louisthebass Posted December 15, 2017 Share Posted December 15, 2017 Like it says in the title, thinking about getting an East pre fitted in my Yamaha TRB5 as the factory supplied one seems a bit limited in tonal variation. Anyone out there done and if so, what are your thoughts on it? Any feedback appreciated... Quote Link to comment Share on other sites More sharing options...
GreeneKing Posted December 15, 2017 Share Posted December 15, 2017 I've owned a couple of TRB5's and I've fitted several East pre-amps, although not in a TRB5. I've got the new Uni-pre in my GMR Jazz 5 at the moment. My advice would be yes, asap Peter 1 Quote Link to comment Share on other sites More sharing options...
ikay Posted December 16, 2017 Share Posted December 16, 2017 (edited) My only caution would be with the pickups. In the early versions (with the slap cut) the soapbars are single coils with a dummy coil and I've read somewhere (on TB I think) about people swapping in a different preamp and getting an annoying hum. Apparently there's some circuitry on the original preamp which deals with this. I have one of these models (fabulous bass) and have often toyed with the idea of swapping the preamp to get a sweepable mid (rather than the three position rotary switch) but been put off by the potential hum issue. If this is in fact rubbish and swapping an East pre in works with no problem then I'd be interested to know! Edited December 16, 2017 by ikay Quote Link to comment Share on other sites More sharing options...
GreeneKing Posted December 16, 2017 Share Posted December 16, 2017 (edited) 1 hour ago, ikay said: My only caution would be with the pickups. In the early versions (with the slap cut) the soapbars are single coils with a dummy coil and I've read somewhere (on TB I think) about people swapping in a different preamp and getting an annoying hum. Apparently there's some circuitry on the original preamp which deals with this. I have one of these models (fabulous bass) and have often toyed with the idea of swapping the preamp to get a sweepable mid (rather than the three position rotary switch) but been put off by the potential hum issue. If this is in fact rubbish and swapping an East pre in works with no problem then I'd be interested to know! When fitting any pre with single coil p’ups it is good practice to shield and connect all the cavities and connect all the earths. This minimises single coil hum. I use conductive paint. My GMR has single coils and It’s quiet. I’ve just fitted a 2EQ Glockenklang into a SGC Nanyo and likewise I had several Mk1 TRBs and the pre is a bit ‘of it’s day’ and can be improved upon imo. Lovely instruments John East’s preamps are very good especially the new Uni version. My GMR Jazz has passive, passive tone and blend and sweepable mids making it very tonally versatile while keeping the original tonal signature. Peter Edited December 16, 2017 by GreeneKing Quote Link to comment Share on other sites More sharing options...
TheGreek Posted December 16, 2017 Share Posted December 16, 2017 JHK has a Goodfellows pre in his TRB5 - sounds fat and nasty - you may have to PM him for some soundbites... Quote Link to comment Share on other sites More sharing options...
louisthebass Posted December 16, 2017 Author Share Posted December 16, 2017 Appreciate the responses so far peeps - my TRB has soapbars (probably manufactured late 1990's as I bought it early 2000). What I'm really missing in the sound is a decent low end as even if I boost the bass control and roll the pickup selector knob onto the front pickup, it all still sounds a bit too midrangey for me. Keep 'em coming! Quote Link to comment Share on other sites More sharing options...
ikay Posted December 16, 2017 Share Posted December 16, 2017 (edited) The circuit diagram for the TRB5 II is on page 7 here - https://www.manualslib.com/manual/539186/Yamaha-Trb-5iif.html?page=7#manual Both the series I and II have single coil soapbars with a dummy coil. The dummy coil is 'balanced' with the active coil on the circuit board to achieve optimum hum reduction. On the series II this balance was adjustable via presets on the circuit board (VR7 and VR8 in the circuit diagram above). Series I had the same setup but without the adjustable presets. Swapping in a new preamp without the dummy coil 'balancing' circuit opens up the possibility of the pickups being more prone to hum. Shielding will help of course, but the benefit of the dummy coil will be compromised. This is what the thread I read about swapping the preamp in a TRB was alluding too. There are a few examples out there of people changing the TRB preamp with good results so it can be done. It's just something to be aware of. If you do get more hum at least you'll know why! Edited December 16, 2017 by ikay 1 Quote Link to comment Share on other sites More sharing options...
GreeneKing Posted December 16, 2017 Share Posted December 16, 2017 (edited) 4 hours ago, ikay said: The circuit diagram for the TRB5 II is on page 7 here - https://www.manualslib.com/manual/539186/Yamaha-Trb-5iif.html?page=7#manual Both the series I and II have single coil soapbars with a dummy coil. The dummy coil is 'balanced' with the active coil on the circuit board to achieve optimum hum reduction. On the series II this balance was adjustable via presets on the circuit board (VR7 and VR8 in the circuit diagram above). Series I had the same setup but without the adjustable presets. Swapping in a new preamp without the dummy coil 'balancing' circuit opens up the possibility of the pickups being more prone to hum. Shielding will help of course, but the benefit of the dummy coil will be compromised. This is what the thread I read about swapping the preamp in a TRB was alluding too. There are a few examples out there of people changing the TRB preamp with good results so it can be done. It's just something to be aware of. If you do get more hum at least you'll know why! That is great. It may be possible to use the existing 'blend' into a new pre-amp. Having met John East on several occasions I know it'd be worth showing him the diagram an asking him if it could be done. That way you could keep the existing arrangement of pickups, blend and control and use it to supply the new pre-amp. An interesting project with huge potential. I'm now wishing I had my TRB4 back. My 2nd ever bass that I bought new from Mansons in College Avenue, Plymouth. Edited December 16, 2017 by GreeneKing Quote Link to comment Share on other sites More sharing options...
ikay Posted December 17, 2017 Share Posted December 17, 2017 (edited) That's an interesting idea, hadn't thought of that! It wouldn't work with the series II as the entire preamp circuit and pots are surface mounted on a single board, but in the series I the Vol/Bal and EQ sections are on separate boards so that might work. The two boards are connected by a ribbon cable (unfortunately soldered, not with an edge connector) so you'd just need to identify the input/output and power supply wires. Edited December 17, 2017 by ikay Quote Link to comment Share on other sites More sharing options...
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