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 Forum index » DIY Hardware and Software » The layout factory
Cloning the CR78 with MIDI
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jbeuckm



Joined: Nov 30, 2008
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PostPosted: Wed Jun 01, 2016 9:01 pm    Post subject: Cloning the CR78 with MIDI Reply with quote  Mark this post and the followings unread

Not sure what is going on with this circuit. It's on a breadboard supplied 12V (not 15 like the original). I built the TTL to trigger circuit so the "C" input pictured is normally at 12V with 2ms pulses down to 0V. The left side of C502 sees about a -10V bump. But the right side of C502 remains silent. I am using a cheapo 3u3H film inductor but have tried numerous different types. What should I try next?


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Grumble



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PostPosted: Wed Jun 01, 2016 10:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

Close to L1 it says 3R, is that the DC impedance? If so, the value of L1 can never be 3.3 uH because they all have DC impedance lower than 0.02 ohm.
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jbeuckm



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PostPosted: Thu Jun 02, 2016 4:42 am    Post subject: Reply with quote  Mark this post and the followings unread

Could that be it? Reading about inductors, it seems that R indicates the decimal point in a microHenry label. If that were the resistance, what would be the inductance? I'll go back and read the service manual.
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Grumble



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PostPosted: Thu Jun 02, 2016 5:28 am    Post subject: Reply with quote  Mark this post and the followings unread

maybe check THIS out?
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jbeuckm



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PostPosted: Thu Jun 02, 2016 6:10 am    Post subject: Reply with quote  Mark this post and the followings unread

Here is a confusing bit from the service manual.


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Grumble



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PostPosted: Thu Jun 02, 2016 6:28 am    Post subject: Reply with quote  Mark this post and the followings unread

My guess is that if the R was a substitute for a decimal point, the value would be 3.7mH (milli Henry).
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jbeuckm



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PostPosted: Sun Jun 05, 2016 6:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

I haven't solved the inductor value question for 1R and 3R700mH yet, but I get the idea that these are rare old parts that might be found in old organs. They might be 1 Henry and 3.7 Henry...

Here is what I'm thinking for the MIDI interface:
https://github.com/jbeuckm/CR78-Controller


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Last edited by jbeuckm on Mon Jun 06, 2016 12:21 pm; edited 1 time in total
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wackelpeter



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PostPosted: Mon Jun 06, 2016 12:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

regarding the inductor values... i opened my CR78 and had a look on the voice board...

there are 7 greater inductors visible...

4 of them with coloured dots yellow green red... all the same colours...
2 having 3R EB printed onto them (one of them beeing in the claves section and the same value i guess as in the rimshot section, judging by it's descripiton in the Service Manual and what's printed on those coils) those coils in the rhythm77 are 700mH by the way...
and 1 having 1R EC (or EG) printed on it...

just thought what about to compare it with the Rhythm 77 Manual, but it seems they have different values used and some minor differences in their schematics even with the same voices...

But in the Rhythm 77 service manuals a bit more information is given on the values of the coils ....
www.burnkit2600.com/manuals/ROLAND_TR-77-SRV.pdf

i would also like to remind you, if this your only voice you "cloned" and it wouldn't start in the rhythm77 i have the triggers are -12V spikes... don't know what the cr78 acutally uses...

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jbeuckm



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PostPosted: Mon Jun 06, 2016 12:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

@wackelpeter Thanks very much for the info and manual! 3R must also be 700mH and maybe 1R is 40mH. Do you have any idea why they call the 45mH out as a "Choke Coil"?

My triggers should be okay because I copied the TTL->trigger circuit and my high bongo works great. You can see the trigger converter (input) and the output amp from stereoping in this schemo:

https://github.com/jbeuckm/CR78-HB.git


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wackelpeter



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PostPosted: Mon Jun 06, 2016 1:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

thats all i found on choke coils...

https://en.wikipedia.org/wiki/Choke_(electronics)

okay don't know about your HB clone... but perhaps a bit of twiddling with some of the values before the actual "voice" could solve the solution as i think a fair portion of the left side from the clave voice schematic is to "form" the correct trigger pulse for the voice beginning to swing...

...and as your powering yours with 12 instead of 15v that could have something to do with it no matter that it works on the high bongo...

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jbeuckm



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PostPosted: Mon Jun 06, 2016 1:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

Uh oh - I didn't intend to spend $58 on the entire project Sad

http://www.mouser.com/ProductDetail/Vishay/TE4Q3TAPJ7003F/?qs=HsFHTXumnCSRf9Fti5Azlw%3d%3d
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jbeuckm



Joined: Nov 30, 2008
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PostPosted: Tue Jun 07, 2016 6:29 am    Post subject: Reply with quote  Mark this post and the followings unread

Would there be any issues building the inductors up serially from available models like this 500mH?

http://www.digikey.com/product-detail/en/bourns-inc/70F501AF-RC/M10176-ND/3074250
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wackelpeter



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PostPosted: Tue Jun 07, 2016 9:51 am    Post subject: Reply with quote  Mark this post and the followings unread

ouch... this is a though price... but having looked at random sites in the net there are not much better alternatives by price... also 700mH seem to be very rare and obsolete...


regarding your other question i simply have no idea, if this would work...

maybe we misinterpreted those values somehow... i have no idea...

but as you're after it i will now try to fix my problem with my CR78...

as it seems it is picking up some impulses that trigger my HB and Metallic/Metronome voice always...

scoping into my unit i see normally the inputs for most voices are high and thus where triggered with a low signal (gnd)

only the voice trigger inputs of my HB have a high output with very short pulses to gnd all the time ( they are affected by the position of my voice selector switch for programming, when on HB the sound is off permanently)

both sounds are triggered via the same quad flip-flop IC113 and they have data inputs 12 (M) and 13 (HB)

the signals on these both inputs are opposite to each other... whilst 13 is low with short spikes to 5V the other is 5V with short spikes to gnd...
i can see the same signals on IC115 which is at pin 13 the same as on IC113 pin12 but here the output on 14 seems to behave normally.... its the same IC type... from what i hear and see on the scope this must be something with the guiro sound... signal triggering on scope and sound to hear make me believe that because i can' read what is written on pin54 (GU T perhaps?)

also in IC 114 pin3 is the signal as from IC 113 pin13... the output for the hex d-flip-flop IC 114 is pin 2 and is the rim shot and taht also works correct...

hmmm..... is the input on my flip flop not correct or is it afterwards... there only come those transistors afterwards Q22 and they look like trannies little 3 legged friends... but the symbol in the schematic looks a bit suspicious... is this an old symbol for trannies?

will scope a bit more around and compare the signal with some working ones... maybe (hopefully) i'll be enlighted soon


p.s. what makes me wonder from where those busses came from which the flip-flops are switched... well in the schematic underneath the bus with the flip-flops there's a bus looking similar and judging by it's description from what i can read... but then where is it else connected...

P.P.S. think i got it... seems really to be the flip-flop not flopping right...
had a look with my scope on the other 2 voices connected to that flip-flop and i have those spikes there at the corresponding inputs too but not at the outputs...

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jbeuckm



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PostPosted: Sun Jun 12, 2016 10:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

Are you saying that the direct M and HB outputs of IC113 would also be opposite? I have SD, BD and HB working with 2ms pulses to +5V (which gets scaled as pulses from 12V down to 0V for 2ms).

I have the TB circuit built, but I can't get any output from either positive or negative pulses. I think the inductor value is the issue there - just like on my C circuit. I have tried a few unknown inductors and a 54mH.

It's worth noting that all CB, TB and GU trigger buffers are on the voicing board (p13) but the rest are on the logic board (p11).
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Grumble



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PostPosted: Sun Jun 12, 2016 11:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Since this is the DIY Hardware and Software section of the forum:

Quote:
Hi DIY´ers! Here we go now with the inductors. Making your own inductors really is no pain! There is no hardcore math or expensive gear involveld


READ about it HERE
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jbeuckm



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PostPosted: Mon Jun 13, 2016 8:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

Is the LC circuit at the TB output a resonant filter? Looking at a known sample on a spectrograph, I see a peak near 4700hz. Since C538 is 33nF, that would imply that L5 is around 35mH. But I have tried a variety of inductors including 27mH and 47mH and I get no output. Maybe something is wrong with my schematic or build Sad


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Grumble



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PostPosted: Mon Jun 13, 2016 11:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

I use this website a lot when working on analog circuits.
The LC circuit is a resonant filter (4.38 kHz @ 33nF//40mH), make sure you have quality components to get the best selectivity (quality factor) of the filter.
This means: for the capacitor the lowest possible parallel resistance and for the coil the minimum series resistor.
Check if you have a pulse between R14 and R16 (maybe change the position of the runner of R15.
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wackelpeter



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PostPosted: Tue Jun 14, 2016 1:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

jbeuckm wrote:
Are you saying that the direct M and HB outputs of IC113 would also be opposite? I have SD, BD and HB working with 2ms pulses to +5V (which gets scaled as pulses from 12V down to 0V for 2ms).

I have the TB circuit built, but I can't get any output from either positive or negative pulses. I think the inductor value is the issue there - just like on my C circuit. I have tried a few unknown inductors and a 54mH.

It's worth noting that all CB, TB and GU trigger buffers are on the voicing board (p13) but the rest are on the logic board (p11).


Not sure about the outputs... may have a look with a scope soon to tell you...
The opposite signal on those busses fed to the flip-flop (which by the way comes directly from the big controller or whatever-chip as it seems) goes to the data inputs of the flip-flop's... as far as i remember these have a common clock input and 4 normal and inverted outputs... from what i remember out of the schematic on some voices the normal and on some the inverted outputs where used to trigger the specific voice...

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wackelpeter



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PostPosted: Wed Jun 15, 2016 10:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Well, checked the outputs going from the logic boards to the voice board...

so far i've found RS, C, BD, LB, LC, SD, CY and HH all voices are active on low... means they stay around 10V or so and the control output for the voice goes down to gnd and triggers the voice...

It's after the flip-flop section and the trannies shown in the upper right on page 22 of the service manual, which can be found here:
http://www.synthfool.com/docs/Roland/

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jbeuckm



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PostPosted: Sat Jun 18, 2016 10:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

What do your signals look like at R667 and R668? I assumed 2ms pulses to 5V for "long" and "short" guiro but my circuit is always sounding right now.
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jbeuckm



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PostPosted: Sun Jun 19, 2016 9:02 am    Post subject: Reply with quote  Mark this post and the followings unread

I figured it out from the explanation on the Stereoping page: "One STOPS the guiro when set high (+5 volt). The other halfens the frequency of the multivibrator when set high."

It really is a hideous sound.
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jbeuckm



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PostPosted: Mon Jun 20, 2016 8:05 am    Post subject: Reply with quote  Mark this post and the followings unread

@wackelpeter If you have a chance, could you tell me what the signal looks like at R566? I built the Metale Beat circuit but I get no output with the normal 12V signal pulsing to 0V for 2ms.
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wackelpeter



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PostPosted: Mon Jun 20, 2016 1:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

I wish i could, but as i wrote somewhere above that flip-flop generating the triggers for Metallic and HighBongo seems to be fu...ed up...

I would strongly believe it should behave somewhat similar to the other triggers on that part of the logic board, triggering the voices with pulses down to 0 volt.

By the way the length of the pulses vary for the different voices... can't give any timings as my scope isn't working properly... but for example bass drum is much wider as high-hat...

On page 30 of the service manual there are some timings and trimmings listed...
so far it looks like the part of the circuit around VR64 to VR66 also belongs to the metallic beat... Don't know if you have this in your curcuit...

edit...

Well i'm wrong... my MB output triggered from the logic board doesn't work as described before, but i still have the MB as kind of a metronome... so it's triggered via the clock signal somehow... means i can check this tomorrow, but know i have to get some sleep first as i must abandon my bed way to early tomorrow... Wink Sad

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jbeuckm



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PostPosted: Mon Jun 20, 2016 9:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes - I definitely have the hex inverter and I think the three square waves are coming through fine. Here is my schemo. Do you see any problems here?


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Grumble



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PostPosted: Mon Jun 20, 2016 10:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

The voltage across R14 is about 0.1 volt max, and is later devided by R570 and R548 to about 3/4 of the 0.1 volt.
Thats not nearly enough to change anything to the voltage at the base of Q510.
I think you should loose R14.
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