Products > Test Equipment
To all the audio guys out there.
David Hess:
--- Quote from: Someone on November 14, 2024, 06:20:13 am ---
--- Quote from: David Hess on November 14, 2024, 01:58:09 am ---
--- Quote from: pope on November 12, 2024, 10:15:32 pm ---The QA403 will output "only" around 20dBu which won't cut it for such measurments.
--- End quote ---
20 dBu is 22 volts peak-to-peak. so the QA403 is probably relying on integrated operational amplifiers with a 30 volt supply. This matters because it means an external amplifier will have to use a higher voltage design making it non-trivial.
--- End quote ---
30dBu/25Vrms/70Vp-p is achievable for a differential signal (as pro audio tends to) on 36V rails so those levels aren't out of this world or impossible to find in commercial products. However pro audio does get off into crazy prices for what it is.
--- End quote ---
The specifications say they are using +/-12.5 volt supplies to generate a 22 volt peak-to-peak output (single ended) with 1.5 volts of headroom. Modern 40 volt audio operational amplifiers running on +/-18 volt supplies under the same conditions could produce 33 volts peak-to-peak single ended, or 66 volts peak-to-peak differential, although driving even a 10 kilohm differential load would be questionable. I am not sure that is a worthwhile improvement, and the limited output current may not be enough. That leads me to a hybrid design with a discrete output to get enough performance with a much greater output level.
I would probably start with the design shown below, doubled and modified to make a differential amplifier, however I do not know anything about its distortion performance. There are plenty of examples online of boosted operational amplifier designs.
squadchannel:
--- Quote from: AVGresponding on November 14, 2024, 10:04:49 am ---
--- End quote ---
Mark's videos are always interesting. :-+ The comments also makes me laugh. :-DD
Amplifier design, well $25,000 is .... :wtf:
It's ok, it's for audiophiles. >:D
Someone:
--- Quote from: David Hess on November 14, 2024, 01:47:16 pm ---
--- Quote from: Someone on November 14, 2024, 06:20:13 am ---
--- Quote from: David Hess on November 14, 2024, 01:58:09 am ---
--- Quote from: pope on November 12, 2024, 10:15:32 pm ---The QA403 will output "only" around 20dBu which won't cut it for such measurments.
--- End quote ---
20 dBu is 22 volts peak-to-peak. so the QA403 is probably relying on integrated operational amplifiers with a 30 volt supply. This matters because it means an external amplifier will have to use a higher voltage design making it non-trivial.
--- End quote ---
30dBu/25Vrms/70Vp-p is achievable for a differential signal (as pro audio tends to) on 36V rails so those levels aren't out of this world or impossible to find in commercial products. However pro audio does get off into crazy prices for what it is.
--- End quote ---
The specifications say they are using +/-12.5 volt supplies to generate a 22 volt peak-to-peak output (single ended) with 1.5 volts of headroom. Modern 40 volt audio operational amplifiers running on +/-18 volt supplies under the same conditions could produce 33 volts peak-to-peak single ended, or 66 volts peak-to-peak differential, although driving even a 10 kilohm differential load would be questionable. I am not sure that is a worthwhile improvement, and the limited output current may not be enough. That leads me to a hybrid design with a discrete output to get enough performance with a much greater output level.
I would probably start with the design shown below, doubled and modified to make a differential amplifier, however I do not know anything about its distortion performance. There are plenty of examples online of boosted operational amplifier designs.
--- End quote ---
You said (and I quoted) that higher than 30V is non-trivial. Yet there are numerous high current drive opamps with 36V supply rails (abs max 40V or higher) that can drive 10k easily, supported by both data sheet typical characteristics and real world uses. The 600Ω request from the OP is a little harder but paralleling operational amplifier outputs is considered pretty trivial in the audio world. Again, a quick perusal of some candidate parts readily finds solutions.
Not hard at all, while sticking with well defined distortion and dynamic performance.
timeandfrequency:
Hello pope,
--- Quote from: Messtechniker on November 13, 2024, 03:58:11 pm ---Because I could not find such a thing, I built one.
--- End quote ---
:-+
Maybe using a high voltage :bullshit: opamp with power output (200 mA) ?
For the power supply, two 30 VA 2 x 24 VAC toroidal transformers + rectifiers + heavy filtering + fuses : https://www.amazon.fr/dp/B00MWRLX8W will lead at least to ± 75 VDC rails (low output load on a small transformer leads to +15 % output voltage).
Signal peak voltage will probably be able to scrape 65 Vp (35,5 dBu). With this power opamp, asking for 20-26 dB of gain is not a problem even with tens of kHz of bandwidth.
Put the opamp on a huge heatsink. Keep all wires/tracks as short as possible.
PS : it would be so nice if the title of this thread reflects what we are discussing about
trobbins:
The OP appears to just want to measure headroom and simple signal stuff, not harmonics down to -120dB, so perhaps any form of battery powered linear amp with sufficient output signal level would seem fine - including an opamp, assuming it can drive the anticipated lowest loads at the max signal. May need to use a few 12V batteries, or 9V batteries, and an opamp with say 30V or +/-15V supply, or multiple of batteries. I have an LM1875 board for that purpose, with a suitable gain to just not clip with available level from my soundcard, but there would be many other simple boards on ebay etc.
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