one catalogue mic pre

[neverlistentome]

I propose the challange of presenting a decent mic preamp that can be built from one order from one catalogue of parts. (be it Allied or Digikey or Mouser or whatever) This would be great for nubes and more than likely a cool design would be easy to order in bulk.
I could definitely see a little bending of the rules (seeing as almost no parts house has any audio grade transformers), but it would be cool to source everything in one call.

 

[gyraf]

Allied or Digikey or Mouser are all US-based, not really useable in the rest of the world.

In reality, sourcing parts is not that hard, once you get to know your local resources - after all, many-many of the common parts needs to be available in some form or the other everywhere on this planet. And don't underestimate the value of being able to find parts on your own.

In the Gyraf-DIY projects, I've tried hard to aim at universally easily-to-find parts - and the less-easy you can find sources for by asking places like here..

Jakob E.

 

[soundguy]

designing something based upon what a distributor carries is a fairly random limitation to constrain your project with. design it around what sounds good with readily available parts not with whats available from allied. digikey has good prices on some stuff but is really high on other prices, allied has some parts that are priced less and has a lousy selection of caps.

your idea seems like a good one, but practically speaking, its not a very good one IMO. Ordering from three places isnt as big of a deal as it might seem. Or maybe Im just used to it. hah.

dave

 

[adamasd]

All of the parts for PRRs Different Differential can be built from parts order from just one place, it uses very common parts. There was also two FET preamps that featherpillow posted, designed by bcarso that can be built from parts that most any supplier will have. Search for Different Differential and Darlington Spinoff. They both use very common parts.

adam

 

[Guest]

[quote author="neverlistentome"]I propose the challange of presenting a decent mic preamp that can be built from one order from one catalogue of parts. (be it Allied or Digikey or Mouser or whatever) This would be great for nubes and more than likely a cool design would be easy to order in bulk.
I could definitely see a little bending of the rules (seeing as almost no parts house has any audio grade transformers), but it would be cool to source everything in one call.[/quote]

i think what he's trying to get across is something for beginners with a very low part count, at the least amount of price with the best performance (noise, headroom, etc) with this type of limitation.

maybe something like this ?

but what about phantom ? would you want that in the circuit as well...i would presume so...

 

[Guest]

[quote author="neverlistentome"]I propose the challange of presenting a decent mic preamp that can be built from one order from one catalogue of parts. (be it Allied or Digikey or Mouser or whatever) This would be great for nubes and more than likely a cool design would be easy to order in bulk.
I could definitely see a little bending of the rules (seeing as almost no parts house has any audio grade transformers), but it would be cool to source everything in one call.[/quote]


i think what he's trying to get across is something for beginners with a very low part count, at the least amount of price with the best performance (noise, headroom, etc) with this type of limitation.

maybe something like this ?

http://www.elecdesign.com/Files/29/5688/Figure_03.gif

but what about phantom ? would you want that in the circuit as well...i would presume so...

by the way: the output is pin 6, not pin 3 - this is a typo on the schematic.

 

[Guest]

here is something else:

http://focus.ti.com/lit/ds/symlink/ina217.pdf

same design basically but with phantom...

 

[tk@halmi]

Isn't hunting for components part of the DIY fun? I think it is. The threads here provide an incredible resource for finding parts. I have found FORUM members friendly and helpful in that respect. For difficult to source components you can always post at the Black Market.

 

[Svart]

hmm i have to disagree on the fun of sourcing parts.. it is exciting when you find something that is totally superior to use but then of course when you are working on a project that has about a million parts and all of them can have many possibilities but you have very little time... irritating, at least to me. sometimes you HAVE to source from different companies.. I bought resistors for a GSSL from digikey.. then I built another and bought the resistors from mouser.. BIG difference. mouser had cheaper Rs by FAR.

just my .02$

:guinness:

 

[PRR]

> maybe something like this ? www.elecdesign.com Figure_03.gif

Not a good plan.

• The chip is a little hard to source.
• Log/Anti-Log pots are hard to find (though DigiKey lists a $2 Panasonic).
• NO input protection.
• No phantom input.
• Supply rails could be higher.
• And the big problem: the output is attenuated, very much at low gains. At lowest usable gain the maximum output might be 1 Volt.

The plan works for fixed-level inputs that must be attenuated to low or zero. It does not work for varied-level inputs that must be output at fairly constant and possibly high levels.

> a decent mic preamp

What is "decent"? I've done a lot of work with dynamic mikes with transformerless 2-transistor preamps (essentially flat phono preamps). Some of that stuff is better than I do now (old-brain issues, not equipment). But these days, if it isn't XLR in and out, someone will laugh. So I've gone XLR in (I hide the 1/4" and RCA line wires behind the stack). Phantom and GitarWorld have given us stunningly good $300 mikes, compared to what I got for $300 in 1978. But I don't think adding 50 transistors along the way has put more music on the recording.

 

[Guest]

[quote author="PRR"]> maybe something like this ? www.elecdesign.com Figure_03.gif

Not a good plan.

• The chip is a little hard to source.
• Log/Anti-Log pots are hard to find (though DigiKey lists a $2 Panasonic).
• NO input protection.
• No phantom input.
• Supply rails could be higher.
• And the big problem: the output is attenuated, very much at low gains. At lowest usable gain the maximum output might be 1 Volt.

The plan works for fixed-level inputs that must be attenuated to low or zero. It does not work for varied-level inputs that must be output at fairly constant and possibly high levels.

> a decent mic preamp

What is "decent"? I've done a lot of work with dynamic mikes with transformerless 2-transistor preamps (essentially flat phono preamps). Some of that stuff is better than I do now (old-brain issues, not equipment). But these days, if it isn't XLR in and out, someone will laugh. So I've gone XLR in (I hide the 1/4" and RCA line wires behind the stack). Phantom and GitarWorld have given us stunningly good $300 mikes, compared to what I got for $300 in 1978. But I don't think adding 50 transistors along the way has put more music on the recording.[/quote]

agreed.

what about the 2nd one i proposed.

is there going to be an issue with a more involved power supply for keeping it simple?

what kind of design or schematic would you suggest?

 

[jensenmann]

Can anybody tell me what R4/R5 in the above mentioned INA217 app note (figure4) are good for? I´m wondering because they didn´t mention the necessity of using them. What´s the benefit of this technique?
the link again:
http://focus.ti.com/lit/ds/symlink/ina217.pdf

thanks
Jens

 

[tk@halmi]

You need R4/R5 to bias the input transistors properly for the INA217. The circuit will not work right without them.

 

[jensenmann]

It seems strange to me that they don´t mention this in the app-note. How do I have to calculate R4/R5?
:thumb:
Jens

 

[Samuel Groner]

How do I have to calculate R4/R5?

Bipolar transistors have a small bias current flowing trough their base. This current will flow through R4/R5 and thus introduce a DC voltage @ the input pins which will get amplified. R4/R5 needs to be small enough to not let this offset affect headroom etc. The exact value of the bias current is not known as it depends on beta which is very variable. However, they quote a max. input current, so you have a worst-case figure at hand.

As a roule of thumb, anything lower than 10k will work fine, values around 5k are typical. Resistors below 2k are not recommended as they set a too low input impedance. Note as well that R4/R5 together with the phantom blocking caps form a high-pass filter; you want the -3 dB point of this filter to be below 1 Hz for best results.

Samuel

 

[Rochey]

My only disapointment wiht the INA217 is that by it's design, it gives an unbalanced output. True - you could throw a DRV134/5 after it to have a balanced output...

I wonder - could the OPA1632 be used as a small mic pre, and provide a direct balanced output for the pre?

 

[jensenmann]

thanks! But know when I think about it I get even more confused. I think I´ll do a reading and have a look on the internal of an Opamp and then ask more
:sam: for you guys
Jens

 

[tk@halmi]

[quote author="Samuel Groner"] you want the -3 dB point of this filter to be below 1 Hz for best results.Samuel[/quote]

Nobody hears that. A lot of pro gear sets it 3dB below 10Hz and that is just fine. Very few humans hear below 20Hz anyhow.

 

[Samuel Groner]

Of course it's not because we would loose bass. But 'lytic stuff starts to distort pretty early, that's why. IIRC Self states that distortion get's measurable around 10x the freq. of the -3 dB point, so 1 Hz is about right.

Samuel

 

[tk@halmi]

Thanks Samual. That is good to know. I don't think any design we have seen around here actually complies with Self's guideline. In fact I have not seen a commercial design that tries to go below 5Hz. It may be measurable, but can it be decetedted by one's ears?