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Audio Research LS7 Preamp Restoration and Enhancement

Audio Research LS7 Preamp Restoration Project and Can DIY Improve It?

Audio Research LS7 Preamp Restoration by Sean Rose

I started with 2 Audio Research LS1 Preamps. Click here to view the beginning of this story.

I bought 2 Audio Research LS1s as the start of a new system. The LS1 is a hybrid FET/Tube/MOSFET design, using a 6922 in the tube role. It is fully regulated on the 400V+ high-voltage B+ as well as the heater supply. The LS7 is very similar, the power supplies are very close, but only uses 1 semiconductor as a current source and four 6922 vacuum tubes in the gain and output stages.

The LS7 is a simpler preamp, despite having more tubes. Its cable routing is shorter, the PC board is less complex and it lacks switching and balance that the LS1 has. The LS7 being a little newer and being in spectacular condition, didn't require a great deal of work. The main change was to replace all the old electrolytic capacitors and upgrade the power supply film caps to Solen Metalized Polypropylene and the audio path capacitors to USA made Auricaps.

Photos

Taping up the PC board to drill IEC power cord hole, 2 RCAs for a second output and mounting holes for the new electrolytic can capacitors.

Audio Research LS7 Preamp Restoration by Sean Rose Audio Research LS7 Preamp Restoration by Sean Rose

The targets to remove. The REL-CAPs and PC board mounted electrolytics. On the LS1s I cutout the tube sockets and replaced with Belton Micalex ones. I haven't done that to the LS7 yet, but I plan to.

Audio Research LS7 Preamp Restoration by Sean Rose
Audio Research LS7 Preamp Restoration by Sean Rose

Electrolytics updated from 470uf + 100uf to 800uf and 350uf. Outputs updated from 2uf to 6.8uf Auricaps.

Audio Research LS7 Preamp Restoration by Sean Rose
Audio Research LS7 Preamp Restoration by Sean Rose

The RCAs cleaned up nicely with some Simichrome polish. Note the additional last set of RCAs I added to have a second output from the preamp. I need two; one for the power amp, one for the subwoofer amp. They are the exact same type as originally used by Audio Research.

Audio Research LS7 Preamp Restoration by Sean Rose

That's a nice picture. Four NOS (new old stock) Sylvania 6922s added. Note I added silicon dampening rings as well in the final assembly.

Audio Research LS7 Preamp Restoration by Sean Rose

Setup and playing with a Rega P3-24, EICO HF-87 and B&W 703 tower speakers. The sound is very, very good.

Audio Research LS7 Preamp Restoration by Sean Rose

So How is the LS7 vs the LS1? Pros and Cons of Each Design

Both preamps sound fantastic and are worthy of a place in any audiophile system. They are both excellent performers and the differences in the 2 are very subtle. I would imagine the LS1 is the best bet for most users, but the LS7 with some serious time spent matching high quality tubes can attain a slightly higher fidelity.

LS1

  • One tube is much cheaper; the solid-state devices make having a premium tube not necessary. The circuit is very forgiving of the typical variations in vacuum tubes
  • 20db gain vs 13db gain for LS7
  • Solid state devices have lower output impedance and can drive solid state amps and longer cables better
  • 6 inputs vs 5 on LS7
  • Balance control
  • Tighter, better low bass and extension
  • Two output RCA jack sets

LS7

  • Slightly better and more open soundstage; better depth and placement
  • The internet rumor of 'lean bass' likely comes from the 2uf output capacitor driving solid state amps; increasing this I hear no lack of bass at all
  • 13db of gain is fine for most systems; however, may not be enough with some equipment
  • DC coupling from input to output makes the tube selection very, very, very tricky as each section difference is multiplied in the DC levels through the preamp
  • Tube selection and matching is critical because of above
  • The trade off for increased hassle of setup and lack of controls is simply a better sound
  • Much, much more expensive to re-tube
  • Only has one RCA output set

I started with 2 Audio Research LS1 Preamps. Click here to view the beginning of this story.