Hey Helix... I have one question about Crescendo?

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Helix,
You send couple of pictures about your Cresendo Amp in following thread:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=2077

1. I quess that your amps transformer have four (2+2) output wires so how many rectifiers do you have in power supply?
One or two?

If you have four outputs, have you attach transformer wires(zero/ground/something) as picture 3. shows?
Or have you made power supply like picture 2. shows?

I have transformer with four output wires.

Or which way is the BEST way?
Or is there some better way?

Thanks...


Yes... I have very bad English...:confused:
 
pic 1 again
 

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Ok

First of all, i am sorry about the pics, i only relized there size after posting them. I get kind of forgetful of how lucky i am about this T1 connection i have:cool:.

Eccu,
1. I quess that your amps transformer have four (2+2) output wires so how many rectifiers do you have in power supply?

Yes that is right, the transformer has two seperate secondarys hence 4 output wires.

The actual transformer is just a standard RS part, 223-8279

I currently have 1 bridge rectifier in the suppy at the moment, so it is connected much like your pic. 1 (you can see it just inbetween the transformer and the bank of caps)

I think i am right in that saying the BEST way to wire it is as in pic. 2

However, i dicided to wire it as per pic 1 because of the protection board's AC detect circuit. At the moment i do not have the magazine with me so i can't remember why i thought this, but i did:D. I think maybe i was wrong and you can use 2 bridges but don't take my word for it! I was worried about some expensive burn-up or something so went for the 1 bridge and made sure it was a rugged one (35A 400V).

Also i think it would be better to move the loudspeaker ground from the point indicated (Amp board) to the center of the smoothing caps? is that right? that way you don't get large currents on the ground that the front-end and signal is using

2) The pics are just links to my website, maybe the 800x600 limit was introduced because of me:D

3) I got ALL of the devices that have to be heatsink mounted including the output FETs and the op-amp fromCricklewood Electronics which is based in the Uk and has a fairly basic website, but if you phone them they are extremly quick in searching for components and very helpful (IMHO)
 
I would go for pic 2.

Reason ? The ground of a system is extremely important. Pic 1 will send the huge charging current spikes for the Electrolytics right through your system ground. Having that point as your reference is like trying to thread a needle standing up in a small boat in high waves - it is never calm and you can´t deal with fine stuff. The sonic signature of this grounding scheme is a very annoying harshness and a significant lack of low level detail. The harshness is there whatever you do with the amp itself. The only way to solve this is to make the ground quiet.

Pic 2 will lead those current spikes directly back to the transformer, completely outside the system ground. You have now your quiet ground. I once turned a very good amp to a VERY VERY good amp by just making this change to the grounding scheme.

It is interesting to note that a typical tube amp with a single supply and a single full-wave recifier will have this type of quiet ground also.

Considering the cost penalty of just one extra rectifier the payback in sound quality is huge. I would never consider designing audio PSU´s without this grounding scheme.

Regards

Syl
 
syl said:
Hi Geobill,

Pic 3 suffers from the same problems as Pic 1. You will have a better end result if you sacrifice the separate supply for L and R channel and go for a common supply with the Pic 2 scheme.

Note how the recifiers should be connected to give a clean system Gnd. See attachment.

Regards/ Syl

So this image is just like pic2, I think.
Edit: Is this pic2 the best psu design, or is there something better somewhere?

Is there any disadvantages if Electrolytics (in pic2 C6-C9) have very big capacitance?
Or is that allways better when capacitance is bigger?
 
Hi Eccu,

They are basically the same, but not with regards to how the rectifiers are connected. Note that in your pic 2 the rectifiers are directly connected to the main ground. Compare with my sketch where the rectifiers are some distance away from the system ground. You need to do that, otherwise the charging current spikes will disturb the main ground just as much as in pic 1 and 3.

No disadvantage with large caps, the more the better (less ripple). The charging spikes will be higher but that is no problem with big enough rectifiers.

Yes, I would say that pic 2 is the best scheme you can use for the main power supply, given that you decided not to use inductors. C-L-C filters are very good and would improve the design, but would give you a cost hit (and two large inducturs to pack in your box).

But don´t just focus on the main power supply caps, you need to think also about the ripple on the supply voltage for the low level circuitry of your power amplifier. Instead of using all of your capacitance budget on the main reservoir, assign 1/3 of your total capacitance budget to an RC low-pass filter that you insert in the supply rails (plus and minus) for the low level part of the amp. The improvement in resolution is VERY big (own experience). 10 - 15 ohms is about right.

(I use 12 ohms / 15.000 uF in one of my power amplifiers). Total capacitance budget is 90.000 uF per channel.

I find the RC-filter approach very appealing due to its simplicity vs the sonic improvement you get.

regards

Syl
 
syl said:
Hi Eccu,

They are basically the same, but not with regards to how the rectifiers are connected. Note that in your pic 2 the rectifiers are directly connected to the main ground. Compare with my sketch where the rectifiers are some distance away from the system ground. You need to do that, otherwise the charging current spikes will disturb the main ground just as much as in pic 1 and 3.


Sorry Syl. Now I don´t understand. Maybe because my bad english.
Is main ground same as audio circuit ground?
And is system gound same as enclosure or transformer center lead(s) or something else?

So I must take some long wires from rectifiers to system ground (in another words transformer center leads), or?



Yes, I would say that pic 2 is the best scheme you can use for the main power supply, given that you decided not to use inductors. C-L-C filters are very good and would improve the design, but would give you a cost hit (and two large inducturs to pack in your box).

How I must connect these inductors if I decide use those?



But don´t just focus on the main power supply caps, you need to think also about the ripple on the supply voltage for the low level circuitry of your power amplifier. Instead of using all of your capacitance budget on the main reservoir, assign 1/3 of your total capacitance budget to an RC low-pass filter that you insert in the supply rails (plus and minus) for the low level part of the amp. The improvement in resolution is VERY big (own experience). 10 - 15 ohms is about right.
(I use 12 ohms / 15.000 uF in one of my power amplifiers). Total capacitance budget is 90.000 uF per channel.


Power supply is common for both channels (left & right) and total capacitance budget is 100.000 uF (ten 10.000 uF), so how I must connect these resistors? (Picture pii.bmp)



Very big thanks Syl!

ps. Picture pii.bmp is only bad draft...
 

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Hello Eccu,

Oops, I was a bit sloppy with the language. In my discussion main ground and system ground is the same. It is the point in the middle between the large caps. Sorry for confusing you.

The transformer MUST have two separate secondary windings for this scheme to work, one for each rectifier. A 3-tap transformer (ac - 0 - ac) will NOT work. See pic below exactly how the wiring should be made.

The C-L-C filter is built just like it looks. Place the inductor in series between two caps.

--------------- L ---------------
| |
C C
| |
gnd gnd


The total budget of 100.000 uF is great. Typical DIY stuff (look for that in commercial amps !). 10 x 10.000 uF. I would take two of those caps and build my RC-filter. That leaves a good 80.000 uF for the output stage to work from.

I looked at your bmp-pic. C2 would be the 40.000 uF and C3 the 10.000 uF. R3 in between at 10 - 15 ohms. C2 feeds the output stage (bipolars in darlington, mosfets, whatever). C3 feeds the input stage and everything up to and including the voltage amplifying stage driving the output stage.

It does help if I could see the basic topology of the amp, because the term "output stage" and "low level stage" can be very different in different designs. The RC-filter must go in the right place or things may not work so good.

Regards

Syl
 

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Very big thanks Syl... This help me LOT.

Yes, I have 4-tap transformer.

1. How many milliHenrys (mH) L must have?
2. Is that any matter where I place this L?
(Look that high resolution ASCII picture :) )

---L--R---- +
| | | | |
C CC C C
| | | | |
-------------gnd
| | | | |
C CC C C
| | | | |
---L--R---- -

3. >C2 feeds the output stage... and C3 feeds the input stage and everything up to and including the voltage amplifying stage driving the output stage.

I have one questions about this thing, but I think it´s easier explain when I get picture about scheme.




I have now week holiday, but I back in business maybe on the next week.
 
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