reverb help

DDR4LYF

I am building a spring reverb with a spring tank that can get built into a pedal board. I bought a spring tank and found a circuit call the stage centre reverb. I built the reverb and now it mostly does what it's supposed to, but there is a crazy ringing sound that is being created over the sound of the guitar and reverb. It uses a charge pump to get the +9V and the -9V. Could that be the culprit? The reverb sound is a very saturated sound, which makes me feel like it is driving the springs a bit hard and so there is this awesome thick wash of reverb under the horrible ringing whine that is coming out. Cool, but there has to be a more subtle setting as well, I think. I suspect that the ringing and 'over-driven' sound might be related, but I don't really know. I also have the wrong pots on, which will get changed soon. I don't think they would do any damage, but again, I'm just a circuit copier at the moment. I get the concepts, but can't do any real calculations... Any help would be so much appreciated!!!

schematic

my circuit

Up close top left is the charge pump and at the bottom is the reverb circuit. The charge pump chip is not the exact one specified, but has the same outputs and leg names, is there something I have to be aware of with swapping chips?

As for the tank, the input impedance is 310 ohm output impedance is 2575 ohm
Input insulated, output grounded.

Not sure if anyone can tell anything from the pictures, but any advice on what to check would also be appreciated.

Attila

ahh the Stage Centre reverb

I looked at exactly the same circuit, without having it in front of me it would be difficult to fault find

Did you try run it without the charge pump, thereby trying to segmenting fault a bit.

Johnny-B

Hi, I've built many effects circuit, including reverbs, but not with a tank. I would suggest that you check the simple things first, like, does the bypass switch work i.e. do you get clean signal through on bypass? Does the LED switch on and off? Is the power supply providing clean +/- 9V dc with little or no a.c.? Secondly, check all your component values to see that you have the right values in the right places. Use a meter to check the resistor values. Check electrolytic capacitor and diode polarities. Thirdly, check your strip board layout. Have you completely separated the two circuits - charge pump and reverb by cutting tracks? Check how many nodes are there in the circuit diagram and how many isolated connections are there on the strip board? Are you sure that you have no solder bridges on the strip board? Perhaps it would help if you posted a circuit diagram, a pic of the reverse side of the strip board and a diagram of your strip board layout. If the pot values are incorrect, what value pots are you using?
If none of these finds the problem, I am in Sunninghill and have a signal generator and oscilloscope so we can check the signal path using a simple sine wave.

AlanRatcliffe

I can't help with the circuit fault-finding, but on the ringing - have you got the chamber isolated from vibration? If it's simply lying on top of the amp, it might just be picking up some acoustic vibration and feeding back.

DDR4LYF

Johnny B wrote: Hi, I've built many effects circuit, including reverbs, but not with a tank. I would suggest that you check the simple things first, like, does the bypass switch work i.e. do you get clean signal through on bypass? Does the LED switch on and off? Is the power supply providing clean +/- 9V dc with little or no a.c.? Secondly, check all your component values to see that you have the right values in the right places. Use a meter to check the resistor values. Check electrolytic capacitor and diode polarities. Thirdly, check your strip board layout. Have you completely separated the two circuits - charge pump and reverb by cutting tracks? Check how many nodes are there in the circuit diagram and how many isolated connections are there on the strip board? Are you sure that you have no solder bridges on the strip board? Perhaps it would help if you posted a circuit diagram, a pic of the reverse side of the strip board and a diagram of your strip board layout. If the pot values are incorrect, what value pots are you using?

How does one check if the power has no ac component?

I am using 10k pots instead of the recommended 50k.
I have poured over the circuit making sure the I transferred every connection from the pcb layout to the vero board, so I am quite sure there is no missing connection.
I have checked most of those things, I will check again.

Johnny B wrote: If none of these finds the problem, I am in Sunninghill and have a signal generator and oscilloscope so we can check the signal path using a simple sine wave.

I may take you up on that!!!

Attila Barath wrote: ahh the Stage Centre reverb

I looked at exactly the same circuit, without having it in front of me it would be difficult to fault find

Did you try run it without the charge pump, thereby trying to segmenting fault a bit.

I will try again with the two batteries method that the original one had.

Alan Ratcliffe wrote: I can't help with the circuit fault-finding, but on the ringing - have you got the chamber isolated from vibration? If it's simply lying on top of the amp, it might just be picking up some acoustic vibration and feeding back.

It is definitely not from amp hum or outside feedback, I moved the tank and circuit around to make sure!

I'll take a few more informative pictures and post them up soon!

Johnny-B

DDR4LYF wrote:
Johnny B wrote: Hi, I've built many effects circuit, including reverbs, but not with a tank. I would suggest that you check the simple things first, like, does the bypass switch work i.e. do you get clean signal through on bypass? Does the LED switch on and off? Is the power supply providing clean +/- 9V dc with little or no a.c.? Secondly, check all your component values to see that you have the right values in the right places. Use a meter to check the resistor values. Check electrolytic capacitor and diode polarities. Thirdly, check your strip board layout. Have you completely separated the two circuits - charge pump and reverb by cutting tracks? Check how many nodes are there in the circuit diagram and how many isolated connections are there on the strip board? Are you sure that you have no solder bridges on the strip board? Perhaps it would help if you posted a circuit diagram, a pic of the reverse side of the strip board and a diagram of your strip board layout. If the pot values are incorrect, what value pots are you using?
How does one check if the power has no ac component?

I am using 10k pots instead of the recommended 50k.
I have poured over the circuit making sure the I transferred every connection from the pcb layout to the vero board, so I am quite sure there is no missing connection.

To check if the power has no ac component, use a multimeter set to ac voltage.
Have you also checked that you have no shorts on the strip board and that you have cut the copper right through where you needed to isolate the nodes on the copper tracks? You sometimes need a magnifying glass to see this but you can check for a short with the multimeter set to ohms.

DDR4LYF

Johnny B wrote:
To check if the power has no ac component, use a multimeter set to ac voltage.
Have you also checked that you have no shorts on the strip board and that you have cut the copper right through where you needed to isolate the nodes on the copper tracks? You sometimes need a magnifying glass to see this but you can check for a short with the multimeter set to ohms.

My multimeter has a continuity test setting, so I used that to check all the copper strip cuts that were made. I will check them again with a magnifying glass! I also ran a knife through the original splits to ensure the tracks are separate. Let's hope I can get this worked out without too much trouble. Maybe if a threaten the circuit with strong words, it will get frightened and start working properly...

TomCat

A ring is likely to be related to a gain issue and the fact that the reverb tank seems to be driven hard may be an indications of the same issue.

Typically, the resistor in the feedback path of an op amp circuit sets the gain of the op amp. The use of the wrong value pot may be the cause of your problem.

Get the right pots in there and then see what happens.

DDR4LYF

Pots changed=> ring significantly reduced. Now testing power supply... I'll keep you all updated!

DDR4LYF

There is no AC component to the power going into the circuit. Now to test the circuit with battery power instead of the charge pump... stay tuned! The DC is +8.3V and -8.3 V, not the full +-9V. Is that a bad thing?

DDR4LYF

Also, does anyone know how I can reapply the links to the pictures for future reference?

DDR4LYF

batteries not working, so I can't check the reverb without the charge pump.. troubling...

Johnny-B

DDR4LYF wrote: There is no AC component to the power going into the circuit. Now to test the circuit with battery power instead of the charge pump... stay tuned! The DC is +8.3V and -8.3 V, not the full +-9V. Is that a bad thing?

This could indicate that you are overloading the charge pump, perhaps due to a short, circuit error or an incorrect resistor value. Perhaps you should measure how much current the circuit is drawing and compare to the chip's specs.

Attila

Jump in your car and visit Johnny .......

Johnny-B

Attila Barath wrote: Jump in your car and visit Johnny .......

Sean, we can arrange something for Saturday if you wish. I've taken a look at the circuit and it's not that complicated. There are 4 op amp stages. The first is an input buffer. The second is a gain stage before the tank. The third amplifies the output of the tank. The wet and dry signals are then mixed and fed through the output buffer gain stage. You could try disconnecting the tank, shorting the input back to the circuit to ground and seeing if you get good clean signal.

Johnny-B

DDR4LYF wrote: There is no AC component to the power going into the circuit. Now to test the circuit with battery power instead of the charge pump... stay tuned! The DC is +8.3V and -8.3 V, not the full +-9V. Is that a bad thing?

Sean, if you are measuring 8.3V at the power to the op amps then this is correct because the charge pump produces +/-9V but the diode in the supply line will drop 0.7V.

Johnny-B

Sean, I've just been checking out the datasheet for the MAX1044 and there is something I've found that could be your problem. Please check that pin 1 on the MAX1044 is connected to pin 8. The boost pin, pin 1, when connected to the +9V, pin 8, increases the oscillator frequency of the charge pump by a factor of 6. Without pin 1 connected, the oscillator will run between 5kHz and 10kHz which is in the audible frequency range. With pin 1 connected, the oscillator will run between 30kHz and 60kHz which is beyond audible range.

Johnny-B

Johnny B wrote: Sean, I've just been checking out the datasheet for the MAX1044 and there is something I've found that could be your problem. Please check that pin 1 on the MAX1044 is connected to pin 8. The boost pin, pin 1, when connected to the +9V, pin 8, increases the oscillator frequency of the charge pump by a factor of 6. Without pin 1 connected, the oscillator will run between 5kHz and 10kHz which is in the audible frequency range. With pin 1 connected, the oscillator will run between 30kHz and 60kHz which is beyond audible range.

I don't know if anyone else is following this thread but it looks like Sean and I have found the problem. Sean has used a ICL7660 instead of the MAX1044 specified. They are almost identical chips but the MAX1044 has a 'Boost' feature which shifts the charge pump oscillator frequency beyond the audible range. The ICL7660 doesn't have this feature so what Sean is hearing is the frequency of the charge pump oscillator typically 10kHz. Sean is going to get the correct equivalent chip, an LTC1044 and try it out.

Attila

DDR4LYF

"Holy rusted metal Batman, the reverb works!"

The chip was wrong! I just got the new one today and it works! I don't have time to test it properly right now, but that will come in time!

Thanks so much to Attila Barath, TomCat, Alan Ratcliffe and especially Johnny B. I would never have figured this out myself! You guys rock!