIPPON CHEMI-CON CORP.: Passive Components
You may be able to get by with something smaller for a single amp if cost is an issue.
They also have a 600PIC 25amp bridge rectifier for $2.50 as well or this,
400V 25A Bridge Rectifier
P.E also has a heatsink that is reasonable it is small but should be okay for 100watts,
Aluminum Heat Sink Kit 218.44 x 58.42 x 18mm
I have seen rectifier+cap boards for a reasonable price but it is still cheaper by far to make your own.
But just in case P.E.'s board looks nice but it is way overpriced at $69 if you ask me,
75V 20A 18800uF Rectifier Board for Amplifiers
I found this one on EBay for $25 and would be suitable only it was to small for my 4-channel build,
68X220UF 63V AC DC Power Supply Board DIY Kit for Power Amplifier D3 | eBay
Here is a Ripple voltage calculator to help you determine what size capacitors is big enough for your application.
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/rectct.html#c4
The 66,000uf I am using (per rail) for 4 amp boards will give me a maximum of only about .7Vdc of ripple with each amp at a full 200watts of power.
jer 🙂
P.S Below is a wiring diagram I found that may help you if this is unfamiliar territory for you. 🙂
http://sound.westhost.com/psw-f2.png
Found here,
http://sound.westhost.com/psu-wiring.htm#s2.2
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One note,
The specs I layed out in the above post are only suitable for the TDA7293 series of chipamps.
The transformers voltages would exceed the maximum ratings for a LM3886 and the TDA7294.
The transformer voltages for those chips should NEVER be more than 28Vac-0-28Vac!!
Cheers !!
jer 🙂
The specs I layed out in the above post are only suitable for the TDA7293 series of chipamps.
The transformers voltages would exceed the maximum ratings for a LM3886 and the TDA7294.
The transformer voltages for those chips should NEVER be more than 28Vac-0-28Vac!!
Cheers !!
jer 🙂
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Transformer Selection
.
Before you can buy anything, you have to decide what you need...dah.
Decide what wattage you want from your amp. Assume 50 watts.
Multiply this by whatever "power supplies have to be bigger" factor you wish. I suggest 3, in which case you're looking at 150 watts.
Use the rule of thumb that watts = volts x amps = VA, so 150 watts becomes a 150VA transformer. So that's a done dealie, you need a 150VA transformer. But you also need to specify voltage.
Use the information in the data sheet to see what voltage will give you the power output you want. For the LM3886 this is about +/- 38VDC.
Multiply this voltage by 0.707. I'll explain why below, but for now just do it.
38 volts x 0.707 = 27 volts. But both positive and negative voltages are needed, so double that to 54 volts.
And this is the transformer you need. A 150VA center-tapped (for + and -) transformer with a secondary voltage of 54 volts. There might or might not be a transformer rated at exactly that, you always have to fudge these things.
Note: Transformers are listed by their total voltage output, not by the center-tap voltage.
Explaining that 0.707:
Catalogs list RMS (root mean square) voltage, which is exactly the voltage you've heard about all your life.
But AC rectifies into DC at the AC's peak voltage, which is higher than RMS voltage. Don't worry, there are multipliers that take care of this RMS-peak problem.
The multipliers are 1.4, and 0.707. The 0.707 multiplier is the inverse of 1.4, but you don't really care about that. The formulas are:
Transformer AC secondary voltage x 1.4 = rectified DC voltage out.
Required rectified DC voltage x 0.707 = required transformer AC secondary voltage.
Additionally, you subtract 1.4 volts from the total DC output because the rectifier diodes eat that.
If you want a fuller understanding of all this, well, off you go to engineering school. I recommend Georgia Tech, because the ramblin' wrecks have a great fight song.
.
.
Before you can buy anything, you have to decide what you need...dah.
Decide what wattage you want from your amp. Assume 50 watts.
Multiply this by whatever "power supplies have to be bigger" factor you wish. I suggest 3, in which case you're looking at 150 watts.
Use the rule of thumb that watts = volts x amps = VA, so 150 watts becomes a 150VA transformer. So that's a done dealie, you need a 150VA transformer. But you also need to specify voltage.
Use the information in the data sheet to see what voltage will give you the power output you want. For the LM3886 this is about +/- 38VDC.
Multiply this voltage by 0.707. I'll explain why below, but for now just do it.
38 volts x 0.707 = 27 volts. But both positive and negative voltages are needed, so double that to 54 volts.
And this is the transformer you need. A 150VA center-tapped (for + and -) transformer with a secondary voltage of 54 volts. There might or might not be a transformer rated at exactly that, you always have to fudge these things.
Note: Transformers are listed by their total voltage output, not by the center-tap voltage.
Explaining that 0.707:
Catalogs list RMS (root mean square) voltage, which is exactly the voltage you've heard about all your life.
But AC rectifies into DC at the AC's peak voltage, which is higher than RMS voltage. Don't worry, there are multipliers that take care of this RMS-peak problem.
The multipliers are 1.4, and 0.707. The 0.707 multiplier is the inverse of 1.4, but you don't really care about that. The formulas are:
Transformer AC secondary voltage x 1.4 = rectified DC voltage out.
Required rectified DC voltage x 0.707 = required transformer AC secondary voltage.
Additionally, you subtract 1.4 volts from the total DC output because the rectifier diodes eat that.
If you want a fuller understanding of all this, well, off you go to engineering school. I recommend Georgia Tech, because the ramblin' wrecks have a great fight song.
.
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I can't help with the transformer, I don't deal in such power levels. If something suggested by somebody else won't serve your needs, then your option is to hunt in Mouser, or one of the other grownup suppliers. Be prepared to be annoyed, they have entirely too many listings with entirely too much data. It might be good to start a new "where can I get a transformer" thread.
Just for familiarity with the subject, here's Jameco's catalog page. Nothing they list is big enough for your purpose, I'm talking about just familiarity with how transformers are listed in catalogs: http://www.jameco.com/Jameco/catalogs/c151/P100.pdf
On a personal note, I know of no advantage that makes toroid transformers worth their higher price.
If I can't help with the transformer, I can with the circuitry, I hope. As posted below.
Figure 1 is simply the usual schematic for a power supply. You're supposed to look at it and think hey, what's the dealie, anybody can build this--which is true, but you do have to sail with care when in uncharted waters.
Figure 2 is the same (literally) circuit, but with notes added that I hope are self-explanatory.
Figure 3 is electrically identical to the first two, but real-world wiring is shown.
Figure 4 shows the chassis bond. This is also called chassis ground, safety ground, and who knows what other made-up names. I insist on calling it a bond because that's the correct term.
Figure 5 brings everything together, showing how the audio circuit connects to the power supply--or so I like to think.
Just to mention it, I'm not making any of this up. These are as suggested by audio gurus of serious reputation.
However, I don't present any of this as "the way you do it." You might expect that power supplies and grounding would be mature technology, with all issues long since settled. But this is partly true, and mostly not. There are different opinions, so take it all for what it's worth to you.
Importantly, I should add that what I'm presenting here is the Cadillac--for you I guess BMW--way of doing things. In contrast, when building just a small preamp or similar, it's not uncommon to just hook all the grounds/commons/returns together in the way that's most convenient. This is the "ground bus" method, and it's likely to work just fine.
But you're dealing with what in audio terms is some pretty significant power, so I suggest going the extra mile.
.
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