Hello,
I would like to buy an affordable audio (pre)amplifier (0Hz to 100Khz) to use as a lab/test equipment (
hobby level).
Ideally this unit would:
- be cheap
- have variable gain settings
- low noise figure
- be capable of amplifying weak signals (<100Khz) up to, say, 10/20V peak to peak (to a high impedance load), with good linear behaviour
- Have some basic low-pass (e.g., <20Khz) and high-pass filters (e.g., >100hz)
One think I'd like to use it, for example, it as audio section in a direct conversion radio.
QUESTION: Do you know of anything with these properties in the audio/music market, or stuff from aliexpress, or good old equipment now available for decent prices in ebay?
I have a nice HP 461A amplifier (linear and +40db) but it's max output is 0.5V (50ohm) and lacks the filtering options, and it is specified to work only on freq. >= 1Khz.
Thank you in advance for any suggestion.
The old Tektronix AM502 1MHz differential amplifier meets those requirements.
Is that what an "instrumentation amplifier" does?
Thanks,
the Tektronix (and also some variants, like the Tek 7A22) looks exactly what I was searching for!
EDIT: if you have other suggestions for more recent (and sufficiently cheap) differential amplifiers and/or instrumentation amplifier please let me know.
It would be desirable to have a
standalone unit.
The AM502 is the stand-alone version of the 5A22/7A22 but typically comes at a premium price. Still, they can still be had for less than $200 in good condition. The less expensive 5A22/7A22 plug-ins can be used as parts donors if necessary, or if you have a 5000/7000 series oscilloscope mainframe, the vertical output can be used with a 5A22/7A22 to supply a signal to another instrument.
There was a discussion thread here with a list of alternatives not too long ago. Check my post which mentions Linear Technology application note 124:
https://www.eevblog.com/forum/testgear/preamplifier-for-noise-measurements/msg3074824/#msg3074824
If you get an AM502 you will also need to purchase a TM500 series mainframe to plug it into. The mainframe supplies power to the AM502 and, with an opt. 2 mainframe, provides a rear panel connection for the amplifier output.
The TM500 series mainframes come in various sizes:
TM501 1 plug-in slot in a bench case
TM502 2 plug-in slots in a bench case
TM503 3 plug-in slots in a bench case
TM504 4 plug-in slots in a bench case
TM515 5 plug-in slots in a travel case
TM506 6 plug-in slots in rack mount case
The TM503 and TM504 seem to be the most readily available and give you several spare slots for future plug-ins. Check out TekWiki for the full range of plug-ins in the TM500 series.