Development of the ODR-1

(by Kai Tachibana)

The idea

It must have been like this in the summer of 1992. We were in Spain to attend a meeting with our UK distributor, JHS. In addition, we visited a wholesaler / distributor in Barcelona to introduce our MS-8 MIDI Switcher. That was not successful. Time was pressing and something new had to come …

On the way back from Barcelona I got the idea to develop also effects pedals. First, there should only be four pedals:

  1. Preamplifier (preamp)
  2. AB switcher
  3. Distortion
  4. Overdrive

To name the devices, I forgave shortcuts. For example, PRE-1 for the preamp / booster. For the overdrive I chose “ODR-1” because OD‑1 was already assigned by Boss.

From left to right: First ODR-1 prototype (late 1992), second prototype (early 1993), First Production Run (March 1993), new case color (silver) – as well as “Natural Overdrive”, far right: A newer version – again in green!

The Concept of the ODR-1

Of course, there were already overdrives from other companies. Especially the tubescreamer of Ibanez was very popular both then and today. Even then I did not like with all the usual overdrives that they had a more or less strong middle hump. At that time I had tested an old Fender Bassman Top (Blackface) with matching 2×12 box. He only managed a mere 40 watts of power, but had a great bluesy sound. He reacted very well to the volume pot of my guitar. I liked that with increasing volume, the tube-overdrive slowly, evenly and continuously increased and now it comes: The basic character of the guitar barely changed.

I wanted to achieve that in the ODR-1! It was followed by weeks, months of intense development, which ultimately produced the ODR-1.


Functionality

Input

For (almost) all effect pedals, I used a JFet circuit as an impedance converter at the input of the circuit. Unlike some other manufacturers, I put a lot of emphasis on a version without an input capacitor, just like typical tube amplifiers. I could also have taken the high-impedance plus input of the first opamp – just like many other companies did for cost reasons. But after long tests the ear decided in favor of the JFet and in spite of the additional expenditure of material and assembly work I stayed with it.

Input Filter

This was followed by a filter to cut off low and high frequencies. In my experience, the subsequent overdrive stage should be fed with less bass (too much bass produces a mellow mud sound!) And less highs (too much highs produce louder, shrieking sound). Incidentally, the cut-off frequencies are reconstructed in the last filter to preserve the basic character as much as possible. That was the goal!

Block diagram

ODR-1 Blockdiagram

Overdrive

This is a combined version with two anti-parallel diodes (Section 1) across the opamp and two diodes (Section 2) at the output. That was new until then, so nobody had done it before me – to my knowledge. The goal was to achieve a uniform overdrive. Unfortunately, many other overdrives have had the uncomfortable way of creating strange and inharmonic sounds in the transition from “just clean” to “using overdrive”. But with my circuit, the smooth transition went well! The result: With the Volume knob on the guitar, the overdrive can be regulated very musicianary.

The output of the overdrive section was followed by some low-pass filters that avoided the otherwise typical “screaming” sound. So create the warm overdrive sound.

 

Sound control “Spectrum”

Many common overdrives used a simple adjustable filter for the high frequencies. It was called “Tone” or “Treble” and actually only reduced the high frequencies that were added by the overdrive electronics. At that time I always called it “Dull Control”. It never sounded so good to me.

After many sound tests I developed the until then, and I still believe, unique double filter control, which I called “Spectrum”. Not only the usual heights are raised or lowered, but also the the lower mids (~300 Hz).

Spectrum Min-Max

For this I used an extra “gyrator” circuit, which can be regulated with the Spectrum control parallel to the height filter. Again a lot of effort for a better sound! In the first tests it turned out that the regulation between neutral (center position of the controller) and left stop (0) acted too strongly. That did not sound so good. As a result, I added even more filters that produced a useful midrange sound in these positions (left to mid). Finally, I can say that in “all” positions of the Spectrum control really good and usable sounds are possible.


Output

As mentioned in the beginning, after the overdrive circuit, a filter had to be created, which restored the previously taken away frequencies. This was done with its own OpAmp level. Then follows a simple impedance converter, also with its own Opamp, realized.

Bypass / Remote Bypass

For effect on / off I used the then usual JFET circuit. This is dimensioned so that the switch rather on/off regulates (fades) than switches. This ensures a crack-free switching! Unfortunately, the signal loses a little bit of level.

A novelty at that time was the extra socket “Remote”. This allowed the ODR to be switched on or off by means of an external momentary button or e.g. switcher. Well, that was no wonder, as we had already built the MS-8 MIDI Switcher before and the effect pedals could be switched with it!

The green case

A Tubescreamer copy??

What annoys me even today: Some testers on the Internet believed that it is a copy of Tubescreamer because of the green housing. Anyone who has read the above comments will have noticed that the ODR-1 is a complete in-house development. It speaks against the testers, of course, if the latest at the “sound comparison” still not recognized.

The design over the years

The funniest rumors are always circulating on the internet. Here I can make it clear that the ODR-1 is basically still built today, since 1993.

Here is a list of minor changes.

1) Input buffer JFET “BC264D”

Unfortunately, the production of the JFet was discontinued in the late 1990s. In particular, this was hard to come by in Korea, where the ODR-1 was built at that time. As replacement came the “BF245C”. Meanwhile, this JFet does not exist anymore. Instead, then came a “BF256B” used. Sonically, there will be no one who can hear the differences. Even metrologically, there is no difference. The JFet works without amplification as a pure impedance converter, as even series variations hardly give a significant difference in sound.

2) Opamp “4558S”

The production of this component was discontinued at some point. This is a 9-pin opamp with the pins in a row (SIL: Single In-Line), and it does not matter how it is built in during production. I hoped for a lower error rate in the production! It was exchanged for the 8-pin version (2×4 pins) of the same type and manufacturer (Samsung®). Unfortunately, that’s the only reason why I had to develop a new board. I did not want to take the then usual 4558D from JRC. This guy, though cheap, had produced very quiet audible noise in our tests, similar to a faraway patter. So again I chose the better dual opamp from Samsung. I also thought that sounds a bit softer.

As a result, the chip system from Samsung has been sold several times. As far as I remember it was first a Fairchild product, later a KIA chip. Or vice versa … Ultimately, however, it was always the identical Opamps.

3) The serial error “Level & Drive control reversed”

Ouch! Yes, the former manufacturer (MUSE) from Korea reversed the two potentiometers. At the level you could not really notice the difference. Worse, however, was the fact that with the Drive control no proper overdrive could be adjusted. The ODR-1 had become a forced lo-gainer. According to information from Korea, only a few (50-100?) Devices were affected. In which year that was exactly, but unfortunately I can not say more. I remember that most of them got into the US delivery. Changing the two potentiometers fixed the error.

Korea: Production-Line from the former manufacturer Muse. Here is the production of the midi foot controller.


4a) The lost battery cover

Unfortunately, it was more and more common that we had to ship the battery compartment cover as a spare part. This was because the U-shaped lid was completely separated from the case and thus easily lost. The remedy was an update of the battery cover with joint, which now anchored on the right side in the former detent. The ingenious thing was (by the way Bernhard’s idea!) That the aluminum housing did not have to be changed. Lost lids were then always (usually free) with the new “captive” version replaced.

4b) The clamped battery compartment

I’m not sure, but I think the 9V batteries have gotten a bit thicker over the years. At least the housing and the battery compartment of the first ODR-1 version had to be modified, because the batteries were stuck when they were inserted with the clip to the left. The battery compartment could still be closed – after that it just did not work anymore. With some skill and a thin ruler you could, after disassembling the device, push back from below the hook from the battery lid to open it again!


The final conclusion

Basically, nothing has changed in the electronic circuit. New ODR-1 sound like old. Slight differences in the sound come from the tolerances of the components – even within a production!

Soon there will be no more wired components. I assume that I will soon be able to design a new version of SMD components for Nobels. Incidentally, the new SMD components are often much better than the “old” THP components (THP: through hole parts). These are e.g. installed in the new Nobels ODR-mini developed by me!