An amp built around a LM3886 or LM3875 is a good example of the ease with which costs for a DIY project can spiral if you allow it - the amp itself is a single chip, but the components around it can be as expensive as your imagination will permit.
If you're new to electronics, you may want to put together a LM3886 amp with good quality components and later experiment with components like PTFE caps or such if you wish.
The main expenses are in the power supply transformers, power supply capacitors, and heatsink - but all of these can be easily found inexpensively at local hamfests, swapmeets, surplus stores, old equipment, or eBay - without sacrificing performance in the least.
As an example, some of the ordinary expenses ($USD) I've come across when looking for parts to build audio systems...
The natural and immediate urge is to throw in the most expensive components available because of the extreme ease of substitution (with strong encouragement of such by vendors) and low absolute cost at the part level, but there are usually better ways to spend those funds. For example, the difference in perceived sound could be potentially far higher by designing an active crossover for your speakers and using an amp per driver, rather than placing expensive components in an amp driving a passive crossover. It's a choice between throwing money at a problem versus learning about where the majority performance losses are in an audio system and addressing those issues.
The LM3886 is well designed and very easy to use - put a case around it with components you can easily afford and listen to the result. Even if you find yourself unable to sleep at night with speculations of other components, it will serve as a control for later experimentation. Also, be sure to read through application notes available from National, TI, Analog, Maxim, etc to get some ideas on general design of the power supply and other supporting components. It's fairly straightforward, really...
Have fun!
-Nikhil
Edit: Added series type for capacitors...
If you're new to electronics, you may want to put together a LM3886 amp with good quality components and later experiment with components like PTFE caps or such if you wish.
The main expenses are in the power supply transformers, power supply capacitors, and heatsink - but all of these can be easily found inexpensively at local hamfests, swapmeets, surplus stores, old equipment, or eBay - without sacrificing performance in the least.
As an example, some of the ordinary expenses ($USD) I've come across when looking for parts to build audio systems...
- Transformers - $10 for a well built 330VA EI core, apexjr.com (if there are a few Signal BL1733A's still available, go for it - perfect for LM3886 chips), free from older equipment also in fine condition.
The LM3886 can average 40-60% efficiency - a transformer should be rated for around 120-150VA or so per channel at the desired supply voltage, at minimum. 300VA is a good size, due to the versatility with other projects and with running two chips from one transformer if need be (surround channels, active crossovers, etc). Also note that the LM3886 is capable of 80w or so into 8ohms with higher supply voltages, without increasing distortion. The datasheet show it as possible, as well as the bridge-parallel version of the amp noted through National - to be tested at +/- 42v and beyond in a car amp soon to see what it takes to destroy a chip under load.
- Heatsink - $5, 12"x8"x1.5" beautiful black anodized aluminum, hamfest
- Capacitors - $0.50 per 10,000uF/50v Philips capacitors, lot of 50 on eBay
- Good quality passive components - Sprague 716P/Panasonic P-series polypropylene capacitors, Panasonic FC series electrolytic capacitors, metal-film resistors - are easily available through Digi-key, Mouser, and other online distributors.
The natural and immediate urge is to throw in the most expensive components available because of the extreme ease of substitution (with strong encouragement of such by vendors) and low absolute cost at the part level, but there are usually better ways to spend those funds. For example, the difference in perceived sound could be potentially far higher by designing an active crossover for your speakers and using an amp per driver, rather than placing expensive components in an amp driving a passive crossover. It's a choice between throwing money at a problem versus learning about where the majority performance losses are in an audio system and addressing those issues.
The LM3886 is well designed and very easy to use - put a case around it with components you can easily afford and listen to the result. Even if you find yourself unable to sleep at night with speculations of other components, it will serve as a control for later experimentation. Also, be sure to read through application notes available from National, TI, Analog, Maxim, etc to get some ideas on general design of the power supply and other supporting components. It's fairly straightforward, really...
Have fun!
-Nikhil
Edit: Added series type for capacitors...
All my many GCs are built using good quality off the shelf parts, Evox rifa for the small caps, Rubicon ZL for the electrolytics, and standard metal film resistors. This was because I was more interested in comparing the different chips, and if I had spent £40 on parts for each one then I would be even more broke than I am currently!
The finished results compare favorably with commercial £1000 amps, even tho I prefer OPA chips to the LMs. If you want to know why, read Peter Daniel's comments in the NJAGC thread, his experiences are similar to mine, we just come to opposite conclusions from a taste point of view
The finished results compare favorably with commercial £1000 amps, even tho I prefer OPA chips to the LMs. If you want to know why, read Peter Daniel's comments in the NJAGC thread, his experiences are similar to mine, we just come to opposite conclusions from a taste point of view
Hell, I Might Even Build One For Myself !.
Hi all GC owners.
I am moving house this easter, and i have dug out a few old chassis that are not worth restoring.
The TINAGC thread is too long to read through, so my \question is - What is the concensus on supply voltages for LM3865 and LM3886 chips, and what is the concensus on sonic differences for these two chips ?.
Thanks, Eric.
Hi all GC owners.
I am moving house this easter, and i have dug out a few old chassis that are not worth restoring.
The TINAGC thread is too long to read through, so my \question is - What is the concensus on supply voltages for LM3865 and LM3886 chips, and what is the concensus on sonic differences for these two chips ?.
Thanks, Eric.
Looking at the datasheet I´d say go with 18V secondaries if you´re using 4Ohm speakers.
This will get the most out of 4Ohms and the least power dissipation with those.
For 8Ohm´s I´d use 24V.
I´m using 18V myself and it´s enough for me with any speaker.
Soundwise I didn´t have the chance to compare.
Others might help here.
If you want to p2p-wire it, use the LM3875 then you don´t have to connect 8 pins (LM3886) but just 5.
Regards
Jens
ok, so more questions!
thanks so far .. helped me lots
1) If apexjr has the signal BL1733A transformers, should i get one or two? (if i'm building monoblocks)
2) If above is not available, would it be wise i order a torroid from plitron (they're in canada, preferably order as much as possible from canada)
3) I know the spirit of gainclone is as simple as possible, therefore no pre-amp. But I need one, switching inputs is simply too much of a hassle for me (have 4 inputs, listen to at least 2-3 different ones all the time). I just built an active preamp, should I use that, or build a passive one (like rarkov)? As suggested before, just a 50k resistor connected to the IN jack and to one end of the 4.7uF cap should do the trick?
I found the schematics for both the gainclone and its PS that were posted by algar_emi earlier in the gainclone thread, http://www.diyaudio.com/forums/showthread.php?s=&threadid=9112&perpage=15&pagenumber=59
and his price list too. That's something a newbie like me needs!!!
The only thing I'm not too clear on is how I'll connect the rectifier diodes, but I'll worry about that later. Other than that, its all good!!
Oh yeah
4) What sort of wire should I use? Something that I can get for maybe $5/foot (for internal wiring) or under. Or should I start off with just normal (what gauge?) copper wire, and work from there?
Thank You
thanks so far .. helped me lots
1) If apexjr has the signal BL1733A transformers, should i get one or two? (if i'm building monoblocks)
2) If above is not available, would it be wise i order a torroid from plitron (they're in canada, preferably order as much as possible from canada)
3) I know the spirit of gainclone is as simple as possible, therefore no pre-amp. But I need one, switching inputs is simply too much of a hassle for me (have 4 inputs, listen to at least 2-3 different ones all the time). I just built an active preamp, should I use that, or build a passive one (like rarkov)? As suggested before, just a 50k resistor connected to the IN jack and to one end of the 4.7uF cap should do the trick?
I found the schematics for both the gainclone and its PS that were posted by algar_emi earlier in the gainclone thread, http://www.diyaudio.com/forums/showthread.php?s=&threadid=9112&perpage=15&pagenumber=59
and his price list too. That's something a newbie like me needs!!!
The only thing I'm not too clear on is how I'll connect the rectifier diodes, but I'll worry about that later. Other than that, its all good!!
Oh yeah
4) What sort of wire should I use? Something that I can get for maybe $5/foot (for internal wiring) or under. Or should I start off with just normal (what gauge?) copper wire, and work from there?
Thank You
Elizard,
You don't need to swap inputs if you can get away from monoblocks. My amp is a integrated version that is fully enclosed and sound excellent. No hum, crosstalk or any other spurious problems. I also cut down on my machining time and material costs. It easier to move and has four inputs. Not as "hifi looking " as monoblocks but I don't care as this amp has spanked every other power unit of friends and neighbors in shootouts. It hasn't gone up against anything more expensive than a couple of Crown A/V Monoblocks ($2k apiece) but did humble one Creek 5350SE owner last week who thought the GC had a richer, warmer and more involving sound. Take a look at the picks and decide for yourself
You don't need to swap inputs if you can get away from monoblocks. My amp is a integrated version that is fully enclosed and sound excellent. No hum, crosstalk or any other spurious problems. I also cut down on my machining time and material costs. It easier to move and has four inputs. Not as "hifi looking " as monoblocks but I don't care as this amp has spanked every other power unit of friends and neighbors in shootouts. It hasn't gone up against anything more expensive than a couple of Crown A/V Monoblocks ($2k apiece) but did humble one Creek 5350SE owner last week who thought the GC had a richer, warmer and more involving sound. Take a look at the picks and decide for yourself
Attachments
I have changed a few things since these picks, like using MSR860 diodes and done some dampening of the transformer mountings. I will be changing out the binding posts soon but that will require some additional drilling of the back plate and downtime I don't want to have.
Here a pick of my rectifiers. Four of these are going into an intergrated AlephX/BOSOZ/APOX-1 unit I am thinking about... ok, ok dreaming about. Look at the datafile for the diodes you have for the orientation and build it from that.
Edit: You built the preamp because all this stuff we do is FUN!
. Don't you need another stereo later in another room?
Anyway, try the monoblock version to go with your preamp. You might need to work out some ground loop hum problems that I encountered when using my GC with my Parasound pre. I ended up loaning my pre to a friend who had his system stolen in burglery, so I built an integrated version. Which, will end up going to my daughter as soon as I can part with it.
Here a pick of my rectifiers. Four of these are going into an intergrated AlephX/BOSOZ/APOX-1 unit I am thinking about... ok, ok dreaming about. Look at the datafile for the diodes you have for the orientation and build it from that.
Edit: You built the preamp because all this stuff we do is FUN!
. Don't you need another stereo later in another room? Anyway, try the monoblock version to go with your preamp. You might need to work out some ground loop hum problems that I encountered when using my GC with my Parasound pre. I ended up loaning my pre to a friend who had his system stolen in burglery, so I built an integrated version. Which, will end up going to my daughter as soon as I can part with it. Attachments
Allright, awesome
Well, I guess you gotta try stuff, eh ..
Still my question about the transformer (my main worry) goes unanswered.
If I were to get the Signal BL1733A from www.apexjr.com/Clearance.htm should I get 2 of them? They're $10/piece (if they still have em) so that's VERY cheap for me .. Would I also need any modifications? Or are they good to go as they are?
Well, I guess you gotta try stuff, eh ..
Still my question about the transformer (my main worry) goes unanswered.
If I were to get the Signal BL1733A from www.apexjr.com/Clearance.htm should I get 2 of them? They're $10/piece (if they still have em) so that's VERY cheap for me .. Would I also need any modifications? Or are they good to go as they are?
Or how about 2 torroidals from plitron, $55/each
I can get them either in 18,20,or 22VAC .. and they're rated at 160VA?
part# 057015201 for the 22VAC version
Would 2 of those be good?
Still, I'd rather get the 2 from apexjr if there isn't anything major for me to do, or a lot of drawbacks from them ..
plitron i'd prefer because they're in canada - cheaper shipping/no customs
I can get them either in 18,20,or 22VAC .. and they're rated at 160VA?
part# 057015201 for the 22VAC version
Would 2 of those be good?
Still, I'd rather get the 2 from apexjr if there isn't anything major for me to do, or a lot of drawbacks from them ..
plitron i'd prefer because they're in canada - cheaper shipping/no customs
I would say they would work fine, but I have always been partial to toroids or R-cores. My boombox upgrade is using a $4 EI though. If this going to be your main listening system for a while and your willing to spend $200 or so, I would buy a couple of Plitron torrids. That will end up costing you $80US for both, but you'll have $120 to spend on cases and parts. Which would be tight but enough. You can get all very good quality parts like the ones Pinkmouse recommended and still stay in budget. Steve at Apex Jr has great stuff coming in all the time. I have gotton almost all of my toroidal transformers from him over the last six months. I did go to Victoria Magnetics for my Aleph transformers though, so I knew exactly what I was getting. You can go with those you saw and refit later if you want but, then there is that dreaded down time again!
Well, it will be my main system for quite a while (at least a few months .. maybe more) .. so yeah, I suppose torroids it is
Now .. which one do I want to get?
the ones rated at 120VA are like $3 less than the ones rated at 160VA so no point in going 120
So I need to get 2 160VA torroids. For secondaries, should I go 20? or 22 (as I believe Peter said he preferred)?
Also, since they're dual secondaries (I think .. i'm pretty sure), do I use both of the secondaries for each channel? meaning I'll need 8 rectifier diodes per channel? Or how does that part work out?
edit: Btw, reading Peter's post in another thread he had a graph up. With 22volts he seems to be getting about 20ish watts into 8ohms .. is that what i should expect? someone mentioned 38W earlier.
What if i went with 31V secondaries?
(sorry for so many questions ..)
Now .. which one do I want to get?
the ones rated at 120VA are like $3 less than the ones rated at 160VA so no point in going 120
So I need to get 2 160VA torroids. For secondaries, should I go 20? or 22 (as I believe Peter said he preferred)?
Also, since they're dual secondaries (I think .. i'm pretty sure), do I use both of the secondaries for each channel? meaning I'll need 8 rectifier diodes per channel? Or how does that part work out?
edit: Btw, reading Peter's post in another thread he had a graph up. With 22volts he seems to be getting about 20ish watts into 8ohms .. is that what i should expect? someone mentioned 38W earlier.
What if i went with 31V secondaries?
(sorry for so many questions ..)
Peter meant 22VAC and the chart is in DC voltages or after rectification. 22VAC is +/-31VDC (22*1.414=31.2) after the rectifiers. If you got 31VAC secondaries you end up with +/-44VDC, which is well outside the optimum operating range of the chips. And no you don't have to use 8 diodes per channel. I only use one bridge (4 diodes) per channel in my Gainclone. My Alephs might use two per channel mainly because of the amperage involved. For $3, get the 160VA at 22VAC torroids. You might need the extra oomph with some larger speakers in the future and the cost is negligible. They are dual secondaries too. Have you read through the datasheets for the chip you want to use? I would use the LM3875 as Jens recommend before. It is also my favorite.
By the way, give Steve at Apex,Jr a call and see if he has any torrids for sale. You can never tell what he got stashed in back.
By the way, give Steve at Apex,Jr a call and see if he has any torrids for sale. You can never tell what he got stashed in back.
ok, that clears it up some
i was thinking of using the lm3875, so that's all good
but still i'm confused a little
since they're dual secondaries, what happens to the second output of each transformer?
i'm using only one, right?
do i just ignore it and make sure to isolate it so it doesn't touch anything, or do i connect both outputs and then rectify it?
man i've so much to learn
i was thinking of using the lm3875, so that's all good
but still i'm confused a little
since they're dual secondaries, what happens to the second output of each transformer?
i'm using only one, right?
do i just ignore it and make sure to isolate it so it doesn't touch anything, or do i connect both outputs and then rectify it?
man i've so much to learn
Oh yeah, and so far, not including a couple minor things (speaker posts and the case itself) the cost of the parts is $208 .. which is pretty good
that's NOT including shipping/customs (not too much in customs, just stuff from digikey, rest is in canada)
so all in all, i think the total will be $300-$350 after i'm all finished
which is about what i was looking to spend (yeah i said $200, but i knew it wouldn't be that cheap .. still, VERY reasonable for something that'll probably smoke most things .. hopefully)
still waiting for a couple answers, but i'll go looking for parts locally tomorrow!
that's NOT including shipping/customs (not too much in customs, just stuff from digikey, rest is in canada)
so all in all, i think the total will be $300-$350 after i'm all finished
which is about what i was looking to spend (yeah i said $200, but i knew it wouldn't be that cheap .. still, VERY reasonable for something that'll probably smoke most things .. hopefully)
still waiting for a couple answers, but i'll go looking for parts locally tomorrow!
Ok there are a couple of ways to do this. One,use two rectifiers per channel tying one secondary to each rectifier. One rectifier supplies pos DC the other the neg DC. The other DC side of the rectifier is tied to the star ground. Or... tie the outer wires of the transformer to one rectifier and tie the inner leads together, like a center tap, and run them to the star ground, which is what I use. Peter, uses the first method and is happy with it. I couldn't tell you if there is a sonic difference as I haven't compared the two methods. Perhaps one of the other guys has. Fred Dieckmann has a lot of experience in this area.
http://www.outlawaudio.com/products/7100.html
This is one of the amps that I have been looking at for some time, 899 and it outputs at 100/channel.
What advantages does this one have over the gainclone and what advantages does the gainclone have over the 7100?
This is one of the amps that I have been looking at for some time, 899 and it outputs at 100/channel.
What advantages does this one have over the gainclone and what advantages does the gainclone have over the 7100?
I tried one bridge against two bridges and two bridges (one for positive, one for negative) sound definitely better. Four extra diodes cost you max $4 and the grounding is more elegant, so it's not worth saving here. It is also what Thorsten recommends
I also tried some big EI transformers with split bobbins, but to my surprise Plitrons sound better. I don't know how much you guys pay for toroids, but 400VA Plitron cost around $70CAD.
I also tried some big EI transformers with split bobbins, but to my surprise Plitrons sound better. I don't know how much you guys pay for toroids, but 400VA Plitron cost around $70CAD.
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