I chucked the lm324s out of a previous design here, the dirty cheap and pin compatible tl084 sounds lots better. I think the slew rate was killing me. Alright for fast signals as long as the voltages were low, but with a 7v peak to peak signal it's gotta be rolling off at the top ...

On 3 Jul 2012, at 12:55, "thomas_escure" < thomas_escure@... > wrote:

>
>
> Hi Dmitry,
>
> I also am very interested about the possibility of replacing ICs to increase the audio quality of my beloved Doepfer modules.
>
> For example, I used to have problems with my A-131s : the noisefloor was a little too high for my tastes and when I tried to increase the input level I wasn't pleased by the distortion.
>
> Then a very kind fellow on Muffwiggler's forum suggested that I replace the LM324 IC (responsible for audio duties) by an LME49740. The difference, to my ears, was astonishing ! So I did this very simple mod on my three A-131s and now I love the A-131, it has become my favorite VCA (and I tried about 6 from different makers).
>
> It must be noted that the IC swap does not really lower the noisefloor, but it handles higher input levels much better (in my opinion) so that noise becomes inaudible. Also when I really push it into distortion I like the caracter of the sound.
>
> I do not own an A-138 for the moment but I will sure try this AD OP470 IC when I get one.
>
> Please let me know if you can find other good sounding ICs for Doepfer modules !
>
> Dieter, if you're reading this please be sure that I greatly respect your work.
> I understand that compromises have to be made when running a product line, that I think is well appreciated by a lot of customers.
>
> Best regards,
>
> Thomas
>
> --- In Doepfer_a100@yahoogroups.com , "therpocc" <dmitry.shtatnov@...> wrote:
> >
> > Dear Dieter, i'm glad to hear about your interest.
> > Concerning the price: you pricelist includes different rack cases having different cost, items such as Hi-End VCO, blue-LED versions of modules and other items. Offering high-fidelity might be just another option. (Finally it can be just another OEM items such as CEM chips, LEDs, sockets etc)
> > I'm not a professional engineer, but you are. So, i believe you can find some more cost-effective components with quality close to this particular Analog Devices component but higher then just plain TL064...
> > Anyway, thanks for your interest.
> > Best regards,
> > Dmitry
> >
> > --- In Doepfer_a100@yahoogroups.com , <yahoo@> wrote:
> > >
> > > Dmitry,
> > >
> > > thank you for the detailed report. That was interesting for me too.
> > > Unfortunately the OP470 is very expensive (~ Euro 15 here in Germany) and
> > > would increase the price of the modules clearly.
> > >
> > > Best wishes
> > > Dieter Doepfer
> >
>
>


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