Topic: Greetings... my new mic preamp.

[fivefishdiy]

80Hz seems to be the magic number popping up often.

What's the dB/octave?   6, 12, 18?

Is a steep or shallow rolloff preferable?

I'm leaning towards 6dB/oct so we don't kill too much of the low end.

How about a compromise... 100Hz (in between 80 and 120Hz) at 6dB/oct?

[stevetoney]

w/r/t DIP switches for hp:
I've used a SP preamp for a few years now
my pre has the DIP switch for selecting the hp cutoff freq
I have never really like this arrangement
because in the field things tend to get 'fumbly' real fast

to change or turn on the hp you have to:
- turn the unit over to read the chart telling you which DIP switches to switch for a particular freq
- find something to switch them with - fingers vary in size and dexterity
then repeat this process when needing to turn them off again

I have often wished for a simple easy switch I could throw for a 80Hz hp
instead of fumbling with a set of DIP switches when trying to capture a great sound out in the field
my 0.02

The basic concept I presented is that the front swich on the face activates the low cut.  Therefore, no field fumbling...only on and off.  The dip switches would be on the inside of the box so they couldn't be bumped around. You'd pre-set the dip switches based on your personal preference by opening the box and setting them yourself.  But this would allow for user selectable settings for both frequency and level cut.  In the end though, it's up to 5fish to decide if the design has space or merit.

[stevetoney]

80Hz seems to be the magic number popping up often.

What's the dB/octave?   6, 12, 18?

Is a steep or shallow rolloff preferable?

If you end up going with a single setting, my vote would be just a scosh higher than 80hz...and 12db. 

Reason I chose 12db is most low cut users I would think would want it for balls-out shows where there's simply no subtleness to the low end.  In that case, I'd rather that the low cut has some nuts to it to really beat down the bass...instead of a wimpy-ness to it which is more fixable in post.  IOW, err on the side of taking out too much bass with the cut rahter than not enough.  My thoughts...

BTW, I'm soft on this though and I'd go with the majority opinion for sure, especially if someone feels strongly.

[sanaka]

Reason I chose 12db is most low cut users I would think would want it for balls-out shows where there's simply no subtleness to the low end.  In that case, I'd rather that the low cut has some nuts to it to really beat down the bass...instead of a wimpy-ness to it which is more fixable in post.  IOW, err on the side of taking out too much bass with the cut rahter than not enough.

Ditto for me exactly. 12dB slope right around 80 or a little higher. Seems some folks are routinely recording kinda low and boosting their whole captured signal by 12dB in post. I tend to try for a hotter capture, and would much rather bump up only the bass in post if the low cut turned out to be a little more than was needed.

Peace,
Sanaka

[anechoic]

any comment on this?

also over on the micbuilders list there was some concern about there being mV of oscillation in your preamp design?
not sure what the poster was referring to here but where is the oscillation exactly? on the rails? output?

[stevetoney]

any comment on this?

also over on the micbuilders list there was some concern about there being mV of oscillation in your preamp design?
not sure what the poster was referring to here but where is the oscillation exactly? on the rails? output?

Not sure on what basis anybody has made this statement.  If you take the time to look through this thread, you'll read about the issues that have been encountered and what has been done to resolve them.  I don't recall reading anything about what you're talking about.

Regarding outsiders commenting on the design and whether there are issues, it's not like anybody has his preamp in their hands to test it themselves to independently determine if there are issues, but honestly, to me that's not all that relevant because 5fish has gone above and beyond in terms of full disclosure in this design and the issues that he's encountered.

So, if they're talking about the concern over microphonic sounds that he discussed a page or two back, that has been resolved as his posts have stated.  If you're talking about signal stability, waaay back a ways he shows some old-silly-scope images that are dead flat. 

 

[anechoic]

sorry I meant for that post to be directed to fivefish
but someone on the micbuilders list had mentioned reading on fivefishes blog something about there being a few mV of oscillation
but the post wasn't specific about where the osc was occurring or what fivefishes plan was to deal with it
so, I am curious in fivefishes response to this statement

[fivefishdiy]

reading on fivefishes blog something about there being a few mV of oscillation

Here's my blog and go read ahead. FYI... this is like May of 2007, the SC-1 pre was just an idea on it's first prototype.

http://www.fivefish.net/diy/sc1/

This is the development blog of my SC1.


Photo of first prototype.

As bad as this prototype looks, it can already do 100Khz!


On testing the VERY FIRST PROTOTYPE.. I had a part there where I mentioned .

Noticed some slight oscillation at the 5th, 6th, and 7th gain settings of the selector switch. So finally fixed that with additional bypass capacitors on the supply rails. We're talking about less than 0.2Volts oscillation on top of a 30Vpp output. So it's insignificant. But still, it's gone now.

As I said, this is Rev1.00 PCB I'm working on and it looks like on my Rev3.00 PCB, I've already incorporated those caps in the design.

Then connected the mic pre circuit output to the balanced line driver. And what do you know... the less than 0.2Volt oscillation fixed itself. The addtl caps weren't needed.

And then a few days later, I posted

 

VU meter readings are better... especially at the 11th and 12th position. Oscillation at the higher gain settings fixed too.

I am curious in fivefishes response to this statement

My comment.... if they're gonna comment about some oscillations I mentioned, man! READ THE ENTIRE STUPID BLOG and preferably have some READING COMPREHENSION. i.e. don't just pick and choose what I said one day and ignore what I posted later on... pick also the part where I said the problem was fixed during the later days. If you have ADHD, don't read my development blog. Just read the last page where everything is fixed, and ready for sale.

The whole blog is my daily diary of what's happening in the course of development and prototyping.

[sygdwm]

mr. fivefish, please lock this thread and start a new one. its under additional options>modify 1st post>lock (i think). then, link to the last thread in the 1st post of the second thread. this happens to every thread at 25 pages.

this thread has been fantastic nerding out material. +t

[fivefishdiy]

Will do... thanks!

Continuation of thread can be found here...
http://taperssection.com/index.php/topic,108569.0.html