Looking at the following datasheet:
http://www.holtek.com.tw/pdf/consumer/8970.pdf
What does OP1/2_IN/OUT do ? The datasheet doesn't say a thing !
Another thing: is it possible to throw in any LFO into the VCO input ?
because although they give a relationship between the resistance and the delay time, we (at least I), do not know the voltage that the IC sees, so wouldn't know the amplitude of the LFO to use ?
Thanks
YH
Actually, it says a lot but you need to use the pictures to find it.
Look at the schematic titled "Echo Mode" near the end, and compare that against the semi-block diagram on page 2. You can see that the chip is configured such that there are two semi-nondedicated op-amps, which are labelled OP1 and OP2. There are also a pair of lowpass filters, labelled LPF1 and LPF2. All four have input and output pins.
In the Echo schematic, the dry signal appears to come in to the 8970 via pin 16 - the LPF1 "in". The recirculated signal also comes through there. You can also see that the recirculated signal seems to pass through OP2 and into LPF2, prior to recirculation.. I have to confess that little info is provided about how it gets to OP1, but it gets there. Note that the .047uf caps shown in the schematic are actually in the feedback loop of that built-in op-amp. Presumably, these can be played with, and the frequency response tailored by intervening between OP2-out and LPF2-in.