FVerb - a simple reverb/modulation pedal

[gcwills]

Hi all,

The motivation for this project started some time ago when I heard a Blackstar amp equipped with reverb. The reverb was generated by a Spin FV-1 DSP IC and I was very impressed with how good it sounded.

Some research followed including the good work by Ice 9 and others here. However I was not too keen to have to program an external EPROM and there didn't seem to be much out there in the way of a really simple diy implementation of a FV1. I started wondering how simple a basic pedal could be using the internal ROM programs with minimal extra circuitry.

So after quite an amount of digging around and prototyping, I came up with this design which is about as simple as a FV1 pedal could be. It was developed with the hope that it will inspire those who have built basic PT2399 pedals to have a go - it uses less components than a Rebote for much more functionality. The simplest incarnation offers hall reverb, tremolo, pitch shift and vibrato and sounds great!

It is also easy to build, using a perfboard rather than a custom pcb.

More constructional information to come!

[Ice-9]

Very nice idea gcwills, I look forward to your postings. 

[Kipper4]

Welcome and me too I look forward to your posts.

[printer2]

Any good place to buy the chip?

[pinkjimiphoton]

brewing popcorn and awaiting updates!!!

[Ice-9]

Any good place to buy the chip?

If your in the UK or Europe then profusionplc is the place to buy the FV-1
In the USA It is Experimental Noize

[deadastronaut]

beer n whiskey ready...

[MetalGuy]

If your in the UK or Europe then profusionplc is the place to buy the FV-1

Banzai also has them.

[gcwills]

Thanks for the interest in my FVerb.

Here is the schematic - click on it to enlarge



As you can see it is a minimal implementation of a FV-1 with not much more than the FV-1 and a TL072 as input buffer and dry/wet mixer.
Some economies have also been taken with only two controls - one for the FV-1 which bridges the POT0 and POT1 inputs in a similar arrangement to the EHX Holy Stain. This allows for adjusting reverb decay, tremolo speed, pitch bend and vibrato with one control. The POT2 input is pulled high to maximise the tremolo and vibrato depth. The second control adjusts the amount of wet signal in the mix. Adjusting this control also adjusts the amount of tremolo and vibrato.

To keep things simple, a SPDT centre off switch is used to switch between the internal ROM programs. I initially used a BCD switch to select all 7 programs, but found that of these 7 programs the two reverb and two pitch modes are quite similar. Also I found that the two remaining chorus and flange modes can be approximated when the pitch mode is set close to unison to create a pretty lush chorus/vibrato mode which I preferred to the chorus or flange modes. This meant that a simple mini centre off toggle switch could be used to select between hall reverb, tremolo, pitch shift and vibrato/chorus. The toggle switch was also much easier to use in operation.

A simple buffered bypass is used which works well, simplifies wiring and uses a cheap SPST switch.

To come are some comments and photos of the pedal internals and on parts availability

[gcwills]

Moving on to building the FVerb.

Perhaps one reason that the FV-1 is not used in diy as much as say a PT2399 is that it is housed in a 28 pin SMD package which is difficult to use in a conventional through hole perf or vero board.
To get around this, I used a pcb adapter which converts the SOIC package to a conventional 28 pin DIL arrangement. The FV-1 can be soldered fairly easily to the adapter with a fine soldering tip and if you happen to bridge adjacent pins during soldering, the excess solder can be removed with solder wick.

Here is a photo of the adapter pcb - AU$1 including post from ebay



By the way, thanks to Ice-9 and MetalGuy for the heads up on sourcing the FV-1 - you can also buy them from Aliexpress.

[smallbearelec]

For U.S. builders, I have the chip, with or without the crystal:

http://smallbear-electronics.mybigcommerce.com/spin-semi-fv-1-with-crystal/
http://smallbear-electronics.mybigcommerce.com/ic-spin-semi-fv-1/

SOIC-To-DIP adapters are here:

http://smallbear-electronics.mybigcommerce.com/soic-to-dip-adapters/

I would be interested in seeing this built in a Bare Box#1

http://smallbear-electronics.mybigcommerce.com/the-bare-box-1/

preferably with a rotary encoder for the program switching. Maybe this one:

http://smallbear-electronics.mybigcommerce.com/rotary-encoder/

It's Alpha RE111F-41B3-15K-20P

[Kipper4]

I'm intrested. Got any demo's ?

[Mark Hammer]

Rich, it is difficult to list, in complete fashion, the number of pedals that use the FV-1 for reverb.

A quick peek at the datasheet/appnote for the FV-1 shows the many ways that the basic FVerb circuit could be appended to, in order to provide varying degrees of additional control.  For instance a single toggle and one additional pot would add more effects and control over an additional parameter.

[POTL]

Subscribe
It's interesting to look at the codes =)

[Kipper4]

Ok I'm gonna be cheeky and ask for the more involved version please.

I'm still not certain if it would need just an ordinary multi pole switch or an "encoded" switch.
Or much about it at all.

I've only ever done one FV1 build. Slackers awesome reverb. It has an eprom and a series or pots.



I have no wish to start programing yet.
That's why I liked the idea. It would be a shame to miss out on half the functionality of the chip by omitting a few switchs and pots maybe.

What is it going to take to access the other effects and parameters ?

[Mark Hammer]

Look at the datasheet.  There are three program-select pins, that can be controlled via a dipswitch or a couple of SPST toggles.  A rotary encoder is slicker, but is not essential unless one is pressed for panel space.  A DPDT centre-on type toggle could also provide 3 settings as a sort of compromise.

As shown in the schematic here (and thanks for that, BTW), one pot input is tied to 3V3, and one pot is used to feed 0-3V3 to the other two pot pins.  Just cut the line from the existing pot wiper to Pot 1, leave Pot 0 in place and install a second 50k pot whose wiper feed 0-3V3 to that pot pin.

[Kipper4]

I've read up a bit more. Thanks Mark.

[gcwills]

Here is an internal shot of the completed FVerb:



After the FV-1 has been soldered to the DIP28 adapter board, the adapter board was mounted on a 24 by 12 hole perf board. The adapter board is fixed to the perf board by soldering a loop of wire through pins 1 and 2 through the perf board and soldered there. Similarly a loop is soldered through pins 12 and 13 and then another loop through pins 24 and 25. This fixes the adapter board firmly to the perf board and allows for the other connections to be made to the FV-1.

There is not a lot more to the board - the TL072 and a 3.3V voltage regulator. I have been too lazy to generate a perf board layout, but perhaps some kind soul here may oblige

The FVerb was built into a standard 1590B with the two pots, mode switch and footswitch mounted on the front, the DC connector at the rear and input/output sockets at the side. I built the prototype initially with a 3 position DIP switch for program selection before the SPDT centre-off program selector switch was installed. This is not needed in a build.

I found that some care needs to be taken with grounding the controls and input and output sockets. I'll provide more details later, but suffice to say I was able to eliminate any extraneous noise with proper grounding.

More to come!

[robthequiet]

I'm in. So simple it almost calls for stacking two in a box with series/parallel option.

[gcwills]

Here is the parts list for the FVerb:

1 X Spin FV-1 IC
1 X TL072 IC
1 X 78L33 voltage regulator
1 X 1N4001 diode
1 X 32.768 KHz watch crystal
Resistors: all 1/4W
1 X 100 ohm
4 X 1K
2 X 6K8
2 X 10K
2 X 22K
3 X 33K
3 X 100K
1 X 470K
2 X 50KB pots
Capacitors:
1 X 15pf ceramic
1 X 1nf 100V
3 X 10nf 100V
1 X 47nf 100V
2 X 220nf 100V
3 X 1uf 25V
1 X 10uf 25V
1 X 47uf 25V
SPST push button switch
SPDT centre off mini toggle switch
DC connector
1590B diecast box
2 X 1/4" sockets
28 pin SOIC to DIP adapter pcb

Most parts can be sourced from the normal suppliers with the exception of the Spin FV-1 IC.
Earlier in this thread are listed some sources for the FV-1. I purchased mine from Aliexpress.
The 32.768 watch crystal can be sourced from ebay - eg http://www.ebay.com.au/itm/5PCS-32-768-KHz-32768HZ-Tuning-Fork-Watch-Crystal-12-5PF-3mm-x-8mm-/301924837830?hash=item464c1f69c6:g:-F8AAOSwa-dWlgWv