Power supply for amplifier question

Joined Feb 27, 2018
21

Hi guys, I am implementing an amplifier(attachment1) on a breadboard first to test out the sound quality distortion etc. I have attached the circuit . I have question about where to connect power and how it is referenced. I attached a second picture and it is circled. What does it mean when it says -18V and -25V referenced to the -30V line. -25V is coming out a regulator, that doesnt make sense to me bc i thought only positive voltages can come out of a regulator. If i understand the schematic correctly, the +30V wire from PSU goes to +30 and -30V goes to the -30V on the schematic and the ground from PSU goes to the GND on the schematic.
How many power supplies do I need to implement this on a breadboard. I used +30V and -30V for the main power(This is a 3Amp max power supply, do i need more current?) and also +5 and -5V for the 555. But no sound came out. so should i also get a different power supply to provide the -18V and -25V.?
I have attached the power part of the circuit(attachment 2) and there are 3 things circled, could any of you explain this part. I am super confused.
Any Help is greatly appreciated.
Thank you

Marc Sugrue

Joined Jan 19, 2018
62
Perhap its easier to get your head around the potential difference (Voltages). Consider this, if you have a volt meter and connected the black terminal to the -30V what voltage would you expect to measure if you put the Red terminal of the meter to your GND connection?

You'd measure +30V which is what your regulation circuit is seeing. So the regulator circuit is seeing a positive voltage with respect to its reference. It is just that this voltage is at a negative potential with respect to you system GND.

So to answer your question you either need a power supply with a +30V and -30V rail with the GND at 0v. Or if you have 2 floating supplies (shown as batteries in the attachment) where the positive rail of one supply is pinned to 0V.

Your 5V should be generated by the zeners in the circuit so no other supply should be needed

I hope this helps

Attachments

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mvas

Joined Jun 19, 2017
538
Am I correct in assuming that you have not built the Power Supply, ie the circuit in image #2?
If you have not built the Power Supply, then yes you need to supply +30v, +5v, Gnd, -5v, -18v, -25v & -30v.
3 Amps may be enough at low volume.

Joined Feb 27, 2018
21

where the positive rail of one supply is pinned to 0V.

Your 5V should be generated by the zeners in the circuit so no other supply should be needed

I hope this helps
Hey, thanks for the detailed reply. I used + terminal of the PSU and connected the - to ground to get +30V and then did the opposite on the other side to get -30V. I did not use ground terminal at all. I think this is where i went wrong.
How would I connect it so I get +30 and -30V referenced to ground?

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Joined Feb 27, 2018
21
Am I correct in assuming that you have not built the Power Supply, ie the circuit in image #2?
If you have not built the Power Supply, then yes you need to supply +30v, +5v, Gnd, -5v, -18v, -25v & -30v.
3 Amps may be enough at low volume.
i did build the circuit, i only used + and - terminal of the power supply to get +30V and -30V. i didnt use the power supply ground at all. what is the thing that i circled in red, is that a fuse or is it telling me that i need 6Amps to run the amplifier?

mvas

Joined Jun 19, 2017
538
Yes, both +30v and -30v is fused at 6 amps and is supplied by an external source
Yes, you need to connect all of the Ground between Amp & Power Supply circuit

Measure & verify at voltages from ground.
All of the Voltage Points in the Amplifier must connect to the corresponding Voltage Point in the Power Supply circuit.

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mvas

Joined Jun 19, 2017
538
Your Bench P/S Channel #1 Red to +30v pin in the circuit
Your Bench P/S Channel #1 Blk to Gnd pin in the circuit
Your Bench P/S Channel #2 Red to Gnd pin in the circuit
Your Bench P/S Channel #2 Blk to -30v Pin in the circuit

Do not use your "Center" 5 Volt output of your Bench P/S.

Is that how you have it connected?

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KeepItSimpleStupid

Joined Mar 4, 2014
3,728
My guess is in serial mode, the leftmost and rightmost supplies will track, but I haven;t read the instructions. One knob probably sets each supply to 0-32 volts. Verify that this happens.

You would connect the - of one supply to the positive of the other, This is your amp reference for +- 30V. Note how the binding posts are layed out.

The Ground pin is optional. It generally allows one to connect + or - to earth. In any electronic system it's best to have one reference to Earth ground. In any system you try to tie all of the high current grounds together, all of the low current reference grounds together to one point.

In an amp, I built, each channel had a separate supply, but everything returned to a star type ground except the inputs. Ground to the inputs of the power amp was connected to a 2.2 ohm resistor to chassis. The star ground was one point on the chassis.

The amp power supply generates voltages relative to the +-30 reference or the point where -30 and +30 are measured from.

Joined Feb 27, 2018
21
Your Bench PS #1 Red to +30v pin in the circuit
Your Bench PS #1 Blk to Gnd pin in the circuit
Your Bench PS #2 Red to Gnd pin in the circuit
Your Bench PS #2 Blk to -30v Pin in the circuit

Do not use your "Center" 5 Volt PS output

Is that how you have it connected?
yes that is exactly how i coneected it, but my circuit doesnt work. I guess there might be wiring issue on breadboard. I will check it tmrw and report back? Do I not use the ground terminal (middle) at all?

mvas

Joined Jun 19, 2017
538
Measure and verify each and every voltage ...
+30v, +5v, -5v, -18v, -25v and -30v vs the "Amplifier Ground Point" in your amplifier circuit.

If that is 100% OK, then check your LMC555 - is it producing a Triangle Wave?

I would have ...
Step #1) Built the "Power Supply" section, debugged and get 100% functional
Step #2) Built the "555 Timer" section, debugged and get 100% functional
Step #3) Built the "Amplifier" section, debugged and get 100% functional
divide and conquer!
Each step is built upon the previous step, but only after the previous section is "known good".

Joined Feb 27, 2018
21
If that is 100% OK, then check your LMC555 - is it producing a Triangle Wave?

Each step is built upon the previous step, but only after the previous section is "known good".
Hey i built the PWM section on breadboard and after 3 hrs of trouble shooting i got a clean wave. I kept giving it -5V to pin 1 bc of the circuit is built in a weird way and then finally i put pin 1 to ground and boom shaka laka i got the wave.
my next objective is power supply circuit so the circuit says -18V and -25V, so it is really +18 and +25 V when refernced to ground right?
let me know i wanna reduce time for trouble shooting

KeepItSimpleStupid

Joined Mar 4, 2014
3,728
You start out with +-30 unregulated.
That +-30 have zener regulators to get +-5
There is a pre-regulator, higher current that adds 12 V to -30 (power supplies in series), so -18 V.
The 7805 gives you 5V relative to -30 or -25V relative to ground.

The Zenier diodes should have their respective voltages across them, 5 and 12.

Between pin 2 (7805) and GND (7805) you will have 5 V

It's definately a very unique design, but nothing out of the ordinary except each supply has different references.
The Zener regulated supplies might be +-10%

The transformer has probably a regulation of +-10% because the line voltage can change that much.

==

Your power supply is capable of two voltages of 30 V at 3A either polarity or 30 VDC at 6 Amps.
Identical Power supplies can be designed so that they can be used in either series or parallel. Series is easy. Each supply is told to output the same voltage.

Parallel is harder. When the supply operates in parallel, one supply is set a little lower than the expected output.
e.g. 29.5 V and the other supply is used as a current source/sink with a voltage limit of 30 V, That's done with the series/parallel controls automagicly.

There is another power supply mode called "tracking" where if you have +-15V, the midpoint is always 1/2 the total voltage in series.
So if one supply after regulation becomes -14.9, the other becomes -15.9. I don't think you have this. This mode increases the CMMR of amplifiers.

To learn about power supplies in general there is an (HP/Agilent/Keysight DC power supply Handbook that you can find on the web.
Search for "dc power supply handbook Keysight"

Joined Feb 27, 2018
21
You start out with +-30 unregulated.
That +-30 have zener regulators to get +-5
There is a pre-regulator, higher current that adds 12 V to -30 (power supplies in series), so -18 V.
The 7805 gives you 5V relative to -30 or -25V relative to ground.

The Zenier diodes should have their respective voltages across them, 5 and 12.

Between pin 2 (7805) and GND (7805) you will have 5 V

It's definately a very unique design, but nothing out of the ordinary except each supply has different references.
The Zener regulated supplies might be +-10%

The transformer has probably a regulation of +-10% because the line voltage can change that much.

==

Your power supply is capable of two voltages of 30 V at 3A either polarity or 30 VDC at 6 Amps.
Identical Power supplies can be designed so that they can be used in either series or parallel. Series is easy. Each supply is told to output the same voltage.

Parallel is harder. When the supply operates in parallel, one supply is set a little lower than the expected output.
e.g. 29.5 V and the other supply is used as a current source/sink with a voltage limit of 30 V, That's done with the series/parallel controls automagicly.

There is another power supply mode called "tracking" where if you have +-15V, the midpoint is always 1/2 the total voltage in series.
So if one supply after regulation becomes -14.9, the other becomes -15.9. I don't think you have this. This mode increases the CMMR of amplifiers.

To learn about power supplies in general there is an (HP/Agilent/Keysight DC power supply Handbook that you can find on the web.
Search for "dc power supply handbook Keysight"