FEMTOVERB /Wavefrontsemi/ PCB layout

[Peter Snowberg]

Well, the board etched beautifully with PnP.  It's fluxed and tinned, and awaiting drilling.

One of the last issues to deal with in using these DRE chips is the effects switching. RJ (another user here) and I came up with a neat way to switch effects as long as you don't need more than 12 of the 16 built-in algorithms.

The DRE has four lines for selecting the program in use. These lines are all pulled high internally by the DRE so without anything connected you get program 16 (or 1111 in binary). Selecting other programs involves pulling from one to four lines low to create a different binary number. The internal programs are arranged in such a way that an encoder that uses "Gray Code" will nicely switch between the options in a sensible sequence. Gray Code was an idea that made it easier to build multi-bit encoders, but the output  order is a long way from 1,2,3,4.  You can use a 4 bit binary encoder, but the effects order will seem like a jumble.

The really good news here is that a simple 12PST rotary switch can accomplish the task with the help of a bunch of diodes. First ground the common connection of the switch. Now from each of the 12 poles, you can connect a couple of diodes to represent the zeros for that selection.

Example:  Say you wanted to select program 6. In binary you represent the decimal number 6 as 0110. To generate this number for switch position 1, you would connect the 1st pole to the cathodes of two 1N914 diodes. Now connect the anode of one diode to the binary 8 input and connect the anode of the other to the binary 1 input of the DRE. The diodes allow the lines you want to be pulled to ground when the switch is in that position, but they don't interfere when the switch is in another position. This is nothing more than an emulation of a 12x4 bit ROM with mechanical addressing.  You can control the order of the effects, it's cheap, it uses easily available parts, and it's not too hard to select three programs to eliminate along with the "vocal cancel" karaoke program. The idea of a rotary speaker simulator with no LFO control is of limited utility too.

[MetalGuy]

The encoders listed on Femtoverb's schematic are back in stock at www.alliedelec.com !

http://www.alliedelec.com/Search/SearchResults.asp?SearchQuery=753-0115&Submit=find+it%21

[MetalGuy]

Here's a layout with component values:

[Mark Hammer]

Thanks!!  That's going to speed things up a lot.

[gaussmarkov]

i feel like a dolt for asking--everyone here seems to be in the loop--but is there a working link to a schem?  the original seems to be nonfunctional.  thanks, gm

edit:  faster than a speeding bullet--there's some of the info i wanted, two posts up. :-)  still a schem would be nice.

[Peter Snowberg]

If you look at the original Femto-Verb post (on this sub-forum) by DaveTV, you get a link to the schematic and more discussion.

http://dstockett.50megs.com/femtoverb.gif

[gaussmarkov]

If you look at the original Femto-Verb post (on this sub-forum) by DaveTV, you get a link to the schematic and more discussion.

http://dstockett.50megs.com/femtoverb.gif

yes, i tried that!    i don't get the image.  i get a "remote linking forbidden" image. 

[Peter Snowberg]

Hmmmm...

It works fine from here. I don't know.

I put a copy here:

http://img.photobucket.com/albums/v280/Snowberg/diy/femtoverb.gif

[gaussmarkov]

Hmmmm...

It works fine from here. I don't know.

I put a copy here:

http://img.photobucket.com/albums/v280/Snowberg/diy/femtoverb.gif

thanks!  it works at home, too.  must be something about my employer's setup. 

[Mark Hammer]

Pretty much all populated now, though no functionality yet.  That blasted 12mhz crystal is around here somewhere!!

A word of advice to first time SMD solderers.  Solder the Wavefront chips on before you start crowding them with the through hole components.  There are a number of passive components whose leads, no matter how neatly trimmed, make it diffcult to get your soldering tip in a position to flow the solder on the pad without providing dangerous heat levels to the chips.

And get yourself some x3.5 reading glasses from the bargain store.  Those pins and pads are small!!

[gaussmarkov]

has anyone scored the chips for this lately?  i wrote to wavefront sales but got no response.  i see in other posts that this has happened before.

[idiot savant]

has anyone scored the chips for this lately?  i wrote to wavefront sales but got no response.  i see in other posts that this has happened before.

yeah, they don't respond to e-mail that well.

I ended up calling, and got Randy Yorsten on the phone(really nice guy BTW). the next day I had my e-mail invoice.

I decided to get 2 full sets of chips since I'm going to try building the Axoris Miss Parker project, and they charged me for less than half of what I ordered.

nice folks!

[gaussmarkov]

has anyone scored the chips for this lately?  i wrote to wavefront sales but got no response.  i see in other posts that this has happened before.

yeah, they don't respond to e-mail that well.

I ended up calling, and got Randy Yorsten on the phone(really nice guy BTW). the next day I had my e-mail invoice.

I decided to get 2 full sets of chips since I'm going to try building the Axoris Miss Parker project, and they charged me for less than half of what I ordered.

nice folks!

excellent!  thanks for the feedback.  i will give them a ring tomorrow.  and thanks also for the axoris miss parker reference!

[MetalGuy]

It took me almost 3 weeks and couple of angry emails to get them finalize my order. Don't rely on emails - grab the phone and talk to them!

[Mark Hammer]

Well, I finally found the 12mhz crystal I had been searching for, stuck in the last few passive components, and finished up my board last night.  Wired it up, fired it up and.........nothing.  The clean analog side works just fine, but I'm not getting anything out of the digital side except for some digital noise.  I hope to goodness that isn't a sign of a blown chip, because this is not somethng I'm going to know how to troubleshoot.
I'm going to give the solder joints the once over today with good lighting and a magnifying glass.  The pads are so close together that the flux tends to bridge the gapsbetween solder pads, and the glint of the flux bridges makes it hard to see if there is solder in there too.

I waswishing I'd have sweet reverb to enjoy and good news to report, but not yet.

Incidentally, there is an extra op-amp stage in the layout that I didn't recall seeing any comment about in this thread.  As near as I can tell from the layout shown, it is simply a hiss-reducing LPF section to clean up the digital path a bit, right?  The other thing not made abundantly clear is that the two pads for "Vol" are the pads for the gain-setting feedback resistor in the output stage, whih can be a pot OR a fixed resistor.

[Peter Snowberg]

I see a missing and rather vital cap... There needs to be a small electrolytic (anything from 1uF up to 22uF, shoot for 10uF) connecting pin 12 of the DRE to ground. That cap provides the reset pulse to get things running so it's not surprising you still don't have sound. The good news there is that the pads required already exist, it's just a matter of adding the cap between the diode going to pin 12 and the ground jumper going to the 10uF next to it.

Once that one is installed if you still don't have sound, verify (with a scope or high impedance logic probe) that the wordclock is present on pin 9 of the DRE. That will tell you that the clocks are running. If you have clocks but no sound, next check for digital data on pin 16 of the DRE and then pin 1.

To check the analog input sections, you can audio probe right up to pins 1 and 2 of the AL1101 ADC. If you have signal and clocks so far, audio probe pins 1 and 2 of the AL1201 DAC. You should be able to get the wet signal from pin 1 of the NE5532 closest to the AL1201.

You're almost there! 

[gaussmarkov]

thanks for the progress report, Mark!  i've been listening for your reverb. 

Once that one is installed if you still don't have sound, verify (with a scope or high impedance logic probe) that the wordclock is present on pin 9 of the DRE. That will tell you that the clocks are running. If you have clocks but no sound, next check for digital data on pin 16 of the DRE and then pin 1.

argh!  my new dmm doesn't have a "high impedance logic probe."  are there any other dmm features that i need for digital stuff?

[Mark Hammer]

Thanks for that tip, Peter.  I'm hoping that's all it is.

Pins 15 and 16 of the AL1201 also seem to me to be just hanging there, and not tied to ground as they are in the Femtoverb schematic.  I linked them and ran a line to ground but perhaps there is some other deeper reason why those connections were not included in Metal Guy's layout?

[MetalGuy]

Hi,

Sorry to hear it didn't work from the first time. The preliminary layout was out long enough to be checked thoroughly and corrected. If anyone finds any other flaws please let me know so I can fix it.

Pins 15 and 16 of the AL1201 also seem to me to be just hanging there

My schematic /version 1.5/ shows they are not connected to anything. In a PM Peter suggested to put pads there - he can explain better why.

I see a missing and rather vital cap...

Actually the cap is there but is connected to  ground and +5V. Should be pin 12 and ground.
Below is a layout with the pin 12 cap fixed:

[Peter Snowberg]

High speed digital logic is beyond what a DMM wants to deal with but you can construct a very simple logic probe very easily.

Here is the recipe for a simple logic probe:

- Grab a 4049 or 4069 inverter. Power that from the same V+ as the circuit under test
- attach a 10M resistor from V+ to the input of one of the inverters. This is your input inverter.
- attach that inverter's output to the input of the next inverter and also to a RED LED with a 1K resistor to ground.
- attach the 2nd inverter's output to a similar red LED+1K to ground.

When there is no input, the 10M will pull that input high causing a low output on the 1st inverter and a high out on the 2nd one. The second LED will light and that shows the input is either open or connected to a high level input. If you touch the input to ground the 1st inverter will now output high and the 2nd one low, causing the 1st LED to light and the second one to go out.

If you touch the 1st inverter output to a clock, both LEDs will light up equally and both be dim.


Mark, do you mean pins 15 and 16 of the AL1101 or the AL1201? Neither chip should have anything connected directly to ground as that may let the blue smoke out. 15 & 16 of the AL1201 should float; they're outputs and as the built-in algorithms are stereo, they also output signal from the other input channel. The pads are there to allow for experiments in mixing the channels. The AL1101 has the 2nd input channel coupled to ground via a pair of 10uF caps to silence them. They're internally biased to 1/2Vdd and should not get grounded directly. There are a couple of extra pads on the utilized input channel to allow for the effective bridging of the used and unused inputs.