© Christian Steingruber. June 2001

Introduction :

The Good News : ANY amplifier in the world can be connected to the Quad ESL speaker

The Bad News : most of them will give up in a cloud of smoke ( self-destruction mode) or damage the delicate electrostatic panels .

Amplifiers for Quad ESL 57

Remarks : the original Quad ESL is difficult to drive, a stable power amplifier is mandatory. A power rating of app. 25 watts is quite right , Class A or tubes preferred . It is highly recommend to use the protection circuitry (Schottky diodes) as suggested by Quad-UK , when the amplifier has a power output higher than 25 watts.

1. Recommended Vintage Stuff / Tubes ( no longer in production )

• Audio Research Classic 30 , D-79 ( and similar models)
• Conrad-Johnson MV-50
• Dynaco ST-70 ( original or Renaissance series )
• Dynaco Mk III monobloks
• Esoteric Audio Research 509 monobloks
• Futterman H3 , H3a, H3aa OTL
• Marantz Model 7 stereo ( original or Renaissance series )
• Marantz Model 9 monobloks ( original or Renaissance series )
• McIntosh MC 275 ( original or Renaissance series )
• New York Audio Laboratories OTL-3 Q
• Quad II monobloks ( original or Renaissance series )
• Quicksilver monobloks
• Radford STA-25 ( original or Renaissance series )
• Radford STA-15 , MA - 15 , MA -25 monobloks

2. Recommended Vintage Stuff / Solid-State ( no longer in production )

• Bedini 10/10 and 25/25 Class A
• Classe Audio DR-2 Class A
• Electrocompaniet "The 2-channel amplifier" Class A
• Goldmund Mimesis model 6 MosFet
• Krell KSA 50 Class A
• Mark Levinson ML-2 Class A
• Nakamichi 420
• Pass Aleph 30 W MosFet
• Pioneer M-22 Class A
• Quad 303 modified by Avondale Audio or Steve McCormack
• Quad 405 or 405-2 modified by Avondale Audio or Steve McCormack
• Spectral DMC 50 Class A
• Stax DA 80 Class A
• Sugden P51 Class A

3. Integrated amps

• Naim NAIT solid-state ( original version only )
• Esoteric Audio Research 859 Single-Ended-Triode
• Jadis Orchestra Pentode

4. Recommended Contemporary Offers

• Atmasphere S-30 and M-60 OTL
• Esoteric Audio Research 861 Triode
• Esoteric Audio Research 534 Pentode
• Graff GM-20 OTL
• Nagra VPA Triode
• Quad II-40 monobloks
• Transcendence OTL
• Vacuum Tube Logic TT-25 Tiny Triode monobloks

5. Not recommended for safe use with the Quad ESL-57 - AVOID !

Generally following items should be avoided in any case :

• Solid-state amps made for pro-audio applications (public address systems)
• Solid-state amps with capacitors in the output-stage
• Cheap integrated amps

Some examples :

• BGW series 200 ( may go into severe oscillation and destroys the treble units )
• Ion Obelisk range ( not stable into electrostatic loads because of capacitor coupling )
• Job series by Goldmund ( not absolutely stable into electrostatic loads )
• Lectron JH 50 ( switch-on thump that may destroy the '57 )
• Quad 306 ( Quad-UK say it shall not be used with the '57 )
• Rotel RA 820 , RA 840 ( good integrated amps but not stable into the '57 )

6. Not recommended sound wise - though quite stable

Amplifiers for Quad ESL-63 / ESL- 98 series

Remarks : quite a kinder load than the original ESL , although the 63 and its successors still need stable amplification with power and control. A power rating of 40-100 watts is recommended anyway , tubes or Class A preferred. Two protection circuits prevent possible damage when high output amps are used .

1. Recommended Vintage Stuff ( no longer in production )

• Audio Research D-79 A
• Conrad-Johnson MV-50
• Counterpoint SA 4 OTL
• Classe Audio DR-2 , DR- 3 Class A
• Esoteric Audio Research 509 / 519 / 549 series ( all monobloks )
• Futterman H3, H3a, H3aa OTL
• Goldmund Mimesis model 6 , model 9
• Marantz Model 7 stereo ( original or Renaissance series )
• Marantz Model 9 monobloks ( original or Renaissance series )
• McIntosh MC 275 ( original or Renaissance series )
• New York Audio Laboratories OTL-3 Q
• Krell KSA 50 , KSA 100 Class A
• Pass Aleph MosFet
• Quad 405 or 405-2 modified by Avondale Audio or Steve McCormack (monobloks)
• Spectral DMC 50 , DMC 100 Class A
• Stax DA 80 , MA 80 , DA 300 all Class A

2. Recommended Contemporary Offers

• Atmasphere S-30, M-60, MA-1 OTL
• Esoteric Audio Research 861 triode, bridged as monobloks
• Esoteric Audio Research 534 pentode, bridged as monobloks
• Graff GM-20 bridged as monobloks OTL
• Graff GM-200 OTL
• Inner Sound ESL amp solid-state
• Nagra VPA triode
• Quad II-40 monobloks
• Quad 909 solid-state
• Transcendence OTL
• Vacuum Tube Logic ST-85 tetrode

3. Not recommended

• Quad 405 ( stable , but mediocre sound - sorry Peter )

The Author :

Christian Steingruber , member of Audio Engineering Society – Austrian Section

Education : Tonmeister studies at the Viennese "Hochschule für Musik und Darstellende Kunst"

Contact via :

Tel. +43 664 4922582

christian.steingruber@utanet.at

English is not my native language, thus please apologize any errors and failures.