AB TESTS

1980's British near-high-end minimalism.

A25 guts, including my opamp mod.

Notes

A25 has a MOSFET output stage, lots of film capacitors, epoxy-fiberglass circuitboards, and is either class A or "high A class AB" depending on your source of information. It gets HOT so whatever class it is, the idle bias is set pretty high.
Uses standard practice of resistors in series with amp output for headphone jack.
This amp is really very nice, sounds nice on my Quad ESL-57's and on other speakers. Sounds more powerful than 29 watts / side. Sounds like class A to me.
I have a schematic for this amp- which is hard to find. If you need a copy, HERE it is.

	A-B TESTS

	Headphone Amps A/B Comparison #6
	Beta 22	Sugden A25 Integrated Amplifier
	Sigma 22 power supply. Three-channel "Active Ground" topology. See http://www.amb.org/audio/beta22/	Sugden A25 is a mid 1980's model, made in England. A25 rated at 29 watts / channel. I replaced the NE5534 op amps in the gain stage with OPA627ab's (on sockets). eBay purchase $125 in 2007.
	DAC: Cambridge Audio DAC Magic - via SPDIF
	Source: Various FLAC Music Files	11/16/2010
	Test conducted using a switch that connected either amp "A" or amp "B" to the headphones; amps were fed in parallel off the DAC.
	I carefully matched the volume levels of the two amps using a 1000 Hz tone & SPL Meter
	NOTE: Using the A-25's headphone jack for this comparison. LCD-2 Bass not quite as powerful / authoritative as the Beta-22, but otherwise good bass. Highs a little rolled off compared to the Beta-22, but curiously female vocalist sibilance is more un-naturally prominent or somewhat exaggerated through the Sugden compared to the Beta-22. High volume setting is required to drive the LCD-2's (50 ohm phones) but good volume level is obtainable. HD-800 Again, bass not quite as well controlled or deep as the Beta-22. Some midrange exaggeration from the Sugden, possibly revealing why this amp is supposed to sound a bit "tubelike." Upper highs rolled off a bit with the Sugden compared to the Beta-22, and yet again there is this false emphasis on female sibilance though not as pronounced as it was driving the LCD-2's. MY CONCLUSIONS This integrated amp (with upgraded op amp) sounded pretty darn good, though not QUITE up to the high standard set by the Beta-22. I did not get that "fatiguing" effect that I got from the Yamaha, which makes me think this amp is either class A or is operating in class A at the level I'm using it at. Sucker gets QUITE hot! Nice little amp, though. You don't see too many of these. Makes a nice bedroom / office speaker amp with possibility of occasional headphone use. Has a phono preamp. This amp shows to me that headphone jacks in integrated amps can sound pretty decent if the amp is approaching high-end in design (as in class-A operation and quality parts.) Not as good as a headphone amp like the Beta-22 or the M³, but better than the conventional wisdom holds.

	1980's British near-high-end minimalism. A25 guts, including my opamp mod. Notes A25 has a MOSFET output stage, lots of film capacitors, epoxy-fiberglass circuitboards, and is either class A or "high A class AB" depending on your source of information. It gets HOT so whatever class it is, the idle bias is set pretty high. Uses standard practice of resistors in series with amp output for headphone jack. This amp is really very nice, sounds nice on my Quad ESL-57's and on other speakers. Sounds more powerful than 29 watts / side. Sounds like class A to me. I have a schematic for this amp- which is hard to find. If you need a copy, HERE it is. Copyright © 2011