Hi All,
For this moths FX-X Submission, I've gutted a broken Radio/Alarm Clock and have been experimenting with
the TA7613 that it contains. (an on-chip AM/FM radio with class-B power amp section)
It produces some great tones! thing is, with the submission date coming closer I have been unable to
splice in a "master volume" control which would be necessary to make it a usable effect.
Right now, it directly drives an 8Ohm speaker load and definitely sounds a lot louder then a ruby...
However tacking on a regular master volume drastically changes the way the effect sounds.
(I've tried 1 and 5k pots to ground)
Any suggestions in adding mastervolume are greatly appreciated!
Schem as below:(http://www.anyplace.nl/pics/diy/Wakeupcall-schem-v1a.gif)
TA7613 Datasheet found at:
http://www.anyplace.nl/pics/diy/TA7613AP%20datasheet.pdf (http://www.anyplace.nl/pics/diy/TA7613AP%20datasheet.pdf)
Oh yeah... It sounds quite unique!!! the distorion is BIG and a little sizzling but controlled. (very AM/FM'y :^)
Turning "beep" al the way up makes it a nasty oscillating fuzz with "bucket" acting as a kind of gate.
The cool thing is the gate (bucket) is VERY controlled and sensitive which is maybe why the volume controls
I've tried dont work. (because of the network "bucket"->"beep"->ground in the schem)
Cheers!
Put in an 8 ohm several watt resistor. Then stick the 1 to 5k pot in parallel.
Quote from: Sir H C on May 24, 2008, 02:15:00 AM
Put in an 8 ohm several watt resistor. Then stick the 1 to 5k pot in parallel.
Just back from the breadboard...
By lack of an 8 Ohm resistor I've wired the small speaker that came with it
in series with the output and a 500 Ohm pot in parallel.
It does attenuate better now, but It still changes the sound of the effect as soon
as I lower the output volume.
The amount of signal to ground seems to play a large role in how it sounds,
I'll just keep poking...
Cheers,
Have you tried the 25ohm rheostat from Radioshack like they use on the Ruby?
Try putting an emitter-follower or even an opamp buffer after the 8 ohm load and before the volume pot. The idea being that you want to pick the signal off the "top" of the 8 ohm load (with the "bottom" of the load being ground) without loading the main circuit.
Heck, maybe even a substantially larger volume pot (in the 100k or higher range) might do the trick; something that would effectively look like an open circuit to the chip in comparison with the 8 ohm load. You would then be at the mercy of the input impedance of whatever device came next in your chain, however. Maybe a buffer is the way to go.
-- T. G. --
yeah just off the top of my head, that seems like way too low a value for the volume pot. I would start with a 500k and work your way down. also, the difference in sound may be a side effect of the high end loss commonly associated with certain impedances when you roll down the volume. trya small value cap across the outer lugs.
I've been at the breadboard again for some tweaking, all the above doesn't work.. >:(
Whatever value pot I use, as soon as I turn it down it cuts out. (i.e. attenuation is between 0 and say ±100 Ohm to ground)
Even then, any amount of change in signal to ground seems to directly change the sound.
I wonder if that is because I've wired this chip up so inappropriately? ;D
Tagging on a buffer changed the sound to I mild compressed distortion on the buffer output.
Mind you, the TA7613's output drives a speaker directly from the Class-B poweramp.
I found connecting a small cap( .022) from output to ground through a 56 Ohm resistor makes it all sound
a bit more focused and controlled. It also dials in nice tremolo like decays to the notes.
(same happens when you roll down the guitar volume)
Hooking it up to an amp still immediately ruins the sound to a whimpy mild distortion...
Which brings me to the idea of applying negative gain in order to control the output.
Is that possible? can you use an op-amp to apply a gain of minus 0.5?
I've got a lot to learn... :icon_biggrin:
Cheers
you could try to use an OT?
QuoteQuote from: birt on Today at 09:37:13
you could try to use an OT?
OT=?
Does 'OT' mean output transformer? (just a guess)
sorry, i'm an amp guy so i almost never say output transformer :p
Quote from: birt on May 25, 2008, 05:17:20 AM
sorry, i'm an amp guy so i almost never say output transformer :p
hmmm, yeah and you don't see that many of them in stomp boxes I guess....
Could I use the transformer that's in the alarm clock?
99.9% sure I can't but it is for this month's "recycled" theme... ;D
Cool idea! I'd like something like that as the noise source in the Geofex telephone filter/noise pedal (http://geofex.com/FX_images/lofi.gif), to try to get a pedal that sounds like you're on AM radio.
That's amazing you figured that out from the data sheet.
Good scavenging mate!
From the data sheet it looks like your only passing signal through the audio amplifier section of the chip. Pin-9 and 12.
The HF Bypass (pin-7) looks to be connected to the AM HF Mixer section only.
How do these different sections interact when they trace to separate pin-outs?
When shall we expect the sound and youtube clips? :icon_wink:
Your endevor has spawned an idea.
what if...
One was to build a simple AM transmitter on one PCB, and AM receiver on another PCB,
put them both into a box with an RF link between them.
Actual AM radio sound?
Dave
Quote from: any on May 25, 2008, 04:18:48 AM
Tagging on a buffer changed the sound to I mild compressed distortion on the buffer output.
Mind you, the TA7613's output drives a speaker directly from the Class-B poweramp.
Yeah, it sounds like you're overdriving the buffer. I didn't fully think that through. But since I've never let that stop me before...
How about making the 8 ohm load into a voltage divider, say a 5 ohm load followed by a 3 ohm load, and take the signal off from the point between them. At that point, or at some other ratio that you find through trial and error, the output might be low enough to not overdrive the buffer.
-- T. G. --
I'll do some more breadboarding trying to get the speaker output down at instrument level.
If that doesn't work I'll probably just record the current speaker output so everyone can at least hear
what I'm hearing.. I recon it would be great for Doom and Stoner type music, it sounds very brutal and moody.... :icon_twisted:
On a side note, the diode pair on the output are two green led's from an old mixing console.
The cool thing is that one Led lights up continuously while the other one is more voltage dependant and only lights up
when played slightly harder. Hooking up a ldr to the second led and wired to "beep" was pretty cool as it would
decrease distortion on harder played notes, effectively acting as a kind of compressor.
If I learned anything from this months theme, there's a lot of fun to be found in random parts!
just a quick update, just been fiddling a bit...
anetwork of 5 Ohm through a 10uF cap to ground and 5 Ohm to ground with the signal tapped a the junction
sounds promising but not quite there yet... I'll have to take another shot at it tomorrow.
"beep" should be a 2k resistor going to a 250k pot which give an even bigger gain range and no dead spot at minimum gain.
There's quite a bit of cool sounds lurking in there!
For some reason that "bypass" pins connection (guitar signal to pin 7) triggers a bit like Tim Escobedo's PWM...
Pot taper is a bit touchy there though.
To bad submission is this week already, so much left to try... :P
Hi All,
The current version is now entered in this Month's (May) FX-X including some soundclips.
Honestly, I couldn't get it to sound as cool as with the speaker set-up, but I still came close.
Volume control is still a problem but it does react nicely to buffers now so I could
easily tame it with my ruby's input gain. It can still get F*#c%n loud though and totally slam the input...hehe...
I'll probably keep tweaking it to see what more lurks in "teh allmighty I-chip"... :P
Cheers
Cool submission. So far it's just you and me who have submitted projects. I'm betting on you for the win, that wakeupcall is so weird, in a good way! :)
Good thing is if they extend the deadline, I'll have some more time to refine the circuit.
(especially the "coma" section is a bit too uncontrolled...)