TR-808 Snare Stripboard

[lysergist]

Thank you LektroiD for the updated components, i did the modifications. I have also added the Snappy Decay mod : C51(C6 in the stripboard version) (0,47µf) changed to 2,2µf, in parallel a 250k (B) Potentiometer with a 22k Resistor in series

Here is how it sounds, short decays and long ones :

---

0003 3-Audio.wav
Description:		Download (listen)
Filename:	0003 3-Audio.wav
Filesize:	8.46 MB
Downloaded:	1168 Time(s)

---

[theauton]

I've just finished building the 808 snare to complement the other fantastic Eric Archer kick and hats modules.
The snare works ok initially and triggers fine but for some reason after a few minutes powered up it starts triggering randomly and soon descends into a constant random chaos of noise.
Anyone got any clues as to why this might be happening?

[artilect99]

I recently built one, and I get nothing from the output. If I listen directly to the pin 1 of the left TL072, I can hear the tone sound for that side. If I listen to the output on the other side (pin 7) of the same TL072, it's locked into a high-pitched whine. Nothing seems to get to the output jack though.

Anyone have any ideas what might be causing something like that?

[elmegil]

Neither one should be making any sound until you hit it with a trigger + accent.

[artilect99]

Yeah, I have accent tied to +12v as I did when testing the 808BD. IC1A makes a tone when I give it a trigger, but IC1B is just a constant whine from power up, around 10kHz I would say. I briefly interrupts when I give it a trigger. This oscillation bleeds into the output of IC1A as well. This monitoring the output pins directly, it seems nothing is making it to the output jack.

[elmegil]

Do you have white noise over at IC2B?

I'm suspicious of your op amps, particularly if you're not getting sound either.

After that, I'd double check all the connections and be sure there aren't any shorts.

[artilect99]

Reflowing everything around the op-amp solved the oscillation, and now with a trigger I'm getting drum tones off of IC1A and IC1B, two different pitches as expected, and white noise on IC2b, but still nothing is getting to the output. The component sounds are all there on the output pins of the op-amps themsevles but it's all getting lost on its way to the output jack somewhere.

[artilect99]

Well I got it working, but I'm not sure exactly what I did. I previously had the level pot replaced by a jumper, as I did with the 808BD, because I mix on a board externally. Replacing the jumper with a 50k pot seems to have solved it, but I can't say why exactly. Shouldn't a jumper there be equivalent to a pot at 0 resistance, i.e. max volume? Or no, because it's in the feedback loop of the op-amp. So then would a 100K give more volume? (I was out of 100k).

[elmegil]

The level pot is in the feedback loop of the output op amp.

A 0 there brings you to 0 gain, or no output.


Errrr Except that there's a 470K there as well. I have no idea then.

[artilect99]

Yeah, I just hadn't looked at the schematic and was stupidly assuming it would work the same as it did on the BD, as I had used a jumper there to remove the level pot.

So would a 100K pot yield more gain than a 50k in this instance? I think I'll try just replacing it with a 100k resistor since I don't need the pot.

Appreciate the help elmegil.

[elmegil]

Except of course 0 in parallel with 470K or anything else for that matter is still 0. So yeah, the logic I described is right. I'm just having a bad brain day.

[elmegil]

The level pot in the bass drum is a voltage divider. If you jumper pin 1 to pin 2, that's the same as having the pot all the way up.

Since the snare does level differently by adjusting gain instead of being a voltage divider, that's why it's different.

The equivalent circuit would be to use a 50K or 47K resistor in place of the pot.

[artilect99]

Yup I get it. It calls for a 100k pot for level, and I only had a 50k pot on hand, is why I was asking about 50k versus 100k.

[Harry Manback]

Hello all. This is my first time posting here but i am a long time viewer of this forum. I am also an electronics noobie with probably a super noob question but here it goes:

I have spent MANY hours on this layout trying to get it to work. I have done all of the troubleshooting i know how to do. I have checked for shorts, checked for appropriate components, swapped out op amps, i have re-flowed everything, i have checked for continuity, i have double checked all of the track cuts and the continuity of those as well to make sure i didn't miss anything. I also tried the diode, resistor, cap trigger network. I get white noise from the output of TL072(B) (using a 2n3904) but i get nothing out of the main output. I am also not getting any discernible output signal from the TL072 (A). I have traced my trigger signal to T2 where it seems to end. I can detect the trigger signal on R3, R4, and the middle leg of T2. Outside of that, its silence.

I've spent a BUNCH of time with the schematic as well as the really awesome diagrams created by Minus and I've got a couple questions. This may be super obvious but i am wondering about the accent piece. I keep seeing people say "tie accent to +12V". That seems simple enough but in looking at the diagram, the accent input appears to be on a track that is also connected to -12V (Row 13) which also appears to be supplying the TL072 with -12V on pin 4. I'm not sure if i am supposed to connect accent right to +12v and remove it from the -12V track? It seems rather counter intuitive to "tie" this to +12V while its also on the -12V track so i must be misunderstanding. I also don't really see this sequence represented in the schematic as far as I can tell. This is most likely me just misinterpreting because I am a newbie but I was wondering if anyone could shed some light on this. I REALLY want an 808 snare. Thanks so much!

[elmegil]

[elmegil]

If you look at the "back side" view, accent is on row 13, and there is a "cut" in the 8th column. This cut is directly underneath R5, and therefore not visible in the "front side" view. This cut is immediately before the wire bringing the -12V down to the op amp.

I would recommend comparing the rest of your cuts to the backside view of the layout an ensure they're all where they ought to be.

I hope this helps.

[Harry Manback]

[elmegil]

So you do need to have a positive voltage on the accent in when you send a trigger. And as you see it's not tied to that -12V rail. When you're ready to come back to it, I would start at the trigger and accent circuitry and make sure the pulse is making it through the initial pair of transistors. Hoping you have an oscilloscope.....

[fou-rieux]

Hey guys. First of all thank you for all the knowledge here. Almost every post/topic helped me
I started building this 808 snare 10 months ago and i still had some issues. The Snare noise came out late. While checking my stripboard and connecting it again, unfortunately I connected the Power reverse so the -12 went to +12 in the stripboard layout and the +12 connected to -12.
Something was smelling, burning etc pp...
However now its not working. I exchanged the ICs for two new one but still nothing. I can't see any damaged parts.
How would you start to search the burnt parts?
What could be the parts that could be damaged directly?

Thanks and greetings,
fou-rieux

ps: one good result anyhow: while trying to find the bad parts i found out i had R9 missing. That could be the error that I was searching for before

[elmegil]

If it's neither of the chips, then the next most likely candidates are the transistors. T3, T4, or T5 in particular because they're basically tied right to the rails.

Also be aware that sometimes the pinouts even for standard things like the BC546's aren't always correct. Not a bad idea to get a cheap component tester off ebay or from alibaba to verify such things.

Since you say you've read all the threads, I will assume you aren't having any issue because of the whole accent/trigger thing.

After that, it's down to sending in your trigger and observing what happens. There are two primary signal paths through the voice -- the "drum" generators and the "snare" generators. The white noise is basically going through a rough VCA whose amplitude varies with the "snappy" pot.

Hopefully you have a scope of some sort, otherwise it will be pretty difficult....

[fou-rieux]

Hey,
I checked the Transistors based on this how to: https://www.pcbway.com/blog/Engineering_Technical/How_to_Find_Faulty_Components_on_PCB.html
they all seem to be fine...

I also checked all the resistors with the multimeter and couldnt find any damaged resistors.

The electrolytic caps all rise in their resistance value so i guess they are ok to. Just with the ceramic capacitors i don't know.... the value of some of them rises and then stops. If I inverse the polarity of the multimeter the value goes down and some dont show anything. Could that be the problem? I'm too much of a noob to get that right
Unfortunatly I don't have a scope :/

If the transistors have different pinouts, I guess it would not have been worked in the first place before my disaster. First of all i want to get back to that state...

I guess I will try by headphones and do some random connections to see where is which sound... O.o

Thanks for you quick reply!

Greets,
fou-rieux

[elmegil]

Ceramic caps are highly unlikely to be damaged by reverse voltage.

That is correct about the transistors.... mostly. Sometimes BJTs will work "backwards", just not as efficiently. That said, it shouldn't destroy them either.

Be careful with your hearing using head phones, but I do agree without a scope, you might be able to make something of it with an audio probe.