There are lots of overstated remarks in the audio world...
Yes, too low S/N ratio especially when it comes to the so (or self?) called High-End !
Best regards!
You're quite on spot with my latest trials with an old cd player where adding some pleasant noise, i'm masking the unpleasant one . I just found the cheapest way to build "High end" equipment , but i know that "cheap High End" is the most hated quote in the Galaxy !Yes, too low S/N ratio especially when it comes to the so (or self?) called High-End !
Best regards!
Superman and Predator are buying their suits from Pierre Calvin too.
I had one chance to work on "Expensive high end" in the past and I know how the market really works and what you really need to make this so called "High End." You can't afford Unhappy Clients an some of them can't get into Pc-Curry's for usual cheap-end as their shoes would risk dust infections.
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I have done quite a lot of investigations there and an article published at the time in Wireless World,
I made a quick page on my website so it can be downloaded directly A solid state switched attenuator | Linear Audio NL
Wonderful article Jan.
What are those "4007 s.p.dt switches" ?
The 4007 is a triple logic inverter.
Wonderful article Jan.
What are those "4007 s.p.dt switches" ?
The 4007 is a triple logic inverter.
There are two versions of the CD4007, one is buffered, the other is unbuffered (4007UB). That one just has 3 pairs of N-P MOSFETs. That's the one I used. It really is just 6 devices in a package ;-)
http://www.ti.com/lit/ds/symlink/cd4007ub.pdf
Jan
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Years ago, I designed a telephony gadget where I used a MDAC to set the gain. As I recall, I did find a MDAC that featured log values, but there were some issues about sourcing, so I just used an common 8 bit MDAC and put a table of dB to binary on a sticker. Just 8 bits gives a 48 dB range. I was worried about distortion but in that application it was completely a non-issue.
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Note that resistor ladders do not have to be R:2R (~=6dB). You can make them 1dB, 2dB, 10dB, and use selector gates to pick a tap instead of summing them. As with any DAC, you will want to mute the output during switching.
You can also PWM an audio signal (~100KHz+) which simplifies the analog part to a single switch.
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Note that resistor ladders do not have to be R:2R (~=6dB). You can make them 1dB, 2dB, 10dB, and use selector gates to pick a tap instead of summing them. As with any DAC, you will want to mute the output during switching.
You can also PWM an audio signal (~100KHz+) which simplifies the analog part to a single switch.
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...argh... not logaritmic sorry.
Also, there will be relatively high signal levels on the switches, which increases distortion. The design in the article I linked to was designed with trying to keep signal levels on switch terminals at all circumstances as small as possible for max linearity.
Jan
Also, there will be relatively high signal levels on the switches, which increases distortion. The design in the article I linked to was designed with trying to keep signal levels on switch terminals at all circumstances as small as possible for max linearity.
Important detail indeed.
The on-resistance of J105 is 3 ohms so the voltage over the switch will be 100x lower than your 300 ohms 4007UBs.
However, I did some calculating and your solution still has lower distortion, and does tackle more details so you are still on top Jan.
Any PCBs left?
I was thinking something like this.
Please critizise.
The gate drive needed for each FET is not the same as any other FET and needs to vary with signal level for low distortion. You could graft on a pile of op amps to servo the Vgs drive for each FET and adapt it to some logic level like 3.3V, but it makes the circuit amazingly complex very quickly.
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