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TR808 BD trigger problem, please help.
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isak



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PostPosted: Wed Oct 02, 2013 3:37 pm    Post subject: TR808 BD trigger problem, please help. Reply with quote  Mark this post and the followings unread

Hi guys.

today i finally built the TR808 BD using this layout..
http://praxistest.cc/wp-content/uploads/2012/02/platine.jpg

i connected the ACX lite mid2cv trigger out to the trigger in of the TR808 BD, i get nothing!
well, i get the osc working when turning the decay pot up, the tone is working, even the pitch works, but i dont get the kick, only the osc sound.
i've checked everything, orientation of the transistors, resistors, i dont know what to check anymore.
maybe i need to trigger with higher V? the ACX midi2cv is only outputting 5V.
BTW what is a CMOS trigger?

any help will be grateful.

cheers,
Isak E.

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elmegil



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PostPosted: Wed Oct 02, 2013 7:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Do you have anything wired to accent?

I went through that particular layout once before and it matches Eric Archer's take on the circuit. And I spent a lot of time crawling around the original circuit when I was troubleshooting a stripboard layout by minus.

The CMOS input basically is a trigger conditioner/gate to trigger circuit--you can feed it with more gate-like things and it will still trigger reasonably. The trigger input bypasses the diode/resistor/cap used for this purpose.

If you have nothing wired to accent, nothing will ever happen with your circuit. The original circuit actually worked a little backwards from what you might expect, looking at that. What this circuit uses as a trigger in was actually just the circuit enable. What actually triggered it was the "common trigger" pulse routed to all voices, which would then operate only if the enable signal was high as well. The common trigger would vary from 4V to 14V depending on the accent setting for a given step, and there would be one pulse for every step based on the rate.

All that said, I have not only wired up minus' stripboard version of this circuit, but also bananuerysm's PCB as well. If you're not driving it from a circuit meant to mimic the 808's setup as I've described it (and almost nobody is), your best bet is to:

1) use the CMOS input, you will get better results in general triggering from arbitrary sources.
2) normal the trigger jack to the accent jack. If you send the same trigger pulse to both points, it should work great. And if you do it with a switching jack for accent, that will let you get some accent variation using that jack when you choose to.

Hope this helps....

Edit: Another alternative would be to just wire the accent line high all the time, or to a pot for manual accent setting, I think I've seen that pretty commonly done.
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isak



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PostPosted: Thu Oct 03, 2013 12:36 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi elmegil and thank you for replying.

As I got up today and saw your reply even before washing my eyes I run down to connect power to accent And it worked! I got 808 kick drum Smile
after making few tests I have further questions..
In the layout they don't say the values of the pots so I used MicroLarge site for the pots values.
For the Tune ENV pot I used 5k, it seems that it's doing nothing!?!
The decay is 500k Lin, when turning it a bit it starts to self osc, this the way it suppose to work?
The extra decay pot Is 100k, it work like a fine "tune" decay, this is how it suppose to be?
Beside that everything works great! I love the pitch add on, it's really cool.

Thanks again man!
cheers,
Isak E.

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elmegil



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PostPosted: Thu Oct 03, 2013 6:46 am    Post subject: Reply with quote  Mark this post and the followings unread

We discussed this version of the circuit (that you linked to) before in the longer thread about 808 stripboard, here's the link: http://electro-music.com/forum/post-369370.html

Tone and Level are 10K pots and Decay is 500K.

"Tune" is a mod, I've typically seen it documented as 100K. It replaces a 47k resistor that sets the frequency of the oscillator.

here's a schematic from Bananeurysm's version, which has these pots labelled:

http://www.anestheticaudio.com/808bd_sc.jpg

The "Tune Env" and "Extra Decay" bits are additional mods, I'm not sure what their source is. Tune Env affects the resistor above the trigger transistor--the pot below it is the more usual "Tune" to change the pitch of the circuit. I haven't tested it, but perhaps it changes the pitch with the envelope, if you follow me? Instead of a constant frequency, changing frequency like disco drums at the extreme end of the scale.

Extra Decay affects the decay feedback loop. Basically that branch of the circuit is part of the Twin T oscillator, and reducing that resistance (the 470K, by putting stuff in parallel with it) makes it more resonant.

If you used the usual resistor values, and you don't have anything installed in the "extra decay" position, then you should not get self oscillation, I don't think. However, if you DO have a pot there, then that's likely the cause of your self osc. If you want the original behavior, omit the pot entirely, and at that point you could remove the 390k or not as you wish since it won't be doing anything.

Edit: So I should not just re-read my own post before I hit submit Smile So yeah, you're using 100K for the "extra decay" but even when that's at it's max, you're putting 490K in parallel with 470K, which brings the resistance WAY DOWN, and will lead to self oscillation. Pull the pot and you should get more typical response.
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isak



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PostPosted: Thu Oct 03, 2013 2:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks for the link.

replaced the tone pot to 10k, works good.
replaced the tune env pot to 50k, still not working or doing something.
the decay pot is 500k and when i turn it all the way it is self oscing, the extra decay pot is all the way down, i guess i have a problem some where, dont know where, i looked but didnt found.
in addition, i think the overall pitch of the kick is high then it suppose to be (even when the tune pot is all the way down), when listening to 808 BD at youtube it was lower then mine.
can i lower the pitch? if yes what should i replace?
whats the original freq of the BD kick?

some sound clip..


808BD demo.wav
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 Filename:  808BD demo.wav
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elmegil



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PostPosted: Thu Oct 03, 2013 3:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, that pitch is too high.

I'd say lose the "extra decay" pot (disconnect it) and see if that helps.

Here's my original stripboard build of this:

http://electro-music.com/forum/phpbb-files/808_1_507.mp3
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isak



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PostPosted: Thu Oct 03, 2013 10:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

ok, removed, it still the same.
but the decay came back to normal tho Smile

any other idea? Confused


EDIT:
Quote:
"Tune" is a mod, I've typically seen it documented as 100K. It replaces a 47k resistor that sets the frequency of the oscillator.

if i'm not mistaken the Tune pot is in parallel with the 47k, not instead, if this is the case eventually it gives me 32.203 kohms not 47k.
maybe i need to put a switch there, do you see my point?
take a look at the attachments .. (marked in red lines)

EDIT2:
When looking at the microlarge pcb, I see that there is a switch that you can choose where it will go through, the regular 47k or the 100k pot.


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elmegil



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PostPosted: Fri Oct 04, 2013 6:53 am    Post subject: Reply with quote  Mark this post and the followings unread

So yes, having it in parallel, and that ending up peaking at 32K or so would leave you higher than the standard pitch. There are two ways to address that: put the pot in series and drop the 47K value down to something you'd want to be the lowest resistance on that leg (which would take some significant rework of the PCB, I think), or use a switch.

So the switch sounds like a good idea Very Happy
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isak



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PostPosted: Fri Oct 04, 2013 8:13 am    Post subject: Reply with quote  Mark this post and the followings unread

i have this thought..
instead of using a switch i want to use only a pot.
i'll connect an 47k pot instead of the 47k resistor, but connect the pot backwards, so when it will be all the way down i'll get 47k and when starting to turn it up it will go up the pitch cause the resistance will go down.

what do you think?

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elmegil



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PostPosted: Fri Oct 04, 2013 10:11 am    Post subject: Reply with quote  Mark this post and the followings unread

I'd think that would work pretty well; you might want a series resistor to keep you from going ALL the way to zero, not sure whether the oscillator could handle that.
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isak



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PostPosted: Sat Oct 05, 2013 7:53 am    Post subject: Reply with quote  Mark this post and the followings unread

hi elmegil

after giving it a thought i would like to put a switches, i want a true bypass of the mods.
after going through microlarge pcb ive decided to do the same way and the same values.

this is what i came up with..
i'll post my finding soon.

cheers.


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elmegil



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PostPosted: Sat Oct 05, 2013 8:33 am    Post subject: Reply with quote  Mark this post and the followings unread

So you're making it match the MicroLarge circuit?

I ask because the 470/390/370K part; the original circuit was a 470K resistor.

Thanks

Pete
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isak



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PostPosted: Sat Oct 05, 2013 8:57 am    Post subject: Reply with quote  Mark this post and the followings unread

yes, this is my attention.
the reason i'm doing it like the microlarge cause its verified by a lot, worldwide.
and your right, the original scheme R170 is 470k.

i hope on doing this today and post sound clips.
for the mean time you can see my panel design, please tell me what do you think about it Smile


cheers,
Isak E.


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elmegil



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PostPosted: Sat Oct 05, 2013 11:08 am    Post subject: Reply with quote  Mark this post and the followings unread

Looks nice. Make sure you normal the trigger to the accent Very Happy
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isak



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PostPosted: Sat Oct 05, 2013 11:21 am    Post subject: Reply with quote  Mark this post and the followings unread

I will, thanks Smile
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PostPosted: Tue Oct 08, 2013 12:40 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi elmegil

ok, i've removed the tune pot only for fine tuning the kick tune.
ive ended up with 43k, i got some BD samples from a friend that got a real 808, he recorded few samples for me.

my new findings are..
808 click - in the real 808 BD the click is high and wide open, sound very punchy very open.
clone click - in the clone the click is not as loud as the original, less punchy, less open.
ive seen in the link you gave me about when you talked about this matter that if i increase the value of the 10k that in parallel with the 10k pot i'll get a lower cutoff, from logic point of view...if i decrease the 10k resistor i'll get more open click (less cutoff)
well...after made some tests and reduce the 10k to 7.5k, 6.2k, 5.1k and no resistor at all, nothing changed Shocked
the tone didnt got open then i was thinking it suppose to open, actually didnt opened at all, maybe i need to replace the 100nF that with it?
i want my click to be higher in vol and more open like the real 808 Sad
BTW i'm using the original 945 and the 733 transistors.

i've attached to sound clips of the original 808BD, just for you to hear how beauty this monster is and for you to have a reference.
first clip is - tone fully open, decay fully open and no accent.
second clip is - tone fully closed decay fully open and no accent.

cheers.


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PostPosted: Tue Oct 08, 2013 1:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Another thing...

When 15V is applied to the accent it is like you always have accent so I used your scheme (again, from the link you gave me) to attanuat it with a pot.
The results was ok but not ok.
When connecting the the midi2cv trigger to the accent there is a tune to the click (I know, sounds wierd), when connecting the 15V to the accent with the pot to attanuat this pitch is deferent, more low click the the midi2cv trigger which is higher click.

Those are my new findings for now.

Cheers.

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elmegil



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PostPosted: Tue Oct 08, 2013 6:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Since the click is in a sense letting a little bit of the trigger pulse through the voice, I'd think that how you trigger it could be important to the sound.

What does it do if you route the trigger to both trigger in and accent? Does it change if you use trigger in rather than CMOS in and short, actual triggers (cmos in is really for triggering off gates and general signals).

I think at having the accent at a fixed level would reduce the energy being input to the circuit. Maybe try fixing the trigger in (not cmos trigger in) at 5V or something and sending the trigger to the accent input? That is more analogous to how the original circuit worked.

I don't know what else to say about the click. In that other thread we were trying to reduce it, not change or increase it.

Staring at that layout is making my brain hurt, I wish they published a schematic of their version.

The only other thing I can say at this point, I think, is if you want the original sound, build the original circuit on breadboard and see if it's better/different. Even without vintage transistors and op amps I would expect that to be closer. Start there, and then add the mods one at a time, verifying the aspects of the sound you're looking for each step of the way. If you can't even get there from the start....maybe try to find the vintage parts?

Finally, I would fall back to Robin Whittle's description of the circuit here: http://analogue-heaven.1065350.n5.nabble.com/TR-808-Bass-Drum-has-variable-punch-amp-decay-td68912.html and see if anything there triggers ideas for how to adjust this. I just re-read it but nothing is jumping at me right now....
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isak



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PostPosted: Tue Oct 08, 2013 8:08 am    Post subject: Reply with quote  Mark this post and the followings unread

You are right.
When connecting permanent power to the accent the sound is effected.
I've tried 15V, 12V and 5V.
after founding this i disconnect the permanent power from the accent and connect the midi2cv 5V trigger and at the CMOS i connected the midi2cv 5V gate.
this is how i trigger the whole deal.
i didnt tried the trigger to the trigger and the accent in yet.


I tried few things to make it closer to the original click.
I put an EQ to the click, boost around 500hrz, it was very close!
So my thoughts are that there is a Q level (resonance), that I need to find a way to boost, or am I wrong?

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PostPosted: Tue Oct 08, 2013 3:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

an update..

i manage to fix the punchy click sound Smile
i put a trimmer instead R166 which control the Env, now the click is high Smile

the only thing that got left is the pitch of the click, i need to get it higher, ill be happy if you can help with that please.

cheers.


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PostPosted: Tue Oct 08, 2013 5:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Unfortunately I'm not clear on what sets that pitch, and I don't have any cycles to measure it Sad Major work release 1am in the morning, still scrambling....
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PostPosted: Fri Oct 18, 2013 6:20 am    Post subject: Reply with quote  Mark this post and the followings unread

hi elmegil

i found a way to control the click with a help of a friend (thanks Sebo Smile )
i used the CMOS trigger in to trigger the BD but it needs to be 1ms trigger for it to sound like the original click.
he told me to lower the 100n cap to like 47n and from there to start checking.
so i did.
47n was a bit high pitch click so i lower it to 33n which was to low in pitch, so i add to the 33n another 4.7n in parallel and it was perfect!
the same click pitch as the original Cool
now the only thing i want to do is to amplify the click a bit for it to be like the original, i wander how... scratch

cheers

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