C-MEDIA CM6206 5.1 USB Audio Sound Card Line-In & Line-Out Bass Extension Low Frequency Response Upgrade

Article Updated: 01 April 2021

C-MEDIA CM6206 is a cheap and solid performance audio codec chip supporting 16 bit / 48 kHz audio, stereo* MIC and LINE-IN inputs. Works out of the box on Windows 10 operating system with stock drivers. Great for hobby recordings & measurements (e.g. using Virtins Multi-Instrument / Oscilloscope, ARTA / LIMP, etc.), despite the fact it has only 16 bit A/D converters and 48 kHz sampling rate! 99.999% of us humans can’t hear the difference between standard 16 bit / 44.1 kHz and 24 bit / 192 kHz audio anyway thanks to low-pass filtering, interpolation and human hearing characteristics.

PART 1: C-MEDIA CM6206 5.1 External USB Audio Sound Card Line-In Bass Extension Frequency Response Modification

C-MEDIA CM6206 5.1 USB Audio Sound Card - Product Photo

C-MEDIA CM6206 5.1 USB Audio Sound Card – Product Photo

C-MEDIA CM6206 – THE PROBLEM

If you wish to start a YouTube or Twitch career, transfer your old audio cassette recordings or vinyl collection to your computer, C-MEDIA CM6206 External USB Sound Card is a very nice solution in case you use a modern laptop without integrated multi-channel audio card and dedicated Line-In or MIC inputs.

Paired with a cheap studio-like condenser microphones such as BM-800 or Neewer NW-700 you can really step-up the quality and get yourself going in the right direction for well under $50 budget.

However, engineers who designed and manufactured this sound board crippled LINE-IN analog recording inputs frequency response in low / bass section by putting very small coupling capacitors! Why oh why ???

CM6206 hardware is perfectly capable going all the way down to a sub-hertz (less than 1 Hz) flat frequency response if desired / required. You can even bypass input AC coupling capacitors to enable DC input, with some precaution (useful for audio oscilloscope applications and DC signal measurements e.g. using Daqarta software).

C-MEDIA CM6206 audio codec is used in many different sound cards, including 7.1 surround models. It supports separate Headphone output, mute, rec mute, digital volume controls, dual mono MICROPHONE inputs and more! Of course, in this 5.1 model not all features are used, but what can you expect from a $5 or $10 sound card? More expensive $20 models come with 7.1 audio, dedicated headphones output, dual MIC and LINE-IN inputs, Volume and Mute controls. In essence, a very solid audio card for the money!

C-MEDIA CM6206 5.1 External USB Audio Sound Card – Line-In Frequency Response Measurements

[1] Right-Mark RMAA without modification (loopback audio Line-In <-> Line-Out)

C-MEDIA CM6206 5.1 USB Audio Card 16-bit, 48 kHz Loopback Line-In Frequency Response Spectrum

RMAA C-MEDIA CM6206 5.1 USB Audio Card 16-bit, 48 kHz Loopback Line-In Frequency Response Spectrum + THD

[2] Right-Mark RMAA without modification (loopback audio Line-In <-> Line-Out)

C-MEDIA CM6206 5.1 USB Audio Card 16-bit, 48 kHz Loopback Line-In Frequency Response Spectrum TEST OVERVIEW

RMAA C-MEDIA CM6206 5.1 USB Audio Card 16-bit, 48 kHz Loopback Line-In Frequency Response Spectrum TEST OVERVIEW

[3] without modification (ARTA FR1 CH loopback audio Line-In <-> Line-Out)

ARTA #1-1 C-MEDIA CM6206 5.1 USB Audio Card Line-In ORIGINAL 20Hz-20kHz

ARTA #1-1 C-MEDIA CM6206 5.1 USB Audio Card Line-In ORIGINAL 20Hz-20kHz

[4] with 4.7 uF input coupling capacitors modification (ARTA FR1 CH loopback audio Line-In <-> Line-Out)

ARTA #1-2 C-MEDIA CM6206 5.1 USB Audio Card Line-In 4.7uF MOD 0.2Hz-20kHz -3dB Marker

ARTA #1-2 C-MEDIA CM6206 5.1 USB Audio Card Line-In 4.7uF MOD 0.2Hz-20kHz -3dB Marker

[5] with 1 uF input coupling capacitors modification (ARTA FR1 CH loopback audio Line-In <-> Line-Out)

ARTA #1-3 C-MEDIA CM6206 5.1 USB Audio Card Line-In 1.0uF MOD 0.2Hz-20kHz -3dB Marker

ARTA #1-3 C-MEDIA CM6206 5.1 USB Audio Card Line-In 1.0uF MOD 0.2Hz-20kHz -3dB Marker

C-MEDIA CM6206 5.1 External USB Audio Card Line-In Modification Video Tutorial

In this video I have upgraded input coupling capacitors with larger values and improved frequency response considerably! In the end of the video is a line-in recording example using C-MEDIA CM6206 5.1 External USB Sound card with and without this modification compared to the original audio, along with the frequency response charts.

Watch Video Tutorial:

Used SMD capacitors: 1608 A (0603) XR7 type

C-MEDIA CM6206 5.1 External USB Audio Sound Card – High Resolution PCB Board Photos with Annotations

Note: click on photos to load full resolution images

C-MEDIA CM6206 5.1 USB Audio Card - TOP & BOTTOM PCB Layers Overlay - Top Side

C-MEDIA CM6206 5.1 USB Audio Card – TOP & BOTTOM PCB Layers Overlay – Top Side

C-MEDIA CM6206 5.1 USB Audio Card - TOP & BOTTOM PCB Layers Overlay - Bottom Side

C-MEDIA CM6206 5.1 USB Audio Card – TOP & BOTTOM PCB Layers Overlay – Bottom Side (Horizontally Mirrored Photo!)

C-MEDIA CM6206 5.1 USB Audio Card - Line-In Input AC Coupling Capacitors Close-Up

C-MEDIA CM6206 5.1 USB Audio Card – Line-In Input AC Coupling Capacitors Close-Up

C-MEDIA CM6206 Chip Close-Up

C-MEDIA CM6206 Chip Close-Up

NOTES

💡 Stereo MIC feature (dedicated L+R MIC inputs) is physically available only on a slightly more expensive 7.1 USB External Sound Card model (USD $20 ~ $25). On 5.1 USB External Sound Card model a single (mono) MIC input is split via C16 and C17 coupling SMD capacitors and routed to respective L+R MIC inputs of CM6206 chip. With some skills it is possible to split PCB wire connection and add 2nd MIC input socket manually if needed on this model, too. Please refer to high-resolution PCB photos with annotations for more details.

💡 Unfortunately it is not possible to directly measure C16 and C17 capacitor values with common multimeters, because there is a resistor network for DC voltage bias connected in parallel (MIC phantom power), but it is safe to assume they are also under-valued and around 100 nF (0.1 uF). If you wish to improve low frequency range linearity, they need to be replaced or upgraded as well. It is possible to use Line-In modified STEREO inputs, coupled with one or two external MIC preamplifiers and one or two microphones (dynamic or condenser type) to make better (more linear) audio recording.

 

PART 2: C-MEDIA CM6206 5.1 USB Audio Card Headphones Line-Out Bass Frequency Extension Modification

So far, we have ONLY modified Line-In recording inputs used to record/monitor analog electronic musical instruments or pair of high quality microphones (via preamplifier — not directly!). What about Line-Out (marked as FRONT OUT) outputs?

C-MEDIA CM6206 5.1 USB Audio Card - Output Coupling Capacitors

C-MEDIA CM6206 5.1 USB Audio Card – Output Coupling Capacitors

If you take a closer look at the output stage on the PCB board you will notice 6x 100 uF electrolytic coupling capacitors connected to their respective color-coded 3.5 mm output sockets. Each capacitor pair is dedicated for L+R main output (C5/C6), L+R rear surround output (C1/C2), and finally c/sub CENTER + SUBWOOFER output (C3/C4), respectively.

C-MEDIA CM6206 5.1 USB Audio Card - TOP & BOTTOM PCB Layers Overlay - Bottom - Headphones Line-Out Mod

C-MEDIA CM6206 5.1 USB Audio Card – TOP & BOTTOM PCB Layers Overlay – Bottom – Headphones Line-Out Mod (NOTE: Corrected Output Coupling Capacitors Polarity!)

⚠️ If you take a closer look at the PCB board, you will notice that the output coupling electrolytic capacitors have their negative minus “-” terminals connected to the CM6206 chip’s side (pins). However, this is very wrong and illogical, because chip operates at single-ended USB +5.0 V power supply and output DC offset is biased at positive +1.40 volts, which allows AC audio signal to swing between 0 V and +2.80 V.

According to official CM6206 datasheet, output coupling capacitors should be connected with their positive “+” terminal at the CM6206 chip’s side, and this is exactly why we marked it as such in our annotated photo! The factory PCB version is technically wrong, and this negative -1.40 voltage will negatively impact capacitor’s life expectancy and performance. Because outputs are ended with 47 kOhms resistors to the ground, capacitors are constantly polarized with reverse voltage and current, even without any external load connected to the output sockets!

C-MEDIA CM6206 5.1 USB Audio Card - Output Coupling Capacitors WRONG POLARITY

C-MEDIA CM6206 5.1 USB Audio Card – Output Coupling Capacitors WRONG POLARITY

Now, if your setup uses external audio amplifier or some other medium-to-high impedance equipment (e.g. 1k ~ 100k Ohms input impedance; CM6206 outputs are ended with 47 kOhm resistors), those 100 uF factory coupling capacitors will be more than adequate. Headphones with 64 Ohms impedance will be fine, and even most 32 Ohms models. Why? Well, most home headphones have issues reproducing frequencies lower than 40 Hz anyway (yes, they can reproduce them in Signal Generators, but in the real music mix those frequencies get lost because of poor frequency response and attenuation), so you will definitely not miss much without this modification.

Headphones with 32 Ohms nominal impedance and decent bass response such as EDIFIER H840 (they go all the way down to the useful 35 Hz in our tests) will be just fine with a -3 dB point at ~ 50 Hz (54 Hz measured in ARTA), but technically still far from Hi-Fi “on paper”. On the other hand, headphones such as SENNHEISER HD 201 won’t gain much because they cannot reproduce anything below 40 Hz properly (forget that 21 Hz from the official specification!). Still, if you test them with pure sine waves with signal generator, there is no doubt that 20 ~ 50 Hz range gets louder with larger coupling capacitors. And let’s not forget that your ears’ sensitivity to low frequencies, head physical profile and headphones anatomy equally play important role in low frequency response.

However, with ultra linear and low-impedance 16~24 Ohms headphones you will definitely notice some bass improvement because -3 dB point will be at 100 Hz and 65 Hz, respectively. Again, we stress out that your headphones must be real subwoofer monsters and linear all the way down to 20-25 Hz to notice any real difference, aside the measurement graphs! Otherwise, the effect of this Line-Out modification will be extremely subtle and barely noticeable if your headphones drivers cannot deliver.

How To Fix Line-Out Low Frequency Response with Low-Impedance Headphones?

Simply replace capacitors C5 and C6 with a higher value one. For 32 Ohms headphones use 1000 ~ 2200 uF / 6.3V, and for 16-24 Ohms headphones use 2200 ~ 4700 uF / 6.3 V electrolytic type. You can even use low-ESR types (usually used in switching power supplies) and solid aluminum electrolytic capacitors (usually more compact than ordinary wet electrolyte types; so you can easily squeeze larger capacity in a constrained space) for best possible audio performance, and low distortion.

C-MEDIA CM6206 5.1 USB Audio Card - 1000 uF Line-Out Headphones Coupling Capacitor Mod Test

C-MEDIA CM6206 5.1 USB Audio Card – 1000 uF Line-Out Headphones Coupling Capacitor Mod Test

NOTE: Capacitors height must not exceed ~ 13 mm (1/2″ inch) or you’ll have to position them horizontally in order to be able to put aluminum enclosure back. Distance between capacitor’s leads (pins or “legs”) is 2.54 mm ideally, but you can bend larger 3.5 mm / 5.0 mm types easily.

C-MEDIA CM6206 Line-Out Modification Measurements

[1] without modification + EDIFIER H840 (32 Ohms) headphones load connected @ output
(ARTA FR1 CH loopback audio Line-In <-> Line-Out) (Line-In 1 uF input capacitor mod applied)

ARTA #4-1 C-MEDIA CM6206 5.1 USB Audio Card Line-Out + EDIFIER H840 + 100 uF Capacitor Factory -3dB Marker

ARTA #4-1 C-MEDIA CM6206 5.1 USB Audio Card Line-Out + EDIFIER H840 + 100 uF Capacitor Factory -3dB Marker

[2] with 1000 uF capacitors modification + EDIFIER H840 (32 Ohms) headphones load connected @ output
(ARTA FR1 CH loopback audio Line-In <-> Line-Out) (Line-In 1 uF input capacitor mod applied)

ARTA #4-2 C-MEDIA CM6206 5.1 USB Audio Card Line-Out + EDIFIER H840 + 1000 uF Capacitor Mod -3dB Marker

ARTA #4-2 C-MEDIA CM6206 5.1 USB Audio Card Line-Out + EDIFIER H840 + 1000 uF Capacitor Mod -3dB Marker

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