oh my NAD (Now w/ Mods)

[Heady Jam Fan]

When I woke up this morning, my tracking info confirmed my Celestion CL80 Speaker and Weber Beam Blocker were "out for delivery."

I got home from my girlfriend's house and was anxious with anticipation, so I decided to take out the old speaker and realized I don't have any tools yet at my new house. "Ok," I figured, "I'll burn some time at Home Depot." I got the essentials and came home, only to realize that the studs were in the baffle in such a way that I couldn't remove the speaker without taking out the chassis.

I pulled out the chassis and reminded myself, "you weren't going to mod this amp." I repositioned the studs and grabbed the chassis to put it back in and thought, "what if I want a tremolo disconnect mod - I never use the trem and I get annoyed by the faint ticking... it would be so much easier just to remove the tremolo now while I have the chassis out." My soldering iron was already hot from unsoldering the speaker, before the tremolo circuit could stutter, "stop" it was disconnected.

Then my brain started ticking. "I have these long wires left over from the tremolo and I already have the V1 preamp tube pulled, so I'm not using the Normal Channel or any of those potentiometers... If one of them is a 1meg Audio Taper, I could do the reverb dwell mod in a jiffy - the old school tank sounds awesome, but just too much decay..." Sure enough, the volume pot was a 1 meg Audio Taper, so I yanked out:
- The 1meg Grid Resistor.
- The lead going from V3's pin 7 & 2 (Reverb Driver) to where the Grid Resistor met the 500pf capacitor.
- The wire from V1 to what was just previously my Normal Channel's volume pot (2nd, wiper, terminal).
- The wire going from what was previously my Normal Channel volume pot (3rd terminal) to the treble pot.
And then I soldered:
- The wiper (2nd terminal) of what was now my Dwell pot to pin 7 & 2 of the Reverb Driver (V3).
- The 3rd terminal my 'new' Dwell pot to the 500pf capacitor.
Obviously leaving the 1st terminal of the new Dwell, previously Volume pot grounded.

I screwed the beam blocker to the front of the baffle (removing two studs to do so), installed the new speaker, popped the chassis back in and rocked the fuck out.
Plus I got to use my new tools.

Pre-mod pics:

The resistor looks like a little brown tic-tac with a light brown, black, green and silver stripe.

The capacitor is hard to see here, but its a light brown 'disc' kinda thing connected at the same junction as the resistor and lead in the image below.

The lead should be easy to find, especially if you've located the resistor and cap (if you haven't trace the lead to them).


Sounds great. The Dwell knob takes away a bit of treble and has a similar effect in general to the standard Reverb knob, but together they give a decent amount of control. I find I get a nice bit of splash in the initial reflection without an overwhelming cavernous decay/tail with the dwell on 7 and reverb on 5.

I can't tell for certain if the Beam Blocker is working because I changed the speaker too, but I'm definitely getting a more tonally balanced sound from various angles. There is still some beaminess, but not as bad and it doesn't sound dark and muddy anymore when I stand off to the side. I don't hear any weird phasiness I got the 5 inch beam blocker - figured it would work best, especially with the large dust cap on a CL80. I know people are really split about beam blockers and those who dislike them swear by the Jay Mitchell foam doughnut, but that looks ridiculous and, contrary to those who use a foam doughnut, I think the treble comes from the center just near the dust cap - when I put my mic there, its brighter and when I move it out, it gets darker.

I think the CL80 sounds fantastic too. Its used and seem pretty broken in, but I'll see if it mellows even more in the next few days. The G12M70 sounded kinda luck mush, the CL80 is smooth but authoritative. Despite the rolled off high end, there is more treble clarity too. All around I think its a great speaker, especially for this application. Way to go Bogner amps - Trey's Shiva made me pull the trigger on this one. Might be my new favorite Celestion.

Oh yea. If this wasn't a long enough post for ya, I'm getting a couple new pedals over the next few days. Probably be writing up a review, comparison on those too! I'm replacing my vintage/original Script Phase 45 with an vintage/original early Block Phase 90 and my vintage/original MXR early Block Envelope Filter with an '84 Ibanez AF9.

I do open her up again, I might just have to repurpose the Normal Channel's treble or bass pot as a midrange pot! I'll have to brush up on whats involved in that mod, I think I need to add to the tone stack.?.

PS - obviously if you try this mod, be safe and careful. You need to know what your doing or you will get shocked and die, probably urinating on yourself and thats an embarrassing way to be found - all pissy and smelly and dead. Your better than that. Solder Safely, doubt be found dead in your own urine.

[tsbot]

Strong work!  Glad to see you put the dwell in it!!

[IamWILSON]

Very cool Heady!  If you want to add a midrange knob, I think using a 25K ohm pot with a .022 mf capacitor into the middle terminal would do the trick.  If you want to add a new pot, I think it would just run parallel to the bass pot too. 

[Heady Jam Fan]

Very cool Heady!  If you want to add a midrange knob, I think using a 25K ohm pot with a .022 mf capacitor into the middle terminal would do the trick.  If you want to add a new pot, I think it would just run parallel to the bass pot too. 

Thanks man!

I'm getting better at this stuff (still a novice), but I don't know all the lingo. Mind if I pick your brain?

You said "parallel to the bass pot." Is that different than a typical midrange control? If so, how? I was pretty much going to follow the Twin Reverb schematic, which seems like its in series: http://www.thevintagesound.com/ffg/schem/twin_reverb_ab763_layout.gif.

I was also going to leave the 6.8K resistor between the bass and midrange pot to set the minimum midrange to the amp's stock tone.

As far as the pot's value, I was originally going to go with a 10k: a lot of the mod directions I found suggested that and its stock for a Twin Reverb. However, that is barely more than the 6.8K resistor (which would be about 7/10 on a Twin's midrange control). A lot of people seem to suggest 25 or even 50k, but I think 50 would be too much: I'd think it would make the other tone controls less effective and would be tricky to dial in.

However, I think the Intensity pot in my amp, which I'm now not using, is 50K. So my next thought was to add a capacitor across terminal 1-3 to 'attenuate' the attenuator's upper range (or value). But I read this can throw off the pots sweep, so I decided not to do this (I'll have to order a 25K pot). What is the purpose of the .022mf capacitor in your suggestion for a mid control? You said it would go to the middle (2nd, or wiper) terminal, so I'm assuming it would not function to diminish the pots range. What is the other side of the cap soldered to? The bass knob?

You don't happen to have a schem for this mod?

Thanks man!
Jon

[fulltone1989]

Awesome work! I definitely respect guys that mod their own amps, I'd be too wary - the farthest I go is my own Bias. Are the mods easily reversible if you go to sell?

[Heady Jam Fan]

Awesome work! I definitely respect guys that mod their own amps, I'd be too wary - the farthest I go is my own Bias. Are the mods easily reversible if you go to sell?

Actually nearly all the mods discussed for Fender amps are reversible. The irreversible ones are ones that require additional holes in the chassis and there are so many unused holes that almost any mod is reversible. I actually reversed both mods this morning to try some other stuff

[Heady Jam Fan]

I undid the dwell mod and trem disconnect.

I liked the dwell, but it had three effects: shortening the reverb trail/decay, decreasing treble, and decreasing the reverb in general. I liked the first effect and could reverse the third effect by turning up the standard reverb knob, but that increases noise. I disliked losing the treble and with less gain doing into the reverb circuit, I got less of a springy initial reflection, which is what I wanted.

The trem disconnect did add gain to the preamp which made it sound stronger and punchier, but it also added bass and made overdrive tones a little less smooth. I decided pulling V1 was good enough for increasing gain in the preamp. On one hand, I could have decreased the bass, but I use the tone controls (particularly on Fender amps) just as much to make the preamp feel, play, function its best as much as to shape the sound. For example, the amp is most dynamic and expressive when the knobs are set where they make the most noise (unplug the guitar, turn the amp on, turn the volume all the way up, turn the eq knobs and you'll hear the noise-level jump at a few spots across the sweep - the amp plays best with the knobs set right at those spots, which is 2.75 out of 10 on my bass knob). I assume the bass is attenuated by the trem circuit because it adds more R-C Networks to the signal chain. Anyway, I preferred a smoother sound with a tighter bass than the umph that the mod provides.

I really like the CL80 speaker still and I haven't tried taking the beam blocker back out, but I like it in there - seems to have a really nice effect moderately diminishing the beam, and not just absorbing treble, but diffusing it.

I also did a 'trem-fix' mod today that just adds a .022uf cap from the 10meg resistor that meets the trem-bug to ground. I think it completely stopped the mild clock-noise (ticking) I heard before.

Decided I definitely like the bright cap removed. Even setting the treble higher after removing it, overdrive sounds smoother.

Lastly, I have an RCA jack in the trem pedal plug with the wire leads soldered together (its not going to a pedal). This keeps the trem on so I can just reach over and turn up the intensity.

Oh yeah - I popped the RCA Short Grey Plate 12AX7 from V1 into V2, replacing the Tungsram/Amperex. It sounds much clearer and a bit smoother despite being a bit brighter. Incredible sounding tube! I also tried the RCA 12AT7 in V1 (all these says are USA 12A*7, kinda like what is said about the tube Trey has in V2), but I preferred the RCA 12AX7. The RCA AT7 beat the Tungsram though. The Mullard RI came in last place; it was clearer sounding than the Tungsram but sounded a bit more brittle and clinical, not as smooth, warm or dynamic.

Finally, I tried out the original Fender 6V6 tubes, but I think they were really on their last legs - I preferred the JJs. The Fender's just sounded a bit weak, but I'll keep them as back up tubes.

[Happyorange27]

You are the MOD GOD!

[Heady Jam Fan]

You are the MOD GOD!

Haha, your work on your bjr is definitely more complex and impressive, just figured drs are popular amps here and I should share.