how is this preamp design ?

[jtvrdy]

Hi,

this is the schema of mic preamp section of my Tascam M700 console,just wondering if is a good desing and how it is compared to other consoles as ssl ?


http://www.vaporstudio.com/shared/micpre.JPG

thanks,

 

[amorris]

very simple design. differential input, to a single IC current to voltage, capacitively coupled. couldnt be more different than an SSL. 9k is balanced throughout and has a dc-servo couple. the transistors used in 9k are thermally linked inside 1 metal can and so on.

 

[jtvrdy]

could it be improved easily?

 

[gyraf]

Very much like the Amek2500 mic pre (look this up).

Make sure to use a good-quality capacitor for the 470uF "C008" - that is probably the biggest simple-improvement.

Jakob E.

 

[Svart]

Much like a mackie type circuit also. A impedance converter setup with opamp unbalancing. A simple design like Amorris said, but could be improved mainly by using matched BJTs and a good quality opamp, the 5532 is good but we don't know what brand as some are better than others.

Gyraf is right about c008, as well as use good caps for c002 and c003 and raise their values to 470uf or so with some 100nf films in parallel. Some debate the film bypassing but it's cheap so why not.

Usually a fairly neutral sounding circuit, nothing too exciting but not too bad either.

 

[Samuel Groner]

Very much like the Amek 2500 mic pre (look this up).

I don't think so--the 2500 is based on the Cohen topology which provides much better performance in many respects (distortion and CMRR likely beeing the most pronounced ones) than the design shown here. The Cohen topology connects each colloector of the input pair to its own opamp. Debalancing is done with an additional stage, not in the first stage.

Agree on the upsizing of C002/C003 though I'd say that 100 uF is well enough. You could replace R017/R018 and C006/C007 with precisely matched components to improved CMRR.

Samuel

 

[gyraf]

Samuel, I agree.. :green:

 

[Svart]

Agree on the upsizing of C002/C003 though I'd say that 100 uF is well enough.

My math says 47uf is fine, but my experience says that real world shows that 470uf is key for good LF dist.

ah but that is just me.. :green:

Bipolar caps too!

 

[Rossi]

I don't think it's just you :grin: Most manufacturers use big caps here and often you can get noticeably better performance by using even bigger ones. I wish I had a source for really big (470u +) bipolar caps.

 

[jtvrdy]

thanks to all !

I opened one chanel ,the opamp says NE5532AN and a big "S" I sopose that means Signetics

on the c008 say:
SME
(M)85ºC
9(2)
DL

on the c002/3
SM
(M)85ºC
83
A(2)

sorry for my ignorance but what means all those numbers on the capacitors and how I can know the brand ?

 

[Svart]

(M) usually means Matsushita, otherwise known as Panasonic.

85ºC is 85 degrees centigrade. the temp rating. get 105 or 125.

the schematic shows the value and voltage ratings needed.

 

[ruairioflaherty]

[quote author="jtvrdy"]Hi,

this is the schema of mic preamp section of my Tascam M700 console,just wondering if is a good desing and how it is compared to other consoles as ssl ?[/quote]

Am I the only one who finds this i bit weird? You've got the console in front of you to listen to but you want others to tell you if it is good from looking at the schematic?

I think before you upgrade the console in any way you spend some time listening with friends to a bunch of different stuff, low gain, high gain, condensers, dynamics, the line in etc etc. If you have some outboard pres to compare it to all the better. Once you've decided on the things you like and do not like about the strip you can then evaluate what mods you could do to get you closer to what you want.

Imagine coming here with a post like "I have console X and I love the ballsy low end on the mic pre but when I crank the gain it gets hissy" - you've got a much clearer goal rather than just aimlessly swopping components you don't understand. I've never upgraded a console and I'm new to electronics but I have been a fulltime recording engineer for years. Don't be afraid to use your ears...

cheers,
Ruairi

 

[ciminosound]

Well a lot of people don't have access to different gear to do serious listening tests. The board might sound fine but maybe it could sound better. Without the ability to do A/B/C tests one never knows.

I'd suggest modding a channel or two with "upgrades" like different opamps, new "better" electrolytic caps and such and listen to see if it sounds better to your own ears before spending a lot of time and money. I mean you might make all these "improvements" and get farther away from your goal. Small steps jtvrdy, small steps.

:sam:

 

[gltech]

I worked a few sessions at a place that one of these consoles, and I thought it sounded very good. This looks like a simple little circuit that could be used for lots of things. Questions:

- What do the letters on the ends of the resistor values mean? For instance, R004 has 'F', R005 has 'NF', while R019 has nothing.
- I assume R020 is gain and is a 1K/10K ganged pot? And there's that extra letter again -- what does the "E" mean?
- I assume the "BP" like on C008 and C009 means bi-polar?
- What voltages are needed for VCC and VEE?

Thanks,
Glenn

 

[SSLtech]

I think that most of the 'F' resistors seem to be at the noise-sensitive parts of the design. With this being the case, perhaps it's the designation for "metal Film" ...?

Keith