• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). There are daily reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Impedance matching questions ...

deuch

Member
Joined
Oct 4, 2022
Messages
8
Likes
0
Hello,

I own a Topping A90 discrete headphone amplifier and a DX3Pro Plus that i'm using as a DAC (RCA output). My Headphone is a Hifiman Edition XS (18ohm/92dB) connected to the XLR balanced output of the A90D

I'm interested with those DACs (for full balanced chain) :

- SMSL SU-9(n) (XLR: 207Ω RCA: 142Ω) [mesured by Amir - XLR: 370Ω , RCA: 122Ω]
- Gustard X16 (XLR: 300Ω, RCA: 100Ω)

And the Topping A90d has 2KΩ for XLR and 10KΩ for RCA input impedance. If i'm correct, the ratio 1:10 for input/output impedance is not respected in this case ... Is it very bad ? What can be the nasty things that can happen in this case ?

Thanks for you help and your knowledge !
 
Last edited:

solderdude

Grand Contributor
Joined
Jul 21, 2018
Messages
13,041
Likes
29,374
Location
The Neitherlands
It is very bad

Welcome to ASR.

There is no 'impedance matching' in analog audio. The 1:10 load guideline is just that... a guideline.
In most cases the load resistance is much higher than the source resistance and most agree that at least a 1:10 ratio is preferred as the source is not loaded too much.
There is impedance matching in RF (Radio Frequency), video and digital transmission.

For line level gear it is only about the attenuation one gets when the load resistance is unusually low or roll-off.
It is not 'very bad' and 2kΩ for XLR is not alarmingly low nor is 10kΩ for RCA.

what can be the nasty things that can happen in this case ?

When the load is unusually low (say below 1kΩ) and the source has a high output resistance you may get a lower signal level than expected due to voltage division.
When the load is unusually low (say below 1kΩ) and the source has a relatively small coupling capacitor in the output you may get some early bass roll-off (acts as a high-pass)
When the load is unusually low (say below 1kΩ) and the source has a very low output current capability you may get some clipping at higher levels (when the current limit is reached).
 
Last edited:
OP
D

deuch

Member
Joined
Oct 4, 2022
Messages
8
Likes
0
So no worries to have with those combos (SMSL SU-9+A90d) or (Gustard X16+A90d) if i understand correctly. Maybe a lower signal level ?
 
Top Bottom