# RAAL-requisite HSA-1b - Switch Drive Amplifier Review

**URL:** <https://forum.headphones.com/t/raal-requisite-hsa-1b-switch-drive-amplifier-review/9973>\
**Category:** DACs and Digital\
**Tags:** headphone-amp, amplifier, sr1a, speakers, ribbon\
**Created:** [January 1, 2021, 8:59pm UTC](https://forum.headphones.com/t/raal-requisite-hsa-1b-switch-drive-amplifier-review/9973 "2021-01-01T20:59:35Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![Torq](https://sea2.discourse-cdn.com/flex016/user_avatar/forum.headphones.com/torq/32/16384_2.png) [@Torq](https://forum.headphones.com/u/Torq)\
**Post date:** [January 1, 2021, 8:59pm UTC](https://forum.headphones.com/t/raal-requisite-hsa-1b-switch-drive-amplifier-review/9973/2 "2021-01-01T20:59:59Z")

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## History and Iterations - HSA-1a vs. HSA-1b

The HSA-1b is a revision to, and upgrade of, RAAL-requisite’s prior, and somewhat short-lived, HSA-1a amplifier - of which there have been two iterations. The initial release of the HSA-1a had two 4-pin male XLR connections for driving two pairs of RAAL-requisite’s “SR1a” ribbon-driver EarField ™ monitors:

 ![RAAL - HSA-1a - Front Deep (1024)](https://us1.discourse-cdn.com/flex016/uploads/headphones/original/3X/5/9/598e69eb8280cf766d6f2034f8b9e883af842951.jpeg)

A subsequent revision, an optional conversion to which was available to existing HSA-1a owners, swapped one of the SR1a outputs for a conventional, balanced, 4-pin XLR headphone output. This also included an adapter cable for driving inefficient/power-hungry conventional headphones, such as the HiFiMan Susvara and HE6/HE6-SE etc., from the SR1a output:

 ![RAAL - HSA-1a - Front (1024)](https://us1.discourse-cdn.com/flex016/uploads/headphones/original/2X/d/dc41ffca959db3df26286620e435970ce29da4d5.jpeg)

The HSA-1b refines the implementation of the HSA-1a, retaining both SR1a (ribbon driver) and conventional 4-pin balanced XLR outputs, adds a 1/4” TRS connection, moves all the switches to the front of the unit, replaces the conventional, potentiometer-based, volume control with a 24 position stepped-attenuator (for perfect channel balance) and adds configurable input level attenuation. The adapter cable for using the “SR1a” output with hard-to-drive dynamic/planar cans is still included.

 ![RAAL HSA-1b - Front (1024)](https://us1.discourse-cdn.com/flex016/uploads/headphones/original/3X/2/9/295767cbea3b03b43ad0c05fe3d5dc1add67f307.jpeg)

I have heard all three of these models, at length, in my own system. The first HSA-1a was on loan. On the basis of its performance, I bought one of the second revision units, and have since replaced it with the HSA-1b.

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