Repair Room #11: Korg Poly 800 Tune-Up

Today, I received a Korg Poly 800 that much less than pitch perfect. This unit was almost a whole step out of tune! So in this post, I go over a tune-up procedure for tuning the Korg Poly 800 to the correct center pitch.

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The Korg Poly 800

Since it’s release in 1983, the Korg Poly 800 has made a name for itself. Having been used by the likes of Depeche Mode and Duran Duran, it’s a true 80s classic synthesizer.

There are a few interesting modifications that apply to the Poly 800, including:

• the addition of Cutoff and Resonance knobs
• a switch for 12dB/24dB Filter Response (as opposed to the default 24dB filter)
• a CV (Control Voltage) input for the VCF
• a hardware/software upgrade (HAWK-800 kits)
• and many more!

The Poly 800 Tune Slider

The Poly 800 sports a “Tune” slider whose principle function is to shift the entire pitch range of the synth. In the center position the normally expected pitch of each key is heard. When shifting the slider to the right the global pitch of the synth is sharpened. Shifting to the left flattens the pitch.

Repairing the Korg Poly 800

The problem with this particular unit is that the entire pitch range has been shifted down a step when the Tune slider is set to the center position. For example, when playing a C note, you hear a Bb.

A quick internet search revealed a post on vintagesynth.com’s forum stating that trimpot “VR1” adjusts the DCO (Digitally-Controlled Oscillator) Pitch. Here’s the original contribution from a user named ‘meatballfulton’:

Here is a list of the [P 800] trimpots and what they do. VR2 and VR5 are the ones replaced in the “Moog Slayer” modification.

VR1 – DCO Pitch adjust
VR2 – VCF Frequency adjust
VR3 – White Noise level adjust
VR4 – DCO Fine Tune adjust
VR5 – VCF Resonance Adjust

Anyway, if all patches are out of tune, VR1 and VR4 are the ones to adjust. Center the tuning control on the front panel before adjusting these.

– meatballfulton of Vintage Synth Forum (August 5th, 2008)

Korg Poly 800 Tuning Procedure

The tuning procedure described by meatballfulton works. The photo below shows the location of VR1 at the top-left of the board.

Firstly, choose a key to base the rest of the tuning off of (I chose the “C” key). Then, get a tuner out (or use a tuner app on your phone). Connect the output to an amplifier, and play the C key. Adjust VR1 until the tuner reads “C”.

Alternatively, if VR1 swings too much to achieve an accurate tuning, you can find and use the fine-tune adjustment trimpot (VR4).

Meet the Author:

Hi, I’m Dominic. By day, I’m an engineer. By night, I repair and modify guitar effects! Since 2017, I’ve been independently modifying and repairing guitar effects and audio equipment under Mimmotronics Effects in Western New York. After coming out with a series of guitar effects development boards, I decided the next step is to support that community through content on what I’ve learned through the years. Writing about electronics gives me great joy, particularly because I love seeing what others do with the knowledge they gain about guitar effects and audio circuits. Feel free to reach out using the contact form!

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Spotlight

This fix was done for Buffalo-native group Seafox. Check out their album ‘Eulogy of the Angels’, available on various platforms.

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