I don't know, could it really be that exciting? It's probably nothing a crappy op-amp (well, maybe a specifically selected crappy op-amp) and a passive 1-pole "tone control" type circuit couldn't do. Not that something like that wouldn't be useful, I think it could be particularly nice for small keyboards/drum machines (I have a nasty little 70's pre-amp thing that I keep around for just that purpose), but it seems like the effort might be better spent building a similar circuit in its own little box.
To: CZsynth@yahoogroups.com
From: ezra.buchla@...
Date: Fri, 17 Aug 2007 14:03:50 -0700
Subject: Re: [CZsynth] cz101 amp: LA4138 (WAS: DIY AC Adapter for Casio CZ-101)
i actually just did this last night. took its supply down to like 4 watts
and couldn't hear any difference. seems to like 7.5v just as much as 9, and
500mA just as much as 1000....
i still want to find those voltage-gain-control and HF-control pins,
though...
On 8/17/07, Scott Nordlund <gsn10@...> wrote:
>
>
> I looked around a bit on google and apparently found the same thing you
> did (soft saturation and frequency adjustment pin)- neat but not exactly
> helpful.
>
> It might be an interesting exercise to run the amplifier chip from a
> separate power source and deliberately give it a low voltage or current to
> see if it starts acting up in a pleasing way. I suspect that it would be
> more worthwhile to try with something a little more analog-based or with a
> built-in speaker (connecting the adapter input to a bench supply), but if
> you want to play around without a datasheet, it could be worth trying.
>
> To: CZsynth@yahoogroups.com <CZsynth%40yahoogroups.com>
> From: ezra.buchla@... <ezra.buchla%40gmail.com>
> Date: Fri, 17 Aug 2007 04:16:51 +0000
> Subject: [CZsynth] cz101 amp: LA4138 (WAS: DIY AC Adapter for Casio
> CZ-101)
>
>
> well sure, it's good to think about the amplifier draw.
>
> BUT i'm not positive that a slightly (or considerably) low current
>
> would be a problem in this case. i'm also not sure it wouldn't be.
>
> the power amp in the cz101 is a sanyo LA4138. i can't find a pinout or
>
> a detailed datasheet for this chip, but other chips in the LA4x series
>
> are self-regulated, with max power output varying between like 2 and 4
>
> watts.
>
> i'd be very curious to know more about the LA4138, if you have any
>
> more detailed information than "hey, didja know? amps draw power!"... :)
>
> i'd especially be curious to know the pinout, cause then i could
>
> determine the actual operating conditions that the chip experiences in
>
> the cz101; without that it's a little hard to figure it out from the
>
> circuit board (or even the schematic if i had one).
>
> it'd be interesting to figure it out, cause there seems to be a couple
>
> possibilities for mods: an external resistor to fix voltage gain (the
>
> chip is reputed to have some kind of smooth saturation), a pin to
>
> change the high-frequency response...
>
> apparently there's an LA4140 series with the same pinout but i can't
>
> find that either.
>
> - eb
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RE: [CZsynth] cz101 amp: LA4138 (WAS: DIY AC Adapter for Casio CZ-101)
2007-08-18 by Scott Nordlund