PI5 from ITMD

[geoscash1]

I tested everything as I built it.

It is at the end of the build, the audio portion that seems to have an issue. when powered up, it almost instantly burns up the 10R (R17) and the 2N3904 (Q3). I started thinking the 3904 maybe backwards but checking the pinout it seems correct (123/ebc left to right from back) so I don't know how to trouble shoot it from this point.

added a pic of my board, a redrawn schematic and bom.


PI5 pcb - schematic & bom.pdf

[Qiaozhi]

I tested everything as I built it.

It is at the end of the build, the audio portion that seems to have an issue. when powered up, it almost instantly burns up the 10R (R17) and the 2N3904 (Q3). I started thinking the 3904 maybe backwards but checking the pinout it seems correct (123/ebc left to right from back) so I don't know how to trouble shoot it from this point.

added a pic of my board, a redrawn schematic and bom.

[ATTACH]34915[/ATTACH]
[ATTACH]34916[/ATTACH]
[ATTACH]34917[/ATTACH]

Try disconnecting R16 (the 5k preset) at the base of Q3 (2N3904).

[geoscash1]

Wont that cut off the output signal from the 4011 all together, or is that just to see if it stops the 3904 and 10r from burning?

Let me ask you a question, I set up R16 and R18 as external panel pots, how would you connect them? I did them with 3 wires, with the third leg of
pots to the labeled end of the pcb label where it arrows to #3, should they only use 2 wires?

Dammit, I hate it when I get confused with these dogon pots and how they wire to the boards. 2 wires, 3 wires, 2 pads connected 1 individual, or 3 individual pads.... uhhhggg..

[bernte_one]

for pot use
on outer and the middle pin act as variable resistor (hind- good possibility to find right value for damping resistor)

if all three pins are wired the pot acts as voltage divider

geocash dont give up i have burned most of my itmd pi projects

but if you connect parts with variable connection for example 2n3904 or bc... please take the data sheet from manufacturer
googles first results are often good but for sure lokk the data sheet

[geoscash1]

Hi bernte,

Well, I'm a pretty driven kinda guy so I don't give up easy....lol ... I'll keep playing with this until I get it working, hopefully that will be sometime in my lifetime...

Here is a pic of how I have it currently wired with the pots, I wanted both of them front panel so there is no trimmers on board. But in the schematics,
R16 has pins/pads 2 and 3 connected and on R18 pins/pads 1 and 2 connected so it splits the connections on the pots but do they still need 3 wires or just 2 and only connected to 2 pins on the pots and which 2? That's what confuses the hell outta me at times....lol..

I do use the data sheets, I have a pile of them in a folder on my desk top so I reference them on everything...good to have them on hand..

p.s. "if all three pins are wired the pot acts as voltage divider" That is something I did not know, thanks for sharing that..

[Qiaozhi]

Hi bernte,

Well, I'm a pretty driven kinda guy so I don't give up easy....lol ... I'll keep playing with this until I get it working, hopefully that will be sometime in my lifetime...

Here is a pic of how I have it currently wired with the pots, I wanted both of them front panel so there is no trimmers on board. But in the schematics,
R16 has pins/pads 2 and 3 connected and on R18 pins/pads 1 and 2 connected so it splits the connections on the pots but do they still need 3 wires or just 2 and only connected to 2 pins on the pots and which 2? That's what confuses the hell outta me at times....lol..

I do use the data sheets, I have a pile of them in a folder on my desk top so I reference them on everything...good to have them on hand..

p.s. "if all three pins are wired the pot acts as voltage divider" That is something I did not know, thanks for sharing that..

[ATTACH]34920[/ATTACH]

You only need to use 2 wires - the middle wire, and one of the outer wires. Which outer wire to use depends on which way you want the pot to react. i.e. do you want the delay to increase when you turn the knob to the right or to the left.

Does the circuit work with headphones and no audio stage?

[bernte_one]

just started

so far may design attached


some missing connection on 4011 (12,11,13) i will continue tomorrow have to sleep

[Polymer]

The updated PI-5 schematic (sent to those that requested it) was created prior to ITMD Second Edition being released. The circuit posted by Geocash is from the book. Hence the slight differences.

If you're not using the control voltage input (pin 5) on a 555, you can add a small capacitor (usually 10nF to 100nF) to 0V to prevent intereference. I typically add the capacitor if the 555 is being used as a monostable, but it's not always necessary if being used in astable mode. Depends on the application. Here (in the TX oscillator) you don't need it, but you can add it if it makes you feel better.

Thank you Qiaozhi! Got that.

Another question to the circuit PI-5:

In the schematic PIN 5 of both 555 timers are now connected via C=100nF to -VB. The data book says connect to GND via the C. This has me confused.
Is -VB = GND in this case?
Does it matter? Please do explain

Just can't get my head around that virtual ground stuff, yet ... aaarrrgggghhh ....

[geoscash1]

Thank you Qiaozhi! Got that.

Another question to the circuit PI-5:

In the schematic PIN 5 of both 555 timers are now connected via C=100nF to -VB. The data book says connect to GND via the C. This has me confused.
Is -VB = GND in this case?
Does it matter? Please do explain

Just can't get my head around that virtual ground stuff, yet ... aaarrrgggghhh ....

Me neither......lol

[geoscash1]

You only need to use 2 wires - the middle wire, and one of the outer wires. Which outer wire to use depends on which way you want the pot to react. i.e. do you want the delay to increase when you turn the knob to the right or to the left.

Does the circuit work with headphones and no audio stage?

Nope, it sure don't now.. not sure if I destroyed something else or not, will have to pull parts and replace with new ones to see. It for sure melted Q3 and burned the 10R (r17) in half with power on for maybe, I mean maybe 3 seconds tops, it was blazing fast no pun intended...lol

I went over every trace and connection to make sure, double checking connections based on the latest schematic you sent me and as far as I can tell, it is right on.
So not sure where to go at this point or even really how to test it any farther other than the outputs of the 555's, op amp and transistors..

[Qiaozhi]

Thank you Qiaozhi! Got that.

Another question to the circuit PI-5:

In the schematic PIN 5 of both 555 timers are now connected via C=100nF to -VB. The data book says connect to GND via the C. This has me confused.
Is -VB = GND in this case?
Does it matter? Please do explain

Just can't get my head around that virtual ground stuff, yet ... aaarrrgggghhh ....

The circuit is connected between the +VB and -VB rails, so the connection to -VB is correct.
The virtual ground is only used by the preamp because it's used in a dual supply configuration. It simply removes the need to generate an extra negative supply voltage.

If you think this is difficult, try getting your head around the power supply configuration of the Hammerhead.

[Polymer]

The circuit is connected between the +VB and -VB rails, so the connection to -VB is correct.
The virtual ground is only used by the preamp because it's used in a dual supply configuration. It simply removes the need to generate an extra negative supply voltage.

If you think this is difficult, try getting your head around the power supply configuration of the Hammerhead.

Uh Oh That is why it is called the Hammer-Head, huh?

Thanks for your reply, it helped - my head feels better

[Polymer]

Geoscash1,

Can just about smell the scent of your "resistor roast" here ... It sure does linger on for a while.

Have you found the cause yet?

What is the resistance of the speaker you used?
Looks like your transistor switched on and stayed on.

I'd try putting a resistor in series with the speaker to say 330 Ohms to limit the power to ~30 mA. Use at least a 0.3 Watt resistor for that.
It would give you ample time to measure & possibly listen to whats going on, before anything could go smokey bear.

I've got all the parts for the PI-5, but have to breadboard it, hopefully soon.

I appreciate your pioneering on this!

[geoscash1]

Geoscash1,

Can just about smell the scent of your "resistor roast" here ... It sure does linger on for a while.

Have you found the cause yet?

What is the resistance of the speaker you used?
Looks like your transistor switched on and stayed on.

I'd try putting a resistor in series with the speaker to say 330 Ohms to limit the power to ~30 mA. Use at least a 0.3 Watt resistor for that.
It would give you ample time to measure & possibly listen to whats going on, before anything could go smokey bear.

I've got all the parts for the PI-5, but have to breadboard it, hopefully soon.

I appreciate your pioneering on this!

Hi Polymer,

No, I haven't messed with it since yesterday and still haven't figured out the issue. The speakers I use are 1-1/4" - 8ohm/0.5watt, little guys and they seem to work well with all my other builds.

I was thinking about that yesterday, maybe adding a resistor but just haven't been back to the bench yet to mess with it.

question, If the transistor is staying on wouldn't that be because of the 1.2k coming off the 4011 pin 10 output to the trimmer/pot connection at R16?

I wish or am hoping George will chime in with some good details and build info for this project. It really has no detail in the book and the new schematic
is different than the original book one (which was an incorrect version).

IMHO, this design or concept seems to me to have good potential but the lack of info on it is quite a hold back especially for some of us builders with no engineering experience other than this site.

I really do suck at difficult math and I know that most of this requires some good skill with figuring out equations and such, not to mention I cant seem to remember from one day to the next anymore...

I have been studying the parts and how they interact and relate to each other but this one quite a bit different to the other things posted and is sort of like a comparator circuit.

Anyhow, thanks for the advice, I'll try the resistor in series with the speaker after I replace the 3904 and R17 again and go from there. It seems I have no oscillation now so not sure what has happened, or I get no wave forms on my scope now so something is amiss somewhere else too...

p.s. yea, that smell is definitely something that lingers and those little darn parts can leave blisters on fingers too...

[Qiaozhi]

I wish or am hoping George will chime in with some good details and build info for this project. It really has no detail in the book and the new schematic is different than the original book one (which was an incorrect version).

There are no constructional details in the book because it is a bonus circuit.

At the moment I'm completely swamped with real work, as I'm trying to complete an important project. Hopefully in a few week's time I might have some free time. Maybe we could turn this into a new project. Please be patient .....