TL071 opamp circuit needed

[space2000]

hi,

i need to bost my input gain for my amp. i have seen that i can use opamp to bost the signal from cd player.

it gose like this....CD player-->--OPamp---> amp

i have TL071 ic for opamp. i need the circuit design for simple way to build opamp.

thank you.

 

[Mooly]

How much gain do you need ? what supplies have you got ?
You need 2 opamps or 1 dual TL072. See image.
The second one is phase inverting but this configuration can sound better to me. You can add a small ( around 4.7 PF ) cap across the 47 K ( This is where you need your 'scope 🙂 )

 

[space2000]

hi mooly,

thank you for your circuit. i want to use it for a gain boster for amp. now i can calculate the gain for the amp.

for Precs-I, what us the highest gain should be? do you know?

thank you for help.

 

[AndrewT]

Hi,
the highest signal from a CD player is about 2Vac.
If you have a 100W into 8r0 amplifier then the highest signal to the speaker is 28.28Vac.
The gain you need is 14.1Times (+23dB).
most amplifiers are set up with a gain of between +20dB and +36dB.
You don't need any more gain in the preamp to achieve maximum power into your speakers.
You need attenuation.

 

[sreten]

Hi,

Something is very wrong if you need to boost a CD players output.

🙂/sreten.

 

[Mooly]

Hi,
the highest signal from a CD player is about 2Vac.
If you have a 100W into 8r0 amplifier then the highest signal to the speaker is 28.28Vac.
The gain you need is 14.1Times (+23dB).
most amplifiers are set up with a gain of between +20dB and +36dB.
You don't need any more gain in the preamp to achieve maximum power into your speakers.
You need attenuation.

Maybe they are quiet CD,s 🙂

 

[space2000]

hi,

if my amp operate with my mobile phone. the sound is very strong and loud as it should be by the wats but when i attach the cd player it's gets flat and low sound like 50% less then mobile phone was used. so i was thinking may be it cause by the gain is too low for the amp.

thank you.

 

[ssmith]

what CD player are you using?

 

[PMA]

I just used one for a DC servo.

 

[space2000]

hi,

i likie to thanks all of you. For the gain control circuit calculation

RF=47k
Rin=22k

Gain= RF/Rin

Gain=47/22 = 2.136db?

thank you.

 

[space2000]

hi,

i likie to thanks all of you. For the gain control circuit calculation

RF=47k
Rin=22k

Gain= RF/Rin

Gain=47/22 = 2.136db?


thank you.

 

[space2000]

Hi Mooly,

the voltage supply should be (+v -V and GND) or only (+v gnd)?

thank you

 

[AndrewT]

for the inverting case
gain = 47/22 = 2.136times = +6.6dB

for the non-inverting case
gain = 10/3.9 + 1 = 3.564times = +11dB

But, note the HP input filters are completely different.

 

[richie00boy]

hi,

if my amp operate with my mobile phone. the sound is very strong and loud as it should be by the wats but when i attach the cd player it's gets flat and low sound like 50% less then mobile phone was used. so i was thinking may be it cause by the gain is too low for the amp.

thank you.

No it is simply because the phone puts out higher voltage than the CD player.

If with the CD player you can turn the amp up and make it clip or distort, you simply don't need a pre-amp.

 

[Mooly]

Hi Space,
What supplies have you available ? You can make either run off a single supply ( with a few more bits ) if you have to, but the split supply is better.
Are you building this into that amp you posted the pics of ?
If you are it's easy, the TLO71 or 72 use so little power that a very simple resistor and zener is all you need for each rail supply.
Remember that R1 sets the input impedance so choose this first then work out what gain you need. The 22K and 47K should be fine though.
If you want the gain expressed as a ratio i.e. db, for the non inverting it is;
20 log*(RF+R1/R1)

And for the inverting it is;
20 log*(RF/Rin)

Are you putting a volume control after the Op Amp. Remember any switch on noise as the circuit settles will be amplified and add to any noise produced by the amp at switch on.

 

[Mooly]

Just to clarify as I have used different terms ( just to confuse you 😀 ), the input impedance is set by the total value of the input resistance for the non inverting one, so that is the two 100k's in parallel. 50K therefore, input impedance for this one.
The inverting input impedance is determined by Rin. So thats 22K

 

[space2000]

hi, my DVD player is Panasonic DVD s2.

how to check the output gain voltage?

as i learned from Dx that the amp max gain voltage arround 720millv.



thank you.

 

[Mooly]

With a 'scope 😉 Why not replace the feedback resistor with a preset ( 100K ) and when you are happy with the gain replace it with the nearest fixed value.

 

[space2000]

hi mooly,

thank you. problem was equalizer setup for output gain.

now it is ok.......

this amp is ok now... thanks for your gain circuit, i will need it for future.

i still want to try another one to build like "class A amp" i never done it b4, using transistor. it can be low wats like 50 to 100w nice to me.

if you have any simple way to build class a amp pls post the circuit to my email address or here.

mitoo_singapore@yahoo.com

best regards
michael

 

[Mooly]

50 to 100 Watts for a Class A amp certainly isn't low. Why not check out some of the designs on the Pass Labs section. Or the original John Linsley Hood design from 1968.