[sdiy] Roland IC

[Tony Allgood]

>What is a good Roland IC source? I need a BA662 VCA IC for my JX3P.

Funny you should mention this, but I have been taking a very good look
at the BA662 this week. It is available from Roland and they still have
reasonable stocks in Japan.

Generally the BA662 doesn't seem to be too different to a CA3080 and a
follower. I spec the BA662 part and the BA6110 in the TB3030. Originally
I thought the two parts were very very similar. The BA6110 does have a
linearising diode network at its inputs. This is similar to the one in
the CA3280 and better than the simple one in the 13700/5517. But there
is a big difference in the BA662 and the BA6110 I have now found. The
BA662's Iabc input sits at one diode drop above its negative supply pin,
0.6V in the TB303 and TB3030. The BA6110 sits at 1.2V. This double diode
drop may cause trouble to you in single supply situations. I hope to
detail this on my website when I have time to write it all out, but
suffice to say the BA6110 is not a drop in replacement for the BA662 in
single supply situations. The TB3030 will work with the BA6110 but there
is a very subtle difference in the way the attack phase is dealt with.

I have now worked out a simple mod to allow the BA6110 to be used in the
TB3030 with a perfect emulation of the BA662. Many purchasers of the
TB3030 semi kit have got BA662s anyway, but those of you with BA6110s
may notice a slight increase in 'bite' with the little mod. I'll put all
the details on the site soon, and update the TB3030 User Guide.

Regards,

Tony Allgood  Penrith, Cumbria, England

Oakley Modular Synth and TB3030:
www.techrepairs.freeserve.co.uk/projects.htm
My music: www.mp3.com/taklamakan