Here is what Bellari/Rolls says (just look at those cruddy noise specs!):

MP105 Tube Mic Preamp
The MP105 provides clear sonic quality and performance for the working musician, studio operator or anyone who needs a preamp with the warm, smooth, analog sound.

The unit features both XLR and 1/4" inputs and outputs with a 37 dB Pad on the XLR input, 48 Volt Phantom Power, and a Phase Reversal switches to adapt to any performing or studio situation.
SPECIFICATIONS
Input Impedance: XLR: 600 Ohms, 100 K W Padded
1/4”: 10 K Ohms
Output Impdance: 50 Ohms
THD: .15%
S/N Ratio: >88 dB
Maximum Input Level: +12 dB XLR, +18 dB 1/4”
Maximum Output Level: +16 dB XLR, +10 dB 1/4”
Pad: - 37 dB
Frequency Response: 20H - 25kHz +/-3 dB

Out of the box this thing is a cool little effect pre for overdriven tube effects.

But then...

Matt over at Black Lion Audio discovered this quick mod. Suddenly you have something that is noisy, but actually sounds pretty nice and thick and balanced.

The Bellari MP105 modification
http://www.blacklionaudio.com/roundsound.htm

The Bellari MP105 is the little blue and white single channel mic/line preamp that Bellari produced a few years ago. They might not even be available new anymore, but they are easily found used on Ebay for around $50 USD. The MP105 isn't a starved-plate design, so it's not as dull-sounding as other low-dollar hybrid preamps.

Black Lion Audio has designed a quick and simple modification to these that'll give you a really nice sounding preamp and DI. It's based on a more comprehensive mod that was done for a friend's MP105.

Here's what to do:

Replace U1 and U2 (BA4560 opamps) with a pair of Analog Devices AD826 dual opamps. They are socketed, so you don't even have to do any soldering.

Replace V1 with the 12AX7 of your choice. Black Lion Audio has long been a fan of the EI ECC83, which is an inexpensive reproduction of Telefunken’s long-plate 12AX7, and the Electro-Harmonix EH12AX7.

Now you're finished, simple as that! You'll enjoy it--it sounds wonderful on LD condensors, and it makes a great secret weapon on bass guitar!

Parts list:

(2) Analog Devices AD826AN, available from Analog Devices

(1) EI ECC83 tube or Electro-Harmonix EH12AX7, available from Triode Electronics

and finally, Matt recomended to me to replace the two pots (they suck in that their values aren't quite optimized to the circuit, and they crackle quite a bit) with clarostat 308NPC 100K pots. at this point, your new parts will cost more than the whole pre.. but you know.

they drop the noise level down quite a bit. now you can use the amp safely with loud condensers, or with quiet mics on loud sources.

this amp it totally key for rock vocals, loud guitars, bass, snare. its colored as heck, has a nice gentle roll off on top. keeps the low lows out. and when you drive it hard you can get all those nice tube artifacts: limiting, distortion... etc.

great for computer recording...

i still have to figure out what to do with the holes in mine, and find some knobs for an 1/8" shaft, but here is mine now:

A word of warning:

Electronic equipment operates on very high voltages. Electricity can be LETHAL. Do not attempt to disassemble, repair, or modify any electronic equipment unless you are qualified to do so. The purpose of this site is only to provide helpful information. The owner of this site is not responsible for any damage to persons or equipment resulting from misuse of this information.

BTW, George, great thread.

For everyone else, please take seriously that electricity can be lethal in many instances. If you are not qualified to do a mod, then please seek out the help of a competent tech. Tube equipment especially can carry high voltages. Be careful out there.

I did this mod, except for the knobs. I might do that next, because it's still pretty damn noisy. You cannot use this pre, even after the mod, on an SM7, for example. Other than that, though, you can get some nice colored sounds from it on vocals and amps.

It sucks as a bass DI, IMO, though, even after the mod.

ha! an sm7 nice one! no WAY thats gonna work.

this pre works best with newish condensers that lean on the brightish side. it tames the top. but it needs all the help it can get in terms of input level.

just to explain what the knob mod does to the noise floor:

before mod i would NEVER have the volume up all the way, i found you had to reduce the volume just a hair to cut out some weird hummy noise thing. AFTER mod. not a problem.

before mod you could turn the gain up maybe to 10 oclock before the noise got silly and only worked with material you wanted blown out.

after mod.. i've gone up past 12 without getting upset by noise.

also as far as a bass DI, the amp is a little on the slow side, and doesnt pass much super low stuff. so its got limited applications. i think it give the DI bass an interesting tone, just not one that you would use a lot.

How hard is the knob mod?

first of all the knobs are $12 each! ouch. they are the same knobs found in super expensive avalon type stuff.

second of all they have a different configuration than that stock ones... so, it isnt a matter of desoldering and resoldering. you have to mount it in a tricky way, and there are a couple of solutions to this

third, the stock knob is mounted very firmly to the board, since it isnt panel mounted they really friggin locked that thing on the board. so its a bit tricky to remove if you want the knob intact.

what i did: by the second knob removal i said: F this crap knob, and just destroyed the thing and clipped out the leads. pretty easy to destroy easy to clip out. you'll need a desoldering tool and nice snips.

second i panel mounted the knobs to the front, and jumped from the board to the leads on the knobs. which is pretty easy to do, but then you have front panel mounted knobs and top mounted buttons. at some point i am going to pop out those buttons, panel mount those as well with nice switches, patch up the holes in the top and 2U mount this guy.

matt is really into the theory of NOT changing the looks of a piece, just the guts. so he uses a lot of hot melt glue and fudges these knobs in the original spot. i dunno how hard this is...

as a general guide, i would consider this a beginner mod: but i wouldnt make it your first! also, as far at tube amps go, this one is pretty decently safe. you have to worry with tube amps in gerneral about the caps discharging on your ass and killing you. but this guy doesnt really have any big caps in it. i forget what the largest value is.. but its a tiny percentage of the caps in other amps i have. so its WAY safer to work on than just about any tube thing (excepting starved plate stuff since they dont run at full voltage they are near enough safe as anything SS).

if you want to do it.. i can walk you thru the whole thing if you are nervous... i think its totally worth it. changed this guy from a one or two trick pony to a uhhh. four trick pony.

last night i threw my cad e300 in omni over the drum stool, ran it through this guy a little saturated (then to my symetrix 501) and it sounded really cool. before i had reserved this guy to close mic only... now it makes a sweet OH mic preamp. again GREAT for bright LDCs like my e300.

Thanks for the tip eeldip. I'll keep it in mind. I've never done a mod where I modified the board yet, so I'll have to think about it.

i started on something different, but everyone says that the first thing you should do is build a fuzz face.

that'll get you used to ordering parts... wiring stuff. drilling holes. everything you need to get going into the deep pit of DIY.

Desoldering of components can be a complete bitch when there are multiple legs attached to the board. The iron isn't enough - you need specialized, though common, tools. Solder suckers and desoldering braids are your friends, and I think the former more useful.

On opamp mods, when they aren't socketed, a lot of people clip out the old chips leg by leg for ease. When doing this, get the sockets to install before you put in the new chips - you won't have the same problem again if you somehow screw up the new chip or if you want to try something else later.

Kit competance is great, but I'm not absolutely sure it translates perfectly to mods. Maybe it's that I feel shakey about kludging up something which already works.

Bear

sorry, no pic, but i just finished a total rework of the 105.

(if anyone has a stock one that i can borrow, i think i need one to compare it to)

besides the pots being replaced, now it has all sorts of component upgrades and the amp circuit has been changed a bit.

now i think the running total for money i spent on this guy is $115 or so?

anyway, proud to say that the bellari is officially NOT the noisiest preamp in my studio. that honor is now conferred upon the built in pres in my presonus firestation.

basically, i did the $8 black lion extensive mod, but matt customized it for the pots i picked out which are much lower valued than stock. he also took out the first amp stage (changed to a buffer stage) cause it was no longer stable with the 100k pots in there.

ok, this is meaningless to some of you i know.

the skinny is: no longer a particularly noisy amp.
no longer has the silly 75db of gain. prolly down to 60db of gain havent measured it yet.

way nicer sounding, much less grainy sounding. smoother highs.

its still a bit slow, but in a really good way. i have started using it for some drum tasks that i never found it useful for. it nicely trims transients in a way that works well for rock drumming. and now i feel comfortable using it for more delicate acoustic stuff.

so in summary:

stock ($50 or so)- cool effect pre. NOISY. rock vocals. guitar amps. slight hollowness.

basic black lion mod ($75 or so)- cool effect pre, less noisy. vocals. drums. amps. hollowness gone.

total rework mod- cool effect pre ($100 or so). not particularly noisy, now can function as general use pre. smooth highs.

(edit: my reasoning was way off, so I rescend any comments.)

Ok, now I've got some data..

The potentiometer (P2) feeds a very beautiful signal from the tube subcircuit to opamp U2B. However, when U2B gets too strong a signal, it distorts. The +12v input to the opamp swings like crazy and the signal gets clipped harshly. Trying out various values for P2 shows that a 75K ohm potentiometer effectively eliminates the opamp clipping, even under a strong signal. (However, I can only find 50K and 100K pots, so you'll have to compromise. I'm going to put in a conductive plastic 50K pot for P2. They cost about $10, but that seems to be the best thing.

http://www.milbert.com/tstxt.htm This is a great article contrasting tube/transistor/opamp distortion. Because of the article, I've committed to staying as far away from opamp distortion as possible (except when I'm trying to be Trent Reznor.)

gaul

glad you have some test equipment around!

i have two of these right now, one with a 500K pot at p2 and one with a 100k pot at p2. besides those differences.. i have some other component mismatches between the two, so i cant do a head to head comparison.

what opamp do you have at U2b? would an opamp with great headroom help? or is it a power supply issue?

If you're talking to me, (shrinks embarrassed) --- well, kinda...

All I've got is LTSpice, and a model of the MP105. If you want the model to play around with, I'll email it to you. LTSpice is a free Windows-based Spice circuit. My email is lkjniu96kjg9 AT hotmail DOT com.

dam.. mac user here.

anyway, so the model probably uses the stock opamps. i BELIEVE most drop in replacements will have more headroom.

the recommended op-amps are discontinued -are there any currently available (to the uk) op-amps i could use instead? I've heard good things about the Burr-Brown op-amps - is there any particular model of theirs that would be better than others for this?

I did this mod, except for the knobs. I might do that next, because it's still pretty damn noisy. You cannot use this pre, even after the mod, on an SM7, for example. Other than that, though, you can get some nice colored sounds from it on vocals and amps.