The UNI-PRE uses separate active and passive signal paths.

In passive mode it retains a genuine passive blend path, so the result still depends on the pickups. In active mode the blend is handled after buffering, giving a smoother and more predictable response.

This design was chosen to retain passive operation while also providing a reliable active blend.

We have many happy players with UNI-PREs in their TRBs.

• We recommend using the PU screen/ground bare wire as the cold connection and the red wire as the hot signal.
• The UNI-PRE doesn’t have a dummy coil input. So, insulate the white wire and leave it unconnected. (do not ground it)
• Since Yamahas are such a great build and, well screened, most don’t seem to have any issues without the dummy coil.

Please check red jumpers are present as shown in pic https://www.east-uk.com/wp-content/uploads/2026/06/red-jumpers.jpg

Did you try a new battery? 

Is the current battery old or a low cost type? 

If the battery is low, it shouldn’t be less that 6V when under load (ie when the preamp is on). 

Please try a brand new known battery and if things get better, see the description below for what’s probably happening. 

We’ve seen there to be lots of dud and battery copies over the last 10 years or so, even whole boxes of reputably named batteries that have little or no power right out of the box. 

Many chips shut down without any noise with a low battery, but often ours, amongst the higher spec chips, don’t. 

An Industrial Duracell, according to their spec sheet, should just last over 100 hours before it reaches 6V. 

NOTE: It’s very important to measure a battery under load of the circuit it’s being used with or with a proper battery tester. (Just measuring with a meter, which has very little loading effect, can be very misleading since batteries recover off-load to seemingly workable voltages, maybe 7-8V) An Industrial Duracell, according to their spec sheet, should just last over 100 hours before it reaches 6V. 

NOTE: It’s very important to measure a battery under load of the circuit it’s being used with or with a proper battery tester. (Just measuring with a meter, which has very little loading effect, can be very misleading since batteries recover off-load to seemingly workable voltages, maybe 7-8V) 

The UNI-PRE is relatively thirsty compared to other units due to an increased number of chips compared to the more regular units. The extra chips are there to allow for the internal frequency wheel settings as well as other features. 

A UNI-PRE takes ~5mA whereas other units with many fewer features may take 2.5mA or less. I take the view that, although power consumption is important, performance is our highest priority, and fortunately, battery capabilities tend to increase as time goes on. 

• Distortion in active mode: The J-Retro and Uni Pre models are not designed to be used at maximum volume in active mode, especially with significant EQ boost. Back off the volume to increase headroom and avoid distortion. 

• Balancing active and passive levels: To achieve similar levels in active and passive modes, fully back off the internal gain preset adjusters, set the EQ to neutral, and adjust the volume as needed. 

We have good number of preamps out there with EMG Actives, and they work well, with happy customers who say they are a good combination.

About Passive Tone Pots

Many of our units have Passive Tones. Our tone pots have the same capacitors as EMG but the tone variation will occur more towards the end of the rotation due to our pots. The maximum effect will be the same as the EMG tone pots. In other words, the passive tone won’t be as smooth as the EMG pots.

+ J-Retro is fine. 

+ J-Deluxe will work fine except the our passive tone is 250K whereas the EMG is 25K. 

* We use the same capacitors as EMG but since our pot is set for passive pickups, although it will still work, all the action will be towards the backed off setting, ie the darkest tone. It won’t be as smooth as the EMG pot, in terms of rotation versus effect. 

+ UNI-PREs have a passive path that isn’t useful with EMG Actives, since the pickups aren’t just a ‘passive’ coil. 

* passive is more is effectively EQ bypass. 

If I connect the red wire (+) to the battery, can the uni-pre 5 handle the EMG impedance? 

+ Connecting EMG Red Wires to the UNI-PRE + Red Wire is fine. 

+ No issue the Pots in the UNI-PRE, each PU has an Input Buffer stage that feeds the Vol &  Blend circuit. 

+ The UNI-PRE Passive Tone is a higher value than the EMG, but it will still work. 

* The Tone Mellow Factor will be the same, but the effect will be more towards to end of the Pot Rotation.