Suggestion Request: audio amplifier - Page 1
Forum section: electronics / testgear

author: mio83
author_rank: Regular Contributor
timestamp: July 21, 2020, 07:34:18 pm
content: 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 cheaphave variable gain settingslow noise figurebe capable of amplifying weak signals (<100Khz) up to, say, 10/20V peak to peak (to a high impedance load), with good linear behaviourHave 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.

author: David Hess
author_rank: Super Contributor
timestamp: July 21, 2020, 10:15:53 pm
content: The old Tektronix AM502 1MHz differential amplifier meets those requirements.

author: cdev
author_rank: Super Contributor
timestamp: July 21, 2020, 11:11:23 pm
content: Is that what an "instrumentation amplifier" does?

author: mio83
author_rank: Regular Contributor
timestamp: July 22, 2020, 07:36:03 am
content: 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 astandaloneunit.

author: David Hess
author_rank: Super Contributor
timestamp: July 22, 2020, 07:00:31 pm
content: 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

author: TimFox
author_rank: Super Contributor
timestamp: July 22, 2020, 08:45:30 pm
content: There are some nice Princeton Applied Research (PAR, later bought by EG&G) differential amplifiers with switchable high-pass and low-pass filters. They can sometimes be found on eBay, for examplehttps://www.ebay.com/itm/Princeton-Applied-Research-PAR-113-Preamp/193498466491?hash=item2d0d6848bb:g:gKsAAOSwx5le2Ud2. Note that I am not warrantying that particular listing, but I have two similar items. I don't know if this model has NiCd batteries: they can be a hassle for refurbishing, but a great help for ground loops.

author: srb1954
author_rank: Super Contributor
timestamp: July 23, 2020, 08:19:34 am
content: 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 caseTM502 2 plug-in slots in a bench caseTM503 3 plug-in slots in a bench caseTM504 4 plug-in slots in a bench caseTM515 5 plug-in slots in a travel caseTM506 6 plug-in slots in rack mount caseThe 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.