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TK Audio BC501-GR - User review - Gearspace.com
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TK Audio BC501-GR
4 4 out of 5, based on 1 Review

Very fully-featured single-VCA bus compressor.


5th December 2021

TK Audio BC501-GR by johannburkard

  • Sound Quality 4 out of 5
  • Ease of use 4 out of 5
  • Features 5 out of 5
  • Bang for buck 3 out of 5
  • Overall: 4
TK Audio BC501-GR

The BC501-GR is a single-VCA bus compressor for the 500 series with pretty much all the features one could expect.

Since I've built a SoundSkulptor CP4500 (another VCA compressor), let's compare it to the BC501-GR:

  • CP4500 is a quad-VCA, the BC501-GR a single VCA. Quad-VCAs should have lower noise (not the case here). Both use THAT 2181 VCAs, the SoundSkulptor (now) in a SOIC-8 SMD package, the BC501-GR in the old-school SIP-8 package (easy to replace).
  • With the CP4500, you're obviously free to choose your own components. While the CP4500 comes with TI OPA2134 FET opamps, I'm using the Orange discrete opamp in mine. The BC501-GR uses the '70s NE5532 which I've previously said sound like shit. The NE5532 is the (almost) bottom-of-the-barrel IC that I would love to never see again in audio because there are cleaner opamps available, even for not much more money than the NE5532 (the LME49723 comes to mind).
  • The CP4500 only has the original (SSL) ratios: 2:1, 4:1 and 10:1. The BC501 a whole lot more, including the low ratios of 1.25:1 and 1.5:1.
  • The BC501-GR also has more attack and release settings.
  • The pots on the CP4500 are continous, the pots on the BC501-GR are detented (left) and stepped (right).

From a practical perspective, building and setting up a DIY product like the CP4500 will take time (calibration and bugfixing more than building for me) whereas a product like the BC-501GR should be ready to go. Speaking of which, the volume matching on the BC501-GR was spot on from the factory (around 0.01 dB) but the distortion cancellation of the VCAs was way off (L: 0.0031 % THD @ 1 kHz, R: 0.023 %!). Thankfully, there are pots to adjust that.

Comparing the distortion to the CP4500, the BC501-GR has less higher harmonics at 1 kHz (good) but power line hum harmonics are suddenly measureable. I blame the NE5532s just because. Check the screenshots below for the measurements.

On the BC501, the VCA and the line driver, a THAT 1646, are socketed but the opamps are not (SOIC-8 SMD). I don't have a problem with the THAT 1646 but I would like the freedom to choose my own opamps. I'll also take the line receiver at the input (a THAT 1256) socketed, thank you.

On to the features and the sound...

At identical settings, both compressors sound very much alike and I don't have a clear preference. There's two samples in the attachments from this worldwide number 1, one is 2:1, 1 mS attack, 300 mS release, the other 10:1, 3 mS attack, 100 mS release.

I think where the BC501-GR really adds something is with the low ratios. Both 1.25:1 and 1.5:1 are really nice together with 10 or 30 ms attack and a fast-ish release. This can be used to really thicken up a mix.

The THD feature adds a ton of even harmonics which I guess tries to mimic valve gear. The grab function felt very subtle to me. I tend to stay away from sidechain highpasses because they usually change the frequency response.

The tactile feeling of the BC501-GR is nice and the detented pots help with recall.

Overall, it's a really good product. Not great without socketed opamps and a better factory calibration, but really good nonetheless. If you want an SSL-style bus comp, it's a great choice.

Edit: Reducing bang per buck to 3 because I had to mess with the VCAs...

Attached Thumbnails
TK Audio BC501-GR-cp4500.jpg   TK Audio BC501-GR-bc501-l-thd.jpg   TK Audio BC501-GR-bc501-l.jpg  
Attached Files

CP4500 10_1 3mS 100 mS.wav (2.56 MB, 70 views)

CP4500 2_1 1mS 300 mS.wav (5.13 MB, 64 views)

BC501-GR 10_1 3mS 100 mS.wav (5.13 MB, 64 views)

BC501-GR 2_1 1mS 300 mS Grab.wav (2.56 MB, 64 views)