Tips on replacing mic preamp components?

[Doc]

I have a couple of Studio Projects VTB-1 mics. I just ran across this
post regarding mods on this unit:

----------------------
"HI everyone. I bought a VTB1 last year and haven't been using it a
lot
because I actually dind't find it much better (if any) than some
Behringer stuff i had. After a while I look inside the VTB1 and found
2 infamous JRC4580 opamps. as well as a JRC2114 and JRC2082. Knowing
how Behringer stuff relies on these opamps I decided to replace them
with something different. After some testing with some common opamps
i
had arround this is how IMO it sounded better:

2 TI NE5532 for the JRC4580s
1 LM833N for the JRC2114
1 LM353N for the JRC2082

As I were there I replaced the "no name" tube for something better.

I found that as a matter of fact the JRC4580s impart a very
unpleasant
characteristics: cold, brittle, hollow are just a few terms that may
well define their behaviour. Why do they use them? The ICs i have
used
as replacement cost the same yet they provide a more musical response
(specially HF).
--------------------------

I've done a small amount of component soldering, but never on
components like these. I managed to complete Scott Dorsey's chinese
mic mod on a Marshall MXL. While not the prettiest job ever done, the
mic actually works.

To desolder/solder components like this, what if any special gear
would be needed? Any tips/tricks?

What I would really be looking for is noise reduction. Has anyone done
this mod and found that it truly reduces the noise level? One of the
things that I see about these pre's are that they're supposed to be
pretty quiet already compared to other similarly priced units.

Thanks

[Mike Rivers]

On Feb 4, 7:32 am, "Doc" > wrote:
> I have a couple of Studio Projects VTB-1 mics. I just ran across this
> post regarding mods on this unit:

> I found that as a matter of fact the JRC4580s impart a very
> unpleasant
> characteristics: cold, brittle, hollow are just a few terms that may
> well define their behaviour.

It makes it sound different from other preamps that cost about the
same. When you're talking about $100 preamps, sounding different is
more important than sounding better to a given set of ears. There will
always be someone who says "Wow! Everything sounds so bright and clear
with this new preamp!:

> Why do they use them? The ICs i have
> used
> as replacement cost the same yet they provide a more musical response
> (specially HF).

They may be essentially the same cost when you buy them a few at a
time at DigiKey, but they probably cost more when comparing the cost
by the thousand.

> To desolder/solder components like this, what if any special gear
> would be needed? Any tips/tricks?

Are they surface mounted, or thru hole? Thru-hole ICs are pretty easy
to desolder with standard tools if you don't mind destroying the ones
you're removing. Cut the pins off where they enter the chip, remove
the chip, and then you'll be left with pins that you can desolder
individually so you don't have to heat all eight at a time. Solder
Wick or a hand-cocked vacuum solder sucker will help clean out the
holes so you can insert the new IC.

Chip Quick (http://www.chipquick.com/) sells a kit for removing
surface mount ICs. It's essentially a flux and low melting point
solder that stays molten long enough so you can heat up all the pins
and flip off the chip. Then you clean it up and solder on a new one.

> What I would really be looking for is noise reduction. Has anyone done
> this mod and found that it truly reduces the noise level?

I haven't done it but it may drop noise a little. Mostly it will lower
distortion and smooth out frequency response irregularities. But it's
also possible that you'll have to make some other changes to prevent
oscillations. That sometimes happens when substituting op amps.

[Scott Dorsey]

Doc > wrote:
>
>To desolder/solder components like this, what if any special gear
>would be needed? Any tips/tricks?

You need a solder sucker. Paladin makes a good one for about twenty
bucks. You also might want some solder-wick braid, some very small
63/37 solder (24 ga is good), a good soldering iron, and some machined
pin IC sockets.

Melt a little solder onto the IC pin... you have to add solder to remove
solder. Give it a few seconds to get hot, then apply the solder sucker
and press the button. Go on to the next pin, then the next.

You may want to try this with chips on an old PC power supply or something
to get the hang of it first. You want a good hot iron... a 25W cheapie will
not work. With too small an iron you will overheat the work because you
won't be able to work fast enough.

>What I would really be looking for is noise reduction. Has anyone done
>this mod and found that it truly reduces the noise level? One of the
>things that I see about these pre's are that they're supposed to be
>pretty quiet already compared to other similarly priced units.

Those op-amps are already pretty quiet, even if they don't sound very
good. That's why manufacturers use them. You _might_ be able to get
some noise reduction, depending on the circuit and what you put in there,
but it may be some trial and error to find a quieter replacement.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Mogens V.]

Mike Rivers wrote:
> On Feb 4, 7:32 am, "Doc" > wrote:
>
>>I have a couple of Studio Projects VTB-1 mics. I just ran across this
>>post regarding mods on this unit:

WRT the named/choosen opamps, I'd be looking into Burr Brown or Analog
Devices over those mentioned.

If it's a somewhat used device, especially which may've been left on
24/7, I'd also be looking at capasitors at relevant positions, though
this possibly require a full set of schematics.
Capasitors may loose the value over time, and can be prone to noise.

>>I found that as a matter of fact the JRC4580s impart a very
>>unpleasant
>>characteristics: cold, brittle, hollow are just a few terms that may
>>well define their behaviour.
>
>
> It makes it sound different from other preamps that cost about the
> same. When you're talking about $100 preamps, sounding different is
> more important than sounding better to a given set of ears. There will
> always be someone who says "Wow! Everything sounds so bright and clear
> with this new preamp!:
>
>
>>Why do they use them? The ICs i have
>>used
>>as replacement cost the same yet they provide a more musical response
>>(specially HF).
>
>
> They may be essentially the same cost when you buy them a few at a
> time at DigiKey, but they probably cost more when comparing the cost
> by the thousand.
>
>
>>To desolder/solder components like this, what if any special gear
>>would be needed? Any tips/tricks?

Apart from the following suggestion, a thermostat controlled soldering
station with a fine tip, and some knowledge in setting correct
temperature. With good practice, a good hobby soldering iron may be
used, but avoid those gas powered devices.

A long thin copper nail may be turned into a elongated soldering tip.
Wind it as a spiral to closely fil the tip of a standard soldering tip,
and bend the other end to suit the job at hand. Carefully round off of
flatten it's tipto ensure good soldering contact, as needed for the job.

But really, if you're asking questions about how to proceed, you may
want to ask some qualified techie to do the mod, instead of risking
ruining you otherwise well functioning device. No pun intended.

> Are they surface mounted, or thru hole? Thru-hole ICs are pretty easy
> to desolder with standard tools if you don't mind destroying the ones
> you're removing. Cut the pins off where they enter the chip, remove
> the chip, and then you'll be left with pins that you can desolder
> individually so you don't have to heat all eight at a time. Solder
> Wick or a hand-cocked vacuum solder sucker will help clean out the
> holes so you can insert the new IC.

Do pay attension to using that sucker right first time. Continued
effords easily results in a strongly miscolored PCB, and the
overeccessive heat abuse may result in the copper strips loosening from
the PCB.
If a large sucker is used (the com in different sizes) it itself can
easily suck a small soldering cobber island loose from the PCB.

> Chip Quick (http://www.chipquick.com/) sells a kit for removing
> surface mount ICs. It's essentially a flux and low melting point
> solder that stays molten long enough so you can heat up all the pins
> and flip off the chip. Then you clean it up and solder on a new one.
>
>
>>What I would really be looking for is noise reduction. Has anyone done
>>this mod and found that it truly reduces the noise level?
>
>
> I haven't done it but it may drop noise a little. Mostly it will lower
> distortion and smooth out frequency response irregularities. But it's
> also possible that you'll have to make some other changes to prevent
> oscillations. That sometimes happens when substituting op amps.

Nod!

--
Kind regards,
Mogens V.

[Arny Krueger]

"Doc" > wrote in message
oups.com

> I have a couple of Studio Projects VTB-1 mics. I just
> ran across this post regarding mods on this unit:

> ----------------------
> "HI everyone. I bought a VTB1 last year and haven't been
> using it a lot
> because I actually dind't find it much better (if any)
> than some Behringer stuff i had. After a while I look
> inside the VTB1 and found 2 infamous JRC4580 opamps. as
> well as a JRC2114 and JRC2082. Knowing how Behringer
> stuff relies on these opamps I decided to replace them
> with something different. After some testing with some
> common opamps i
> had arround this is how IMO it sounded better:
>
> 2 TI NE5532 for the JRC4580s
> 1 LM833N for the JRC2114
> 1 LM353N for the JRC2082

> As I were there I replaced the "no name" tube for
> something better.

> I found that as a matter of fact the JRC4580s impart a
> very unpleasant
> characteristics: cold, brittle, hollow are just a few
> terms that may well define their behaviour. Why do they
> use them? The ICs i have used
> as replacement cost the same yet they provide a more
> musical response (specially HF).

I'd like to see a carefully run listening test that would confirm that.
Constructor's ear is a common disease.

> To desolder/solder components like this, what if any
> special gear would be needed? Any tips/tricks?

What's the context - SMT devices?

> What I would really be looking for is noise reduction.

Not all that easy because lots of cheap gear has a fairly impressive noise
figure.

> Has anyone done this mod and found that it truly reduces
> the noise level? One of the things that I see about these
> pre's are that they're supposed to be pretty quiet
> already compared to other similarly priced units.

That's because the cost of op amps with good noise figures is low and
getting lower. Larger gain-bandwidth product is now also getting easier to
buy, and improving it only helps until it gets so high.