I tend to agree
I tend to agree with you Fred & Haldor. I haven't really understood why the practice seems to be widespread, unless it is the difficulty in obtaining chips. But EVERYBODY (in the US, at least) seems to carry the LM3875 and its only around $6 ea. To me, if the heart of the amp is $6 and that's too much to pay, then maybe it'd be better to save a little more money prior to beginning the project.
It does seem OK for guys doing development, even on the hobby level, when there's a likely group buy involved (like the remote volume control etc), as in the end, it expands the sale of chips. Otherwise, I'm not a big fan of the process either.
Sandy.
I tend to agree with you Fred & Haldor. I haven't really understood why the practice seems to be widespread, unless it is the difficulty in obtaining chips. But EVERYBODY (in the US, at least) seems to carry the LM3875 and its only around $6 ea. To me, if the heart of the amp is $6 and that's too much to pay, then maybe it'd be better to save a little more money prior to beginning the project.
It does seem OK for guys doing development, even on the hobby level, when there's a likely group buy involved (like the remote volume control etc), as in the end, it expands the sale of chips. Otherwise, I'm not a big fan of the process either.
Sandy.
The only justifieble reason to ask for free samples if you can't obtain the chip any other way or the distributor in your area has a min order requirement of at least 20 pcs. That happened to me with CS8420 and TDA7294. But I also asked only for 2.
If you can get a chip from Digi Key for $6 it's unethical to ask for free samples.
If you can get a chip from Digi Key for $6 it's unethical to ask for free samples.
Re: Ccomparisons please
I have built few of those gainclone amps by now and everybody who listens to them is impressed. They are very dependant on construction techniques and all the parts used. With proper choice you can get an amp which might be "on a very short list of some of the best amps that I have heard for low power applications" as one respected audiophile comented to me and his amp wasn't probably as tweaked as mine
.
The full potential of the amp can only be achieved when proper platform/feet/ placement is employed and it can really produce magic then. It is safe to say that this amp is a fair competition to most tube and solid state designs and having the best feaatures of both. I can't say how it compares to Aleph2 because I didn't built one.
I'm using Aleph X in my main system and 2 Gainclones in my other systems, and I have to gladly admit that all those amps provide very satisfying listening experiences.
I was playing a bit with tweaking Aleph X, because at some times I thought that Gainclone is better. So I did some mods and the sound was still murky and no sparkle and immediacy. So yesterday I changed the feet and their points of support, plus I added some 1/4" woood and acrylic strips to isolate the feet from the floor and the improvement was dramatic. The amp (Aleph X)changed completely with a level of resolution and air I never experienced before. I think it is better than Gainclone now.
rick57 said:
I have built few of those gainclone amps by now and everybody who listens to them is impressed. They are very dependant on construction techniques and all the parts used. With proper choice you can get an amp which might be "on a very short list of some of the best amps that I have heard for low power applications" as one respected audiophile comented to me and his amp wasn't probably as tweaked as mine
.The full potential of the amp can only be achieved when proper platform/feet/ placement is employed and it can really produce magic then. It is safe to say that this amp is a fair competition to most tube and solid state designs and having the best feaatures of both. I can't say how it compares to Aleph2 because I didn't built one.
I'm using Aleph X in my main system and 2 Gainclones in my other systems, and I have to gladly admit that all those amps provide very satisfying listening experiences.
I was playing a bit with tweaking Aleph X, because at some times I thought that Gainclone is better. So I did some mods and the sound was still murky and no sparkle and immediacy. So yesterday I changed the feet and their points of support, plus I added some 1/4" woood and acrylic strips to isolate the feet from the floor and the improvement was dramatic. The amp (Aleph X)changed completely with a level of resolution and air I never experienced before. I think it is better than Gainclone now.
As I have written in previous posts I have had production amps from Jadis(tube) ,Naim 180 and 250 and also DIY Aleph 5 mono's resident at home.
The amp I am using now is an OPA 549 based power amp/gainclone pretty well tweaked with BG'(N)s as main caps and bypass caps, schottky bridges etc.
I really feel that this amp is quite ahead of the others mentioned above within reasonable power levels and efficient speakers. It combines and betters many of the strengths of the above amps.What can I say- I am very happy with it at the moment and I don't feel I can better it at this stage.
The amp I am using now is an OPA 549 based power amp/gainclone pretty well tweaked with BG'(N)s as main caps and bypass caps, schottky bridges etc.
I really feel that this amp is quite ahead of the others mentioned above within reasonable power levels and efficient speakers. It combines and betters many of the strengths of the above amps.What can I say- I am very happy with it at the moment and I don't feel I can better it at this stage.
Newbie list of questions
(1)
Is the plitron 077015201 a good trafo for this project? It is 300 VA, 22-0-22. Also I was wondering if anyone would know an approximate height of this trafo? I have some heatsinks but they are only 4 inches high. If it didn't fit I guess I would have to build a separate power supply.
(2)
Peter Daniel, How many winds did you add to get enough to the blue LED?
(3)
Is the MUR460 good for the rectifier?
(4)
How much heat do will I need to dissipate at full volume?
(5)
Has anyone had luck with the nichicon 50v 1000uf on the power supply?
Thanks a ton!
-Brent
(1)
Is the plitron 077015201 a good trafo for this project? It is 300 VA, 22-0-22. Also I was wondering if anyone would know an approximate height of this trafo? I have some heatsinks but they are only 4 inches high. If it didn't fit I guess I would have to build a separate power supply.
(2)
Peter Daniel, How many winds did you add to get enough to the blue LED?
(3)
Is the MUR460 good for the rectifier?
(4)
How much heat do will I need to dissipate at full volume?
(5)
Has anyone had luck with the nichicon 50v 1000uf on the power supply?
Thanks a ton!
-Brent
225 VA X 2 trafos are 18V.I am using a balanced type minimised resistor only input.47k to ground then 10k then 220k on both channels (220 k to ground on the non-inv side).I know that scientifically this does not give similar input impedances on both phases and we've had some discussion on this on previous posts with yuei wang but maybe I was a bit lazy to change this since with the bosoz the balanced connection sounds much better to my ears than the single ended variation which I have tried.I haven't played around with different resistors yet but I am using Welwyn RC55 0.1%.I have bypassed w 2.2uf polycarbonate and 0.1uf tin and foil on the bridge.This was even better than two 1uf BGN super-e types which surprised me since I liked the BGN a lot as main chip caps. The chassis is damped with DEDSHETE material and the feet are RDC cones.
I am thinking about testing with batteries power. Its not that difficult. Would a couple of 12v motorcycle batteries do I wonder?
I already have one from my Harley.
I am thinking about testing with batteries power. Its not that difficult. Would a couple of 12v motorcycle batteries do I wonder?
I already have one from my Harley.
protos said:
Wouldn't need anything as large as a motorcycle battery unless you wanted to use the amp for really long periods of time. But whatever you use you'd need four of 'em (a pair in series for each rail) unless you can get by with about 6 watts or so.
Some 7 Ah SLAs would work fine if you just want to use a pair, or some 10 or 12 Ah SLAs if you're going to run them in series pairs.
se
Maiming Naims and kicking Pass?
Better than a Naim 180 and 250? How could that be?!
"They are very dependent on construction techniques and all the parts used."
ALL decent amps are. Fairly high gain bandwidth and levels of negative feedback which this type of amp has, can make layout and decoupling more demanding than for low feedback amp. I think part changes may more audible because there are so few of them. The inverting topology takes this down to about two critical resistors per channel. That makes comparing resistors not too painful. I think a large degree of success with this amp is it is simple enough to get a decent stable layout (except for a certain Frenchman) and use decent parts. It is a good learning tool for tweaking and sounds very nice. The same attention to layout, decoupling, parts quality for a discrete design can probably go even further. Could these be some the factors for the success of Hugh Dean's kit amp as well as many opamp based preamp circuits? It is pretty funny that the things that can really make a good amp are being discovered on IC amps designed for non high end applications........
Better than a Naim 180 and 250? How could that be?!
"They are very dependent on construction techniques and all the parts used."
ALL decent amps are. Fairly high gain bandwidth and levels of negative feedback which this type of amp has, can make layout and decoupling more demanding than for low feedback amp. I think part changes may more audible because there are so few of them. The inverting topology takes this down to about two critical resistors per channel. That makes comparing resistors not too painful. I think a large degree of success with this amp is it is simple enough to get a decent stable layout (except for a certain Frenchman) and use decent parts. It is a good learning tool for tweaking and sounds very nice. The same attention to layout, decoupling, parts quality for a discrete design can probably go even further. Could these be some the factors for the success of Hugh Dean's kit amp as well as many opamp based preamp circuits? It is pretty funny that the things that can really make a good amp are being discovered on IC amps designed for non high end applications........
Peter Daniel said:
I tried batteries on my TDA7294 Gainclone and it worked wonderful. I used 4 (2+2) 12V/7.2Ah batteries. Most notable improvement was in highs (more detail + smoothnes), but overall, there was more air, detail and quieter background. Highly recommended!
Unfortunately the batteries were not mine, and I didn't find time yet to make charger and buy 4 batteries. 
miguel2 said:Hi,
While I am waiting for the OP549's I am looking for a transformer. I have read the OPA549 datasheet and got some doubts confusing me. It says that this chip can handle 8A continuous or 10A intermitent. If I consider a 25V supply, from the datasheet the output of the OPA549 can go to +/-21V. So for 8A we have the maximum power of 336W?! I think I made some error here
Miguel
The peak power is actually half of what you specified, and the RMS power is about 119W. But that assumes a 2.6 ohm load! For an 8 ohm load, power should be about 39W RMS. For a 4 ohm load, it's about 78W RMS. Of course, this all assumes adequate cooling to keep the chip in its safe operating area.
I built a mono amp last week, with the OPA541, using +/- 40V rails. It was just a quick project for a small PA application, but it sure is impressive sounding.
Peter Daniel said:
Any recommendations on a charging supply? I don't know much about that battery stuff.
Some kind of multi-stage charge controller will be easier on the batteries. Also, keep in mind that the deeper you discharge them each time, the fewer cycles you will get. To maximize battery lifetime, it's best not to go much beyond 80% DOD (depth of discharge) before recharging.
I'm thinking about using this for charging: http://www.st.com/stonline/prodpres/standard/vregs/13vlt_1.htm
It's very cheap (2.50 EUR/$) and easy to implement.
It's very cheap (2.50 EUR/$) and easy to implement.
Thanks Sparhawk. My speakers are 8 ohm nominal but I read somewhere they can go to 5 ohm at some frequency ranges. So if I consider 4 ohm I have 78W (maximum). Again, assuming a +/-25V supply, and knowing there is 4 V drop on the chip we have +/-21V output and therefore (P=VI) 1.9A maximum
Or should I forget this thing and say 78+78=156W. Double of this goes to a transformer of 300VA.
But I would like to understand those calculations
Miguel
Or should I forget this thing and say 78+78=156W. Double of this goes to a transformer of 300VA.
But I would like to understand those calculations
Miguel
miguel2 said:Thanks Sparhawk. My speakers are 8 ohm nominal but I read somewhere they can go to 5 ohm at some frequency ranges. So if I consider 4 ohm I have 78W (maximum). Again, assuming a +/-25V supply, and knowing there is 4 V drop on the chip we have +/-21V output and therefore (P=VI) 1.9A maximum
Or should I forget this thing and say 78+78=156W. Double of this goes to a transformer of 300VA.
But I would like to understand those calculations
Miguel
I'll try to explain a little better.
The amp can swing +/- 21V, so with a 4 ohm load, the current is:
21V / 4 ohm = 5.25A
The peak power is then:
21V x 5.25A = 110.25W
When the amp is fed a sine wave, the RMS output power is going to be:
110.25 x 0.707 = 77.95W
I think your mistake was in using 2 x 21V (42V) in your calculations. You have to remember that the speaker is referenced to 0V, so at any point in time, you can swing +21V or -21V, but not both at once.
A 300VA transformer should be adequate for two channels. The peak power requirement for two channels is about 220VA (2 x 110VA). So 300VA is plenty.
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