SquiddlyDiddly

Some tight tolerances and a lot of fun to solder.. after some basic tests for shorts this will go into the ultrasonic bath for a quick clean..

First version of my TAB1043 drop in substitute, just need to solder a second one, runs some tests and see what it sounds like..

Agreed, resistor not required, but a 10n cap ground cap would be good, which is what the Wal XLR uses and per Jensen circuit you shared. My Wal preamps use a Vishay MKT1813310405 0.01uF Film Cap, Funkles use a penny style Ceramic Disc cap (possibly a Vishay), same 10n/0.01uF value

I guess it is the way the Wal pickups are wound with individual pole coil outputs, the Zobel input filters (one per pole output) and the distortion from these 2 nodes which contribute the majority of the Wal sound and not a slew-limiting TAB1043..? I think the genius part of your Waly design is your own input filter design (rather than Zobel input filters) which allow you to use single coils pickups other than Wal/Turner multi coil style and still get the Wal sound?

Outstanding work RonC!!!!!! I wonder how many Wal players actually use the XLR output - my Wals have an OEP A262A5E 1+1:6.45+6.45 trafo (so probably a Wal specific version of the commercially available A262A3E). Funkle's Wal has an RS 217-804 (which is no longer available) trafo, also a 1+1:6.45+6.45 trafo and looks to be a rebadged OEP - none of these OEP trafos are expensive transformers (£18). The DI boxes in our studio are based on the Bo Hansen design, which use a mixture of Haufe ST8456 (£60) and Llundhal 1538 (£65) trafos, the Bo Hansen design also takes the A262A3E, which to my ears sounds a couple of pegs down in quality compared to the Haufe and Llundahl. In other words, I would record my Wal, using the jack into one of my Bo Hanse DI boxes and skip the cheaper Wal OEP transformer. I cant replace the OEP trafo on the Wal pre amp PCB with the Llundhal (its too big), but I could fit the Haufe ST8456 via an adapter board to make its pins match the OPE A262A5E - another thing to try out one day..

Question to Funkle - are you happy for Stas and myself to keep posting our documentation and analysis of the Wal preamp to your thread, or should we start a separate thread? - I don't want to be accused of hijacking your thread..

Great work Stas! This is the best, properly measured, analysis of the Wal preamp I have seen shared online, well done!!

Yes, I wondered that too, the slew rate for the TAB1043 is 0.02 V/us for +/-9V with a bias current of 1uA, which would imply that it the TAB1043 is slew-limiting and thus partly the source of the Wal sound. But there are other factors in the Wal circuit that could contribute more, which is why I wanted a drop in replacement to make it easy to measure and compare.. Plus there are other quad Op Amps with a similar slew rate to the TAB1043 which I can try.. I started down the path of cloning the preamp to make it easier for me to measure, I have created a schematic for the version of the Wal preamp which came with my Mk II 4 and MkII 5 string Wal basses, these preamps are different to the Mk I 4 string, the latter only supports 4 string pickups. I don't know which version of the preamp comes with the Mk III Wal bass or the 6 string Wal. It's easier in a lot of ways for me to do it this way, as I know I haven't transcribed the circuit incorrectly..! Later, when I have more time to check it, I will share my version of the Mk II schematic, which is absolutely complete and doesn't miss out any parts..

To help answer the question "what is the source of the Wal tone?", I have designed a drop in TAB1043 replacement, using a surface mount TL064 SOIC 14 quad op amp soldered onto a DIP16 sized PCB .. I'm just waiting for the PCBs to arrive, then I can try it out.. I suspect it will prove that the TAB1043 is not the source of the Wal sound, but we will see!! And this will also mean that all Wal basses can live after the supply of TAB1043s have disappeared..