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Eric Archer TR808 kick bass veroboard clone issues
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dcjim



Joined: Nov 03, 2012
Posts: 8
Location: brooklyn

PostPosted: Tue Jul 28, 2015 6:38 am    Post subject: Eric Archer TR808 kick bass veroboard clone issues
Subject description: Voice and delay work though possibly quiet and with loud click on trigger, tone and level don't
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Hello all

Just finished a TR808 kick clone on veroboard using Eric Archer's layout

http://www.ericarcher.net/wp-content/uploads/2014/07/tr-808-bass-drum-diy-project.pdf

I've never done a veroboard build before (as in dot rather than strip layout or PCB) and it was challenging but happily the basic voice and delay work at least so I imagine my problems are just teething troubles

Here are my issues

1) I think the voice is quiet. I'm testing with a Roland Microcube through the line channel and the amp is at half volume giving a full but not deafening level. I imagine it should be very loud at half volume, they're quite beefy those little Roland amps

2) When I trigger the voice it is proceeded by a loud click, and not a musical one at that. However the voice does sometimes trigger without this. I'm not entirely sure of the circumstances. Happens when I fiddle with the trigger arrangement maybe, so no click, just a nice round boom. I am triggering as follows: with 'accent' tied to +12v I'm touching 'trigger' against the +12v rail. I wondered if it was just the clumsiness of crocodile clips and bits of wire so I tried wiring in a momentary push switch. Didn't help. I am using the diode-resistor-cap network Eric suggests between the trigger input and the trigger circuit. I intend to trigger the unit from an Arduino which would be only a +5v trigger but I don't have a spare ATMega right now to test

3) The tone pot doesn't work. I have checked connections and continuity around this part of the circuit. I assume the tone pot should make a noticeable difference? I'm using a 10k pot as per the original schematics and Eric's notes

4) The volume pot doesn't work. I have checked connections and continuity around this part of the circuit. I'm using a 10k pot as per Eric's notes but NOT as per original schematics - the value of the level pot is not specified but the parts list names 500k, 10k and 100k in use. The schematic identifies delay as 500k and tone as 10k so by deduction the unidentified level pot should perhaps be 100k?

Now ... obviously I need to give the whole thing a thorough check but any obvious pointers before I do would be helpful to narrow down the search and any expected voltage readings would be good. I have measured the TL072 and it's getting +12v and -12v where it should.

Hopefully it's something simple and so far it sounds great!

Thanks
Jim
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elmegil



Joined: Mar 20, 2012
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Location: Chicago
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PostPosted: Tue Jul 28, 2015 3:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Try tying accent and trigger together instead of just tying accent high.

There's an older stripboard discussion of the bass drum circuit here somewhere that had a lot of discussion around the click, that might be helpful to read.

Can you post photos of your work? That might make it possible to spot errors that you're missing after looking at it over and over again (been there, done that, felt stupid when someone pointed out the problem, but it got fixed!)
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dcjim



Joined: Nov 03, 2012
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Location: brooklyn

PostPosted: Thu Sep 17, 2015 6:00 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
Try tying accent and trigger together instead of just tying accent high.

There's an older stripboard discussion of the bass drum circuit here somewhere that had a lot of discussion around the click, that might be helpful to read.

Can you post photos of your work? That might make it possible to spot errors that you're missing after looking at it over and over again (been there, done that, felt stupid when someone pointed out the problem, but it got fixed!)


Hello, thanks for your reply sorry it took a while to respond.

I got my original problems ironed out, basically I ditched the point to point Eric Archer stuff (too hard to debug) and started building all the stripbaord voices. I've completed bass, snare, hats/cymbal/cowbell noise source and open and closed hats - I plan to do cymbal and cowbell (as they're half done with the noise source anyway) then place it all under Arduino control driven by MIDI in and stick it in a 1U rack. That'll be phase 1, phase 2 will be other voices and some kind of sequencer.

The voices I've done sound awesome, very pleased with them. A friend who knows his 808s and has golden ears says they're spot on too.

I wanted to ask you how you triggered your voices from an Arduino? I have a fair bit of Arduino experience and did quickly try just tieing the voice trigger inputs to a digital out from the Arduino but no dice. What am I missing? My manual triggering configuration for each voice is a momentary SPST switch with, as you say, trigger and accent tied then the SPST shorting to +ve - it works fine with occassional duplicate triggering which I put down to the switches not being debounced. Also worth mentioning I used Eric Archer's trigger buffer circuit on every voice which does make a big difference.

Thanks
Jim
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elmegil



Joined: Mar 20, 2012
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PostPosted: Thu Sep 17, 2015 7:19 am    Post subject: Reply with quote  Mark this post and the followings unread

Since the Arduino is essentially just a different kind of microcontroller than what was in the 808, I replicated the accent circuit from the schematics. I never did complete the rest of that project (though I have my voices still hanging around), but it's good to understand how the circuit is meant to function generally.

I left Eric's trigger processing in place too, but going back to the original the way it was intended to work was this:

There was a system clock that was combined with the accent level, to create a clocking trigger 1 ms wide and between 4 and 14V tall depending on the setting of the accent pot and the accent gate. Most clone circuits treat this as the "accent" input, but really it's the primary trigger.

This trigger is going to all the voices, every step. THEN each voice additionally has an "enable" input. This is what Eric (and others) uses to trigger (after the processing circuit).

The combination of the trigger and the enable signal would cause a voice to fire, and the level of the trigger determined how much "accent" it had.

This is all based on the schematics on pages 8 & 9 of the service manual.


So when I was doing this with my Arduino I would set the enable input first and as quickly as possible send the accent-processed trigger. I don't remember clearly now, but while I left Eric's processing in place, I may have sent the enable to the point *after* that, bypassing it. The trigger processing is good for standalone modules, but if you're slaving it to a controller, I think the original technique is more likely to sound like the real deal.

The accent / clock / trigger is 1ms wide, there's a timing diagram on page 4.

Hope this helps....
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dcjim



Joined: Nov 03, 2012
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PostPosted: Thu Sep 17, 2015 7:21 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
Since the Arduino is essentially just a different kind of microcontroller than what was in the 808, I replicated the accent circuit from the schematics. I never did complete the rest of that project (though I have my voices still hanging around), but it's good to understand how the circuit is meant to function generally.

I left Eric's trigger processing in place too, but going back to the original the way it was intended to work was this:

There was a system clock that was combined with the accent level, to create a clocking trigger 1 ms wide and between 4 and 14V tall depending on the setting of the accent pot and the accent gate. Most clone circuits treat this as the "accent" input, but really it's the primary trigger.

This trigger is going to all the voices, every step. THEN each voice additionally has an "enable" input. This is what Eric (and others) uses to trigger (after the processing circuit).

The combination of the trigger and the enable signal would cause a voice to fire, and the level of the trigger determined how much "accent" it had.

This is all based on the schematics on pages 8 & 9 of the service manual.


So when I was doing this with my Arduino I would set the enable input first and as quickly as possible send the accent-processed trigger. I don't remember clearly now, but while I left Eric's processing in place, I may have sent the enable to the point *after* that, bypassing it. The trigger processing is good for standalone modules, but if you're slaving it to a controller, I think the original technique is more likely to sound like the real deal.

The accent / clock / trigger is 1ms wide, there's a timing diagram on page 4.

Hope this helps....


Thanks for the speedy reply! And to send the pulse you'd write the pin high then a 1ms later set it low?
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elmegil



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PostPosted: Thu Sep 17, 2015 7:27 am    Post subject: Reply with quote  Mark this post and the followings unread

I would add that the accent processing I'm talking about is the section made up of Q27, Q31-34, and the two 4011 gates (don't be confused that one is listed as a NAND and the other is listed as an OR with inverted inputs -- the gate is the same, it's a 4011). I implemented the gate section with discrete transistors rather than a whole chip. If you like I can reverse it and post the stripboard, but probably will be sometime this weekend before I do that.
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elmegil



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PostPosted: Thu Sep 17, 2015 7:27 am    Post subject: Reply with quote  Mark this post and the followings unread

dcjim wrote:

Thanks for the speedy reply! And to send the pulse you'd write the pin high then a 1ms later set it low?


Yup Smile
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