Hi Folks,
I have a preamp that outputs at a maximum of 3 volts.
But my amp recommends not using a preamp due to the output signal voltage being too high.
I would like to reduce the maximum output voltage of the preamp to match the maximum of the amp (which below is marked as 0.520v)
How would i go about this, is it as simple as placing a metal film resistor in the signal path which is routed to ground?
Or perhaps creating a potential divider for each channel out of resistors and outputting from the mid point?
Below is the specs of the amp.
I should mention that the reason why i want to use a preamp, is because i would like balance, treble, bass and volume control which is provided very conveniently in a Hi-hi preamp.
I have a preamp that outputs at a maximum of 3 volts.
But my amp recommends not using a preamp due to the output signal voltage being too high.
I would like to reduce the maximum output voltage of the preamp to match the maximum of the amp (which below is marked as 0.520v)
How would i go about this, is it as simple as placing a metal film resistor in the signal path which is routed to ground?
Or perhaps creating a potential divider for each channel out of resistors and outputting from the mid point?
Below is the specs of the amp.
I should mention that the reason why i want to use a preamp, is because i would like balance, treble, bass and volume control which is provided very conveniently in a Hi-hi preamp.
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Yes, you can basically use a voltage divider if you do not feel comfortable modifying the preamp for reduced gain. You should, however, have somewhat of an idea of both the preamp's load driving capabilities and the power amp's expected maximum source impedance (something like a 4k7/1k divider should not pose much of a problem for many preamps but would be somewhat shy of the maximum 600 ohm source impedance demanded by some Class D amps).
The Preamp kit i am using uses Phillips 1524A chip if it helps with the answer?
https://www.quasarelectronics.co.uk/kit-files/datasheets/tda1524a.pdf
https://www.quasarelectronics.co.uk/kit-files/smart-kit/1070.pdf
https://www.quasarelectronics.co.uk/kit-files/datasheets/tda1524a.pdf
https://www.quasarelectronics.co.uk/kit-files/smart-kit/1070.pdf
TDA1524, ugh. What a noisy bugger. I don't think you can reduce gain with this one, so voltage divider it is. Minimum load is like 2k, so 4k7/1k should work fine from that side. Hiss levels may still be annoying (100 µV / 5.7 + 32 dB ~= 700 µV) and as such may eventually prompt replacement of preamp. A standard HiFi-grade preamp exhibits far lower noise, with 12.5 µV (about 1/8 of yours) being considered run of the mill.
What's the power amp?
What's the power amp?
sgrossklass could you suggest a suitable preamp kit which would be less noisy, or at least the model of IC I should be looking for in a decent preamp?
Reducing gain of IC internally will also reduce THD as shown in the data sheet. SO, add a resistor in serial with the upper leg of potentiometer connected to NO:1 of TDA1524.
For the value of resistor, you need to calculate it with corresponding dB values.
Or, you can try-see. Start with a 47K.
For the value of resistor, you need to calculate it with corresponding dB values.
Or, you can try-see. Start with a 47K.
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How deep into the preamp do you want to dig? Post #2 here might be of interest, also perhaps post #18: http://www.diyaudio.com/forums/analog-line-level/270048-too-much-signal-voltage.html
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How deep into the preamp do you want to dig? Post #2 here might be of interest, also perhaps post #18: http://www.diyaudio.com/forums/analog-line-level/270048-too-much-signal-voltage.html
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Correct. Jumper P3 is replaced with a dropping resistor, so called because it has no purpose except to drop some voltage.
The schematic seems to show P3 as a trim pot. You could as well use a pot instead of a resistor, in which case P3 would become something of a range selector, and P7 would be the vernier adjustment. All of which would be trouble and expense to no useful end, but you could.
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Ah yes the trimmers! They are 25kohm.
Taking note from #18 of below, i might as well replace the trimmer with a 150kohm and dial it up until only .5v is output from each channel.
http://www.diyaudio.com/forums/analog-line-level/270048-too-much-signal-voltage.html
Taking note from #18 of below, i might as well replace the trimmer with a 150kohm and dial it up until only .5v is output from each channel.
http://www.diyaudio.com/forums/analog-line-level/270048-too-much-signal-voltage.html
Thanks again for all the help folks.
Forgive my question which will now make me look like a complete electronics noob......
Is the method i should be using to test the output voltage of the preamp:
1) Turning the main volume pot to its lowest resistance (i.e its highest volume)
2) Play some music through the preamp (loud as possible)
3)Put a voltmeter (AC) connected to the output ground and an output channel and turn the trimmer until 0.520v is reading? (seeing as 0.520v is the input sensitivity of the power amp)?
Forgive my question which will now make me look like a complete electronics noob......
Is the method i should be using to test the output voltage of the preamp:
1) Turning the main volume pot to its lowest resistance (i.e its highest volume)
2) Play some music through the preamp (loud as possible)
3)Put a voltmeter (AC) connected to the output ground and an output channel and turn the trimmer until 0.520v is reading? (seeing as 0.520v is the input sensitivity of the power amp)?
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Yes. Preampli volume>>max
The volume of source (which is input for your ampli)>>max
It may be a little difficult for you to adjust the trimmer while playing music. You can use your PC soundcard output for a signal 1KHz that has an amplitude equal to your ampli's max input.
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