Repair your Cambridge Audio 840E volume contol issues

Many people with Cambridge Audio 840E (and I think 840A) preamps have reported strange volume behavior where the volume levels will suddenly change. Recall that these are the pre-amps with the relay controlled discrete resistor ladders and the Terrapin modules. There has been a lot of speculation posted on the web as to the root cause for this problem, including bad relays and bad volume knob encoders. Cambridge has since changed the design, removing the relays altogether and replacing them with solid state switches. Some, like myself, believe this is a step backward and would like to find a solution to the original faults with the discrete relays.

I own an early version of the 840E that was sent back to CA for re-work. Their service department added a separate relay board (containing the 28 relay array) with Omron G5V1 relays instead of the Massuse ME-3 relays that originally came from the factory. I was assured by Cambridge Service that the new relays cured the problem, but a few years later my volume control issues returned. I purchased a replacement set of Omron relays and replaced the Omrons supplied by service, and this did the trick for another 4 years or so. When looking into the specs on the G5V1, I found a most unusual disclaimer by the manufacturer:

"• Long-term Continuously ON Contacts

Using the Relay in a circuit where the Relay will be ON
continuously for long periods (without switching) can lead to
unstable contacts, because the heat generated by the coil itself
will affect the insulation, causing a film to develop on the contact
surfaces. Be sure to use a fail-safe circuit design that provides
protection against contact failure or coil burnout."

So what Omron is saying is that these were never designed for continuous use, as one might have in a volume control left at the same volume level for long periods of time. Further, it appears heat and high temperatures are at the root cause of the issue. If you look at the relay array for the volume control, the Cambridge design has these relays mounted as close together (side by side in two rows) as they can fit, and the center relays can get very hot. Due to the design of the volume ladder, not all relays are on at any one volume setting. There are also volume settings where the power generated by the relay array is maximum. From a document sent to me by Cambridge audio, it show that the current drawn by the relay array is a maximum of 271 mA at -32 dB, but drops to 131 mA at -30dB and 178 mA and -38 dB. The -32 dB area is where I see my volume instabilities, so it appears it may be related to power generation (and high temperatures) in the center mounted relays in the array. There are also high current levels at -16 dB and -8 dB (271mA) and -4, -2 dB. Of course, with the volume up above -8 dB, volume jumps to 0 dB are much less noticable when they occur.

So what can be done?

I was told by CA that the Omron replacement was the only one available. Turns out not to be true. I have found that Fujitsu makes a better relay that is plug and play replacement (SY-9W-K) for both the Omron and the Massuse relays. The Fujitsu relay has two contact options as well, one of which is much better for the ladder network. Let me explain. In the Omron spec sheet for the G5V1, there is a MINIMUM current rating of at least 1 mA. That means the circuit must flow a minimum of 1 mA to keep the contact resistance stable. Another condition violated by Cambridge Audio Engineering. The Massuse ME-3 is similar. The Fujitsu, however, has two contact configurations, one at 1 mA minimum and the second at 0.1 mA. The latter is more suitable of low current audio use. I believe the contact material (Pd/Ag under Au) is better as well. Finally, the Fujitsu relays are Japanese made whereas the Omron and Massuse are Chinese made. The Fujitsu relays have no continuous duty disclaimer in the spec sheet like Omron has.

Besides relay replacement, it is wise to do everything you can to keep internal temps down. I have my upper cover mounted on 1/4" stand offs to allow air to circulate inside the pre-amp. Mine is an early version without the vents. I have also mounted small aluminum heat sinks on the relay arrays to re-distribute the heat generated in the center units and lower their temperature.

Hope this post helps some of you who like the 840E and do not want to trash an otherwise fine sounding piece of gear due to the irritating volume control issues.
Dear Friend,

Thank you very much for your reply.
I understood what you said.
Is it a good idea to use socket strips? Couldn´t it cause bad contacts after some time?
What type of socket strips did you used?
It is true that it is very interesting to make future replacements easier.

Thank you for sharing this solution with us. 
Socket strips are optional, of course. If you are careful with the soldering iron, and have a good vacuum de-soldering tool, soldering in the relays is OK. With socket strips, you only solder once, and any replacement afterward is easy. Do not overheat these pc boards or the traces will lift and then the board is useless. If you solder, you will probably not get more than two relays change outs before the board is destroyed unless you have a nice temp controlled industrial vacuum de-soldering tool like a Hakko. This is because the boards use plated through holes and it is very difficult to get all the solder out of the holes on the topside of the board where the relays sit. If the solder is not completely removed and you pull the relay off, you will lift the traces with the relay as it comes off.

I use high quality gold plated MACHINED socket pins/strips. You can get these at Mouser or Digikey electronics distributors. They are a bit tricky due to the odd spacing of the relay pins, and Cambridge did not space the relays exactly on 0.1" spacing. I cut the unused pins on positions that are not used but left them in the strip. I believe I ran the strips horizontally across the rows of relays. This requires the fewest socket pins, but the running length must be broken up into two or three sections, as the spacing tolerance is not exactly 0.1".
dhl: Thanks for your reply. I'm not sure why I just saw/viewed it now?

I purchased yet another 840E (I love this thing -and its reasonable price).

The original one-owner had not experienced these volume-control issues, but low and behold, I'm experiencing (loud-ish/sharp/snappy) 'crackling' sounds coming through my R-Channel loudspeaker -loud enough to be concerning to the health of the drive-units !

My 840E (on the other hand) has no ;crackling' sounds but does exhibit the 'runaway' volume problem -in addition to cutting/out (abruptly/sharply -and loud) as the volume control is approaching higher volume attenuation (numerical reading "38" (and lower) on the display.

It's a PIA that remarkably CA refuses to either admit -or offer up a permanent solution/fix. That's the most disappointing aspect. 

If I knew of a better sounding/built preamp anywhere near the 840E's price (new or used), I'd gobble it up. However, in my 40-years of hifi experience, its proven difficult to find not only  a great sounding preamp -but one of reasonable (cash) outlay has proven illusive. (lol)

So, I remain with my wounded peamp -not giving up on her so easily !

Thanks for your help.


Thank you so much for this post, and keeping my 840A out of the skip bin.

3 years on, the Fujitsu's still working correctly?

It is the same omron relay in the 840A v2, that you name.

There are 2 possible causes of volume problems, the relays AND the encoder... If you're as lucky as me it will be both.

If the volume works smoothly when using the remote, the problem is the encoder.
RE: CA 840E Volume Attenuation Circuit (Resistor/Relay)

09-30-2016 6:27pm

dhl: Thank you very much for your most useful/needed explanation
of the volume issue impacting the CAmbridge Audio 840E preamp.

I purchased a second 840E (I love this thing !) that was recently returned
to me from CA Canadian distributor Plurison (Naim-Focal) for this very issue.
( supplied the 28 Fujitsu SY-9W-K relay's as you referenced.
Pluison Repair Depot also replaced the P/S cap's, 'Encoder' -and replaced the
stock faulty/shitty relays with the Japanese Fujitsu's.

Preamp sounds great ! Once again. 

As dhl pointed out, the 840E is worth the effort to 'restore'. I'll go further by saying
it's an exceptional, high-resolution line-stage that easily competes with far greater
priced alternatives.
BUT, this  repair MUST be undertaken; shorting/over-heated stock relays  emit such powerful/loud noises (crackling, "pop's") as to endanger loudspeakers. IT IS, quite 
In Canadian dollars, the 28) Fujitsu (SW-9-W-K) relay's cost $90. CAD.
Labour 'stings'(costing me $240. CAD), a few other pieces/parts, shipping and you're
into $450. (CAD). Plurison used the original (volume) circuit board without issue, I was 
informed !

Was it worth it ? You bet. The 840E is a fantastic, high-resolution, articulate, dynamic
and musical performer; if one can be purchased (used/excellent condition with full/complete factory packaging -you'll need it) between $600-$800, undertaking the demanded repair will
add another few hundred dollars (depending on labor charges) and you will revel in superb SQ. It IS, that good/excellent ! (Oh, and one should/must consider improving top-cover ventilation for the 840E -that inexplicably comes with no top-plate ventilatin holes.
Options would include:
A) Drilling (carefully) holes in the OE top-cover, or
B) Find/buy a top-plate/cover from the newer CA 851 series that offers proper (and desperately required) ventilation; the 851A? Integrated/Amplifier top plate -that has the most extensive ventilation, or the L/R sided 'vent' from the 851N, 851D, 851C etc. 
(Keep in mind the 851 Silver Top-plate is much brighter (different color/tone) than te painted steel top-plate of the 840 series. Perhaps the color black is better here ?
C) Consider using/purchasing a smoked/tinted' plexiglass (3mm/, 1/8" thick) and cut to required size -not forgetting proper ventilation considerations. 

dhl, thanks again for your excellent original post and subsequent replies.

BTW, these Fujitsu relay's are NEAR SILENT in operation -and that's wit the top-cover off / removed - I can barely hear it operating/clicking.      

peter jasz