Reg Mods Update

[Jim in Idaho]

Pat, what you want are stacked metal film caps. I think the ones I used were .22mfd. Gary Brown down in Florida ( an SL user and electronics tech) sent them to me. He sent me a couple of different pairs. The ones I have left are Rubycon IH224J. The capacitance varies with frequency, but averages about .222mfd. Get the closest matched pairs you can. I don't recall exactly what these are...either 1 or 2%

Jim

[Jim in Idaho]

My understanding is you're "shorting" across C42 by running a jumper across the test points. (easier than installing the jumper across the cap itself). When I get around to this mod, I'm going to install a switch to turn it on and off.

Jim

[Melano87]

9 hours ago, CaliGold said:

@gflores71 on making the "jumper" on c42... How and  what am I soldering together here? The two test points mentioned or? The nomenclature from the email got me a little confused...  I see how the three pad diode smd was removed at d21 a  "jumper" was completed but the c42 is a two pad resistor smd. Are we wiring the two c43 pads together after removal of resistor or one of the test points to one of the pads or both? I'm lost...  Also,Does R75 resistor get removed/jumpered too? Thanks and sorry to pry but I'd like to complete this mod asap and get some testing / results posted for any other folks out there that were left looking for more sensitivity from the TDI SL.

@Jim in Idaho please freel free to share your knowledge on how this mod would be completed too (C42 and R75)

Thanks so much again to everyone. 

Pat

The jumper is made with the Test Points 2 and 31.

When I made this modification, I soldered a wire on the TP31, a wire on the TP2, I installed a switch (2 positions) next to the speaker (only place really available), I twisted the two wires up to the switch.

Why a switch? Because as the gain increases you have to be able to “control” it and there are places where it is difficult. So when I need it and possible I put it in the ON position.

Don't touch R9 - R75 - C42

On TDI SLs manufactured after 2015, D20, D21 and C56 are absent (modification taken into account by Whites). On those before 2015 they are present.

 

I also installed a potentiometer for adjusting the audio volume (like on the Beach Hunter)

[Jim in Idaho]

really great pics...many thanks!

Jim

[Melano87]

[CaliGold]

2 hours ago, Jim in Idaho said:

Pat, what you want are stacked metal film caps. I think the ones I used were .22mfd. Gary Brown down in Florida ( an SL user and electronics tech) sent them to me. He sent me a couple of different pairs. The ones I have left are Rubycon IH224J. The capacitance varies with frequency, but averages about .222mfd. Get the closest matched pairs you can. I don't recall exactly what these are...either 1 or 2%

Jim

Yes I know what yo buy just no one has them and digikey and mouset say they’re obselete and panasonic doesn’t make them anymore. I posted a pic of what digikey said was “similar “ it had 63v which is fine but they’re 2% tolerance. I’ll probably order them and instal this next week. Thanks to all for clarifying the gain mod with switch. How much gain are we talking? Is it bad to not have the switch installed? Would the machine go haywire using the normal gain pot? 

[Geotech]

The caps can be just about any film-type: polypropylene, polystyrene, PPS, etc. What you want is a cap with low microphonics. Then you want to match the 2 caps to 1% or better. So if you get 2% caps, order 4 or 5 of them and then hand match two of them with a cap meter.

On C42, I would not put a dead short there, rather put a 1k resistor across it. The reason is, there is a switch (U7d) that grounds that node and by shorting C42 the switch now grounds the opamp output (U12a). That's called "opamp abuse" and no one wants to be accused of that.

 

[Jim in Idaho]

Many thanks for the explanation and schematic Karl. I think the mod called for a jumper from test point 31 to test point 2? I'm not sure where TP 2 would be.

Jim

[CaliGold]

56 minutes ago, Geotech said:

The caps can be just about any film-type: polypropylene, polystyrene, PPS, etc. What you want is a cap with low microphonics. Then you want to match the 2 caps to 1% or better. So if you get 2% caps, order 4 or 5 of them and then hand match two of them with a cap meter.

On C42, I would not put a dead short there, rather put a 1k resistor across it. The reason is, there is a switch (U7d) that grounds that node and by shorting C42 the switch now grounds the opamp output (U12a). That's called "opamp abuse" and no one wants to be accused of that.

 

Thanks Karl!  If you have time can you comment on weather a on/off switch for this c42 resistor mod would be helpful or even necessary if one like myself is running mostly a 8x6 sadie with largest coil being 14" Coiltek TDI Series mono. (and the Miner John 8x12 on occasion). I'd rather avoid making the on/off. I would even forego using that 14" coil at all on this machine if the gain mod would make the switch absolutely necessary. 

 

*Also thanks for info on the c21 etc caps, sweep mod. They're hard to source online below 5% or 10% tolerance. Can I get away with say 3% or 5% tolerance on the cap models? I realize the "pair" ultimately used will have to be 1%...

 

ALSO... Man! you guys are quick with the helpful info! I owe you guys lots of gold found pics and imagery. I promise this fall/early winter will be epic...  I definitely owes you guys one on the DP forum.

[CaliGold]

50 minutes ago, Jim in Idaho said:

Many thanks for the explanation and schematic Karl. I think the mod called for a jumper from test point 31 to test point 2? I'm not sure where TP 2 would be.

Jim

Hi Jim, here is closeup of c42 (in blue) and those Test Points 2 and 31 ( in red)...

so your opinion is valuable too, do you think with coil below 14" the on/off switch on this c42 gain mod is absolutely neccesary? Thanks!

 

Pat