I have built one of Audiosector.com's LM3875 Premium Kits into 2 x monoblock amps. I plan to run 1 x transformer and rectifier board for each amplifier. I was planning to use 2 x 300VA 25-0-25 toroidals [one for each monoblock] but think that I might use 300VA 18-0-18 instead. I will be using the amps to drive my Sonique Slim 66 http://www.sonique.com.au/slim/66.htm speakers which are 6 ohm so I thought that 18-0-18 would be more suitable. I also have some B&W 603 S2 which are 8 ohm that I might use too.
Basically I want the amplifier to be a fexible as poosible for various speakers [they will be used primarily with the Sonique's though] and also wondered weather 300VA per channel is overkill. Should I just go for 160VA? I want to make the monoblocks the best that they can be and 300VA toroids are not really much more expensive than the 160VA ones. And should I go for an 18-0-18 or 25-0-25 transformer? Thanks
Basically I want the amplifier to be a fexible as poosible for various speakers [they will be used primarily with the Sonique's though] and also wondered weather 300VA per channel is overkill. Should I just go for 160VA? I want to make the monoblocks the best that they can be and 300VA toroids are not really much more expensive than the 160VA ones. And should I go for an 18-0-18 or 25-0-25 transformer? Thanks
Chip, from my own experience, the 18 volt transformers do work much better with 6 ohm speakers than the 25 volt versions.
You can get away with 80VA per channel as a minimum but more power won't hurt. In fact, for reasons I can't go into here, a 300 VA transformer (in a typical set-up) is better than a 160 VA for reasons not related to power output.
You can get away with 80VA per channel as a minimum but more power won't hurt. In fact, for reasons I can't go into here, a 300 VA transformer (in a typical set-up) is better than a 160 VA for reasons not related to power output.
Hi,
18Vac or so is ideal for a 40hm speaker load.
25Vac or so for 8ohm.
For 6ohm somewhere in between would get maximum reliable power.
Checkout the B&W. Although you say 8ohm they may be 4 to 8ohm, which would require the amp to be designed for the 4ohm part of the load.
For a single channel monoblock the minimum is 60VA for 60W output.
I and many others recommend around VA=1.5Times output power.
But transformers with this low a VA also have a high regulation.
To avoid some of the down side of poor regulation specify a higher VA.
Thus instead of 90VA use 150VA.
Above 150VA, the potential gains are quite small, but could be audible. I suggest 300VA as an absolute max for 60W.
BTW,
applying the 1.5Times rule would indicate that 300VA is suitable for around 200W of output power. Many will rubbish the suggestion that 300VA is useful for a 60W ClassAB amp. There's only one way to find out. Try it.
18Vac or so is ideal for a 40hm speaker load.
25Vac or so for 8ohm.
For 6ohm somewhere in between would get maximum reliable power.
Checkout the B&W. Although you say 8ohm they may be 4 to 8ohm, which would require the amp to be designed for the 4ohm part of the load.
For a single channel monoblock the minimum is 60VA for 60W output.
I and many others recommend around VA=1.5Times output power.
But transformers with this low a VA also have a high regulation.
To avoid some of the down side of poor regulation specify a higher VA.
Thus instead of 90VA use 150VA.
Above 150VA, the potential gains are quite small, but could be audible. I suggest 300VA as an absolute max for 60W.
BTW,
applying the 1.5Times rule would indicate that 300VA is suitable for around 200W of output power. Many will rubbish the suggestion that 300VA is useful for a 60W ClassAB amp. There's only one way to find out. Try it.
A couple more thoughts.
I find dual mono produces a clear improvement in sound quality so always recommend two transformers over one.
If you go with 300VA, which I agree with Andrew is the sensible maximum for a chip amp, and put both in the same enclosure then switch them both on and off independently, ie with a power switch for each transformer. That way you can get away without a soft-start.
And, DON'T put them both in the same enclosure if it is made of metal. Don't ask me why not, I don't know what happens but the sound is better when you don't. Perhaps the magnetic fields are somehow 'shorted' by the metal case, I really don't know but I can hear the difference even removing the metal lid of a metal case.
I find dual mono produces a clear improvement in sound quality so always recommend two transformers over one.
If you go with 300VA, which I agree with Andrew is the sensible maximum for a chip amp, and put both in the same enclosure then switch them both on and off independently, ie with a power switch for each transformer. That way you can get away without a soft-start.
And, DON'T put them both in the same enclosure if it is made of metal. Don't ask me why not, I don't know what happens but the sound is better when you don't. Perhaps the magnetic fields are somehow 'shorted' by the metal case, I really don't know but I can hear the difference even removing the metal lid of a metal case.
I plan on making 4 x separate enclosures for the monoblocks. Two for each channel - one housing the toroidal, rectifier and filter caps and the other housing the amp, heatsink etc.
So it sounds like 160VA would probably be plenty however the 300VA is only about $20 extra per toroidal...
It also sounds as though neither the 18v or 25v is going to be the most flexible... I probably need 21V or 22V secondaries for the best of both worlds... Would 25V [35V rectified] be too much for a 6 ohm load even if the heatsinks were large enough? The Sonique speakers may dip down to 4 ohm too... something to keep in mind.
So it sounds like 160VA would probably be plenty however the 300VA is only about $20 extra per toroidal...
It also sounds as though neither the 18v or 25v is going to be the most flexible... I probably need 21V or 22V secondaries for the best of both worlds... Would 25V [35V rectified] be too much for a 6 ohm load even if the heatsinks were large enough? The Sonique speakers may dip down to 4 ohm too... something to keep in mind.
Hi Chip,
the complexities of separating the PSU from the amplifier are not easy for a newbie to comprehend.
This proposed separation does not help overcoming the " two amplifiers in a single box grounding" problem.
I recommend that each monoblock be stand alone with PSU + Amplifier combined for your first foray into amp building.
the complexities of separating the PSU from the amplifier are not easy for a newbie to comprehend.
This proposed separation does not help overcoming the " two amplifiers in a single box grounding" problem.
I recommend that each monoblock be stand alone with PSU + Amplifier combined for your first foray into amp building.
I hate to be a broken record when it comes to this, but Steve at ApexJr.com has a good selection of surplus transformers for much cheaper than you would get elsewhere. Plus, he supports the forum, so go support him!
On a side note, I used 80VA transformers--dual mono--to power my office amp and have never had an issue, but then again, I am not really trying to peel pain with them.
On a side note, I used 80VA transformers--dual mono--to power my office amp and have never had an issue, but then again, I am not really trying to peel pain with them.
I don't understand Andrew. Surely we are only talking about physical separation of the PSU (transformer/rectifier) into a separate 'box'. How can that be difficult to understand? As far as I know, it doesn't change anything electrically except that we need an umbilical connection to the 'box' with the amp section.
questions that need to be askedNuuk said:
I don't understand Andrew. Surely we are only talking about physical separation of the PSU (transformer/rectifier) into a separate 'box'. How can that be difficult to understand? As far as I know, it doesn't change anything electrically except that we need an umbilical connection to the 'box' with the amp section.
1.) where to put the rectifier?
2.) where to put the smoothing?
3.) where to put the power ground?
4.) where and what needs a Safety Earth?
5.) where to put the Audio ground?
6.) where and what size of Local Decoupling?
7.) do we keep the various ground separate through the umbilical?
8.) will making the amp a two channel version require further thought on the grounding?
9.) will the PSU be two channel or shared or dual output?
10.) probably many more.
Now, see if we can reach agreement on the answers to each of these questions.
Will a Newbie even understand why these questions need to be asked?
Will a Newbie be able to weigh up the pros & cons for each of the conflicting answers?
Do you see why I said ?
I know that I don't have all the answers.
Many of those questions, if not all of them bar the rectifier location can apply to an all-in-one amp too.
My first ever GC was a monoblock design with the PSU in a separate case and worked fine. Of course, I am always assuming that a newbie will start off with one of the most basic designs (and an easy to drive speaker).
My first ever GC was a monoblock design with the PSU in a separate case and worked fine. Of course, I am always assuming that a newbie will start off with one of the most basic designs (and an easy to drive speaker).
IMHO the quick and simple answers:AndrewT said:
1.) where to put the rectifier?
Close to the transformer, away from the amp inputs.
2.) where to put the smoothing?
Do you mean rail capacitors? If so, right after the rectifier. Also, you should always connect your amp rails directly to the caps, rather than then rectifier pins.
3.) where to put the power ground?
If you are using a center tapped transformer with one rectifier, it should be connected to the ground of each rail cap and then back to the star ground. Don't connect the transformer's center tap directly to ground for best results.
For dual secondaries/ rectifiers, again, take the ground from each rail cap and not the rectifier or transformer.
4.) where and what needs a Safety Earth?
Any metal chassis should be connected to ground. If multiple parts of the chassis are insulated from another (like, say, by a plastic standoff for the lid or something goofy like that) any metal part not in good electrical contact with the main chassis section should be tied back to ground.
5.) where to put the Audio ground?
I always take it directly to the star ground. If there is any problem, you can put a low value resistor in there to "isolate" the signal ground.
6.) where and what size of Local Decoupling?
Decoupling caps (meaning the ~0.1-1uF caps) should be as close to the power input pins of your chip as practical.
7.) do we keep the various ground separate through the umbilical?
If you have the extra wire, sure! Why not? Let's put this caveat in, though: I'm assuming you have already grounded your power supply and are pulling these two ground wires from the star ground.
8.) will making the amp a two channel version require further thought on the grounding?
Not really. Everything still goes back to the "star". . . . I don't quite follow this questions.
9.) will the PSU be two channel or shared or dual output?
Aren't we talking about a dual mono design here? I am confused by this question.
10.) probably many more.
Now you are just being difficult! Despite the admonitions of many here, chipamps are really difficult to screw up. You will more than likely get a pretty good amp if you can follow the simple build guide that comes with pretty much every chipamp kit.
NEVARRR!!!!
No, but if you aren't willing to learn and experiment, you should go to Best Buy. Not knowing is a starting point, but knowledge is a journey. (sorry, I couldn't resist)
Hi,
Thanks Dfdye for your opinions on the separated PSU from dual channel power amp.
I happen to agree with answers 1 through 3.
I disagree, or am undecided, with the answer or adequacy or guidance offered for all of the remainder of the questions 4 through 9.
Does anyone else want to contribute?
Thanks Dfdye for your opinions on the separated PSU from dual channel power amp.
I happen to agree with answers 1 through 3.
I disagree, or am undecided, with the answer or adequacy or guidance offered for all of the remainder of the questions 4 through 9.
Does anyone else want to contribute?
Thanks all for your comments. Although this is my first Chip-Amp, I think myself to be fairly electronically minded and with all the help from forum members don't think there will be many problems...
I would have expected that separating transformers from amplifiers would only make for a better, lower noise amplifier in the end without any major complications to its design... I am planning to build the enclosures from 40x40mm western red cedar slats laminated together with an aluminium bottom and back that all the electronics are mounted to. So provided that the aluminium bits are earthed correctly to the mains earth there shouldnt be too much of an issue. Maybe I will have to run an additional earthing wire from the metal parts of the amplifier enclosure, through the umbilical, to the metal of the psu enclosure and then to safety earth...
I would have expected that separating transformers from amplifiers would only make for a better, lower noise amplifier in the end without any major complications to its design... I am planning to build the enclosures from 40x40mm western red cedar slats laminated together with an aluminium bottom and back that all the electronics are mounted to. So provided that the aluminium bits are earthed correctly to the mains earth there shouldnt be too much of an issue. Maybe I will have to run an additional earthing wire from the metal parts of the amplifier enclosure, through the umbilical, to the metal of the psu enclosure and then to safety earth...
I have made some revisions to my enclosure design and am now looking at going for only 2 enclosures. Basically just trying to keep costs down. One for each monoblock, each one housing the toroidal and amp etc.
Still undecided about what voltage toroidals to go for though...
Is a 3mm thick aluminium plate sufficient to sheild the amp from the toroidal?
Still undecided about what voltage toroidals to go for though...
Is a 3mm thick aluminium plate sufficient to sheild the amp from the toroidal?
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.