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Old 29th June 2018
  #4
Gear Maniac
 
Hi guys,

We're happy to answer any questions about the Camden 500 feature set and the performance we've achieved. We're also happy to explain any part of the spec and why it matters. So feel to ask anything!

We know the specs can be confusing and hard to translate into things that matter - like the most important question - does the mic pre sound good? So I thought I could explain a bit more. Our specs show is that Camden 500 is perhaps THE cleanest, most transparent, most linear (both frequency and phase!), and lowest noise preamp ever designed. I'm going to use the Millennia HV-37 (not the HV-35 Millennia's 500 series version as the HV-37 performs better) for comparison- one of the cleanest/most transparent mic preamps I've ever used and a very highly regarded preamp by most- to show how good the Camden 500's noise, distortion, and linearity specs really are. I'll be taking spec information on the Millennia HV-37 from their specs:
Millennia HV-37 | Millennia Music & Media Systems

And this Sound-on-Sound article:
Millennia HV37 |


Frequency Response

We document the Camden 500's frequency response as follows:
±0.25dB, <5 Hz to >200 kHz, 35dB gain
<±1dB, <5 Hz to >200 kHz, max gain

The HV-37's is documented as follows:
< 10 Hz to > 200 kHz
typical -1.0 dB @ 10 Hz < 10 Hz to > 200 kHz
typical -1.5 dB @ 200 kHz


We spec down to 5 Hz (this ensures no subharmonic distortion) and have only ±0.25dB of deviation throughout the entire frequency range of 5Hz to 200kHz. And even at max gain, we achieve impressive linearity. Note we spec what gain value our frequency response is tested at - this is important to us as too often mic preamps have uneven response at different gain settings and often poor performance at max gain.

It's also important to understand that linearity within the audio band (20Hz - 20kHz) is important when sizing up a transparent/linear preamp, but it's also important to see what the wider bandwidth is of a preamp outside of the audio spectrum. Having a larger bandwidth provides a multitude of benefits including 1) better audio band linearity, 2) less phase shift, 3) less intermodulation distortion 4) less sub-harmonic and upper-harmonic THD. Both Millennia and us spec up to 200kHz to address the high-frequency. For low-frequencies - the HV-37 is spec'd at 10Hz and the Camden 500 at 5 Hz.


Phase Shift

We document the Camden 500's Phase Shift as follows:
<2.25°, 40dB gain, 20Hz to 20kHz
<4°, Max gain, 20Hz to 20kHz

The HV-37's is documented as follows:
< 2 degrees deviation (35 dB Gain, 50 Hz - 20 kHz bandwidth, +27 dBu Out)

Phase shift in preamps can be higher than 3600° (we were really shocked when we measured that as well!) across the frequency spectrum on entry-level mic preamps! Imagine your low end in a kick drum or bass instrument arriving almost 30ms (almost enough for you to distinguish two separate sounds), and your high-end arriving 10 wavelengths later than 1kHz with everything between on a spectrum and all the chances for phase cancellation when you start stacking in a mix... This manifests in the "smearing","muddiness", and "lack of punch" that you hear. Even high-end transformer-based preamps will have > 60° phase shift across the spectrum as transformers , by nature, introduce some phase shift (typically between 25° and 60° at 50Hz). Sometimes this causes a slight "unison" effect on transformers which can make a source sound "bigger" or "Stereolike" - which can be great! But it's an artefact nonetheless that may not be desirable.

Phase shift can be addressed by high-end transformerless designs like the HV-37 but the Camden 500 sets a new standard for phase linearity. Note that the Camden 500 is spec'd down to 20Hz whereas the HV-37 is spec'd at 50Hz. And, in our opinion, low-end phase shift is the most important to mitigate and control and gives you a tighter and punchier bottom-end. And just as with frequency response, we spec our phase shift response at Max Gain as well.


Noise

We document the Camden 500's Equivalent Input Noise (EIN) as follows:
<-129.5dBu, 150 ohm source, unweighted
<-131dBu, 150 ohm source, A-weighted
<-135.5dBu, Inputs common, unweighted

The HV-37's is documented as follows:
-130 dB EIN, 60 dB Gain, 10 Hz - 30 kHz, Inputs common

Equivalent Input Noise (EIN) measures the noise floor of a circuit. In terms of how this affects audio - the lower the noise floor, the "cleaner" your recording is and the more dynamics you have (quiet parts are actually quiet!). It's especially helpful as with a lower noise floor you have more dynamic range for compression and similar effects. But the confusing thing with EIN is how it's measured - A-weighting, inputs common/shorted, unweighted with a load (50-150 ohm), and others. The way it's measured is hugely important in understanding it's performance and which preamp actually is the quietest...

We spec our EIN performance the 3 different ways we most commonly see it. if we compare apples to apples with the HV-37, we see the Camden 500 is 5.5dB quieter at the common spec - inputs common. But an amazing sign of the Camden 500's low-noise performance is the 150 ohm unweighted number - the number which best illustrates the noise performance you can achieve with a microphone attached - which is an unbelievably low -129.5dBu.



THD (Distortion)

We document the Camden 500's THD+N as follows:
<0.0004%, 1kHz test tone, 10 Hz - 20 kHz bandwidth, 35dB gain, 24dBu out

The HV-37's is documented as follows:
< .003%, Typical < .001%, 35 dB Gain, 10 Hz - 20 kHz bandwidth, +24 dBu Out

THD (Total Harmonic Distortion) is a measurement which shows how much distortion is being added to the signal. The lower the number, the less distortion. The tricky thing is THD can sound "good"! Most transformer-based designs have very high THD numbers. But this distortion sounds good - it's an iron-core of the transformer "saturating" and introducing low-end and high-end harmonics in nice places. But THD can often sound bad as well - as with entry-level mic preamps when the front-end transistor is "saturating" due to hard, nasty clipping, or with A/D converters when digital artefacts are the distortion. So all we can really objectively say is - the LOWER the THD ratio the more transparent the preamp is.

It is said that THD is inaudible at between 0.1% and 0.05%, but THD rises in the low-end and high-end of the frequency spectrum and becomes harder to achieve at high gains. So a preamp that is 0.05% THD at 1kHz might be as high as 0.5% THD at 50Hz and a transformer-design might be as much as 5-10% THD at 50Hz! But most brands only post the THD ratio at 1kHz because it's the smallest number... We achieve <0.0004 THD at 1kHz, whilst we achieve <0.0008 from 20kHz-20kHz from min gain to 40dB of gain. And <0.01 from 20Hz-20kHz at max gain (68dB of Gain)... So THD is still inaudible even with 68dB of gain!

Both us and Millennia spec THD+N, which is actually the distortion plus noise ratio together - a more challenging number to hit! So if we're talking THD only, the Camden 500 will be <0.0001% THD.


Intermodulation Distortion

We document the Camden 500's Intermodulation Distortion as follows:
<0.0006%, 50Hz and 7kHz, 35dB gain, +15dBu out
<0.0008%, 50Hz and 7kHz, 35dB gain, +20dBu out

The HV-37's is documented as follows:
< .0006% +12 dBu Out, 50 Hz & 7 kHz, 35 dB Gain
< .001% +20 dBu Out, 50 Hz & 7 kHz, 35 dB Gain

This is the industry's crude way of showing that THD is low across the entire frequency band (beyond the audio band). If you have bad distortion artefacts high in the audio band or above, it can then intermodulate with other distortion products in the low frequencies and appear in the audio spectrum... And the worst part about Intermodulation Distortion is it's completely harmonically unrelated - it sounds harsh and nasty, unlike "pleasant-sounding" THD from transformers and valves, and will only produce "bad-sounding" distortion.

Hope this is a semi-decent explanation of some of the more confusing and important specs in preamps. If anyone wants to know any more or has any other questions, we'd be happy to explain more!