OnkartGromt - Grombass v1  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
Post Reply
User avatar
wayshot
Information
Posts: 2
Joined: 04 Jan 2016, 07:10
Location: Skage, Norway
Been thanked: 7 times

Post by wayshot »

First post from this long time lurker. I've had this bass distortion pedal for many years, but I still haven't seen anyone checking out its circuit, so I decided to try. It's handmade in Norway by the small pedal builder OnkartGromt. Info: https://onkartgromt.no/bass/index.php/product/grombass/

Getting the PCB out of the enclosure was quite a challenge, at least without de-soldering the DC input and the two mini-switches. But I wrestled it out and took decent pictures of both sides. Figured out the circuit, whose design is far from a typical TS clone:
There's one NE5532 and one 2N5088. The first 5532 stage is the input buffer, feeding the other 5532 stage whose gain is adjusted with the "Turbo" control. The 2N5088 is the last stage, with the selectable clipping diodes in its feedback loop. There's one capacitor in series with each diode pair to keep the bass frequencies undistorted. The "Gear" control sets the amount of bass frequencies by adjusting the collector voltage, measured between 8.3 V (min) and 0.9 V (max). The output of the 2N5088 feeds the volume control.

Will post a readable schematic later, stay tuned. Here's a few pictures:

20220525_182852.jpg
PCBtopp.jpg
PCBbunn.jpg
Last edited by wayshot on 26 May 2022, 11:14, edited 2 times in total.

User avatar
wayshot
Information
Posts: 2
Joined: 04 Jan 2016, 07:10
Location: Skage, Norway
Been thanked: 7 times

Post by wayshot »

Here's the schematic, hopefully without major errors. I've left out the in/out jacks and stomp switch, as it's a typical true bypass system. The alternate control names on the schematic are from the domestic "Nynorsk" version of the pedal.

EDIT @May 27th: Updated schematic, corrected HiCut switch circuit.

v1.02
v1.02

Post Reply