Vibracaster - or "How to turn your Valvecaster into a Tremolo"

[DiamondDog]

OK, has anyone else had a go at building a 12au7 version?

I've built the version without the rate LED, and I'm not getting a lot  happening. The Valvecaster 'donor' was a working ptp 12au7; the gain and volume pots were moved and replaced with 100K resistors; the tone pot and cap was removed. It was retested again prior to the Vibe graft.

The additional circuit has been wired up on a bit of perf according to the v2 au7 schematic earlier it the thread.

I have powered it with regulated 15v, 12v and 9v. I have tried BC547, 2n5088 and 5089, and 2n3904 in the circuit.

When switched in, there is no effect, just the clean and much-loved valvecaster tone.

Interestingly enough, despite swapping the pots over 3 times for new and checked pots, there is a rumble when the depth pot is moved.

I have removed the 4148, and while I understand that was there for the LED, there is no evidence of any LFO ticking.

I'm pulling power off pin 5 and ground to pin 4. I am getting good voltage at the board. I have split the power off to its own supply with no change.

Here is my rough perf layout.

Any thoughts? Anything obvious?

DD.

[frequencycentral]

Sounds like the PSO may not be running. I'm at work now, but later I will suggest a few tests!

[kurtlives]

I don't think your issue is with Rick's circuit it is probably an error on your part.

Without having the time to check your layout...are you sure it is correct and you have oriented the transistors properly?

R5 should have nothing to do with Q2 in your layout.

[DiamondDog]

I don't think your issue is with Rick's circuit

I didn't say it was... Rick's done a great job, but I can't see any references to anyone else making the AU7 circuit. I'm looking for ideas. I'm very aware that I've probably made a stupid mistake- I normally do when the voltage is low like this! 

Without having the time to check your layout...are you sure it is correct and you have oriented the transistors properly?

As you can see from my layout, I acknowledge that the 547 are 'reversed' to the 5088/9 etc. And it's the first thing I check (voice of experience...    )

R5 should have nothing to do with Q2 in your layout.

R5 goes across C & B of Q1; Q1's C goes to Q2's B. Therefore R5 'touches' Q2. Pardon me if I've got me B & C mixed up- it's 00:12 here...

Good input tho- Cheers!

(I still reckon I've overlooked something obvious!)

DD

[frequencycentral]

I can't see any references to anyone else making the AU7 circuit.

I'm basing my assumption that it will work identically with a 6111 or 12AU7 on the fact that I breadboard my first tremolo, Bipolar Disorder,  using a 6111 but built it using a 12AU7. For a while until I disassembled the breadboarded version I had two, one 6111 and the other 12AU7. So from that experience I'm 99.9% convinced that anything that works with a 6111 will also work with a 12AU7.

I guess the thing to do here if for you to post some voltages, specifically from the PSO part of the circuit. We'll compare them with mine and find the fault. By the way - the three caps in your PSO are NP right?

Rick

[DiamondDog]

Hey, Rick.

I can't see any references to anyone else making the AU7 circuit.

I'm basing my assumption that it will work identically with a 6111 or 12AU7 on the fact that I breadboard my first tremolo, Bipolar Disorder,  using a 6111 but built it using a 12AU7. For a while until I disassembled the breadboarded version I had two, one 6111 and the other 12AU7. So from that experience I'm 99.9% convinced that anything that works with a 6111 will also work with a 12AU7.

Fair enough- and it's been great work you've done! All I'm hoping to do is help out- I've got boxes of 12a*7s but no 6111s about... 

I guess the thing to do here if for you to post some voltages, specifically from the PSO part of the circuit. We'll compare them with mine and find the fault. By the way - the three caps in your PSO are NP right?

Rick

The caps are 474 MKT. Resistors are .5W 1%. I've just run a scalpel around the perfboard to make sure there's no bridges.

Voltages with 5088s:

Ref voltage, 18V using a 317T down to 11,9 V.

That voltage across pins 4 & 5, and across 9V/GND on the board.

Q1 :
C  11,1V
B  11,2V
E  11,7V

Q2
C  11,7V
B  11,6V
E  11,1V

(    hmmm...)

Out if interest, V at lug 2 of depth is 10,6.

Turning the rate down and listening closely, it may be that the effect is running too quickly (However, I wouldn't rule out wishful thinking or the power of suggestion.) I don't have a scope here.

I may go off to the breadboard and knock up one with the LED to see if there is any action happening... Any other directions I can check out?

Cheers, DD

[frequencycentral]

Definately a short somewhere - the emitter of Q1 connects to earth, so it shouldn't read 11.7v.

You need to have a poke about.........

I can't post readings until the other end of the day. I'll also give you a quick way to connect a temporary rate LED just for a visual sign of life.

Later!

[Jimmy-H]

Hi There,

I don't think it's a short!
Rather a bad connection.
Because it's what you said Rick: Q1 can't be 12 volt, because it's connected to ground.
So there's a bad connection to ground.

[frequencycentral]

OK. Pretty hard to get voltages from an oscillating oscillator!

This first set were taken with the PSO oscillating, but with the depth control removed. I still have the original PSO in a little corner of my breadboard right now. The blank values are because they are changing as the PSO oscillates.

Q1

E: 0.032
B:
C:

Q2

E:
B:
C:11.92


This second set of voltages were taken with the depth pot removed and the speed pot removed to stop the oscillating. Probably more meaningful.

Q1

E: 0.032
B: 0.657
C: 5.54

Q2

E: 4.96
B: 5.53
C: 11.92

I hope this helps. I suggest you remove the speed and depth pots and check the voltages against mine, just work with the PSO part of the circuit, thats where your problem is.  All your voltages appear to suggest that you have a serious short circuit to the positive power rail somewhere.

You can get a visual check on oscillation by inserting a red LED between Q2's collector and +ve. It will flash a little weakly though. You should remove it before you complete your build, as it will cause ticking otherwise.

The way I go from breadboard-to-build is to draw a schematic which I then build from, with no reference to the breadboard, so I'm the first person to beta test and verify the schematic.

I have removed the 4148, and while I understand that was there for the LED, there is no evidence of any LFO ticking.

The 1N4148 is nothing to do with the (now defunct) rate LED circuit. I put it there to cut the PSO bleeding into the audio path.

Good luck, and please report back!

Rick

[frequencycentral]

<blockquote><removed by request></blockquote>


You could compensate for the gain loss by using a 3pdt switch.

One pole selects the PSO or earth to the second triode's cathode.

One pole increases the plate resistor to the second triode from 100k to 220k when the tremolo is switched in. Probably better to do it the other way around though, have a 220k at the plate, and when the tremolo is switched out the plate resistor is decreased by paralleling another 220k with the one already there.

One pole for a status LED!

Hope that makes sense!

[kurtlives]

I was thinking of using a DPDT.

One side selects normal trem circuit the other shunts the second triode's cathode to ground.

The other side of the switch for LED.

[Br4d13y]

yy! just got some vero and transistors and ordered the 6111! vibracaster you are goin' doin!

[Br4d13y]

yy! just got some vero and transistors and ordered the 6111! vibracaster you are goin' doin!

oops. forgot the "a"   i meant yay.

[SirElwood]

<removed by request>

[DiamondDog]

OK. Pretty hard to get voltages from an oscillating oscillator!

I hope this helps. I suggest you remove the speed and depth pots and check the voltages against mine, just work with the PSO part of the circuit, thats where your problem is.  All your voltages appear to suggest that you have a serious short circuit to the positive power rail somewhere.

You can get a visual check on oscillation by inserting a red LED between Q2's collector and +ve. It will flash a little weakly though. You should remove it before you complete your build, as it will cause ticking otherwise.

The way I go from breadboard-to-build is to draw a schematic which I then build from, with no reference to the breadboard, so I'm the first person to beta test and verify the schematic.

I have removed the 4148, and while I understand that was there for the LED, there is no evidence of any LFO ticking.

The 1N4148 is nothing to do with the (now defunct) rate LED circuit. I put it there to cut the PSO bleeding into the audio path.

Good luck, and please report back!

Rick

PSO bleeding would give a tick, no???

I'll get back to this later; I have to go into rehersals now for the silly season in OZ (ie Summer, beaches, parties, etc.) , so I'll be unable to do any serious soldering until the middle of February. Back to the The Tone God's Bullitt for now!

Good luck- you've done a great job on these circuits! I appreciate your work!

Cheers,

DD.

[frequencycentral]

PSO bleeding would give a tick, no???

I'll get back to this later; I have to go into rehersals now for the silly season in OZ (ie Summer, beaches, parties, etc.) , so I'll be unable to do any serious soldering until the middle of February. Back to the The Tone God's Bullitt for now!

Good luck- you've done a great job on these circuits! I appreciate your work!

Cheers,

DD.

Correct, PSO bleeding would give a tick, so in you case it would be good as it would confirm the PSO is running. Shame that you have to wait so long to debug - that would do my head in! If I have an effect that need debugging I simply can't sleep until it's done!

Tone God's Bullitt was very inspirational to me re. tube tremolos.

Enjoy the beach and parties while I freeze my ass of through another British winter! 

[frequencycentral]

Quote from: SirElwood on September 24, 2008, 05:14:21 A<removed by request>

[kurtlives]

Just finished up the boost/overdrive section of the Valvecaster and it is working perfectly. Haven't wired the oscillator in yet and tested it. Hopefully I can get to that tomorrow night. That will be the real test, see if my vero part of the oscillator is correct.

I did find that a bypass cap on the first triode's cathode (gain pot) can increase the gain quite nicely and add more "bam" all around. Might be neat to have a little toggle switch for some added gain. I used a 47mF btw, just boosts all frequencies.

Ill probably incorporate the bypass cap switching into the tremolo/overdrive switch. Probably not a good idea to have a overly distorted tremolo.

[frequencycentral]

Just finished up the boost/overdrive section of the Valvecaster and it is working perfectly. Haven't wired the oscillator in yet and tested it. Hopefully I can get to that tomorrow night. That will be the real test, see if my vero part of the oscillator is correct.

I did find that a bypass cap on the first triode's cathode (gain pot) can increase the gain quite nicely and add more "bam" all around. Might be neat to have a little toggle switch for some added gain. I used a 47mF btw, just boosts all frequencies.

Ill probably incorporate the bypass cap switching into the tremolo/overdrive switch. Probably not a good idea to have a overly distorted tremolo.

Good work Chris!

Distorted tremolo can sound great - I built my Vibracaster as a tremolo only. I've been overdriving it with my Red Star Drive set to clean boost, sounds great!

Don't forget the new cap next to the Depth control.

[kurtlives]

Just finished up the boost/overdrive section of the Valvecaster and it is working perfectly. Haven't wired the oscillator in yet and tested it. Hopefully I can get to that tomorrow night. That will be the real test, see if my vero part of the oscillator is correct.

I did find that a bypass cap on the first triode's cathode (gain pot) can increase the gain quite nicely and add more "bam" all around. Might be neat to have a little toggle switch for some added gain. I used a 47mF btw, just boosts all frequencies.

Ill probably incorporate the bypass cap switching into the tremolo/overdrive switch. Probably not a good idea to have a overly distorted tremolo.

Good work Chris!

Distorted tremolo can sound great - I built my Vibracaster as a tremolo only. I've been overdriving it with my Red Star Drive set to clean boost, sounds great!

Don't forget the new cap next to the Depth control.

Pulled out that 3.3mF cap from my bin and put it in the enclosure to remind me

Where did you learn about oscillators btw?