Chip amp power supply- a beginners guide

Finally find probably one godd schematic for regulated power supply that will fit my trafo 32-0-32v / 5A to use for LM 3886 amps.

The transistors will be MJ2955/2N3055.

Any suggestion?
 

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pirej said:
I'm trying to get 35v regulated as max. for stereo LM 3886.

The above schematic is OK with my trafo 32-0-32v?
depending on tolerances and actual mains supply voltages you may get a regulated +-35Vdc from a 32Vac.
But, you may suffer from occasional drop outs in the regulators when high current demand coincides with low supply voltage. This could be so rare that it effectively never happens during normal operational conditions.

If you find that drop outs are occurring then reducing the output voltage by a volt or two may cure the problem.

Where are the rectifiers?
 
THNX Andrew and all...

Sorry, but I was impressed with GC with my Canton CT 920DC. Previously I had a technics SU-V-670 and was trying to hear some parts of any music composition...

That was real reason to use two other trafos 32-0-32v to make another for my colleagues...

Rectifies were not drawn...Just the trafo..

Thnx...
 
Hi Nuuk, a couple of questions...

1) For the ground loop breaker circuit, which of these bridge rectifiers should I use?
2) You say "Place a small Class X1 rated capacitor (around 0.1 uF /275 volts is fine) across the switch contacts. "... how does that not short the switch given that we're switching AC (which a cap does not block, correct?)
3) Is this switch ok for the light bulb tester?
4) I'm a little confused about the "zero volt line"..the diagram on your site shows it connected to an I/O jack. Is that the ground of the jack it's connected to? would that be the same thing as signal ground? And how would I do a loop breaker with a dual mono gainclone? (I plan to put both channels of the amp and PSU all in one case) Wouldn't connecting the zero volt line to both power supplies (and both channels' I/O jacks) defeat the purpose of dual mono? I know dual mono requires 2 transformers and 2 rectifier bridges, but will it also require 2 IEC sockets & power cords?
 
Hi,
you can't do dual mono in a single box.
You can fit two monoblocks in a single box, but the grounding has to be done to allow two channel working. This is usually a compromise for all multichannel amplifiers. However, it can be made to succeed, but don't ask me, because I have never been able to build a two channel amplifier as quiet as a monoblock, ever. Similarly, I have never been able to build a steel cased amplifier as quiet as an uncased amplifier.

Calculate the impedance of your 100nF capacitor at 50 & 60Hz.
Now, calculate the AC current that will flow through that impedance at your main's supply voltage. This is ~ the current that flows when the switch is open.
If you fit Y rated caps on the lines to ground, do the same calculation for 10nF. This will give the Earth Leakage current. In the UK this Earth Leakage current must not exceed 25% of the trigger rating of the RCCB protected circuit. i.e. the total Earth Leakage current of all the appliances on a 30mA RCCB circuit must not exceed 7.5mA. That's why I have 5 RCCBs supplying my house and why I do not have an RCCB feeding my listening lounge.

If you don't know how and where to fit a switch on your light Bulb Tester then don't fit one.
The Bulb Tester works perfectly without a switch.
on=amp wiring fault,
off=possibly OK and allows you to check/measure operating voltages.
 
AndrewT said:
Hi,
you can't do dual mono in a single box.
You can fit two monoblocks in a single box, but the grounding has to be done to allow two channel working. This is usually a compromise for all multichannel amplifiers.
ahhh crap...looks like I'll be going with stereo for now then
AndrewT said:
Similarly, I have never been able to build a steel cased amplifier as quiet as an uncased amplifier.
hmm really? interesting
AndrewT said:
Calculate the impedance of your 100nF capacitor at 50 & 60Hz.
erm..how? I do know V=IR to find the current once I get the impedance though. Whatever that current is, I guess it means the amp will consume that when it's turned off, right?
AndrewT said:
If you fit Y rated caps on the lines to ground, do the same calculation for 10nF. This will give the Earth Leakage current. In the UK this Earth Leakage current must not exceed 25% of the trigger rating of the RCCB protected circuit. i.e. the total Earth Leakage current of all the appliances on a 30mA RCCB circuit must not exceed 7.5mA. That's why I have 5 RCCBs supplying my house and why I do not have an RCCB feeding my listening lounge.
huh? what's an RCCB?

AndrewT said:
If you don't know how and where to fit a switch on your light Bulb Tester then don't fit one.
The Bulb Tester works perfectly without a switch.
on=amp wiring fault,
off=possibly OK and allows you to check/measure operating voltages.
I know where the switch goes, I just wanted to know if the one I linked to is the right type & ratings
 
Redshift187 said:
Residual current circuit breaker. AKA ground fault circuit interrupter (GFCI), ground fault interrupter (GFI) or an appliance leakage current interrupter (ALCI).

It detects if the current on the live is different than the current on the neutral (which happens when some is going to safety earth) and disconnects the power.

Ahhhh ok, I know what a GFCI is...damn acronomical (<-even a word?) differences between countries :D
 
ahhhhhh I get it all now...fortunately I don't have to worry about it since my circuit sure as hell isn't on a rccb/gfci. I live in an old house and we only have those in (some of) the bathrooms. And 4.5mA is nothing as far as 'wasting' unused elecrticity. Thanks Andrew :cheers:


wait, I thought from the pic on Nuuk's site that it was a ceramic disc cap?? What type of a cap am I looking for? Mouser only had 4 different 0.1uF ceramic disc caps with high enough voltage ratings, and they didn't seem to be what Nuuk was describing... http://www.mouser.com/Search/Refine...6292+4294624808+4294572367+4294572368+1323043

or one of these? http://www.mouser.com/Search/Refine...572368+4294438739+1323043&Ns=Voltage+Rating|0
 
Hi,

also thanks to your help I was able to build my first chipamp with power supply.
As suggested here I always used the lightbulb tester. When I connected the speakers cables (without connecting the speakers) the lightbulb tester lighted.
The speaker cables I used were cat5 cables, the 4 colored wires of the cable connected together to obtain the positive wire and the 4 white wires connected together to obtain the negative wire. I used in the past this cables without any problem (not checked with the lightbulb tester anyway).
When I changed the cables and used simpled stranded wires the lightbulb did not light and the amp is now working fine.

Can you explain me why and, more important for me, is it possible that some problem is still present in my amp?

Thank you


Renato
 
Hi,
could the capacitance of the CAT5 be upsetting the stability of the amplifier causing some oscillation, just sufficient to power the bulb?

The usefulness of that bulb tester astounds even me.

I wish I had known about it decades ago.
I found it on this Forum some while after I asked how to phase dual primaries.
 
voltage calculation

Please excuse any stupidity in my post; I'm willing to risk that since there might be some use for others in a very basic question:

Assume one employs a configuration with one transformer having dual secondaries, and two rectifiers, as in the attached image. For the purpose of an example, let's now say we have 22 V secondaries. Consequently, times 1.4, we have somewhere around 31 V after rectification.

Now, if we power two chips with this arrangement (i.e. one rectifier per amp); we're running them at 31 V, yes?

But if I power one chip with this arrangement (i.e. two rectifiers per amp); are we not running them at 62 V?
 

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you have two ~31Vdc supplies.
They are isolated and can be used independently.
However, it's more likely that the amp will require a dual polarity supply.
The twin rectifier arrangement gives ~+-31Vdc, almost the same as the single rectifier arrangement when a centre tap is used for the zero volt line.
 
AndrewT said:
it's more likely that the amp will require a dual polarity supply.

Yes, that's the key! Each amp gets positive V, negative V, and Gnd. To send only a pair of lines to an amp ( V and Gnd ), one will need a single supply version of the amps, another beast entirely.

I know this is supposed to be simple, but it seems to me this is a crucial distinction especially for a beginner!

LOVE the DD stuff; it is fantastic, really helpful.
 
How do I know which parts are suitable?

After reading the beginners guide I would like to implement some of the recommendations but I am unsure of which parts to use.

Mains Switch Capacitor
I am having trouble finding a Class X1, 0.1 uF, 275 volt capacitor as indicated in the guide. Could someone tell me what search criteria to use or provide me with a link (e.g., mouser)?

Ground Loop Breaker Circuit
There is a parts list in the guide, but does not specify voltages. Could someone tell what voltage rating I need for the following parts (or a link is even better)?

  • 35 amp bridge rectifier
  • 100 nf capacitor
Perhaps the voltage ratings are dependent upon the power supply. If so, can someone give me a guideline of what to use.

Bulb Tester
While I'm at it maybe someone can point me to appropriate push to make switches.

When I am done, I will post a BOM with links for others to use in the future.
 
the switch capacitor can be either X1 or X2.

The disconnecting network can be assembled from low voltage parts.
50V cap and 50V rectifier.
But, the rectifier and the resistor must have high current ratings. These must survive longer than it takes the mains fuse to rupture and for the arc to extinguish.

Build a simple bulb tester first without any switches and become familiar in how and why it indicates as it does. The switch/es can be added later.