SL+ to BE mods

[CrazyNutz]

Interesting regarding the cathode follower's cathode bypass cap. So you think it's taking some mid-range honk, like 600Hz or 800Hz?

I don't think the cathode bypass has the same effect of boosting gain on frequency's when applied to a cathode follower like this. If you look at where that 500pf cap ties in you can see/think of it's interaction with the tone stack. It's 500pf to ground right where the signal enters the treble cap, and the slope resistor. Placing it across cathode followers cathode resistor is just a convenient location.

 

[djd100]

I agree, thanks for pointing that out.

I'll try a 500pf on the V2B cathode follower's cathode bypass next, but it's sounding really good already with it's BE bright channel and it's relatively stock Plexi normal channel blended together (typically about 60% - 40% BE Bright/Plexi Normal.

Interesting regarding the cathode follower's cathode bypass cap. So you think it's taking some mid-range honk, like 600Hz or 800Hz?

I don't think the cathode bypass has the same effect of boosting gain on frequency's when applied to a cathode follower like this. If you look at where that 500pf cap ties in you can see/think of it's interaction with the tone stack. It's 500pf to ground right where the signal enters the treble cap, and the slope resistor. Placing it across cathode followers cathode resistor is just a convenient location.

 

[CrunchBunch]

I think it's important to note that Randall had some revisions to their PCB's through out the years, so the various PCB's parts designation numbers are not always the same etc.

Just a FYI...

This will not be a problem if a picture is provided. Although some component numbering has changed, the locations are almost identical. There are also later revision boards that have more component locations/options, but again the locations of the carried over components are largely identical.

 

[CrazyNutz]

Man, I'm itching to get a plexi module and mod it like yours with the dual concentric pot.

At any rate all that matters is what sounds good to you. It's so easy I would give it a shot to see if it's something you like.

I agree, thanks for pointing that out.

I'll try a 500pf on the V2B cathode follower's cathode bypass next, but it's sounding really good already with it's BE bright channel and it's relatively stock Plexi normal channel blended together (typically about 60% - 40% BE Bright/Plexi Normal.

 

[CrazyNutz]

So through experimentation, BE Schematics, and looking at pictures of H.B.E mods I think this is pretty much how to mod a SL+ to an H.B.E.




These are pictures of H.B.E. Mods

 

[CrunchBunch]

That's an excellent way to show the changes. Top work CrazyNutz.

I've got the C3/R16/R7 combo on a DPDT switch so I can switch between 22n/4.7k/100k and 2n2/2.7k/0. The first mode is a thick brown sound and the second is a truckload of gain. To avoid blocking distortion in V2A R27 must be changed to something in the 56k-470k range depending on how loud you play.

Also, R10, R15 and R27 should be 2-3W resistors to reduce noise (electrically, 1/4W resistors will work fine, but these grid resistors have the potential to introduce a lot of noise if their power ratings are too small).

 

[withmittens]

yes, thank you for that drawing. nice of you. Your mods seem to look different, is this because you have them on switches and whatnot? and have nicer caps in there?

 

[CrazyNutz]

yes, thank you for that drawing. nice of you. Your mods seem to look different, is this because you have them on switches and whatnot? and have nicer caps in there?

No problem.

Yes my mods at the moment are a bit different from the drawing. The drawing is based on what I see on the two pictures of the H.B.E. mods.

I plan on setting my module up to match the drawing, probably with c45 switch, and I got my mpsa06's in so I'll finish the SAT switch. All in all I'm still experimenting.

 

[CrazyNutz]

Got the wima mkp4 caps in. Tried one in the first (built-in) stage, and while it look nice, it sounds like crap. Killed the mids, very muddy at low volume, and ear piercing/icepick at high volume. I know you have to give caps time to break-in but I've never heard it this bad. I put the stock cap back in.

 

[CrunchBunch]

Does your multimeter have a capacitance meter? If so, worth measuring the original and new cap to see if the values are different. I really haven't been able to tell any difference between cap types where the values have been the same...

 

[CrazyNutz]

Does your multimeter have a capacitance meter? If so, worth measuring the original and new cap to see if the values are different. I really haven't been able to tell any difference between cap types where the values have been the same...

Yes, I have a capacitance meter ( it also measures leakage & ESR ). The stock/measured value there is 0.1uf, thats what the WIMA measures. I have tried a Mallory 150 there and it sounded good.

 

[CrunchBunch]

Finally got a chance to add the saturation switch. It basically does what it says - adds "saturation". Sounds pretty good for diode clipping and does give another distortion variation to the module. Can't say it knocked my socks off but its on there now.

Couple of notes:

- signal output of the module is lowered with the sat switch engaged because it adds additional clipping. It actually reduces gain (by clipping) but increases distortion;

- used a push/pull on the volume knob - great place to put this because you've got to tweak the module volume when you engage it;

- not as nice sounding as running higher gain elsewhere in the module (eg. no R7, 2.7K R16 etc.)

 

[CrazyNutz]

Yup got my SAT switch in with MPSA06's. Yes the volume drop is normal, the BE100 does the same.

Interestingly, it is a little lack luster as you described. Mine sounded better when I was using 2n3904's, I was also grounding to the chassis. So I don't know if it was the chassis grounding, or the other transistors that made it sound better. I'll do some experimentation.

 

[CrazyNutz]

- used a push/pull on the volume knob - great place to put this because you've got to tweak the module volume when you engage it;

You could wire in an extra resistor to your push pull that would increase the volume when you engage the SAT

 

[CrunchBunch]

...Mine sounded better when I was using 2n3904's...

Interesting. I might experiment with using LEDs but with the amount of potential gain on tap with the MTS topology I'm unmotivated to spend too much time on it.

Other options are to explore different places to connect it.

C45 switch will probably be the next thing I play round with.

 

[djd100]

I tried the 500pf on V2B's V2B cathode follower and it did scoop the mids a bit, though on my modified Plexi that just made the upper mids harsh (on the BE Bright channel anyway), so I removed it.

My Plexi's V2A is different as well, so that's likely why etc.

All in all mine is sounding good so I'm probably done for a while until I get to crank it up through a real cab (just been monitoring via studio monitors and a Two Notes Torpedo CAB with a virtual Bogner 4 X 12 with Greenbacks so far).

Thanks for the great thread, nice to have other knowledgeable people here! I'll be watching to see the results as you guys move forward with the complete BE mods!

Thanks.

My thought is that the 500pf plate bypass cap on V2A will cut the highs and fizz a bit, while the 500pf cathode bypass cap on the V2B cathode follower will bring the highs back sans fizz (and with additional second harmonics for smoothness etc), we'll see?

Yes 500pf plate bypass does indeed cut the fizz. However the 500pf bypassing R30 Is kind of a mid voicing thing I would say, It does not add any fizz, seems like it knocks the upper mids down. It takes some of the HONK out from what I can tell.

 

[CrazyNutz]

Yeah, that one is really just a matter of taste, that's actually just part of the voice switch on the be100.

On a side note I have a stock plexi module coming (should be here today) I'm going to mod it with the dual concentric pot like yours. I'm really trying to pack in all my current amps into this MTS system. I have a BE modded plexi, and stock 68 plexi, and a vht pitbull. So with my HBE modded SL+, and my Dzilla(sounds close to my VHT), and the plexi I should be good.

I have a good idea of how to mod the plexi module with the dual pot bass/treble channel, but If you would not mind could you post some pictures?

Thanks

I tried the 500pf on V2B's V2B cathode follower and it did scoop the mids a bit, though on my modified Plexi that just made the upper mids harsh (on the BE Bright channel anyway), so I removed it.

My Plexi's V2A is different as well, so that's likely why etc.

All in all mine is sounding good so I'm probably done for a while until I get to crank it up through a real cab (just been monitoring via studio monitors and a Two Notes Torpedo CAB with a virtual Bogner 4 X 12 with Greenbacks so far).

Thanks for the great thread, nice to have other knowledgeable people here! I'll be watching to see the results as you guys move forward with the complete BE mods!

 

[djd100]

Have fun converting your collection! I've got all of my favorites in MTS now, life is "GOOD"! If you haven't yet, try a Two Notes Torpedo for your tube power amp sim and cab sim needs, for great tones at any SPL DI'd and/or via cabs (FRFR or guitar with lightweight solid state power).

Here are the modded Plexi pics (ignore the partial BE mod and the lifted 500pf for V2B's cathode follower's bypass as I haven't fully removed it yet).

Note that my good friend and bass player who's a real EE did the concentric pot mod (beautiful soldering work etc), while I did the BE mod (hack job LOL!).

Yeah, that one is really just a matter of taste, that's actually just part of the voice switch on the be100.

On a side note I have a stock plexi module coming (should be here today) I'm going to mod it with the dual concentric pot like yours. I'm really trying to pack in all my current amps into this MTS system. I have a BE modded plexi, and stock 68 plexi, and a vht pitbull. So with my HBE modded SL+, and my Dzilla(sounds close to my VHT), and the plexi I should be good.

I have a good idea of how to mod the plexi module with the dual pot bass/treble channel, but If you would not mind could you post some pictures?

Thanks

I tried the 500pf on V2B's V2B cathode follower and it did scoop the mids a bit, though on my modified Plexi that just made the upper mids harsh (on the BE Bright channel anyway), so I removed it.

My Plexi's V2A is different as well, so that's likely why etc.

All in all mine is sounding good so I'm probably done for a while until I get to crank it up through a real cab (just been monitoring via studio monitors and a Two Notes Torpedo CAB with a virtual Bogner 4 X 12 with Greenbacks so far).

Thanks for the great thread, nice to have other knowledgeable people here! I'll be watching to see the results as you guys move forward with the complete BE mods!

 

[CrunchBunch]

That's very cool. Thanks for sharing.

 

[CrazyNutz]

Awesome thanks a ton!

Yeah I've heard people raving about the Two Notes Torpedo. I should get one, my wife would love not having to hear me cranking through a 4x12

Have fun converting your collection! I've got all of my favorites in MTS now, life is "GOOD"! If you haven't yet, try a Two Notes Torpedo for your tube power amp sim and cab sim needs, for great tones at any SPL DI'd and/or via cabs (FRFR or guitar with lightweight solid state power).

Here are the modded Plexi pics (ignore the partial BE mod and the lifted 500pf for V2B's cathode follower's bypass as I haven't fully removed it yet).