making Digial Amp -- TA2020-20 --

It was difficult to adjast volume.
I couldn't lessen the volume enough.

So I canged a position of a variable resistor.
I tried to placed it in place of return resistances (20k ohm).

It is dangerous because gain may become infinite when a bad electrical connection of VR (gariohm) will happen.
In order to avoid this tragedy, I connected 2pin and 3pin of VR.
If gariohm is happened, the gain will be under 1/2.

Now I'm satisfied.

GND should be stable.
I heard it is good to connect GND to a post that is buried in a yard.
I can't do that because I live in a apartment.
Hoping improvement, I connected GND to the case of amp instead of a yard.
There was a little improvement.
It might be effective to avoid noises.

Result: I feel low pitch sound got stronger.

The time has come to say good bye to KMG 3300uF.
They worked well.
In order to satisfy me, I threw a relief.
It is MUSE FX 3300uF/16V.
I bought it for 170 yen at Yahoo Auction.

MUSE FX is a audio capacitor that sounds gently.

Sorry for troublesome wireings.

The sound changed dramatically.
1: volume got increased (Does it get high efficiency?)
2: It got more deep.
3: It got more easier to tell vocals apart.

This modifying bore good results.
This capacitor's role is important because almost every electrical charges are given from their savings.

I made a bass reflex speaker. (making bass reflex speaker)
Speaker impedance was changed from 6 ohm into 8 ohm.
So I had to change the output capacitor value.

BG-PK 0.33uF (for 6ohm)
into
BG-PK 0.22uF (for 8ohm)

I'm now satisfied with my audio system.
I feel comfortable hearing musics from it.

TA2020 has a problem of pop noise.
When I turn on and off, a pop noise goes bang.

I thought that the cause of this might be DC offset.

I found a article about DC offset in the datasheet of TA2024C.
It appears at 11 page.

I found a potentiometer was sold at very cheap price, I bought it.
But it was 5k ohm. It will be easy to adjast DC offset if the value of potentiometer is as high as 50k ohm.

RIKEN's resistor is famous for good sound.
It helps to sound vividly.

These are potentiometers.
They are so vivid.

I love it.
BlackGate has privided me with marvelous deep sound.

I made the same circuite as the one which were appeared in the TA2024's datasheet.

I couldn't remove a offset voltage under follow.
Left: 70mV
Right: 6mV

70mV was so high that I couldn't remove POP noises.

I thought it would be able to adjast deviding +5V.
I must give up.

additional diary:
I tested DC offset without connecting TA2020 input and GND, so DC offset never approached 0V.
When I connected IN1 and IN2 to GND, the DC offset got close to 0V.

But a small POP noise sounds yet.
It is smaller than before, but I'm not satisfied.
The cause of it may not be DC offset.

Interestingly, the sound got more clear and vivid.
This is mysterious for me.
It seemed that DC offset should be 0V.

after this

I found a 50k ohm blue potentiometer, I changed yellow to blue.
I bought them 80yen per one.
They are 3296W made by BOURNS.

Please give me a imformation of removing POP noise.

I couldn't remove POP noise completely by adjasting DC offset.
I guess that it will be caused by the process behavior of the voltage changing while power on and off.
I tried a delay relay circuit to wait output until power supply was stabilized.

I refered following sites.
Transistor Switches
RC_circuit - wikipedia

This is a delay relay circuit using a transistor switching.

(If you click, the figure will expand.)

I designed a relay would be on 4.2 seconds after amp's power was on and it would be off when the power supply voltage was under 10V.

I calculated t, delay time, by following method.
time constant: C(R1+R2) = 1000uF * 10470ohm = 10.47s
The transistor will be on when the voltage between a base and a emitter get 0.6V.
R1, R2 and Tr will have 12V -10.1 = 1.9V altogether because it is descended by a zener diode.
0.6V accounts for 31% of this 1.9V.
Then read the time when the voltage gets dropped till 31% reffering the figure of "Capacitor voltage step-response" in site "RC_circuit - wikipedia".
In my case, it gets 31% when it gets 0.4 times as long as the time constant value.
So I got following.
t = 10.47 * 0.4 = 4.188s

Actually, it took 4 seconds to get relay on.
I don't have enough confidence in this calculation method, but it may be correct.
If there is mistake, please notice me.

Be careful about determining R1.
I designed that Ic, collector current, would be 60mA because the standard current value of relay was 41.7mA.
60mA would be enough for the relay.
R1 = (12V-0.6V-10.1V) / (60mA/300) = 6.5[kohm]
2SC1815 was GR grade, so its amplification would be 200-400 and the voltage between Base and Emitter was 0.6V.

But I didn't have 5kohm risistance, I adopted 10kohm which was in my stock.
It was a gamble.
10kohm would be lack for current supply of relay.

two points of contact, two circuits relay G5V-2 DC12V 283yen OMRON

2SC1815 GR 21yen

I set parts.

I used low ESR capacitor for C.

result
power on: success
power off: failure

When I switched amp on, there was no POP noise.
I can say goodbye for POP noise when power on.
It would be OK that I adopted 10kohm resistor as R1.
But I can't say goodbye when power off.
POP noise goes bang about 0.5 seconds after and the relay gets off about 2 seconds after I've turned off.
I don't know that I can cut down the time shorter than 0.5 seconds by increasing the value of zener diode close to 11.4V.
I guess the reason of this will be that it takes longer time to drop power supply voltage than the time constant value of relay circuit because of huge capacity of amp's smoothing capacitors.
If you want to remove POP noise completely, it will need another relay circuit that will quickly respond to power switch when power off.

The other day I simulated this circuit using "LTspice/SWitcherCAD3".
It seemed to be quite ridiculous to simulate after completion, but I din't care any more.

I used a 9V zener diode model because I couldn't find 10.1V one.
Values of the other parts were the same as the actual circuit.
Vcc, the power supply voltage, was set as following.
0 - 0.1s: 0.6V - 12V
0.1 - 20s: 12V constant
20 - 22s: 12V - 0.6V
I set initial voltage as 0.6V because there were some charges in smoothing capacitors when I switched off.

Relay will be on 4 seconds after Vcc gets 12V.
I(RL) will be maximum to 33mA, 10kohm has seemed to be so high.
I regret that I haven't simulated in advance.

I had already stablized the 12V line, but I didn't provide any measure for 5V.

TA2020-20 has a own regulator inside of it and supplies 5V from 30pin.
2pin and 8pin recieve 5V from it.
2pin: V5D(digital 5V input)
8pin: A5D(analog 5V input)

2pin and 8pin are connected to some impotant parts in TA2020-20.
5V should be stabilized.

I inserted decoupling capacitors between 2pin and 3pin, also 8pin and 7pin.
Their values are recommended to be as high as some hundred uF.

The capacitors of 0.1uF roles to absorb high frequency noises.

This is C1, 22uF NICHICON MUSE ES 16V UES1C220MEM 47yen.
It should be higher value, but I didn't have such capacitor in my pocket.

C2 is OS-CON.
OS-CON is very famous.
100uF SANYO OS-CON 20V 20SA100 231yen
It offers unbelievable sound and I can't believe that it is electrolytic capacitor.

changes by this modifying
Low pitch sound got more powerful.
This modifying is very effective.
I felt that this modyfying evokes comfort and affluence.

after this, supplying 5V from a external switching regulator

It was convenient that a 5V switching regulator was left in my parts box.
I tried to supply 5V from it instead of a regulator in TA2020-20.
It was TA4805S(5V 1A) that I bought for $1.

I placed laminated ceramic capacitors (0.1uF) between each terminals of the regulator.

I connected its output to 2pin and 8pin in exchange of 30pin(TA2020-20 VGEN).
30 pin should be none connect.

There wasn't enough space to set a heat sink, so I united it to the case instead of a heat sink.
Because TA4805S is molded package, it is unnecessary to take a measure for isolation.
I sticked it by double-faced tapes.

I'm about to blowout by lacking in space.

change of sound by this modifying
It changed dramatically.
It got being sharpen and vivid as if I changed from cassette to CD.
It seemed to be good for audio device that volutage supply is given by independent regulator rather than built-in one.

I decided to put letterings because I couldn't distinguish ON from OFF.
I bought a lettering set for about $2.

It was easy to letter.
My amp looks like as if it appeared in the market.