When embossing records, there are several technical considerations that can significantly impact your results. Here are some key insights I've gained through testing different equipment configurations and approaches.
Mono vs Stereo Considerations
While stereo content had been reported to be embossed, the results are rarely satisfactory. I personally don't think this is a limitation that can be overcome with better technique - there was a theory that the 'lean back' of the embossing stylus was 'wiping out' stereo content. I did try reversing audio, and embossing a record in reverse. A fun experiment, and it did seem to increase the stereo content, but ultimately it increased surface noise.
Why Mono Works Better
The issue comes down to head rigidity. Stereo cutting heads (using the standard 45/45 configuration) need to move in both vertical and lateral axes. This flexibility, while necessary for stereo, becomes a serious liability when embossing. The increased cutting weight typically causes coil misalignment, shifting the coils from where they should be in the transducer assembly and causing unpredictable results.
Moving iron mono cutting heads, generally have a more rigid assembly, with their armature held tightly in place, this tends to provide much more reliable results and the resulting audio has less effect from the blank surface itself.
Stylus Behavior and Performance
Important: Stylus Orientation Effects
Conical embossing styli can have 'good sides' and 'bad sides'. If you're on a bad side, you'll notice:
- Difficult groove tracking
- A noticeable drop in response around certain frequencies
The fix is straightforward - remove the stylus, rotate it 45-90 degrees, and test again with pink noise. I have noticed the drop I see at 6-7kHz tends to disappear once I have found the correct orientation.
Equipment Protection
Protecting Your Equipment
For protection, my amplifiers use 1A MCBs. These provide two types of protection:
- Quick magnetic trip for short circuits
- Thermal trip via bimetallic strip for sustained overcurrent
MCBs are particularly good for this as they provide clean breaks that won't affect the signal and react quickly. This protection is crucial when working with lower frequencies which require more current and could potentially damage your coils.
Signal Processing Options
ADAU1401 DSP Capabilities
While not a necessity, a DSP like the ADAU1401 can be valuable. It allows you to:
- Feed i2s digital audio from a Raspberry Pi Zero - considerably reducing noise
- Output to 4 channels with separate EQ's
- Implement independent volume controls
This setup provides additional flexibility and control over your audio processing chain, though it's not required for successful embossing.