Review: Phase Linear 700b Amplifier

Category: Amplifiers

I have on a mission to find a clean natural sounding amp to power the ALIII. The ribbon drivers present a very difficult load. I found a 700 b rebuilt by an electrical engineering professor who does it as a hobby. WOW. So this a a mint 700b and maybe upgraded slightly from original. Without going into long analysis of music this amp has massive power and transparency and it does sound more tube than solid state unless you drive it to clipping. The closest thing I have heard that compares is the Boulder or Levinson amps which are thousands of dollars. In 1978 money this amp approached the $5000.00 price tag. Anyway I only paid $500 and what a steal. It is like buying a Ferrari for the price of a Chevy Cavalier. And being vintage it will go up in value. I would avoid overdriving. However, if this amp was used on efficient speakers of the cone design one would be operating at about 5-10 watts giving you massive reserves and low distortion. This amp would probably blow a high efficiency speaker. I assure you that you will be listening to all your music all over again. This amp proves that solid state does not have to sound harsh.

Associated gear
Carver ALIII speakers
Carver CT17 preamp

Similar products
Audio Research, Krell/ Mark Levinson
I hope you enjoy it.
Yes I had one of these new in the late 70's. It will clipp at 625 a side into 8 ohms. It is one hell of a power house. mine built up so much heat I has to run a box fan on it. this is while it was in its cabniet.Also recently had the sries 2 700. nice also. The levinson will make much more tranparent sound on the proper speakers. Enjoy It !
Twl...Put that in your Lowther, and smoke it...literally!
Yep. What a way to go!
Sometimes I have nightmares about hooking up a Phase 700 to my Lowthers!
I first heard the Fuzz Linear in the mid 1970s; great amp for driving Bose 901s.
You will find some interesting reading about these amps on this Official Phase Linear web site. Dean is the last PL factory trained technician still doing repairs.

This amp is indeed a powerhouse, however, proceed with caution. These amps were well known to short out and take the speaker drivers out with them.
This amp when refurbished is an excellent vintage performer but is not designed to handle planer loads which can drop below 2 ohms. Use this only on conventional 8 ohm speakers otherwise the amp will overheat.
All phase Linears ran hot. I sold these amps in the early 70`s. Put a fan on it, & it`ll drive low efficiency 4 ohm spkrs. all day & night long. Might, & I`ll hedge here, even deal with 2 ohm dips that aren`t that common.
I have a Series II, and have had no trouble with it. It does make some pops when turned off. It really opens up the speakers. This was a legendary amp in the seventies. For $400.00 at the pawn shop, it was a steal.
I still have the series 1. It ran hot and I installed fans in the back to keep it cool. It destroyed many a great speaker-- and I would not have had it any other way-- Nothing today comes close.
Yes I had the original 700B when it first came out then the series2. I could get 625 per channel out of it then i would start taking drivers out. Tweeters then mids then woofers:)
This is a follow up. This amp as well as any vintage piece should be restored with a complete rebuild if it is to be used on a regular basis and maintain reliability. About $700 to upgrade and restore this amp. But at this point we are then talking about a different piece of equipment. I do not recommend this amp for difficult loads.
Not a bad solid state amplifier from the 70's.....Mr. Carver was right about having sufficient power to handle musical peaks. I ran mine for about twenty-odd years with nary a problem. I bought mine back in 1976 (Series 1), and it ran reliably day-in day-out, year-in year-out. The only thing that went bad was that the lamps behind the VU meters burned out. It was the most powerful stereo amp back then when it came out (350 wpc). I still have my Phase Linear 700B, safely in storage and in perfect operating condition, but it has been long retired. Other amps resided in my system since then; now I have tube monoblocks. Maybe one day I'll dig out my Phase for fun and hear how it sounds with my present system.
I know I'm late adding a follow-up 2 1/2 years after the last one but I just inherited a 700B amp; 4000 pre-amo; 1000 noise reducer and I don't know a thing about them other than the little I've picked up on the web. This equipment has been stored by several members of the same family. It belonged to a deceased family member and even though no one wanted to use it, no one wanted to get rid of it either. I feel very fortunate to have inherited it but am on a fixed income and can't afford $700 to rebuild the amp, let alone the other two components. I was considering cleaning it up, both inside and out, applying deoxit to the switches and connectors and possibly purchasing a variable transformer to bring it on line very slowly. Beyond that, I am lost and I certainly do not wish to destroy this valued equipment. Help!!!
The 700B is good but for some reason the 400 sounds even better (I owned both). These direct coupled amps were probably the best sounding SS amps of their times and certainly outdistanced the Crown DC300 & D150s which were their major SS competitors. Both Phases had very anemic power supply capacitors and the sound can be significantly improved by outboarding more. And yes, they can handle 4 ohm loads easily and run a little hot so a whisper fan is a good idea.