it is with much sadness and regret that for parts in the flying squirrel i say goodbye to the LM13700M, a part with a huge and rich history, having seen its first emergence into the world around 1967 even predating the moon landing. the reason is simple: the bias for the diodes is 3x 0.7 volts and on rails of +/-2.5V it's simply not enough. i'm seeing silence at low volumes... and then huge clipping. i simply don't have time to resolve this.
instead unless there's a good reason (e.g. conexant responds to enquiries) i'm going with the CM108AH and keeping the TDA2822 as a speaker amplifier. the reason for choosing the CM108AH: no good reason other than the datasheet contains an example schematic and there were no NDAs required to get hold of that datasheet.
l.
luke.leighton <luke.leighton <at> gmail.com> writes:
it is with much sadness and regret that for parts in the flying squirrel i say goodbye to the LM13700M, a part with a huge and rich history, having seen its first emergence into the world around 1967 even predating the moon landing. the reason is simple: the bias for the diodes is 3x 0.7 volts and on rails of +/-2.5V it's simply not enough. i'm seeing silence at low volumes... and then huge clipping. i simply don't have time to resolve this.
For those of us with electronics experience but maybe not name recognition of ICs: the LM13700M is a dual op-amp, which Luke may be trying to configure as a Class B amplifier (push-pull). Since his input voltage is so slight, the circuit is spending too much time in cutoff, except where it reaches saturation.
Luke, using a class B amp is going to result in crossover distortion. I think that's what you're seeing. So, you're replacing your homebrew power amp with a C-Media USB Audio device? Is this directly connected to the USB lines, or after a hub?
Derek
On Tue, Oct 29, 2013 at 1:20 PM, Derek dlahouss@mtu.edu wrote:
luke.leighton <luke.leighton <at> gmail.com> writes:
it is with much sadness and regret that for parts in the flying squirrel i say goodbye to the LM13700M, a part with a huge and rich history, having seen its first emergence into the world around 1967 even predating the moon landing. the reason is simple: the bias for the diodes is 3x 0.7 volts and on rails of +/-2.5V it's simply not enough. i'm seeing silence at low volumes... and then huge clipping. i simply don't have time to resolve this.
For those of us with electronics experience but maybe not name recognition of ICs: the LM13700M is a dual op-amp,
dual _transconductance_ op-amp. normally used with +/- 15V rails but can go down to +/- 5V, and there are reports of people managing to go lower than that but losing some of the characteristics... which i didn't know about before picking it.
which Luke may be trying to configure as a Class B amplifier (push-pull).
ah no - it's going straight into the ADC.. ok it was ... the output's only 2mA which is (was) more than enough for the STM32F or the ATSAM4. all i had to do was get it up to a 0-3.0V swing.
basically i needed a voltage-controlled pre-amp for the microphone.
Since his input voltage is so slight, the circuit is spending too much time in cutoff, except where it reaches saturation.
basically yes.
Luke, using a class B amp is going to result in crossover distortion. I think that's what you're seeing. So, you're replacing your homebrew power amp
just an OTA. the speaker phase was using a proper class B (TDA2822) - i learned the hard way that the input for that is line-out levels (and i was trying to put the DACs *directly* into it. a 240k/20k resistor divider solved that one...) but that's another story.
with a C-Media USB Audio device?
yes. ok if conexant get back to me fast enough i'll use their part instead.
Is this directly connected to the USB lines, or after a hub?
through a hub - there's only one USB connection from EOMA68 so everything (including the ATSAM4S) goes through a hub.
l.
arm-netbook@lists.phcomp.co.uk
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Derek -
luke.leighton