Topic: Greetings... my new mic preamp.

[fivefishdiy]

UPDATE: October 2008
This is the latest photo of the TS-2 Preamp prototype.

Thanks to all the tapers that offered their suggestions, feedback and support!
The 1st batch of units are currently in production.... Serial #003 to #010.


ORIGINAL THREAD FOLLOWS
---------------------------------
Hello all. I make mic preamp kits for the homestudio/recording studio crowd. Usually, they're racked in a 1u case, with AC power and everything.

About 6 months ago, I started making a wallwart/battery powered preamp version, and finally just finished it a few days ago. A customer who's been following my progress emailed me and said this new pre may be a good fit for the "tapers crowd." I said "Huh?" and he explained what tapers are all about... apparently, he's into it and directed me to this site.  I browsed around this site and this looks like a cool place to be.

Well, I have to say I didn't design this for compactness, because my original intent was this will be used in a studio. Anyways, I'm looking for feedback on what features are useful for tapers? (Size, battery power life, what else?) Maybe I can come up with something or modify this existing pre.

Some pics.





Brief list of features:
Gain 6dB to 72dB gain
XLR input
XLR output
48V Phantom power switch  (yes, it's really 48 Volts)
Soft start phantom power (no thuds when switching ON or OFF)
DC Servo
Balanced driver stage (can drive 600 ohm loads at long distances)
Powered by 12VDC wall wart (or battery)
From my testing... will work down to 6Volts, with phantom power falling down to about 36V with a 6VDC power input)

Here's an audio sample of the noise level... powered by a 12VDC wall wart, gain set to +72dB, volume at max, input XLR terminated with 150-ohm (to simulate a mic connected).

http://www.fivefishstudios.com/audio/SC1Solo-NoiseTest.mp3


MODS:
If this post is out of line or needs to be moved somewhere, I apologize.

I'm not selling these yet, as I'm not ready... this is just a prototype. Right now just looking for input and suggestions for features tapers would like to see.

Thanks!

[eric.B]

:::clappping::::   

nice! 

suggestions..   consider having unbalanced outputs, the ability for it to be run at 6-9volt max, and recess the knobs..   

Im sure there will be more posts on this thread with further input Im sure..    enjoy the tapers section!  ::tip cap::

[OOK]

Welcome to the board!

Very cool.  If you are open to suggestions here are some from a taper perspective....just my opinion.

2 channel and or four channel versions
in a as small as possible metal case say 9"x7"x2" say brushed AL. or black AL.
first Variable knob for +or- 10 db
second indented knob in 10db increments from 6 to 76DB give or take
Runs on anything from 6volt to 12 volt
XLR input switchable line level to mic level
XLR outputs and RCA outputs.
Good LED metering.
Recessed front panel so knobs aren't acidently bumped
power switch on the front panel not the back
ability to turn phantom power on or off for dynamic mics or ribbons
and very low noise floor at maximum gain.......
Oh yes a fair price.....it can't break the bank.....tapers aren't rich but will spend for a good reliable product.

Anyone else want to add?

T+ for your project
if its good it will be the rage of the board!  There is always room for more pre's
 
Peace OOK

[fivefishdiy]

Thanks for the welcome and comments. I appreciate it very much!
Great suggestions, some that I haven't even thought of.  Keep 'em coming.

BTW, this mic preamp design works with dynamic mics, condenser mics, FET condernser mics, tube mics and ribbon mics. No problem with gain settings or operation on any of them.  (Check out MIX magazine May 2008 issue, this mic pre design was used in the gear review of a Peluso vs. Neumann mic.)


2 channel and or four channel versions
I think my PSU can handle that (2 ch). The current consumption of the mic preamp is only +/-17mA. (And 5mA of that is being used by the LED phantom power lamp, otherwise it's only +/-12mA)...

and YES, it runs internally on +/- split rail voltages. About 30V+ peak to peak voltage.  Plus TRUE +48V for the phantom power.

in a as small as possible metal case say 9"x7"x2" say brushed AL. or black AL.
Noted. ... The case I'll be using is 6" x 4" x 1.5" and an option for 6" x 4" x 2.5"...  single channel, extruded aluminum (not plastic), with anodized aluminum front and rear panel.

first Variable knob for +or- 10 db
I'm using a high-quality Bourns sealed potentiometer, conductive plastic... (will not get dusty, scratchy or worn out like carbon pots).  It functions as a "trim/volume knob"... from cutoff to 0dB (i.e. no trim).

second indented knob in 10db increments from 6 to 76DB give or take
I'm using a high-quality sealed Grayhill 12-step, 1-deck selector switch.  Gain adjustment is 6dB increment in 12 steps, from +6dB to +72db gain (balanced out). If unbalanced output, it will be from 0dB to 66dB gain.

Runs on anything from 6volt to 12 volt
Check. Done.

XLR input switchable line level to mic level
The current mic inputs can be used as line level inputs. Just set the gain switch down to 6dB.

XLR outputs and RCA outputs.
I think this is doable. Just need another jack. My balanced line driver stage behaves well with single-ended loads.

Good LED metering.
What is the definition of "good"? 
I have a separate VU meter kit, but it only has 5 LEDs. Will run from 4V to 24VDC input (has on-board regulator).

if an LED VU is required, the 2.5" case height is probably needed.

Recessed front panel so knobs aren't acidently bumped
Good idea. I think this is more on the chassis/case construction... so need something to "guard" the knobs from being adjusted accidentally. I have to think about this one.

power switch on the front panel not the back
Hmmm... I don't have this. Need to add a power switch. 

ability to turn phantom power on or off for dynamic mics or ribbons
Done... and my phantom power is a soft start. The 48Volts is ramped up gradually from 0V to 48V over a span of few seconds. So there is no big THUD when you turn on/off phantom power.  Same thing when you turn it OFF, no big THUD... it's decayed down from 48V to 0V.

and very low noise floor at maximum gain.......
Is this good enough?  http://www.fivefishstudios.com/audio/SC1Solo-NoiseTest.mp3

Oh yes a fair price.....it can't break the bank.....tapers aren't rich but will spend for a good reliable product.
I think the most common pre is the SoundDevices pre for tapers, is that right? Or do most go the DIY approach?

I don't have any pricing on this yet... still need to get quotes for extruded aluminum case with anodized front and rear panel.


QUESTION:
Is needing an external battery pack a big deal or a deal breaker?  I don't have room for an internal battery. Hmmmm....


At the moment, this just a single channel mic preamp.  In the future I'll be converting this to SMD and cut the size further in half, or cram 2 channels on the same board. But that's a far future.

Thanks for the comments.

[bugg100]

This all looks great! 

Possibly consider locking power input option for the field tapers.  External batteries are ok, many here run 9 volt li-ion external DVD player batteries.

One case with dual pre's is what many wind up with, we are MOSTLY stereo tapers some 4 channel though.

Integral (to case) metering is a must, 5 led at a minimum as those of us running 16 bits need to run HOT! The more fine grained the metering , the better.

Thanks for your interest in our input.

Joe

[JasonSobel]

Good LED metering.
What is the definition of "good"? 
I have a separate VU meter kit, but it only has 5 LEDs. Will run from 4V to 24VDC input (has on-board regulator).

if an LED VU is required, the 2.5" case height is probably needed.

well, my opinion of "good metering" would be something like a light for signal, maybe lights at -30, -20, -12, and then a lot more details between -12 and 0, maybe a light at -9, -6, -3, -1, and an "over" light.  Of course, that's my idea of good metering for digital levels.  In this case, it's not an A/D converter, and generally speaking, I think we'd want to hit the clipping point of whatever A/D we're using (either external on the onboard A/D of our decks) before overloading the pre-amp.  So now that I think about it, the metering on the pre-amp doesn't have to be as detailed, because the digital levels wouldn't necessarily correspond, depending on the sensitivity of whatever A/D we are using.

and speaking of how well your pre-amp will work with different A/D's and decks, it would be very helpful to know the maximum output level (in dBu) when the pre-amp is pushed to the limit (i.e. when it overloads).  That way we all can know how hot to run the pre-amp based on whatever gear we've got downstream, and we can calibrate our other equipment most effectively.

Recessed front panel so knobs aren't acidently bumped
Good idea. I think this is more on the chassis/case construction... so need something to "guard" the knobs from being adjusted accidentally. I have to think about this one.

check out the Grace Design V2 and V3's for really good recessed switches.

Oh yes a fair price.....it can't break the bank.....tapers aren't rich but will spend for a good reliable product.
I think the most common pre is the SoundDevices pre for tapers, is that right? Or do most go the DIY approach?

I don't have any pricing on this yet... still need to get quotes for extruded aluminum case with anodized front and rear panel.

some people use sound devices pre-amps.  they are small and nice pre-amps.  but there are many pre-amps that people like to use.  The Grace Design V2 and V3's are very popular, there are the Oade m148 and m248 pre-amps, the Neve Portico 5012, the Sonosax SX-M2, Aeta PSP-2 and PSP-3, Aerco MP-2, church audio pre-amps, etc, etc...  I'm sure that there are many more as well, but this list is just off the top of my head for some more popular ones.

QUESTION:
Is needing an external battery pack a big deal or a deal breaker?  I don't have room for an internal battery. Hmmmm....

some people prefer internal batteries.  But for many people, external batteries is no problem.

At the moment, this just a single channel mic preamp.  In the future I'll be converting this to SMD and cut the size further in half, or cram 2 channels on the same board. But that's a far future.

honestly, I don't think there will be much interest with just a single-channel pre-amp.  The vast majority of people here record 2 channels, and some people have made the jump to 4 (with the advent of affordable, small, 4-channel recorders).  But really, I think the vast majority of people wouldn't bother with two single-channel pre-amps.

Thanks for your interrest in our little community here.  It's always great to have more options for gear, and to have the designers here in the community and listen to our wants and needs.

- Jason

[fivefishdiy]

it would be very helpful to know the maximum output level (in dBu) when the pre-amp is pushed to the limit (i.e. when it overloads).

The mic pre can do +22dBu, then it goes to the balanced line driver which adds another +6db gain. The balanced line driver max output level is rated +27dBu.

One case with dual pre's is what many wind up with, we are MOSTLY stereo tapers some 4 channel though.

honestly, I don't think there will be much interest with just a single-channel pre-amp.  The vast majority of people here record 2 channels, and some people have made the jump to 4 (with the advent of affordable, small, 4-channel recorders).  But really, I think the vast majority of people wouldn't bother with two single-channel pre-amps.

Wow! It should have been obvious but it didn't hit me till now. It needs to be 2 channels, AT LEAST, for tapers use. You're right! 

The above pre was originally designed for the recording/home studio, where only one instrument is recorded at a time during tracking... i.e. designed for a different purpose.

I don't think this particular layout will be well suited as a tapers preamp right now.

To do this properly and make it a real tapers preamp, I think I need to start from scratch. Use a wide but shallow case, new layout, put 2 (or 4) channels side by side,  integrate the VU meters, add a clip indicator, maybe add a high-pass/low-cut filter, add an unbalanced out, design it really small and compact, add room for battery (if possible), etc. What do you think?

Thanks for all your feedback. It's invaluable.... time to go back on the drawing board and really design a proper tapers preamp. 

Oh well, I thought I can adapt the above preamp for tapers use, but now I can see it's almost there but really it's not, still a long ways to go.  Tapers have a different set of requirements.

[SmokinJoe]

Tapers are a very opinionated bunch.  You can start holy wars on this stuff, and the various features, and the subtle flavors.  Some of the most popular preamps for tapers are below. Look at those features and you will see where people are coming from.  The V3 has steps and trim pots, the others have 0-100% knobs.  Some people like this one, some like that one.

- the Grace Designs V3 (which contains an A/D, but has analog out too) http://www.gracedesign.com/products/V3/V3frame.htm
- the Apogee Mini-MP (analog in and out) http://www.apogeedigital.com/products/minimp.php
- Sound Devices Mix-Pre http://www.sounddevices.com/products/mx2master.htm

Personally, I think it's really important to have good level meters on the pre if it includes an A/D > bitbucket.  If it simply provides boost, and I'm determining the final levels on another box with it's A/D (my R4 or R-09), I'm going to be watching the meters on the box with the A/D even if they suck, so in that case, I don't care if the pre has meters at all.  YMMV.

Seriously, if you want to consider entering this market, you should package one up and loan it out to responsible people who can run it, and get some tapes up on the "Live Music Archive" at www.archive.org.  The world is full of great preamps, but we don't touch most of them, because no one wants to be the first one to drop some money on something he can't sell later if he doesn't like it.  Even if you stuff two of those boards into one box and run it, people may find out it runs sweet, or that it's way too bright, or some other descriptor, and then you can decide if you should start to think about a 2 channel box, or just forget about us altogether.

[KLowe]

awesome!  thanks for your interest and best of luck to you.

Look forward to some samples 

[illconditioned]

it would be very helpful to know the maximum output level (in dBu) when the pre-amp is pushed to the limit (i.e. when it overloads).

The mic pre can do +22dBu, then it goes to the balanced line driver which adds another +6db gain. The balanced line driver max output level is rated +27dBu.

One case with dual pre's is what many wind up with, we are MOSTLY stereo tapers some 4 channel though.

honestly, I don't think there will be much interest with just a single-channel pre-amp.  The vast majority of people here record 2 channels, and some people have made the jump to 4 (with the advent of affordable, small, 4-channel recorders).  But really, I think the vast majority of people wouldn't bother with two single-channel pre-amps.

Wow! It should have been obvious but it didn't hit me till now. It needs to be 2 channels, AT LEAST, for tapers use. You're right! 

The above pre was originally designed for the recording/home studio, where only one instrument is recorded at a time during tracking... i.e. designed for a different purpose.

I don't think this particular layout will be well suited as a tapers preamp right now.

To do this properly and make it a real tapers preamp, I think I need to start from scratch. Use a wide but shallow case, new layout, put 2 (or 4) channels side by side,  integrate the VU meters, add a clip indicator, maybe add a high-pass/low-cut filter, add an unbalanced out, design it really small and compact, add room for battery (if possible), etc. What do you think?

Thanks for all your feedback. It's invaluable.... time to go back on the drawing board and really design a proper tapers preamp. 

Oh well, I thought I can adapt the above preamp for tapers use, but now I can see it's almost there but really it's not, still a long ways to go.  Tapers have a different set of requirements.

Nice job!  I like the simplicity of this, just based on THAT/INA chips.  I also like the battery power.  Make it run with a variable input voltage 6-12V and you're golden.  Oh yeah, make sure it will not fry if polarity reversed .

Of course to fit the taper crowd you'll want a rugged case, and Neutrik (sp?) combined XLR/TRS connectors, and probably a pad, and a line/mic switch.

Other things (I think already mentioned) are locking and/or recessed switches, especially for phantom power.

Finally, remember the competition.  SD mixpre/ Shure FP24 (transformer based preamps) are approx $500, so you'll have to come in at or less than this target price.

  Richard

[OOK]

At the moment, this just a single channel mic preamp.  In the future I'll be converting this to SMD and cut the size further in half, or cram 2 channels on the same board. But that's a far future.

Thanks for the comments.

For what we do as tapers it gotta be atleast 2 channel.  Carrying one pre is much better that carrying 2 pres unless it is absolute audio nirvana most people will pass this up if its a single channel. 

As far as metering I like this suggestion:

well, my opinion of "good metering" would be something like a light for signal, maybe lights at -30, -20, -12, and then a lot more details between -12 and 0, maybe a light at -9, -6, -3, -1, and an "over" light. 

I am really looking forward to see what you come up with.  What is the measurement on the noise floor?

As far as price IF you are talking strictly a two channel pre without an AD section, somewhere between 500 to 1000$ is what I would consider reasonable.  This goes without saying, but I will say it anyway just make sure your using the best possible parts for the money.

I like the comment:  You can start holy wars on this stuff, and the various features, and the subtle flavors.  This is so true.  There are a lot of people on this board who will open the box to peek inside at the quality of your components.  I personally wouldnt know the difference.  I go by what sounds good to me, its so subjective.

Some of the mics we tapers use are:

ADK TLs
AKG 391
AKG 451
AKG 480
AKG 414
AT 3031
AT3032
AT4041
AT 853
Averson
Beyerdynamic 930
Bussman Audio
DPA 4011
DPA 402-1-2-3
Earthworks
Joesphons
MBHO 603 or 648
Microtech Geffel
Neumann 140
Neumann 184
Oktava
Peluso
Rodes
Schoeps cmc6 mk?
Sennheiser
Studio Projects
THE audio
Violet Designs

I think I hit them all give or take...............

Peace OOK

[fivefishdiy]

you should package one up and loan it out to responsible people who can run it, and get some tapes up on the "Live Music Archive" at www.archive.org.

Great idea! Well, I'm new here... so who are the responsible people here? 

Okay, I'll put this single channel prototype in a case, loan it to some trusted people to give me feedback, and we'll see how it goes.

BTW, this is NOT a new or untested preamp design... it's been in use in home and commercial studios around the world... been selling them as kits for a year now.

What's new here is the "battery-powered/12VDC" powering option and that's when a customer told me about tapers and pointed me to this website.

Even if you stuff two of those boards into one box and run it, people may find out it runs sweet, or that it's way too bright, or some other descriptor, and then you can decide if you should start to think about a 2 channel box, or just forget about us altogether.

I like "passionate users" about their craft. I think this will be fun and challenging. It will be cool if this design also gets accepted by people recording "in the field." Right now, I just have people "in the control room/booth" using it.

Just PM me if you're interested in BORROWING it to test. I don't have a bunch of prototypes to loan out (and remember, this is just single channel), so not all may get the first crack at it but eventually I'd like to give everyone the chance to use or listen to it.  To make things simpler, I'd prefer just USA users for now, and user must be willing to give me feedback (good and bad), be able to give me audio samples, and also post audio samples on the board too. 

ok.. time to get working putting this in a case.

Thanks all.

[Todd R]

Just sticking my head in this thread, since this looks like a promising option.

Ok, I'll put in my two cents, though as already mentioned, you'll probably get a lot of opinions, many saying the opposite thing.  My few thoughts:

Stick with 2ch.  Folks wanting to do 4ch can get 2 of your preamps.  I'm guessing that hitting a small niche market means getting as many customers as possible, so no sense making a 2ch version and a 4ch version.

Since I have a Grace V3, I really like the design of a stepped gain with a 0-10db trim.  I kindof think that the 10db steps makes more sense than the 6db steps if you already have 10db trim, but that is no big deal.  If you can design it so you don't get a spike or pop when you step up the gain one step, that is great, since sometimes tapers will need to make this change while recording.

I agree with smokinjoe -- meters on a preamp aren't that important, I'll be watching the meters on my recorder or my AD.  You can probably get by with 6 LEDs -- 2channels with -24db or -18db to show signal present, then -12db or -9db, then -3db or -2db.

If you make it deep, say more than 7-8", make it narrow and put the XLR connectors on the side.  Or make it wider and shallower and put the XLR connectors on the back. 

Batteries -- internal is def nice, but perhaps not required.  I don't know if you get into problems with UL listing or whatever if you put batteries in, esp something like li-ion or li-poly.  12v isn't bad, but full 48v phantom with 7.2-9v is nicer since those batteries are a bit easier to find.  If you need 12+ volts, it might be nice to use the li-poly 9v (500mah) or NiMH 9v (300mah) -- see thomas-distributing.com.  If we could get this type of battery and just put 2 of them inside, with your low power requirements, that might enable runtimes of 6+ hours and be easily rechargeable.

Thanks for thinking about this market!!!

[fivefishdiy]

Thanks for the input. Keep 'em coming. I'm starting to get that "butterfly" feelings in my stomach when a bunch of ideas are starting to fit together like a jig-saw puzzle. I guess it's called excitement, HA!

12v isn't bad, but full 48v phantom with 7.2-9v is nicer since those batteries are a bit easier to find.

I checked my notebook, and yes, we can still get 48Volts from a 6VDC input.  The split rail power supply for the chips though went down, but still +/-2.5V above the min. voltage required by the chips. So it still works.  The "ideal" is 9VDC input... we get the 48V and the split supply voltage drop to power the chips isn't so bad.

I've drawn a preliminary sketch of what I want the "SC-1 Tapers Edition" preamp to be.  I'll start laying them out on CAD towards the end of this week.

Anyways, I did some more testing tonight on my proto... and here are some photos. (I love photos

Testing... my single channel pre prototype. Phantom power ON, with the LED indicator lights on.


from a 12VDC input, let's measure the phantom power voltage.

Hmmm 47.94 Volts... Close enough... if I could have adjusted the trimmers for a more exact 48.0 Volts, but phantom power is not picky. This is good enough for testing.

Hook up scope and try to measure the ripple on the 48V line.

Hard to see... but the camera's shutter speed captured some signs of ripple. The scope is set to 50millivolts per vertical division.

Let's magnify it... set scope to 20mV per division.

Okay, now we can see some ripple caused by my switching PSU. According to the scope, the measured peak-to-peak ripple is 12 mV (or 0.012 Volts peak-to-peak).  In RMS, that's 0.004Vrms.

It took me about 6mos. (working on and off)  to fine-tune my converter PSU design for no RFI, buzzing interference, and get the ripple to where I like.

Photo of an earlier prototype PSU... (this one needs to be at least 3 inches away from the preamp XLR inputs for it not to cause interference...  so it's no good for tight spaces where everything is crammed together in a portable case... it's fine though for a 1u Rack in a studio.) Shown is the same preamp design with input and output transformers, -20dB Pad, polarity reverse and a true balanced Active DI input for electric guitars/bass.

[Kindguy]

Is that a Jensen transformer on the bottom pic to the left?

Oh yea welcome aboard!