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ba662 clone
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page Previous  1, 2, 3, 4 [all]
Author ba662 clone
jhulk
the ba662 is very similar to the 3080 current runs a little different

but are similar the buffer on the ba is different to the lm13600/700 as its a npn/pnp type on the ba and its a wilson current mirror on the lm

i fitted both trimmers one for input bias and one for output bias on the th version

and your right the buffers on the jup4 have no connection so i could do away with those connections just need ota cell

there are a few diffeent types of ota core emu used a few different ones

the ssm2030 the current mirror in box is a ota its based on the ssm2020 cell
which is a diff current pair connected to the ota core the buchla 158/258 discrete versions are very similar in discrete designs to the emu design

the same design is also used in the ssm2040 filter core theirs a an data sheet for the ssm2020 and it has circuits for filters vca and oscillators vc eq rm and am modulators.

all using the same type of ota cell it was very similar up unto the ssm2124 they changed the design when they went to the ssm2164

i have done all of these as a discrete component version.

i also have a version of the ca3280 i would like you to look at guest as its a very involved chip with lots going on
guest
jhulk wrote:

i also have a version of the ca3280 i would like you to look at guest as its a very involved chip with lots going on


cool, would love to check it out. my concern with the CA3280 is that i felt it needed matched quads to really do well. also, you can get almost identical performance from an LM13700 plus an opamp.
loki
Jamie,

There is not really any point in using the LS318 and LS358 in your BA662 clone. Log conformance isn't an important characteristic of transistors in a current mirror. For transistors of the same geometry, delta Vbe and beta to a lesser extent are everything you want to know.

For matched transistor pairs you might try the MMDT4401 npn pair and the MMDT4403 pnp pair. These transistors have larger base-emitter area and, as a consequence, low rbb and low rbe. The rbb has a significant effect on the noise performance of the transistors. The late Marshall Leach posted material about low noise audio design on his web site. Still available. An editor at an audio magazine he did a preamp design article for recommended the 2N4401 and 2N4403 as a secret ingredient of the mixing console designers.

Reference the National Semiconductor Discrete Databook from 1978, available at the Internet Archive, for die photos and characteristics of different transistor processes.
ablearcher
After reworking the BA662 clone a couple times I gave up and ordered it assembled from from synthcube.

Same result, inserting it into the juno 6 (IC18) causes the oscillator leds to turn off and no sound will come out. Remove it and the juno 6 works fine except on some of the voices the filter will not resonate correctly.

What's going on here? Does the clone not work in this case or am I missing something?
guest
i will take a look at the juno6 schematics and see if there is anything that might be wrong. all of the synthcube stock is tested before shipping, so it should have been a good unit. a couple of quick ideas:

1. is orientation correct?
2. maybe something else is blown in the circuit that caused the original ba662 to get blown?
guest
my schematics dont have good labels. is it the resonance feedback control amplifier? the one with R2 and R3 connected to its inputs?
guest
assuming its the resonance control amp (which seems very likely), then there shouldnt be any problems using it there. with the amp removed, measure the voltage on all of the pins in the socket/board. they should be:

1. 0V most likely (its current, not voltage at this node)
2. 0V with 50mV signal
3. 0V with 50mV signal
4. -15V
5. -15V
6. 0V with 50mV signal
7. +15V
8. +15V (maybe a bit less)
9. +15V

its most likely TR1 blown. you can test this node without inserting an IC by putting a diode between pin1 and pin5 (anode to pin1), and seeing if it does the same thing where the leds go off. you can also just put your meter in current mode (start with a high current setting - 1A or more) and measure the current between those pins. if its more than 1mA there is a problem.
dougt
ablearcher wrote:
After reworking the BA662 clone a couple times I gave up and ordered it assembled from from synthcube.

Same result, inserting it into the juno 6 (IC18) causes the oscillator leds to turn off and no sound will come out. Remove it and the juno 6 works fine except on some of the voices the filter will not resonate correctly.

What's going on here? Does the clone not work in this case or am I missing something?


I still have original Roland BA662s in stock if you want to get one.
aabbcc
jhulk wrote:
HOW ABOUT THIS TH VERSION IT USES T0-71 SIZE METAL CANS OR YOU CAN MATCH

2n3904/2n3906 for cheap

easier to solder 40mm/20mm


Did anyone try this with 2n3904 and 3906? I know synthcube sells the ba662 clone but this looks like a fun little project smile
tupinamba
jhulk Where could I get a few of those BA662 clone boards? I like the non-smd approach... ;-)
Thanks!
Jaytee
Pretty sure jhulk stopped posting here a while ago. Try the Logan Soloman Facebook group.
tupinamba
Ok, great, thanks for the tip! So jhulk is Jim?...
Cheers!
Jaytee
I think jhulk is Jammie/Emma.
flts
Jim Soloman is/was aquatarkus on this forum (I think?), he's the other person in the duo. Emma Logan is jhulk - or actually, Jammie Logan is jhulk, but he's posting from his wife's account.

Or that's how I've understood it at least...
aabbcc
flts wrote:
Jammie Logan is jhulk, but he's posting from his wife's account.


And I don't even know where to start about how weird/creppy/Idon'tknow/strange that is seriously, i just don't get it

Anyhow those BA662 boards would be very easy to recreate and order and would good first eagle/kicad for anyone smile
tupinamba
OK, ha ha, this is fun!
Yes, those boards are a pretty simple Eagle project, but if the Eagle or Gerber files already exist, or if Jammie has some spares... :-)
Maffez
guest wrote:
jhulk wrote:
i did these for the jup4 modular voice im working on


the only difference between the core of the LM13700 and BA662 is the control input. but, if this is driven with a current source, then that doesnt matter.


hey ho, sorry for necroposting and asking a potentially dumb question

by difference you mean pin 4 of BA662? thinking about an lm potentially utilized as vca in an sh101 circuit

cheers!
LED-man
Just remember the pcb won’t fit in all circuits because of the size.
guest
the LM13700 has the almost the same core, but a completely diffferent buffer (pins4,7,8), so the clone is really the best bet for the 101 (been used in plenty at this point).

as for the size, it is slightly taller due to the headers used as pins. but, if you just used bare pins, it would be the same size:

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