I figured I'd give my impressions of JDS Labs Subjective 3 - a three band analog EQ housed in an enclosure similar to the O2 headphone amplifier. I listen to multiple sources that don't have EQ - so having an easy way to adjust the sound seemed like it was worth a try.
The nice thing with JDS Labs is they take care with product design and provide detailed specifications. They are also accessible, I had hoped to avoid an additional power cord and wall wart. Both their O2 and the Subjective 3 use 15VAC so I hoped to use one transformer. I emailed JDS and asked if it was possible to split the power between the two. John replied within 24 hours saying he had tried that, but it resulted in a 60Hz ground loop. So two transformers it is!
For those interested the following blog posts provide more information that I could hope to. The one caveat being he didn't say what he used to measure the device.
http://melp242.blogspot.com/2018/02/jds-labs-subjective3-tone-control.html
http://melp242.blogspot.com/2018/02/jds-labs-subjective3-part-2.html
His biggest complaint would be the channel imbalance the device creates. I don't have a great way to measure this, but gave it a shot. I used multimeter and 2kHz sine wave and found about a 0.006V increase in the channel imbalance with device in line and all the tone controls in their middle position from a 2V source. Subjectively, I can't hear any change in the channel balance fortunately.
The nice thing about the device is that it uses a relay. In the off position or if the device is unplugged it defaults to full bypass. So you can leave the device inline and fully defeat the tone controls.
My biggest gripe with the device is the gain. I should have remembered this from my 1980s hifi days of inserting 10 band equalizers into tape loops. JDS labs does mention it, but it is pretty well buried in the product page. The device provides around 15dB or so of gain. On an amplifier designed like the O2 that means that with a 2Vrms source you can overload the input. Fortunately my lower gain is 1X, so no issue. But other O2 owners may not be so fortunate. This also means that depending on my source and the amount of EQ applied my high gain of 3.5X may be unusable.
Despite the channel imbalance and the gain issues I'm happy with the device. It's quite satisfying to be able to adjust the sound with something physical and easy to access instead of digging through menus and fiddling with software EQ.
The nice thing with JDS Labs is they take care with product design and provide detailed specifications. They are also accessible, I had hoped to avoid an additional power cord and wall wart. Both their O2 and the Subjective 3 use 15VAC so I hoped to use one transformer. I emailed JDS and asked if it was possible to split the power between the two. John replied within 24 hours saying he had tried that, but it resulted in a 60Hz ground loop. So two transformers it is!
For those interested the following blog posts provide more information that I could hope to. The one caveat being he didn't say what he used to measure the device.
http://melp242.blogspot.com/2018/02/jds-labs-subjective3-tone-control.html
http://melp242.blogspot.com/2018/02/jds-labs-subjective3-part-2.html
His biggest complaint would be the channel imbalance the device creates. I don't have a great way to measure this, but gave it a shot. I used multimeter and 2kHz sine wave and found about a 0.006V increase in the channel imbalance with device in line and all the tone controls in their middle position from a 2V source. Subjectively, I can't hear any change in the channel balance fortunately.
The nice thing about the device is that it uses a relay. In the off position or if the device is unplugged it defaults to full bypass. So you can leave the device inline and fully defeat the tone controls.
My biggest gripe with the device is the gain. I should have remembered this from my 1980s hifi days of inserting 10 band equalizers into tape loops. JDS labs does mention it, but it is pretty well buried in the product page. The device provides around 15dB or so of gain. On an amplifier designed like the O2 that means that with a 2Vrms source you can overload the input. Fortunately my lower gain is 1X, so no issue. But other O2 owners may not be so fortunate. This also means that depending on my source and the amount of EQ applied my high gain of 3.5X may be unusable.
Despite the channel imbalance and the gain issues I'm happy with the device. It's quite satisfying to be able to adjust the sound with something physical and easy to access instead of digging through menus and fiddling with software EQ.