Hi
I would like to ask about the R1,R3 resistors (in the base of the ouput transistors) which are 1.2 ohm/ 2 watt.
Is there a reason that you use a 2W resistor because if i'm not wrong even a 0.5W resisstor would be fine, with a min hfe=50 for the output transistor this resistor would have
P=0.5A * 0.5A *1R2 = 0.3W and the output would be 0.5A * 50 =25A.
I wouild like to use good quallity resistors for the circuit (PRP or HOLCO) but for 2W i would have to use MILLS resistors which cost 5 times more and i was wondering if i can avoid it...
Thank you
Alex
I would like to ask about the R1,R3 resistors (in the base of the ouput transistors) which are 1.2 ohm/ 2 watt.
Is there a reason that you use a 2W resistor because if i'm not wrong even a 0.5W resisstor would be fine, with a min hfe=50 for the output transistor this resistor would have
P=0.5A * 0.5A *1R2 = 0.3W and the output would be 0.5A * 50 =25A.
I wouild like to use good quallity resistors for the circuit (PRP or HOLCO) but for 2W i would have to use MILLS resistors which cost 5 times more and i was wondering if i can avoid it...
Thank you
Alex
MikeB said:
Thanks Mike.
If I buy the V-RKT-LN 225.25, do I also need the NT-KE 10/35TS-HA (Power supply for Amps)?
And what is with the Thel transformer? Would this fit?
Prim: 230V
VA: 50
Sek.-Wicklungen: 2x30V + 2x6V
Leerlauf-spg.: +15%
mögl. Spannungs-Kombinationen: 2x24V, 2x30V, 2x36V
d x h kg: 82x39 0,8
But I need also the "Siebung" STV 4700/63 in addition?
Thanks a lot for answering my stupid Noob questions
No way. It has only 50 VA power, you will need 300-400VA for a stereo setup.
Ther perhaps cheapest transformer solution for powering two Symasyms is buyling two toroids "RKT 12012" from Reichelt. They are rated 2x12V/120VA rated. If you put all 4 secondaries in series, you will have 2x24V/240VA for less than 40 Euros.
Of course you need rectification and filtering between the transformer and the amplifier boards. You may go for a readily availeable soultin like the Thel board, but that's the most expensive way to do it. Using two rectifier bridges and at least 4 10000µ/40V capacitors will do the job and costs much less.
Hi Markus, as you are a beginner, you might not want to go expensive as a start...
May i suggest a cheaper toroid here , the "SE-RKT 225.24" or "SE-RKT 330.24".
If you are already shopping at schuro, go here or here , and get 2x 22.000µF 40v or 4x 10.000µF 40v.
At reichelt you can simply buy a rectifier like the "B250C25A" (or stronger) and most of the rest.
Holger, i am not a fan of the double rectifier...
Mike
May i suggest a cheaper toroid here , the "SE-RKT 225.24" or "SE-RKT 330.24".
If you are already shopping at schuro, go here or here , and get 2x 22.000µF 40v or 4x 10.000µF 40v.
At reichelt you can simply buy a rectifier like the "B250C25A" (or stronger) and most of the rest.
Holger, i am not a fan of the double rectifier...
Mike
HBarske said:
Hard to see any benefit from it. Doubled loss in diodes, doubled dioderinging, doubled price. (okay, price is negligible)
There is a discussion about that in the "Bob Cordell Interview: Power Supplies" thread.
Until now, a real benefit from 2 bridges is to get rid of mechanical hum in the transformer caused by unbalanced loading. (Did not have that problem yet)
Mike
Ah yes, thx Mike. Went through it all 😱.
Doubled loss and doubled noise - agreed.
I have found it useful to get the secondaries of the transformer connected very "late", behind the filtering caps, if possible on the star ground (if any).
Despite the balancing issue, there is indeed no real need to use two bridges, perhaps this scheme might be an alternative to serve my wishes with one bridge only:
Doubled loss and doubled noise - agreed.
I have found it useful to get the secondaries of the transformer connected very "late", behind the filtering caps, if possible on the star ground (if any).
Despite the balancing issue, there is indeed no real need to use two bridges, perhaps this scheme might be an alternative to serve my wishes with one bridge only:
Attachments
Okay, thanks Holger and Mike for your answers.
I think I will buy the V-RKT-LN 225.25 and maby the NT-KE 22/63S because then I have also the circuit board.
Makes it sense, to have more VA like the V-RKT-LN 300.25 or just waste of money?
I also totaly forgot to mention, that I want to build two Mono SymAsym as power amplifiers for my front system (Sidewinder from HobbyHiFi 2/2004), which has a low efficiency factor with a audio pressure of only 85 dB. Therefore I need some extra power.
The SymAsym will be connected to my Yamaha Sourround Receiver on the Pre Out.
I think I will buy the V-RKT-LN 225.25 and maby the NT-KE 22/63S because then I have also the circuit board.
Makes it sense, to have more VA like the V-RKT-LN 300.25 or just waste of money?
I also totaly forgot to mention, that I want to build two Mono SymAsym as power amplifiers for my front system (Sidewinder from HobbyHiFi 2/2004), which has a low efficiency factor with a audio pressure of only 85 dB. Therefore I need some extra power.
The SymAsym will be connected to my Yamaha Sourround Receiver on the Pre Out.
A bigger VA rating is no mistake - if it is useful is another thing. 300 VA for a mono SymAsym is a little bit overkill. even 225 VA is far more than enough. Remember: Mike powered two of his amps with one "V-RKT-LN 225.25". I think the "SE-RKT 225.24" Mike suggested is a good thing.
The supply board looks okay, but it is not cheap. As you will have to get your amplifier PCBs etched anyway, you could go a lot cheaper with a DIY rectifier/capacitor board.
The supply board looks okay, but it is not cheap. As you will have to get your amplifier PCBs etched anyway, you could go a lot cheaper with a DIY rectifier/capacitor board.
Markus, are your speakers 4ohm or 8ohm ?
If they are 8ohms, 2 of the 160VA transformers will be way enough.
Also, 2x10.000µF per channel will be enough.
I think, the "SE-RKT" is good enough, that saves a lot of money.
Building your own rectifying will also save a lot of money, the mentioned metalbridge costs 1.10€, the BC-056 caps with 10.000µf 3.48€ each...
Mike
If they are 8ohms, 2 of the 160VA transformers will be way enough.
Also, 2x10.000µF per channel will be enough.
I think, the "SE-RKT" is good enough, that saves a lot of money.
Building your own rectifying will also save a lot of money, the mentioned metalbridge costs 1.10€, the BC-056 caps with 10.000µf 3.48€ each...
Mike
MikeB said:
Unbalanced trafo problems are negligible with bifilar wound secondaries, in fact this is quite often done on toroids. Often only to replace a single thick wire, which tends to stress the winding machine and enamel on the wire itself if it is wound onto a smaller core, with multiple thinner wires. All it takes then is to separate the wires.
However, this is not the real reason one would want to use dual rectifiers.
You want to use them ONLY if you have two separate windings (so no center tap), and the reason why you use them so is to reduce the common path of cap charging current and amp rail current. More below.
HBarske said:
If you look carefully at your connection - you will notice that the part of the wire connecting the caps to the star ground now adds to the internal cap ESR/ESL, and although you may not see problems in the ground point, they are just transferred to the power rails. This is not the worst problem, either.
Your two ground lines each carry alternate half-wave rectified curents for each power rail. Routing of these wires is CRITICAL - the loop area formed by them must be kept to a minimum, or this current loop will induce an imprint of the charging currents elsewhere. Essentially, these two would have to be twisted together.
Even then you still have the problem that there is longer than necessary common path for the cap charging current and amp psu rail current.
When making a single bridge power supply, it is quite essential to connect the 'center tap' of the two PSU rail caps by the shortest possible wire. This is because you want to add the minimum possible additional common path for charging current and the actual power rail current demanded by the amp. Normally, you do this by mounting the caps as close as possible so you can use the shortest wire link between - of the positive rail cap, and + of the negative rail cap. Normally a common path is already minimized for the power rail terminals of the caps as you join the rectifier side and the amp side of the rail at the single terminal of the cap itself (NEVER join them together, then route a wire to the cap terminal).
Rectifier side and amp ground side must join in ONE point along the 'center tap' link between the two caps. If multiple points are needed, keep rectifier side and amp ground side separate, eg. join two windings into one center tapped wnding, then connect that point with a separate wire (even if only a few mm long!) to the common point between caps. Connect all ground points of the amp side into a star ground point, then connect this point to the common point between the two caps with a separate wire, (even if the wire is only a few mm long). The reasons become obvious if you draw all these wire parts as discrete resistances.
There are a few other tricks that can be used if the actual points become rather large, such as separate links forming a capacitor center tap, one for the rectifier side, one for the amp side, or when multiple amps are supplied from the same rails, etc. It is wort hoting that using multiple caps connected 'in a line' from rectifier to amp reduces this problem as the links between caps form a PI-filter of sorts, which to a degree separated the paths of current from the rectifier and the amp.
Also, keep all 3 wires on rectifier (center tapped secondary via bridge to center tapped DC) side and 3 wires on the amp side (power rails and power ground(s)) side braided together in order to reduce induction.
However, all of that becomes a moot point with dual windings and dual rectifiers. You can braid the AC side, and the DC side of the rectifier and connect the DC side to each cap right at the terminals. Forming a center piont then becomes FAR less of a problem because any charging current going through the link between the caps will only be due to interwinding capacitance, for bifilary windings this will also be effectively reduced because the actual potential difference between these windings is zero at any given point in the winding! Although the capacitance (such as it is) will conduct HF hash better, with a few nF attempting to pass current through a thick piece of wire, the voltage drop across this wire is reduced by several orders of magnitude WRT to normal single rectifier situation. The common path for charging and audio currents is reduced as much as possible, only to what is internal to the cap (no help there anyway).
I am not really going into an argument regarding diode switching noise. It needs to be taken care of either way, and with diodes, if you have tamed one, you know how to tame them all, be there 4 or 8. However, the decison to have extra diode drops when two rectifiers are used, rests with deciding if it is worth the reduction in common current paths between rectifier and amp - this becomes the more important the lower ESR the caps are, and the further appart their terminals are (due to physical size or mechanical arrangement). I would also tend to expect that the importance of this rises with additional cap management, like parallel lower value caps, snubbers etc. However, the importance of using this arrangement drops when multiple parallel filter caps (with or without extra cap management each) are used, because of the aforementioned 'PI filter' action.
Hello all,
I see you 've spoken about PSU with one or two rectifier. They are a french DIYer ( Zenquito conceptor ) who have also thinked about it, his thoughts http://perso.orange.fr/jm.plantefeve/alim.html ( In French )
I see you 've spoken about PSU with one or two rectifier. They are a french DIYer ( Zenquito conceptor ) who have also thinked about it, his thoughts http://perso.orange.fr/jm.plantefeve/alim.html ( In French )
HBarske said:
Holger, you are right with the amplifier PCBs, so I will build als the rectifier/capacitor board by my own.
MikeB said:
Mike, the speakers are 4 ohm.
After reading your webside and the K+T again, I decided to build two Symasym in one case with one 300VA transformer.
Thanks again for your great help.
Hi Markus, just did a very basic rectifier/capacitor board.
It's stuffed with discrete bridge rectifier (4 TO220 types, for example MUR860) and two BC056 caps up to 22000µF/40V. Might be the right thing for one channel of your amp.
Yes, one rectifier, central ground...
Perhaps you might find it useful. The attached Zip file contains schematic, board with component placement, and a hires PDF for making the PCB.
It's stuffed with discrete bridge rectifier (4 TO220 types, for example MUR860) and two BC056 caps up to 22000µF/40V. Might be the right thing for one channel of your amp.
Yes, one rectifier, central ground...
Perhaps you might find it useful. The attached Zip file contains schematic, board with component placement, and a hires PDF for making the PCB.