Old Amps that can still Kick Butt


Not being a believer that time necessarily = progress, I would like to offer the following example of a sonic gem that has transcended time and can totally kick butt in a modern milieu:

The Robertson 4010. I got one of these about two years ago because it was in immaculate condition, the price was so low and I was inquisitive. I hooked it up and let it warm up for a couple of days. OMG this thing was in the super amp league: Transparency to die for, slam that you couldn‘t‘ believe for for a 50W amp.. Peter Moncrieffe wasn‘t wrong in his review of this amp: this thing is in the Sterreophile Class A component category hands down. Even after all these years.

What amps have you encountered that have defied time and can still kick butt today?


Previewpesky_wabbit
@lou_setriodes

B&K EX442/ST-140
PS Audio 200C/CX
VSP Labs Trans Mos 150
Acoustat TNT120/200
Moscode 300
Berning EA230
Onix OA21/21s
Tandberg 3012/3012a

It’s been fun reading through this thread and seeing some blasts from the past.

I built a DH500 from a kit in 1985, then moved on to a New York Audio Labs Moscode 300 about 2 years later (that one’s a bit obscure, and was surprised to see it mentioned! I actually got to meet Harvey Rosenberg...a very colorful and interesting character, as so many of these high-end entrepreneurs are!). My next amp was a Distech LS-2 based on the B&K ST-140. Ironically, I just picked up one of the last of the B&K ST-140s for my son as a graduation gift....he’s gonna love it!
@knotscott / @lou_setriodes -     Did either of you ever perform any of the mods, to your Moscodes?                                         Great amp!
@knotscott / @lou_setriodes -     Did either of you ever perform any of the mods, to your Moscodes?     Great amp!


Other than changing some tubes, I didn't do anything else to mine.
Most of the amps listed here will sound fine at low volume. But if you want to blast they’ll get painful. The mark of a good system is one that sounds smooth and detailed (not brightness masquerading as detail) even at high volume.


The problem is caused by insufficient feedback. At low frequencies the feedback is fine, which is why they can play bass well. But as frequency is increased, the distortion goes up with it because the design lacks the Gain Bandwidth Product needed to support high levels of feedback at high frequencies. This results in harshness and brightness since that is how the ear perceives the higher ordered harmonics generated by the amp.

You can’t just add more feedback; you might exceed the phase margin of the amp, causing it to oscillate.


Its a compromise.


I have a lower powered Radio Shack amp that sounds fine as long as you don’t push it hard. It tends to make the 2nd harmonic as its primary distortion product and that masks a good deal of the higher orders. But at higher volume levels there isn’t enough lower ordered content to mask anymore- and so it gets harsh. But if I run speakers that have enough efficiency, the amp never gets to those volumes and it sounds fine.

Put another way, even though a lot of the amps mentioned so far can make quite a bit of power, matching the speaker to them (using an easier to drive speaker) is paramount to getting the most out of them.
I did have the ROWLAND 8T for about 10 years and had no trouble selling it to a fellow Audiophile who still loves it.A classic to be sure.