Aqua Boy with v3205 's

[gtr2]

My first post for tech help...    

Ok, I've got a fully functioning aquaboy up and running.

Info on the build
Double Delay board
BBD's v3205 's
No other modifications...yet  
Adjusted bias trims and clock by ear.
Mix, delay time (about 550ms max), and repeats all function properly

Problem
I believe I'm exceeding the headroom on the v3205's as the repeats are distorting (not clock noise).

EDIT: Solution
I'll save you from reading through the rest of this rubbish...  unless you want to   http://www.madbeanpedals.com/forum/index.php?topic=1553.0

Troubleshooting done so far
Pin 8 (VGG) on both v3205's has a voltage of 6.5 (operating range of bbd is 4-8)
With the repeats set to one repeat, signal probe shows increased volume level into pin 7 (as expected), then the repeat out of pin 3 and 4 has distortion.

I tried changing the value of r15 per a suggestion in a previous post.  I don't really see how this would help but it was worth a try.  No change.

It seems like the posts with this same problem on FSB and here were all with the v3205 bbd's with the double delay mod.  (I guess it must make the headroom problem more noticeable with the two chips)

I really couldn't find any more info on solutions to this problem only that others have had it.  I guess I could decrease the value for R19 to increase the input voltage closer to 8v, but I don't think that will increase the headroom enough.

So my question is: what's the best way to decrease the input volume to pin 7.  Change to a lower hfe transistor?  Change a resistor somewhere?

I read a gear page post on the headroom between different bbd's and the guy from Malekko said that the v3205's require a much more "balanced" circuit to have nice clean repeats.  They use it in the 616.

Thanks to anyone who read this whole post, I know it's long, but I'm not only trying to help myself but possibly others in the future.

josh

[madbean]

Admittedly, I have not done a dual delay v3205, so I haven't had to deal with this problem.

When you swapped R15, what value did you use?

The goal here is to bleed a little more signal to ground, so picking a low value for R15 will enable this to happen. A socket there and some experimentation might yield more positive results.

An increase in the Bias pot to 50k may further help this.

To raise the headroom, you could instead substitute a 7v or 8v regulator. I think I might have a 7v one. Or, you could use an 8.2v Zener in place of R19 which might be just enough to get it to operate in the correct range. I have some of those as well. I'd be happy to send the regulator and zener along to you.

Changing the preceding transistor will not have any noticeable effect since it's used as a buffer to make up signal lost from the filtering network.

[gtr2]

I used a 100kB pot to tweek the r15 spot.  I should have clarified.  It's still subbed in, so I may try tweeking it some more.   I'm gonna sleep on it for now...  Maybe I'll dream up something    I'll post any progress.  Thanks for offering to send those parts!  Hold on for now, I'm digging through some stuff on the v3205 scattered through the net.  I also want to dig a little more with the signal probe first.

josh

[slash555]

r15 is the key as i recall. i put 33k or 39k and it was alot better but not perfect. you need to rebias it after u change r15.
i didn't build or heard 3005 version but cool audio one is not working as it should. it still needs some work to clean those repeats. i build 2 and few friends bulit 4 or 5 and everyone have same problem - DISTORTED REPEATS.

i had just 1 bbd, not 2 as you do.

[gtr2]

Thanks slash!  I'll have to put my potentiometer around there and recalibrate.  It's worth a try.  I've also heard the output is "hotter" on the v3205's.  The distortion is not to bad with one repeat so I'm wondering if the repeats are distorting through the feedback loop, maybe when it passes through Q2.  I'll have to check this out when I get home today with a signal probe.

I really wanted to get some mn3005's but I was afraid of putting up the cash only to get fakes...  I wouldn't mind spending the money if I knew they were the real deal.  This is frustrating     I'm a delay junky and I really need to get this right.  I've got a fair share of analog bbd's, tape echo's (ep-4, re-201), and digital delays, so I've got a pretty good idea how much "grit" there should be and I'm not even close to acceptable at this point.

I've been looking for schematics of delays that use the v3205 like the 616 malekko with no luck.  I'm sure the aqua puss reissue had some tweaks done to accommodate the v3205 but there is no schematic out there for the reissue version either.

I'm gonna get this right one way or another.  This is such a great project and the board layout is incredible Bean!

Josh

[slash555]

no problem! if you find any improvements be sure to share with us
good luck

[gtr2]

Ok, here's where I'm at and what I've discovered to this point.

I switched to probing with a solid state amp instead of possibly overdriving the preamp tubes on my normal practice amp.

So with the feedback off (I pulled out R31 to eliminate any feedback, I socketed it when building to adjust the oscillation point)  I signal probed everything up to the v3205's, it was a nice boosted clean signal going into the v3205's, going out of the v3205's the initial input signal is distorting.  It sounds like it's running through a dirt pedal when I probe the output on the v3205.

While probing the output of the v3205 i started adjusting the 100kB pot I placed in the r15 spot.  What I found is I can eliminate about half of the distortion but not all of it.  When you turn the pot past this to less resistance it makes some warbling unbearable noise which ironically isn't distorted 

So long story short I feel I need to lower the input signal that's riding into the v3205's.  Where and how can I do this?

Thanks,

Josh

[madbean]

Hmmmm... okay. How about a voltage divider right a pin7 of IC3? You could pull C15, then put it back in with a 10k in series after the positive side. Then at pin7, you put another 10k to ground. This will cut the signal in half feeding into the BBD.

Probably the easiest way to go about this is to pull C15 and put in two temporary wires (or a socket) the test the voltage diver out on the breadboard.

[gtr2]

Thanks for the quick reply.  I'll check that out and report back tomorrow.

[gtr2]

I unsoldered C15 and inserted some leads connected to a breadboard for reinserting c15 and forming a voltage divider using two 10k resistors.

(Side note: the fabbed boards are much harder to unsolder than etched boards.  The solder really sucks down in those holes and forms a pretty bulletproof setup which is great until you need to get out the component.  )

It definitely cut down the signal to pin 7 of the v3205, but I think to much.  I was unable to bias the chip to get anything out the pin 3 output.  I only got squealing.

I'm going to try using a 10kB potentiometer as a variable voltage divider tonight to have a little more flexibility with the input signal strength.

Someone on one of the forums said the sweet spot for the v3205 is at 5v?  I might try changing the value of r19 as well to see what happens at 5v and at 8v.  Right now I'm sitting around 6.4v.

At this point I'm pretty much at the max of what little knowledge I've got with this stuff, we'll see what happens.

josh

[madbean]

You can alter the amount of voltage divide by offsetting the two values...which is pretty much what you will get with a trimpot.

The v3205 claims a wide range of operating voltages (4-8v) but I have my doubts about this. I got really good results at about 7v.

Don't give up! We'll get it there.

[gtr2]

I've been making some good use of my "extended lunch break" 

I may be on to something here...

I found that the one successful dual delay with the v3205's on fsb had used a different clock generator. 

So I looked at the V3102 data sheet (what I used) http://docs.google.com/viewer?url=http://www.coolaudio.com/docs/datasheet/V3102_DATASHEET.pdf&chrome=true

This data sheet says "Direct driving capability of up to 4096-stage BBD's" well I've got 2 4096-stage BBD's

The MN3101 clock driver data sheet says it is able to drive two MN3005's (equivalent to 8192 stages)
No problems I saw were ever reported with the DD mod not working for the mn3005's either and they used the mn3101.

I also found this from nelson on FSB:

Quote from: reverofratiug on March 20, 2008, 09:23:17 PM

I´d like to know if there´s any other way to reduce, or even stop the distortion on the coolaudio´s V3205. Am I doing something wrong?

And on more question. if is possible to use two 3205 on the AD3208 how can one 3102 chip ("Direct driving capability of up to 4096-stage BBD") drive two 3205 (4096-stages each)Huh

Nelson Replied:

The capacitance of the clock input of the 3205 filters and rounds off the clocking signal of the 3102. The way to avoid this is to buffer the clock signal with a CD4049, this will deliver a nice square clocking signal and reduce distortion. Also allowing you to drive more than 4096 stages with a single clock.

Take a look at the EHX Echoflanger schematic for an example of this.


This could explain why the single version of the v3205 is fine but problems arise with the double delay mods using the v3102 clock driver.

The problem may not be with the input signal level after all.  Where should I go from here?  Ive got a cd4049ube in stock but I don't know how to go about buffering the clock signal.  Or is there a suitable clock driver I can substitute in place of the V3102 that will drive both BBD's.

whew...I think that's all for now...

Josh

[slash555]

excellent progress! i'm anxiously waiting this to resolve i have prepared ddt boards but didn't use them because of annoying distortion. maybe it won't be just waisted time money after all

[gtr2]

I've been digging deep through old forum posts, strange and unusual places on the internet, and I've got piles of printed of schematics scattered through the house.  Hopefully we can figure this out.

Josh

[slash555]

i would gladly help but i don't have skill's, i'm just guitar player. i could verify/test progress