Custom Audio Preamp

CAE 3+ saga


If you ask a guitarist to quote an influential guitar preamp model, chances are he’ll tell you the legendary ‘CAE 3 + SE’. Indeed no other piece of gear has had such an impact in the business as much as this one. Synonymous with very high-end and legendary users like Steve Lukather, guitarist from Toto, this device has made and continues to make players dream.

The product has been continuously improved from 1991 until around the beginning of 1994. I could not detail all the differences here as it would take too long and those who would be interested in knowing more can always contact me.

However, there is one important thing to know. There are three different front plates (see photo). Two rather dark and one clearer.

The first one that says “Custom Audio Electronics” is from 1991 and 92. The second one, with similar color, stamped “Custom Audio Amplifiers”, corresponds to models from 1993 to 1995. The last one of lighter color, appears in 93. What we can notice is that the mention of  ‘SE’ appears only on the last model. But most preamps with the intermediate one are actually what is called a SE, i.e the final version.

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Depending on whether the market was American or European, the front plate included the famous acronym SE, or was omitted as relevant to the model. The versions without the two letters were sold in Europe until stocks were exhausted, that is to say at the end of 1995. While the SE front plate was already common in the USA since mid-1993. The product is the same. So you may have an SE without knowing it !

Nevertheless, we can detail the main differences between the very first version and the final version. On recent models, you should note less gain on the crunch channel and more gain on the lead channel, with a different equalization, both softer and with a bigger sound compared to the earlier models.

The clean channel has never been modified except on very rare models. There is a special clean channel called ‘full SE’ built into a few units. A Full SE model has a much larger gain, which is for connoisseurs like channel 1 boost mode of the CAE OD100 head.

Additional equalization has also been modified. On the first models of the brand, the sound was more scooped. Over time, the SE models (whether the logo is visible or not) have gained a more neutral equalization when the settings are at noon. Owners of the first versions however, have received reassurances that any version of the CAE 3+ can be brought to the level of the last version. It is an operation that is both uncomplicated and inexpensive.


How to date your preamp ?

Date and labelling on the front plate determine the true identity and age of the preamp. To date yours, it’s very simple. The first two digits correspond to the year, the next two digits to the month, and the last three digits to the actual production number of your device.

For example, serial number 9408417 indicates that the pre-amp was manufactured in August 1994, and that it is the 417th.


CAE 3++

When you know John Suhr and his passion for everything guitar, it’s hard to imagine that the man could stop there. While John may have been a co-founder of CAE with Bob Bradshaw, he has not been in the company for years. The Suhr brand has meanwhile become synonymous with a famous guitar brand and follows its path. But the paths did not really separate. John Suhr continued working on the CAE 3+ preamp until around mid 2000’s

So these famous mods, what are they ? In fact they are not really mods but often a return to the original Specs. The original transformer was not toroidal, the heaters regulator much more powerful and the clean channel was in black face mode.

Here are the details of the work to be done :


Crosstalk fix

In simple words Crosstalk (Xtalk) is deterioration of a signal caused by another signal Early 2000’s JS found out a little Xtalk problem in the preamp due to some parts of the circuit to close to each other. So this is not really a mod, it just put parts where they should have been. No major tone change, but a slightly thicker ch3 to my ears. Have it done when you have the opportunity.


Black Face mod

The 3+ preamp have, unlike many other on the market (Soldano, Egnater, just to name a few), discrete circuits for the clean and saturated channels. When all channels share the the first gain stages you have to do compromises.You’ll never get the best of both. Only discrete circuits can because your typical Marshall and Fender are different from the start. You already know how great the clean channel of the 3+ is. It’s pure Fender type circuit, with a few values changed.Stock it is brighter than a vintage Fender black face .The so called BF mod allows the channel to be less bright but have more warmth “sparkle at the same time”. You loose some harsh trebles for some “magic star dust”.  If you find your clean channel already too dark then it may not be an option for you..Anyway my experience tells me that if it is so something is making your tone dull somewhere in the chain. So far no one I know stayed with the stock clean after hearing the BF mod in THEIR preamp. Keep in mind that this can be fine tuned to your guitar, rig and preference . New Suhr OD100 head have a clean channel closer to this than to the stock 3+SE clean. As a side note : Some preamps called “FULL SE ” do exist..they are very rare and I have had one in my hands once.Those have a hotter clean channel than can go to crunch .  IMHO regular clean channel is way more useful.


Transformer swap

This the mother of all « mods » and actually if you didn’t know, a return to the original prototypes specs. For those who do not know this little story here it is again :  EVH was recording F.U.C.K when the preamp was still a proto .and one of those ended in his hands..he used it on the record and liked it.When it was time to give it back he of course requested a serie unit when it would be ready.But when he got it he said “not the same..not as good”. The difference was that the power transformer had become a toroidal one to help with noise and weight. In the early 2000’s John Suhr decided to have this tranny resurected and started to have them build to his specs..I remember the first time I installed one in my own preamp..I strummed a chord and Woa… that was more artificial compression that happens suddenly when you don’t expect it..a REAL dynamic response ..and Warmth, warmth, warmth !!! The whole sound is much more pleasing, singing, musical and thick …I personally cannot stand the preamp with the stock tranny anymore.. the Suhr tranny is THAT better. Everyone who have had one installed only had one thing to say ” Why the hell didn’t it happen before could I have played without it before ? ”  Really if you do not have it you do not know what you’re missing… Note that a different tranny was used from 2004 up to very recently… this one have several problems and I have seen several blow and burn …it doesn’t sound like the original and if the Suhr is a step up this one is definitely a step down.


Voltage mod

This mod affects only ch2 and raises the plate voltage later in the circuit The result is somewhat similar to the tranny swap… you get much more dynamic ,punch and thickness..less compression but a response to your playing very close to an amp head.


Heaters regulator swap

Heaters are a very sensitive part of your preamp..when voltage fluctuates too much your regulator can just stop working’ll get some tone loss and hum .. We have enough of problems with tone change when voltage fluctuates so if we could at least  eliminate the heaters problem .. it is now done with this new technology offers low dropout regulators  that are less sensitive to what your unit receives This mod consist you guessed it, in changing the stock old regulator for a new one, a better one’ll be happy to have it when the venue will offer crappy voltage 😉 While you’re at it verify that the Heaters circuit have 2A diodes and not 1A..the circuit asks for 2A and some units shipped with 1A.



If you have a 91/92 model you may benefit from this.. another opto was added around late 92 because some ch2/ch3 bleed was heard into the clean channel..if you want to know if this is happening to you this is what to do clean channel but put volume on zero ..leave the gain where you usually set it or slightly higher …now play a few chords and listen if you hear some of the drive channels bleeding ..on some units it is quite prominent ..usually the more gain you use the more you will hear this..  I definitely advise that you add this component if your preamp do not have it whether you hear the bleed or not.


Basic and Advanced Maintenance

Here’s about everything you need to know to keep your preamp healthy Tubes need to be changed after a period of time that greatly varies.If you play your preamp once a year they won’t wear out as fast as if you play 5 hours/day. Tubes can go bad and they do not warn you before doing so. Always keep at least a couple of pre tubes with you at gig. As for tubes choices anything labelled 12AX7/ECC83/7025 should work.There is plenty of choices and only you knows what will be your fav . I personally use Ruby 12AX7AC5HG+.  Next thing to check out are Filter caps… Those things do wear out slowly but also need to be changed after some people will tell you that 10 years is a maximum..others will tell 20 etc etc… I have recapped many preamp this year and most being at least 15 years old ,all did benefit from the change. The older the preamp ,the more drastic the effect was on tone clarity ,punch etc… Filter caps are there to filter hum..if you leave old caps in your preamp it will start to hum.That was the case of a couple preamps I recapped. It must be noted that caps value did change with time.Values used are 33µ,47µ,68µ and 100µ..It may not talk to you but you must know that the higher the value the more bass you get and the less fluid and singing the tone is IMHO.. From 33µ to 68µ you’ll get a slight change and everything is ok but the 100µ value is definitely not ok to my ears and doesn’t sound right  I routinely use 47µ on recaps and that is for me the best value.Note that it is the value you find into Suhr’s OD100 series of amps  Next thing to wear out are plate resistors but that should not be a problem to worry about too much..I have seen a couple fail though.  Again apart from tube change leave this to qualified techs. A few thing to check out : Your preamp circuit ground and chassis ground are connected together at one place only..that is the input jack..this one must always be tight to the front plate..and the front plate must always be tight to the chassis .it might be a good idea to verify if you have corrosion between the front plate and chassis.  If you have some sort of hum you may have one of the 1/4 socket on the back not isolated from the chassis..ONLY the front should be in contact. Check this too  If you have some hum when connecting an original 3+ 4 buttons footswitch, your problem is a ground loop caused by the cable..have it properly wired.  If you have a problem with your rear input then the problem is..front input ..yes.. The signal is routed there all the time with a contact socket..You can try to clean it or even bent the connector but I suggest changing it if something is wrong. Into your preamp is a little silver device into a brown cage close to the power transformer.. This thing is a regulator and it’s main chassis carries the must be tight contact with PCB ..if it becomes loose you’ll overheat your unit and you’ll get into problems. Just verify that the screws are not loose. Do not over-tighten this !!!  Pots can get dirty with time..the solution is Deoxit spray..BUT if you have a preamp from 95 and some years up you’ll notice that your gain, mids and EQ pots are smaller. DO NOT spray Deoxit those pots as they will become so loose you could turn them with your breath. Use a dry cleaner spray on those. Clean all 1/4 sockets with Deoxit once a year or so.

That’s about all you need to know for Maintenance 🙂

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Preamp Mods

All the mods are not compatible with all models. If you want to know which mods are available for your own unit, feel free to contact us.

Black face mod
X talk fix
Voltage mod
Tranny Swap
Regulator mod
Alpha to CTS pots
Omeg to CTS pots
10 € / pot
3+ to 3+SE
Opto add on