x0x with BA6110 back to BA622A. How?

[deejayraoul]

I have a BA622 in an old broken 303 clone, but it would be nice to really compare side by side with the 6110 with the flick of a switch. It's not that important i just think it would be a nice tweak. I'll see how far i'll get with that.

[Nordcore]

First: I don't like to waste precious rare vintage parts, needed for keeping old synths alive, for new circuitry.

Than: if you want to put a BA662 in, the current mirror must be disconnected (take Q3 out). That is a current input, paralleling up two of them does not work well, besides that it halves the control current for each of the chips in the best case.


The main difference between the two is the gain, the BA6110 is a little louder. If you try to keep it close to the original you'd lower R128 somewhat, to get the same level.

But if you're are going to replicate the sound of the original, you might look for something different. When I had a TB303 here I observed that it has much slower VCA Attacks and Releases than to be expected. I have no idea how that is done technical, the control current for the BA662 was the same than in my XOX, just the audio was noticeable slower. As if the BA662 has a slow control response - which I could not explain.

As long as I don't know where it comes from I had no chance to "clone" it - so I just rebuild the same behavior:

Xoxbox VCA envelope mod for anti click. Or more original timing with C42A=100nF

declick.png (143.28 KiB) Viewed 1258 times

To get the timing my "reference" TB303 had: C42A should have 100nF.

The timing here is in the 2ms range, so don't expect too much effect. The most obvious is the "click", the rest is slightly "harder", when Attack and release are faster.

[deejayraoul]

Thanks for your insights. Could it be that the aged components in the original 303 result in out of spec values and different envelope times? In response to the 'rare parts for rare synths': how many dealers or technicians keep a small stock of rare parts that are not being used? What's wrong with me using, or at least trying out the part in the x0xb0x until i may need it for one of my 'rare' synths?

[Nordcore]

Nothing wrong with curiosity, trying out such things, understanding what is happening...

I just don't like it, when people start to hunt down holy original parts for absurd prices on Ebay, believing that would put the magic from the original sound in their builds.
Especially when it is obvious that there *is* a huge difference in behavior (as I've described above), which is not explained by the difference of the two chips.

Could it be that the aged components in the original 303 result in out of spec values and different envelope times?

Don't think so. There are just no parts to cause that.
As told: I have no clue where the cap is, which causes the (relative) slow VCA attack and release time of the original 303 I had here.
But I'm pretty sure there is no aging process which could add a cap in the several nF range...