I have joined the Dark Side (well not really)

[Chef]

that's nice stuff aiiieeeght

 

[anderbass]

Hey Psycho, I tried out my 400+ DI signal today and noticed it seems to be working allot better than it used to...
Have you tried yours lately?

I had previously considered my DI to be very distorted and pretty much unusable. I seem to remember serveral other people reporting the same DI results with their 400+.

Just for a test today, I ran my DI directly to my (standalone Alesis HD-24) recorder without using any line-amp. With using just the channel one input, (set as high as 8) I got a really great and a fairly clean/usable and hiss-free DI recording with the master as high as 7 and the amp playing very-very loudly.
With no line-amp, my recorders input-level readings were peaking around -24DB when the amp was played very loudly, so I'd say the DI signal is definitely at a good signal level and not to high or hot. (I do plan on adding a line-amp for serious recording)

Blending channel two's input immediately resulted in a progressively fuzzy(er) signal as it was increased, but I still got a fairly usable DI signal for rock type music at most all preamp and master knob levels.

I guess I really shouldn't be too surprised that my DI also sounds much-much better now, but I certainly am.
Just like my amp, the DI sounds and works considerably better now...

 

[Bob Moulton]

I took Psycho's advice and just got my 400+ back from my tech (fellow T/B member timv) yesterday.

Tim instaled an adjustable bias mod, two Chinese 12AX7's he'd tested/selected out of my stash of used spares (1 Groove tube 12AX7 and a Mesa STR SPAX7A), and then instaled a (quote) well balanced 12AX7 in the 3rd slot (JJ), and a well balanced 12AU7 in the 4th or left position. (older used tube that only seems to be labeled "USA 12AU7A")

(I believe I'm quoting my tech correctly here)
He stated that after the bias mod, my amp still only maxed out at around 270 watts (clean) due to its transformers limited capacity, but each side of its power section was now much better balanced and showed much less crossover distortion . He tested and found a surprisingly large variation in my two year old set of (Matched) JJ power tubes and arranged them into 2 groups of the closest matching sets, while exchanging one that tested much lower with a better matching JJ he had in stock. He also cleaned and tightened all my power tube socket conectors to better fit my JJ's power tubes somewhat smaller than normal sized pins. (I think I read somewhere that the newer JJ's power tubes now come with normal sized pins)

When I picked it up, he didn't really expect me to notice a huge improvement, but I definitely do.

Previously, my (fully) JJ equipped 400+ has always had me constantly knob twiddling in a futile attempt to tame its somewhat harsh upper-mids while trying to compensate for the comparatively thin sound I got while playing upper register notes with my basses.

The tone now is very rich, full and much more three dimensional sounding at nearly any imaginable knob settings compared to before. The upper register notes now ring out full and much thicker sounding, the harsh upper-mids are completely gone and the lows are allot tighter. It simply sounds better in every way.
I know the real test will be with my band. I've only spent a while trying out different combinations of preamp channels, tone knob and push-pull settings, but I honestly cant make this thing sound bad now, no mater how I set it.
Psycho already stated this, and I completely agree that my tone knobs are absolutely much more responsive with this different tube arrangement compared to my previous JJ's.
My Mesa seems to be a plug and play amp now, and I've always considered it to be anything but...
I'd highly recommend the bias mod and a similar tube arrangement to anyone not completely satisfied with their 400+.

The small panel in the center is the adjustable-bias pot board he built and instaled to a previously-existing mounting hole. (looks like its always been there)

I'd like to thank both Psycho for his tips/PM's and especially timv for the wonderful job he did on my amp.

Hey Anderbass & Psycho, I was wondering how much this mod would run from a respectable tech? That's if I can find one in the Metro Detroit area that knows what they are doing.

Any advice would be greatly appreciated.

 

[anderbass]

This job shouldn't be terribly expensive, but I cant say for sure. My amp tech is a friend that works out of his home and tends to drastically undercharge me. My guess would be somewhere between one to two hours of bench time, plus maybe $20 for adjustable bias supplies, plus any tubes or other work needed. The only thing I know for sure is Its well worth having done.

 

[Foxworthy925]

How do you guys think I should go about trying to find an amp tech in my area who's capable of doing this type of thing for my 400+?

 

[anderbass]

I'm not sure if many of the authorised M/B techs are gonna be very gung-ho about doing the adjustable bias mod or not as it kinda goes against Mesa's point of view. Although I sure like knowing that a tech is very familiar with my particular model.

You guys could always start a thread asking for recommendations in your area...

Here's some links that may help you both:
http://www.mesaboogie.com/US/Dealers/dealers___support.htm

Detroit area:
http://www.talkbass.com/forum/showthread.php?t=101455
http://www.google.com/search?source...T4DMUS_enUS221US222&q=amp+tech+Detroit+area++


SF Bay Area:
http://www.google.com/search?source...=1T4DMUS_enUS221US222&q=amp+tech++SF+bay+area
http://www.google.com/custom?domain...;S:http://www.talkbass.com;LP:1;FORID:1&hl=en

Good luck.

 

[Foxworthy925]

Thanks for the reply anderbass. That's extremely helpful.

 

[Munjibunga]

With the thread title, I thought you were going to say you bought a solid-state amp!

Asad

Yeah, I was thinking either Walter Woods or Glockenklang. But no. All is still right with the world. Nothing to see here, folks, keep moving.

 

[Fealach]

I've mentioned the mod to the current owner of my old 400+, as well as the tube swaps. I play at his place with another (sort of) band and could easily use the 400+... except it sounds underpowered and gainy compared to the way it sounded years ago when it was mine. Sadly, he is firmly in the "if a tube fits, use it" camp and thinks proper bias is for sissies, and if it sounds good the tubes are obviously within acceptable range of the amp's bias point. Unfortunately, it doesn't sound good, not compared to how it used to.

No, I'm not contributing or offering any advice, just sharing a sad story. At least it gives me a reason to use my Sound City, which had been up for sale but is now back in Favored Amp status.

 

[Psycho Bass Guy]

Hey Psycho, I tried out my 400+ DI signal today and noticed it seems to be working allot better than it used to...
Have you tried yours lately?

I've not used the DI at all, but it seems as though maybe the amp needed a 12AU7 for a driver all along. Maybe Mesa just subbed a 12AX7 so they wouldn't have to carry another type for sale.

 

[Psycho Bass Guy]

Yeah, I was thinking either Walter Woods or Glockenklang. But no. All is still right with the world. Nothing to see here, folks, keep moving.

I'd figure you'd have thought "Markbass" with all the hype/propoganda that's been on here about them.

 

[Munjibunga]

I'd figure you'd have thought "Markbass" with all the hype/propoganda that's been on here about them.

Maybe, but I don't believe I've posted a single word about Markbass here (until now). Well maybe one word. I played through one at Guitar Barn, and I might've said it's OK.

 

[Psycho Bass Guy]

Maybe, but I don't believe I've posted a single word about Markbass here (until now). Well maybe one word. I played through one at Guitar Barn, and I might've said it's OK.

Not questioning your motives; just thinking of maximum irony...

 

[anderbass]

I've not used the DI at all, but it seems as though maybe the amp needed a 12AU7 for a driver all along. Maybe Mesa just subbed a 12AX7 so they wouldn't have to carry another type for sale.

Ten-four to that.

I was kinda thinking the adjustable bias mod and the resulting "better balanced power section/less crossover distortion" (my tech noted) might also be greatly improving the Mesa's power-stage type DI system.

 

[Tim1]

Hey Psycho, when I did the JJ preamp swap with my 400+ I was advised that both the first tube(next to the volume control) and the driver tube should be balanced. Never really understood what balanced means other than they select it, but is it really important that both are balanced?

 

[Psycho Bass Guy]

Hey Psycho, when I did the JJ preamp swap with my 400+ I was advised that both the first tube(next to the volume control) and the driver tube should be balanced. Never really understood what balanced means other than they select it, but is it really important that both are balanced?

"Balanced" in the context of a preamp tube means that each half of the tube has an equal gain factor. 12**7 tubes are actually two tubes in one. Each "half" of the tube is a triode gain stage. In some tubes, the halves are supposed to be dissimilar. IE: a 12DW7 has one half with the gain of a 12AX7 and one half with the gain of a 12AU7. When a tube is said to be balanced it implies that each half has been measured and the gain factors (transconductance) are identical. Normal production tolerances can make a tube have a 20% difference in gain between the two and the tube will still be 'in spec.'

Does it matter in a bass amp? Not in the least. Gain differences in the preamp don't matter because each "half" is doing something different anyway. It also matters very little in the driver because the output stage bias controls and compensates for any dissimlar drive voltage.

 

[Bob Moulton]

I'm not sure if many of the authorised M/B techs are gonna be very gung-ho about doing the adjustable bias mod or not as it kinda goes against Mesa's point of view. Although I sure like knowing that a tech is very familiar with my particular model.

You guys could always start a thread asking for recommendations in your area...

Here's some links that may help you both:
http://www.mesaboogie.com/US/Dealers/dealers___support.htm

Detroit area:
http://www.talkbass.com/forum/showthread.php?t=101455
http://www.google.com/search?source...T4DMUS_enUS221US222&q=amp+tech+Detroit+area++


SF Bay Area:
http://www.google.com/search?source...=1T4DMUS_enUS221US222&q=amp+tech++SF+bay+area
http://www.google.com/custom?domain...;S:http://www.talkbass.com;LP:1;FORID:1&hl=en

Good luck.

Thanks a lot anderbass!

 

[anderbass]

Thanks a lot anderbass!

Thanks for the reply anderbass. That's extremely helpful.

Yer welcome, but my motives are questionable... I'm kind of enthused about this and wanna hear more about someone else's results. My descriptions of bass tone usually come off sounding like maybe I'm just one string short of a P-bass...

I'd imagine some amps will benefit more than others, but mine is just flat a better amp now. My tone knobs are reacting much better allowing all kinds of crazy new possibility's. The really cool thing is no mater how I adjust it, my amp only seems to produce different flavors of good now. I take that as a very good sign...

 

[Vanni]

Great 3d with super informative posts!!!

I have an old Boogie 400+, bought 2 years ago, immediately modified with the bias adjustable trimmer.

However there are original Mesa Tubes installed.

Even with the original tubes I have that weird sounding upper midrange, and I lose a lot of time trying to dial out it, and turning knobs to search some good sound... and trying to make G and D strings sound thick.

BTW the head with just the adjustable bias mod is a real monster, it's louder than stock 400+s.

Anderbass, I use the DI, and no one told me it sounds bad or distorted... maybe is only the bias correct setting (BTW I don't play very loud... so I don't push hard pre or power amp).

PBG, yesterday evening I tried to bypass the pre, plugging directly my bass in the power amp... great sound! So full, warm and fat!!! The power section sounds really GREAT!!!


BTW, In two weeks I have to go to my tech, to do a full retube... I remember my old Buster, after the bias mod and a full Sovtek retube, it sounded twice better than my 400+.

I would like to try Sovteks WXT+ in the power section, and Tung Sol 12AX7 in the preamp...

ciao!
Vanni

 

[Psycho Bass Guy]

Vanni,
I feel that substituting the driver tube with a 12AU7 will make the biggest difference in tone, particularly, the problematic midrange. Try that first.