Am 12.10.2012 10:15, schrieb Richard Prosser:
> OK Alex.
>
> try
>
> I've adjusted the gains etc to be close to your needs - some
> adjustment may still be required. I set the second input at 15.4V as
> this is 100x the 154mV for input1.
Thanks Richard. When writing 100x I was talking about the relationship=20
between the signal AFTER the transformer, ie at the Node "Transformer",=20
154mV/6 =3D 25.67 mV. And that is Vpp, the voltage in the simulator is=20
amplitude, so it's 1283mV or roughly 1.2V Amplitude for V3.
> Reduce R27 for more input2 gain if
> you need it.
I changed R27 to 33k and V3 to 1.2 Volts. BTW: I get a flat line at the=20
peak. Does that mean distortion? If so how to increase the gain without=20
hitting the limits?
> The output load of 20ohms will be a problem - the opamp probably won't
> work too well into that low a load. 6V pk-pk into 20 ohme works out at
> about 330mA pk-pk.
Basically all my headphones "say" is that 3V is the maximum voltage to=20
be applied. 25 Ohms was a good guess. I just measured the resistance to=20
be 90 Ohms on the left channel and 103 Ohms on the right channel. So as=20
I connect both headphones' inputs, the common resistor should be 48=20
Ohms. Add to that 1 kOhms and you get 65.5mA at 3V.
> Also the frequency low end response is limited by the transformer.
> You'll need to check the exact parameters of your transformer to get
> a good estimate.
This ( http://www.mikrocontroller.net/attachment/156735/NFU.pdf ) is all=20
I know about the transformer.
>
> Re the opamp - apart from the output current, I'm not sure what to
> suggest. Add in a proper audio output amp chip perhaps. Or include a
> simple 2 or 3 transistor output stage, similar to your earlier input
> amplifier.
Which circuitry would you add to make the voltage be around 2 - 2.5=20
Volts (resp. 4 - 5 Volts Vpp) without distortion?
How do you compensate the offset?
>
> Hope this assists.
Yes it does quite well. Thank you for your time so far. Current schematic:
Alex
>
> Richard
>
> On 12 October 2012 20:19, Alexander Winnig
> wrote:
>> Am 12.10.2012 05:34, schrieb Richard Prosser:
>>> Ciruit2 should be OK with a few tweaks.
>>>
>>> But some questions arise also.
>>> 1. what is the frequency range of interest?
>> 10 Hz to 20 kHz.
>>> 2 The desired 3V output - is that pk-pk or rms?
>> Vpp =3D 6V. This is the MAX! It shouldn't be reached when the input sign=
al
>> is at max, it should be around Vpp =3D 4V to 5V then.
>>> 3. What are the actual input signal levels?
>> Vpp before transformer should be 0.154V or 154mV max.
>>> 4. What is the supply? If it is a 9V battery, then your 30ohm biasing
>>> resistors are going to drain it fairly quickly.
>> Yes I am.
>>> Better to use higher
>>> value resistors and bypass with 10uF or larger caps.
>>>
>>> Other Comments:
>>> You have the transformer turns ratio set at 1. This isn't in
>>> accordance with your 1.6:1 statement above.
>> On my transformer there is "1:6, RPrim =3D 4.6 Ohms, RSek =3D 180 Ohms".
>>
>> Do you mind modifying my circuitry (
>> https://www.circuitlab.com/circuit/ru78q2/zusammenfugen/ ) using your
>> ideas and republishing it? Makes this conversation a lot easier.
>>> Are you actually going to use a '741? If you are, then you will have
>>> limited gain for any reasonable frequency range. And noise may be an
>>> issue also.
>> I have
>>
>> LM358
>> LM393
>> 741CN
>> LM2901N
>>
>> at my disposal. Which one would you recommend? Or would you rather
>> recommend building an amplifier the way I did in the first schematic ie
>> using transistors?
>>
>> Alex
>>> RP
>>>
>>>
>>>
>>> On 12 October 2012 16:06, Alexander Winnig
>>> wrote:
>>>> Both signal sources are being shown at max amplitude. My goal is to mi=
x them
>>>> so each signal source has the same volume and the final result is not =
to
>>>> exceed 3 volts.
>>>>
>>>> Here's the current schematic.
>>>>
>>>> https://www.circuitlab.com/circuit/x6hjxg/verst2/
>>>>
>>>> Feel free to modify and repost the link.
>>>>
>>>> But I thought that maybe I can save a lot of components and do it like
>>>>
>>>> https://www.circuitlab.com/circuit/ru78q2/zusammenfugen/
>>>>
>>>> Factor between source one and source two is about 100. Thus the resist=
or
>>>> values R24 and R27 to make them even. But is is not quite satisfactory=
.. It
>>>> seems that -(V(Transformer)/R27 - V3/R24) * R12 is not -3 Volts as you=
'd
>>>> expect from an adding amplifier. Also there's something wrong with the
>>>> transformer. It's an 1:6 transformer that should produce about 0.013V =
on the
>>>> output side.
>>>>
>>>> I am not sure but I guess it is a better approach to optimize circuit =
2
>>>> rather than the old one.
>>>>
>>>> Alex
>>>>
>>>>
>>>> Am 12.10.2012 04:05, schrieb Richard Prosser:
>>>>
>>>> Maybe you meant something more like this? (Minimal Changes and one
>>>> input changed to 200Hz to separate the inputs).
>>>>
>>>> RP
>>>>
>>>> On 12 October 2012 14:16, Dave Tweed wrote:
>>>>
>>>> Alexander Winnig wrote:
>>>>
>>>> I created this https://www.circuitlab.com/circuit/r2kea4/verstarker/
>>>> circuit. You can open it and simulate it in your browser, no additiona=
l
>>>> software needed btw.
>>>>
>>>> But simulating creates a weird pattern. Is this really the output or
>>>> just some flaw in the simulator?
>>>>
>>>> What you see is an amplifier on the left side and a signal mixer on th=
e
>>>> right side. So the result of the first amplifier acts as second source=
..
>>>> Measurement is taken at R15.
>>>>
>>>> What I see is what looks like the ground node of the mixer connected t=
o the
>>>> output of the amplifier, and the upper input to the mixer connected to=
the
>>>> amplifier's power supply. Surely this isn't what you intended.
>>>>
>>>> -- Dave Tweed
>>>> --
>>>> http://www.piclist.com PIC/SX FAQ & list archive
>>>> View/change your membership options at
>>>> http://mailman.mit.edu/mailman/listinfo/piclist
>>>>
>>>>
>>>>
>>>>
>> --
>> http://www.piclist.com PIC/SX FAQ & list archive
>> View/change your membership options at
>> http://mailman.mit.edu/mailman/listinfo/piclist
--=20
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