I have started on building an entirely new system for my living room. Transformers and many parts for my hand built monoblock amps are on back order or delivery dates months out. So I turned to the preamp I am going to use with them.
I bought 2 Audio Research LS1s (same as LS9 minus built in phono stage) for the project. The LS1 is a hybrid FET/MOSFET/Tube design, using a 6922 in the tube role. It's fully regulated on the B+ as well as the heater supply. I know there is huge debate over this, but I am quite fond of the idea.
The black LS1 was in mint condition and the silver LS1 arrived in terrible condition, nothing like the seller described. But my plan was to modify one, compare to stock and decide if I could actally improve the preamp. So I kept it. What that added was a restoration as well as modification.
The goals of this were:
So having the preamps, this is how the Silver LS1 restore and modification went:
So the verdict?
Well it looks great and is very clean. The corrosion is removed and halted and hard to even see where it was. The sound is a definite improvement over the stock LS1... there is a slightly darker background, there is definitely more top end and air. The LS1 has exceptional low end by default, but it still tightened up nicely, but then again all of the signal did. It's less harsh with the GE tube as well. Most of the LS1 issues that were critiqued in the press are sins of omission (it's an entry level ARC pre) and these changes remedy them IMO. There was such an improvement in the sound, even my significant other went, it does sound better. And she has 0 interest in audiophilia or electronics.
I am certain any high quality modern capacitor is an improvement over the Rel Cap and Wonder Caps in these old units for those wondering... and this seems to be a popular internet question.
So part 2 is going to be to redo the black LS1 as well, but using premium parts. I am planning on using Auricap XO capacitors and probably will stiffen the power supply even more.
Have a look through the pics to see begin to end progression.
I bought 2 Audio Research LS1s (same as LS9 minus built in phono stage) for the project. The LS1 is a hybrid FET/MOSFET/Tube design, using a 6922 in the tube role. It's fully regulated on the B+ as well as the heater supply. I know there is huge debate over this, but I am quite fond of the idea.
The black LS1 was in mint condition and the silver LS1 arrived in terrible condition, nothing like the seller described. But my plan was to modify one, compare to stock and decide if I could actally improve the preamp. So I kept it. What that added was a restoration as well as modification.
The goals of this were:
- Replace all the electrolytics with new ones as this pre is pretty old at this point
- Update the audio signal and possibly the power capacitors
- Not break a single connection of the Litz wire anywhere in the preamp which meant try to salvage the RCA jacks
So having the preamps, this is how the Silver LS1 restore and modification went:
- Polish RCA Jacks with Simichrome metal polish and a rotary tool
- Carefully clean front panel and knobs with bleach spray to remove years of dirt and film
- Clean pots and switches with CRC 2-26 spray - an electrical contact cleaner I prefer to Deoxit and it's way cheaper and available at Home Depot
- Cut off hardwired power cable
- Cut and drill aluminum for can capacitor and IEC radio filtered power jack
- Sand top and bottom to bare metal to get rid of corrosion and bad paint
- Soak hardware in white vinegar to neutralize and remove corrossion
- Sand handles of corrosion spots and bad paint
- Respray the top, bottom, handles and hardware with black rust inhibiting paint
- Blow out as much aluminum bits and dirt as possible with canned air
- Sprayed 32 oz white vinegar through out pre and scrubbed with acid brush to neutralize corrosion
- Sprayed with 32oz 91% isopropyl alcohol to work on dirt and oil
- Sprayed with multiple cans of CRC Lectra Clean and Contact Cleaner to work on dirt and oil
- Replace all Rel Cap and Wonder Cap with 630V Solen Fast Caps (metalized polypropylene) in power section and Dayton (film and foil) 250V/400V capacitors in audio path - the film in regulated suppy was bumped from 2.0uf to 4.7uf and the last output cap went from 5.0uf to 6.2uf. All others are same value
- Replaced Sprague 100uf/450V with Illinois Cap 100uf/450V and added a JJ 100 + 100uf/500V can capacitor
- Move the 7815 regulator to the chassis as it gets very hot and it is visible where it darkened the board from heat. It stays very cool in this position.
- Replace the EH6922 with a NOS GE 5670W and added silicone tube dampening rings
So the verdict?
Well it looks great and is very clean. The corrosion is removed and halted and hard to even see where it was. The sound is a definite improvement over the stock LS1... there is a slightly darker background, there is definitely more top end and air. The LS1 has exceptional low end by default, but it still tightened up nicely, but then again all of the signal did. It's less harsh with the GE tube as well. Most of the LS1 issues that were critiqued in the press are sins of omission (it's an entry level ARC pre) and these changes remedy them IMO. There was such an improvement in the sound, even my significant other went, it does sound better. And she has 0 interest in audiophilia or electronics.
I am certain any high quality modern capacitor is an improvement over the Rel Cap and Wonder Caps in these old units for those wondering... and this seems to be a popular internet question.
So part 2 is going to be to redo the black LS1 as well, but using premium parts. I am planning on using Auricap XO capacitors and probably will stiffen the power supply even more.
Have a look through the pics to see begin to end progression.
Attachments
Looks like a great job of restoration. It goes to show what talent and a DIY heart can do to bring back what others might have considered to be too much work. I've always considered that unit to be a very fine one. At any rate you can be very proud of the fine work.
I've been playing with powder coating and would probably coated the chassis if it were mine.
I've been playing with powder coating and would probably coated the chassis if it were mine.
Thanks everyone for the feedback. To answer the which cap Q, I used Illinois 100uf/450V + 100+100/500V JJ for the high line and Illinois 5000uf/50V to replace the 1500/35V on the low voltage rail. The chassis is black anodized aluminum and looks as good as day it was made. Nothing needed there.
Part of the build was an experiment to see if the pre and those caps were as good as people say. The Rel Cap and Wonder all measured correctly upon removal. But if you go the other way in time, the #1 improvement from 1960 (or even the 70s) to when this preamp was made was in capacitor materials and construction. And we've had leaps and bounds since then. Part of the test was would modern, affordable high quality parts be better because of those improvements?
I used the exact same tube (EH6922 and GE5670) in the stock unit (which is mint condition) and this totally trashed restored one. There is no comparison on which sounds better. It's not currently the black stock one.
The Solen caps are only in the power supply. I wouldn't choose those for audio signal.
The Dayton caps are all true film and foil, not metallized poly like the Solens. (note they make both, be careful which you buy) They are the best sounding cheap capacitor you can buy in the USA. (that is my opinion)
But seriously, it made a huge difference in the quality of the sound. I was perfectly content to leave the black unit in its mint condition state. But after doing this, there is no way I am leaving it stock. All of those old capacitors are coming out. I am going to do that unit too.
One thing I forgot, I replaced the 1N4005/1N4006 with 1N4937 fast recovery 1A/600V diodes as well.
Thanks again everyone. It was a fun project and the outcome was an improved piece of gear to enjoy for years to come.
Part of the build was an experiment to see if the pre and those caps were as good as people say. The Rel Cap and Wonder all measured correctly upon removal. But if you go the other way in time, the #1 improvement from 1960 (or even the 70s) to when this preamp was made was in capacitor materials and construction. And we've had leaps and bounds since then. Part of the test was would modern, affordable high quality parts be better because of those improvements?
I used the exact same tube (EH6922 and GE5670) in the stock unit (which is mint condition) and this totally trashed restored one. There is no comparison on which sounds better. It's not currently the black stock one.
The Solen caps are only in the power supply. I wouldn't choose those for audio signal.
The Dayton caps are all true film and foil, not metallized poly like the Solens. (note they make both, be careful which you buy) They are the best sounding cheap capacitor you can buy in the USA. (that is my opinion)
But seriously, it made a huge difference in the quality of the sound. I was perfectly content to leave the black unit in its mint condition state. But after doing this, there is no way I am leaving it stock. All of those old capacitors are coming out. I am going to do that unit too.
One thing I forgot, I replaced the 1N4005/1N4006 with 1N4937 fast recovery 1A/600V diodes as well.
Thanks again everyone. It was a fun project and the outcome was an improved piece of gear to enjoy for years to come.
Other sleeper caps worth trying are the 940 and 942 series from Cornell-Dubilier. Not as lush as oil caps but way less expensive. Favourites of John Broskie and available from Mouser.
A new production tube worth trying is the Gold Lion Genalex (Russian reissue) E88CC. More refined (and more expensive) than the EH 6922, IMHO.
S.
A new production tube worth trying is the Gold Lion Genalex (Russian reissue) E88CC. More refined (and more expensive) than the EH 6922, IMHO.
S.
I addition to the fast recovery rectifiers you may also want to install Quasimodo optimised snubber networks on each transformer secondary: Simple, no-math transformer snubber using Quasimodo test-jig
Take care,
Doug
Take care,
Doug
