Hi all,
I'm new to this higher power amplifier stuff, having only built headphone amps and a couple of DACs before - so please bear with me whilst I ask what might be some rather obvious questions.
I think(??) I want to build a Gainclone as they seem to be simple to build, reasonably inexpensive, of a good audio quality and reasonably compact.
I was looking at building the LM3886 stereo kit from chipamps.com to power a pair of these older Infinity speakers (use what you got right?) - but it would be nice to keep using it in the future.
I am GUESSING that 40W into 6ohms will be enough, my current amp is 25W and seems to be enough for most situations. Let me know if I'm wrong. I haven't really found what I should be aiming for in terms of amp power vs. speaker power without destroying anything.
In my digging I think I've figured out that I'd like to use a 225VA toroidal transformer with 2x0-18V secondaries which rectified would give just on +/- 25V. If I'm reading page 14 of the LM3886 Datasheet properly I'm figuring this would give me about 40W output power at 6ohms?
The 225VA transformer gives just over 4A on each of the secondaries, where the datasheet tells me that 40W output into 6ohms requires 3.65A = sqrt((2x40W)/6Ohms).
Hrm, I think I just realised that I'm building two of these (stereo) off one transformer so perhaps I need a higher VA rated unit?
I want to avoid the cost of a custom wound transformer and RSwww.co.nz had a Nuvotem unit I mention above for $65 NZ + tax - so it would be great to know if it is truly suitable. The next step up is a 225VA or 300VA unit with 2x25V secondaries - which recitfies to +/- 35V - this appears to be good for 8ohms, but would mean I'd need a big heatsink for 6ohms.
I am planning on heatsinking the LM3886 chips to the side of a custom chassis built from aluminium, I envisaged something between 5mm-10mm thick, 75mm high and 200mm long on that side. If that stays too hot I will move to a finned heatsink.
I had planned to add a volume pot - something like a Dual 50K ALPS RK27 - found on eBay an elsewhere. This is AFAIK a pretty standard value - let me know if I'm wrong 😉
And grounding? I take it the signal grounds are NOT tied to the chassis ground (which I assume would be tied to Earth?)
I think that's it - thanks in advance 🙂
I'm new to this higher power amplifier stuff, having only built headphone amps and a couple of DACs before - so please bear with me whilst I ask what might be some rather obvious questions.
I think(??) I want to build a Gainclone as they seem to be simple to build, reasonably inexpensive, of a good audio quality and reasonably compact.
I was looking at building the LM3886 stereo kit from chipamps.com to power a pair of these older Infinity speakers (use what you got right?) - but it would be nice to keep using it in the future.
I am GUESSING that 40W into 6ohms will be enough, my current amp is 25W and seems to be enough for most situations. Let me know if I'm wrong. I haven't really found what I should be aiming for in terms of amp power vs. speaker power without destroying anything.
In my digging I think I've figured out that I'd like to use a 225VA toroidal transformer with 2x0-18V secondaries which rectified would give just on +/- 25V. If I'm reading page 14 of the LM3886 Datasheet properly I'm figuring this would give me about 40W output power at 6ohms?
The 225VA transformer gives just over 4A on each of the secondaries, where the datasheet tells me that 40W output into 6ohms requires 3.65A = sqrt((2x40W)/6Ohms).
Hrm, I think I just realised that I'm building two of these (stereo) off one transformer so perhaps I need a higher VA rated unit?
I want to avoid the cost of a custom wound transformer and RSwww.co.nz had a Nuvotem unit I mention above for $65 NZ + tax - so it would be great to know if it is truly suitable. The next step up is a 225VA or 300VA unit with 2x25V secondaries - which recitfies to +/- 35V - this appears to be good for 8ohms, but would mean I'd need a big heatsink for 6ohms.
I am planning on heatsinking the LM3886 chips to the side of a custom chassis built from aluminium, I envisaged something between 5mm-10mm thick, 75mm high and 200mm long on that side. If that stays too hot I will move to a finned heatsink.
I had planned to add a volume pot - something like a Dual 50K ALPS RK27 - found on eBay an elsewhere. This is AFAIK a pretty standard value - let me know if I'm wrong 😉
And grounding? I take it the signal grounds are NOT tied to the chassis ground (which I assume would be tied to Earth?)
I think that's it - thanks in advance 🙂
Hi raromachine
Good luck.
There is really not much difference between 40W and 25W, but the extra may be welcome all the same. Generally, a higher power amplifier will be better for your speakers provided you use it sensibly. A small amp pushed hard may be harmful to your tweeters.raromachine said:
I think the 225VA will be enough for stereo. You may find a benefit of a larger xfmr will be that your amp will reproduce peaks more convincingly, and recover from them a little better. Recommended 😉
Yes, it is. I use Alps, no complaints.
Good luck.
Hiya lndm - thanks for your reply!
So I might be better off to go up to a 300VA 2x0-25VAC (-/+ 35V DC rectified) transformer and up the output power.
This would mean I'd be able to keep using it if I went to larger speakers in the future, the quality of the sound might go up in some instances and
And downside being that I'd need to invest in more serious heatsinking?
So I might be better off to go up to a 300VA 2x0-25VAC (-/+ 35V DC rectified) transformer and up the output power.
This would mean I'd be able to keep using it if I went to larger speakers in the future, the quality of the sound might go up in some instances and
And downside being that I'd need to invest in more serious heatsinking?
Some might say that with the higher supply rails, the sound quality would be almost as good as with the lower rails. I think it is a fine point and a fair compromise, whatever you choose will be good.
Larger speakers are not necessarily harder to drive. In fact, larger speakers are sometimes easier to drive and further, some larger speakers are more efficient requiring less power for the same loudness.
I should add here that your calculated current draw per channel of 3.65A is much higher than the average current for almost any type of music programming even during operation into the clipping region.
A power supply with sufficient filter capacity will integrate the current transients over time so that the integral, which the transformer sees, is a less transient looking level that defines the average of the audio current.
To put that simply: A transformer rated at 4A should really do it unless you expect to crank out a steady wave at clipping level all day long.
To add: Anything bigger than required is nice to have anyway, I love to over-do my designs a bit to allow for reliability, stability, and solidity. (And just to say it is -capable- of more than it's really rated for). 😉
A power supply with sufficient filter capacity will integrate the current transients over time so that the integral, which the transformer sees, is a less transient looking level that defines the average of the audio current.
To put that simply: A transformer rated at 4A should really do it unless you expect to crank out a steady wave at clipping level all day long.
To add: Anything bigger than required is nice to have anyway, I love to over-do my designs a bit to allow for reliability, stability, and solidity. (And just to say it is -capable- of more than it's really rated for). 😉
Thanks lndm and Dou - some interesting points and good information 🙂
Is there any way to estimate what the load on the transformer might be? Do I need to worry about regulation ratings (and what exactly do they mean - the further you are from the VA rating the higher Vout?) on higher VA rated transformers?
Also - does anyone have a primer on understanding speaker Wattage and sensitivity ratings? I clearly need to read up on this.
Getting there 🙂 - raro.
Is there any way to estimate what the load on the transformer might be? Do I need to worry about regulation ratings (and what exactly do they mean - the further you are from the VA rating the higher Vout?) on higher VA rated transformers?
Also - does anyone have a primer on understanding speaker Wattage and sensitivity ratings? I clearly need to read up on this.
Getting there 🙂 - raro.
hm, there's a lot of good info on the web about this, though it can, like anything on the web, be difficult to find.
A good place to start is the Elliot Sound Products site. There's more good information and ideas crammed inta that site than I've seen in a lot of things. He has an excellent projects section and articless section on his site:
Rod Elliot's Artilces Rod Elliot's Projects
As far as load on the transformer, this will depend mostly on what is being amplified. For example, if you set the amplifier to amplify a pure sine wave at its rated power output, you'll be placing a full RMS load on the transformer which easily exceeds your transformer rating in this case.
The key here is that you are more likely going to be listening to music. The average power of most music is very low compared to the peak or transient power that occurs on beats or crescendos. This depends a bit on the dynamic range of the music, ie; if the dynamic range of the music is very wide, you'll find the peaks sometimes rise many times higher than the average power level. In highly compressed music, as on FM radio, you'll find the power is distributed much more evenly between loud and soft. This leads to a really lifeless sound.
What it means is that you could play a compressed recording really loud and not worry about going into clipping because of the compressed nature of the transients. This means more average power and thus for listening at high volume, a relatively steady load on the amplifier.
Luckily, you're still not going to find much that's compressed so far that you have to worry.
As far as regulation ratings go in transformers, they tell the designer how well the output of the transformer holds its voltage level during load. All transformers exhibit this 'droop,' and some a lot more than others.
At the first few percent of the power supply load, you'll see some droop occur. This is with the rectification and filtering in place of course. That's because the capacitors become overcharged due to overshoot, pumping, AC line peaks, etc, and the voltage drops to its normal value under just a small load such as that required to bias the amplifier.
Then when you start drawing power, the transformer output will droop just a small bit. For example; I have a 2000VA transformer in one amp I designed and it normally sits at 126V rail-to-rail when idle. At full output on 4ohms (about 500W per channel), the voltage will drop considerably to 117V at times depending on AC line conditions.
I don't have any reading material handy on transformer regulation but someone else on here should be able to fill you in on specifics.
When I get back to the computer, I'll fill you in on speaker info if no one has beat me to it.
A good place to start is the Elliot Sound Products site. There's more good information and ideas crammed inta that site than I've seen in a lot of things. He has an excellent projects section and articless section on his site:
Rod Elliot's Artilces Rod Elliot's Projects
As far as load on the transformer, this will depend mostly on what is being amplified. For example, if you set the amplifier to amplify a pure sine wave at its rated power output, you'll be placing a full RMS load on the transformer which easily exceeds your transformer rating in this case.
The key here is that you are more likely going to be listening to music. The average power of most music is very low compared to the peak or transient power that occurs on beats or crescendos. This depends a bit on the dynamic range of the music, ie; if the dynamic range of the music is very wide, you'll find the peaks sometimes rise many times higher than the average power level. In highly compressed music, as on FM radio, you'll find the power is distributed much more evenly between loud and soft. This leads to a really lifeless sound.
What it means is that you could play a compressed recording really loud and not worry about going into clipping because of the compressed nature of the transients. This means more average power and thus for listening at high volume, a relatively steady load on the amplifier.
Luckily, you're still not going to find much that's compressed so far that you have to worry.
As far as regulation ratings go in transformers, they tell the designer how well the output of the transformer holds its voltage level during load. All transformers exhibit this 'droop,' and some a lot more than others.
At the first few percent of the power supply load, you'll see some droop occur. This is with the rectification and filtering in place of course. That's because the capacitors become overcharged due to overshoot, pumping, AC line peaks, etc, and the voltage drops to its normal value under just a small load such as that required to bias the amplifier.
Then when you start drawing power, the transformer output will droop just a small bit. For example; I have a 2000VA transformer in one amp I designed and it normally sits at 126V rail-to-rail when idle. At full output on 4ohms (about 500W per channel), the voltage will drop considerably to 117V at times depending on AC line conditions.
I don't have any reading material handy on transformer regulation but someone else on here should be able to fill you in on specifics.
When I get back to the computer, I'll fill you in on speaker info if no one has beat me to it.
Duo said:
The output voltage of a transformer is typically given as under full load. To obtain the numbers, take the difference between the full load voltage and the no load voltage, then divide by the full load voltage. Multiply by 100 to convert to a percentage.
A person might assume that all xfmrs will have a load regulation figure based on quality of manufacturer, however, it often has to do with size. A transformer of the size you are looking at usually has a load regulation of better than 10%, and higher than about 500VA is often better than 5%.
Combined with the safety margin you've already considered, therefore, there are two reasons that a larger xfmr will give better load regulation.
This is really more important in an amp that draws a varying amount of current, as Dou covered. A large filter can partially compensate for a small xfmr. Some would say it's not as good, some would say it's good enough. I feel that if size and budget say yes, that I will say yes too, but there is the law of diminishing returns that puts an upper limit on the benefit.
Also, I prefer to use smaller filter capacitors for their sonic qualities, though they can be doubled up. This is not necessary though, just a preference.
The 225VA trannsformer should do fine for your proposed amp. Any unregulated supply is going to float high some and then droop some (relative to the floating voltage if not below the rated (at full load) voltage). The speakers, transformer and chassis/sinking seem a good match, you could do it all differently but then that's the reason to do ANOTHER gainclone. IMO, no matter how you did the first one you will want to try something new on the next.
Thanks ! and thanks again Dou and lndm 🙂
Looks like all I have to do now is wait for Chipamp.com to get some kits back in stock (I've priced PCBs and similar quality parts and can't get it anywhere near as good a price shipped to NZ).
Hah - that's always how it starts: 2 soldering irons, 3 multimeters, a tonne of components, 5 headphone amps and 2 DACs later...
Looks like all I have to do now is wait for Chipamp.com to get some kits back in stock (I've priced PCBs and similar quality parts and can't get it anywhere near as good a price shipped to NZ).
Hah - that's always how it starts: 2 soldering irons, 3 multimeters, a tonne of components, 5 headphone amps and 2 DACs later...
I've just looked at Jaycar. Chipamp.com does their dual mono kit for $50US so I guess thats about $70AU. They do the board, common parts with filter caps plus rectifier parts, minus heatsinks and power xfmr as far as I can see.
Jaycar do the modules with components including chip for $27AU each channel, plus about $14AU for their stock rectifier and filter caps for two channels. So it seems to be about the same price.
Jaycar's stock heatsink x 2 and stock power xfmr will cost a further $80AU.
Jaycar do the modules with components including chip for $27AU each channel, plus about $14AU for their stock rectifier and filter caps for two channels. So it seems to be about the same price.
Jaycar's stock heatsink x 2 and stock power xfmr will cost a further $80AU.
amp
I have purchased all my gear from rs and they are great. They are a little expensive but you are guaranteed o f getting good parts. I bought a teroid from Jaycar and it was crap. Noisy thing from China.
I have made two amps using LM3875. One was standard, standard power supply with a little 160VA teroid.
The other was made using a bigger supply 225VA 25-0-25. I also used some more filter caps, I think it was about 3-4000uf per channel. As well as using two 35amp 400v rectifiers with 22nf 1000v snubbers across them.
The second one definitely sounded better. I would definitely use a bigger tranny. I thing this is where all your money should be spent……POWER SUPPLY.
I would get my boards from Daniel as this is a good way to start. But think about ordering more, because after you have finished one you’ll want to it all again. And remember to order all your parts from rs together as you get free delivery when you spend over $100.
Cheers
Brett
I have purchased all my gear from rs and they are great. They are a little expensive but you are guaranteed o f getting good parts. I bought a teroid from Jaycar and it was crap. Noisy thing from China.
I have made two amps using LM3875. One was standard, standard power supply with a little 160VA teroid.
The other was made using a bigger supply 225VA 25-0-25. I also used some more filter caps, I think it was about 3-4000uf per channel. As well as using two 35amp 400v rectifiers with 22nf 1000v snubbers across them.
The second one definitely sounded better. I would definitely use a bigger tranny. I thing this is where all your money should be spent……POWER SUPPLY.
I would get my boards from Daniel as this is a good way to start. But think about ordering more, because after you have finished one you’ll want to it all again. And remember to order all your parts from rs together as you get free delivery when you spend over $100.
Cheers
Brett
Re: amp
Stop right there! I've looked at the quality of the bits you get in either kit, and I'd have to say that the Chipamp ones are definately much better for the cost! The transformers are definately cheaper from RS, the only think I can find which isn't are the 6A EMI filtered sockets. Actually, from what I can see they don't seem to offer the Gainclone like module in NZ... pity there is one not 1km from where I work.
I second your thoughts about RS - good service from them so far, a little pricy, not as bad as Farnell though. Good tip on the free shipping too.
Errr - who or what is Daniel?
As for ordering more - I'm supposed to be going abroad later this year, so I'm trying desperately not to amass more things to do!
Thanks guys - 🙂
lndm said:
Stop right there! I've looked at the quality of the bits you get in either kit, and I'd have to say that the Chipamp ones are definately much better for the cost! The transformers are definately cheaper from RS, the only think I can find which isn't are the 6A EMI filtered sockets. Actually, from what I can see they don't seem to offer the Gainclone like module in NZ... pity there is one not 1km from where I work.
enzedone said:
I second your thoughts about RS - good service from them so far, a little pricy, not as bad as Farnell though. Good tip on the free shipping too.
Errr - who or what is Daniel?
As for ordering more - I'm supposed to be going abroad later this year, so I'm trying desperately not to amass more things to do!
Thanks guys - 🙂
Actually, because someone might find it usefull:
I priced the LM3886 sterro kit at ~$100 NZ shipped.
The Transformer, some LEDs, a Knob and some other junk/bits at around ~$100 NZ from RS.
The 50K ALPS RK27 Pot at ~$40 NZ shipped from Ebay, Tangent or AMBs store.
The IEC Socket, RCA connectors and Speaker connectors at ~$40 NZ from Jaycar.
I've allowed $100 NZ for the aluminium for the case - machining is ~0 as I have the mad hookups 🙂
That's a total of ~$380NZ.
I've not priced wire or other boutqiue bits, as I seem to have lots and don't think I will appreciate the subtleties of silver etc and hey my current NAD512 amp doesn't have them and it sounds good to me.
I priced the LM3886 sterro kit at ~$100 NZ shipped.
The Transformer, some LEDs, a Knob and some other junk/bits at around ~$100 NZ from RS.
The 50K ALPS RK27 Pot at ~$40 NZ shipped from Ebay, Tangent or AMBs store.
The IEC Socket, RCA connectors and Speaker connectors at ~$40 NZ from Jaycar.
I've allowed $100 NZ for the aluminium for the case - machining is ~0 as I have the mad hookups 🙂
That's a total of ~$380NZ.
I've not priced wire or other boutqiue bits, as I seem to have lots and don't think I will appreciate the subtleties of silver etc and hey my current NAD512 amp doesn't have them and it sounds good to me.
Point taken about Jaycar and agreed. You'll notice I used the word 'stock' a few times, assuming you'll want to make your own judgements. If you're interested, the kit is on page 19 of the 2006 catalogue. My catalogue has New Zealand shop locations on the back so I assume you might have the same one.
http://www.coilws.com/Toroidal Power Tx/Toroid_Pwr_PN.php?orderby=data3&orderdir=desc
Your transformer search is over.
EDIT: Oops...this is a U.S. site. Shipping will be ridiculous...🙄
Your transformer search is over.
EDIT: Oops...this is a U.S. site. Shipping will be ridiculous...🙄
Daniel
Sorry, Daniel runs the international segment of chipamps.com.
his site is:
www.audiosector.com
Where are you getting your alps pot from, as I bought mine from RS and they are quite pricey?
I found that it wasn't actually the kits that cost the money, but all the incidentals.........
They kept adding up, a connector here, wires,......
I made two cases, but my third was a stripped out home theatre case I got off Trademe for $75. Which isn't too bad considering the price you pay in this country for alluminium.
Sorry, Daniel runs the international segment of chipamps.com.
his site is:
www.audiosector.com
Where are you getting your alps pot from, as I bought mine from RS and they are quite pricey?
I found that it wasn't actually the kits that cost the money, but all the incidentals.........
They kept adding up, a connector here, wires,......
I made two cases, but my third was a stripped out home theatre case I got off Trademe for $75. Which isn't too bad considering the price you pay in this country for alluminium.
Re: Daniel
Transformers cost a lot.
🙄
Just a fact...
enzedone said:Sorry, Daniel runs the international segment of chipamps.com.
his site is:
www.audiosector.com
Where are you getting your alps pot from, as I bought mine from RS and they are quite pricey?
I found that it wasn't actually the kits that cost the money, but all the incidentals.........
They kept adding up, a connector here, wires,......
I made two cases, but my third was a stripped out home theatre case I got off Trademe for $75. Which isn't too bad considering the price you pay in this country for alluminium.
Transformers cost a lot.
🙄
Just a fact...
Time
I had to be very careful how I bought all my parts. I made sure that I was spending $100 per order, but spacing out all my purchases so as not to freak the misses
She wood freak if she really knew how much money I'd spent at RSNEWZEALAND.
After buying one dud tranny, I would never scimp on this again. Buy good quality power supply parts, as this is where the diference lies between an average and a good sounding amp(well, In my humble non guru view).
Yes trannies are expensive, try buying in New Zealand dollars.$80-150 a pop.
I had to be very careful how I bought all my parts. I made sure that I was spending $100 per order, but spacing out all my purchases so as not to freak the misses
She wood freak if she really knew how much money I'd spent at RSNEWZEALAND.
After buying one dud tranny, I would never scimp on this again. Buy good quality power supply parts, as this is where the diference lies between an average and a good sounding amp(well, In my humble non guru view).
Yes trannies are expensive, try buying in New Zealand dollars.$80-150 a pop.
Re: Daniel
Ah I see - no 3886 though, am I right in thinking that the 3875 is less powerful? I can't really see a difference. Will look at the datasheet tonight.
Alps pots from:
http://www.amb.org/shop/
AMB audio shop
and/or
http://www.tangentsoft.net/audio/shop/
Tangent's Audio Parts Shop
Shipping is still some $$ - but they're both friendly and fast 🙂
The 50K RK27's are the ones you want, both sell the PCB mount style.
enzedone said:
Ah I see - no 3886 though, am I right in thinking that the 3875 is less powerful? I can't really see a difference. Will look at the datasheet tonight.
Alps pots from:
http://www.amb.org/shop/
AMB audio shop
and/or
http://www.tangentsoft.net/audio/shop/
Tangent's Audio Parts Shop
Shipping is still some $$ - but they're both friendly and fast 🙂
The 50K RK27's are the ones you want, both sell the PCB mount style.
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