Marshall AS100D and Phantom Power

Hey Cakewalkers,

I'm considering buying a Marshall AS100D and playing through condenser mics for both vocal and instrument. Trouble is that the Amp's phantom power supply only puts in 15v. I was hoping that it would be 48v.

Does anyone have this amp so that they can let me know what condenser mics sound like with the 15v?

Cheers

Rodders

Well it seems to be the kind of gear you can't get real specs for.

Where are you getting the impression it's 15v[sic]DC?

My first thought was that you might be describing a balanced line that might be dedicated to a balanced connection to a guitar with dedicated active circuit that required power. (in other words it could replace a 9volt battery in a acoustic guitar... that had a balanced output) but that would be highly specialized. Les Paul used a solid body guitar set up like this in the Seventies. Danny Gatton had a custom, active electronics, remote power rig as well.

I think it's more likely they are running traditional 48vDC on the mic inputs and we just don't have easy access to a spec sheet. I highly doubt they are running T-Power mic circuits.

Go get us some more info. :-)

best,
mike


edit to add:

OK I finally saw the PDF and I'm looking at the schematic.

yeah 15vDC and it's not wired as "standard" (I really don't think there is a standard) phantom power... as it is now it would RIP A RIBBON MIC IN HALF within moments of mistaken exposure to the "phantom"... very not cool!

Whacky... maybe they really were thinking of active onboard electronics, balanced output guitars.

At least my CMC6/MK41 Schoeps would work well (they go down to 6vDC) with them... no wait a minute... the impedance is all off :-)

Honestly, you might want to reconsider the term "great amp"... that achievement would be sort of a rare occurrence over at the Marshall shop. :-)

Hey Mike McCue,

Shocking isn't it. I looked in the manual from the official marshall website, images are below.

This afternoon I went to my local music dealer and tried this amp out, but when I asked if I could mic up a condenser to hear what it sounds like I understandably got the cold shoulder. I always seem to make silly requests when trying out gear.

http://i199.photobucket.com/albums/aa184/rodneysaccess/AS100D15v.jpg

http://i199.photobucket.com/albums/aa184/rodneysaccess/AS100DBlock.jpg

Thanks for your interest

Rodders

Hey Guys

Maybe there are some alternatives to buying a Marshall Acoustic, but over here in the UK the Fender Acoustasonic's are way over priced as are the Fishmann.

Beagle, I like the idea of providing my own power, its just extra cost and extra luggage.

Mike McCue, Would an AKG C100S which is a 9v condenser work?

Cheers

Rodders

I'd check each mic's specs before assuming anything.

Most Nuemanns and many pro grade AKG mics only have a +/-4vDC tolerance.

Also one must consider current capability... Most music industry grade equipment provides a bare minimum of current capability on the phantom power supply. So, if you place a 9-48vDC mic on a so-so supply... and it's operating at 9vDC you will draw more current than at 48vDC. If you hit the wall of current capability your are running something similar to a *starved plate design*... and I don't think most people really do that on purpose.
It's one reason so many folks using music industry grade gear have wildly different experiences with mic performance.

Re: CS1000S... I believe that is an electret condenser mic... they typically run on small batteries because they use almost no current.

I'm simply ignorant of the CS1000... you may have made a very savvy choice with that selection.

Let's see what others have to say.

best regards,
mike

Hi everyone,

I had a comment to make yesterday but felt I should do some reference checking before saying something incorrect. I happened to have one of my marathon 6 hr phone conversations with my friend Gary who is one of my personal audio/electronics mentors (we're plotting our own tube based mic preamp construction... but he presently lives 5 hours away).

Kriz, I get the impression you think I get into too much "mumbo jumbo". To whatever extent I can, I apologize for leaving you with this feeling. I hope you understand that I just have a sincere love for this stuff... it took me years to learn some of the gotchas and phantom power is one of the real gotchas in our business/craft/avocation etc.

Today I refreshed my memory about amplifiers and power supplies.

Here's my concern:

1) I was not aware how many newer mics are spec'd as able to run between 9-48vDC (+4vDC tolerance gets you too 52vDC) but after a quick look at a lot of prosumer mics I find this to be the case.

2) That's not necessarily a good thing.

It offers the benefit that you can use the mic at lower voltage but I don't see anyone acknowledging the most basic idea that running the Field Effect Transistor ( the amplifier stage in the microphones built in preamp ) at a lower voltage will lower headroom.

The implication of this is that a mic run at 9vDC that could have been run at 48vDC will have a totally different sound character when pushed. The lack of headroom will be experienced as crunch and grain... and unless one specifically wants a distorted effect I doubt any of us would spend any amount of money on a mic that we knew was not going to operate at its best. To extend that logic further... plugging a FET amplified mic into anything lower than 48vDc will reduce the ability of the mic to sound as smooth and nice as it has a potential for.

My mentor Gary reminded me that FETs will run even more cleanly at higher voltages than 48vDC but that the 48vDC convention comes from early Neumann designs that used a Nuvistor tube.

"It might be a stretch to think that someone is going to run a Neumann through this thing"

That's exactly what Greg Mackie said when he designed the 16 input 1604 mixer with just enough current at 48vDC to power 4 modern transformerless true condenser microphones.

That's why I had to learn about phantom power supplies... because 15 years ago I could afford some nice mics but the Mackie offered so much value for the money (still does) that I couldn't afford to pass up that value by going to the next level... which 15 years ago was a BIG jump.

If you start dragging down the phantom power supply voltage it's the roughly equal to running a starved plate design. (A FET has a "drain" rather than a plate) I hope that metaphor is familiar enough that we can consider that "starved voltage" is not what most people look for in a microphone unless a special effect is desired.

One curious aspect of this is the idea that a company like Neumann can maintain their reputation for quality by simply stating clearly that their microphones do not operate to spec below 42vDC. They do that with a simple statement. What a great way to maintain quality.

AKG seems to bend the rules... as the mics lower in price they suggest that you can operate them at lower voltages. I believe this is merely a practical reaction to the real life situation where so much music industry grade gear simply isn't capable of providing a stable 48vDC at the required current draw. I don't think it should be considered an endorsement or suggestion that the circumstance is ideal.

Here's the most important part. You are not going to recognize the effects of sag UNLESS it's really bad or you have experience with the mic in a fully powered preamp, BUT you are going to have to deal with the fact that you have captured a dirty sound that is not going to respond to EQ or any other effect with the grace that a nice sweet clean signal will.

It will send you in the direction of wondering why some recordings need to be labored over just to get a mix working while other recordings just seem to mix themselves.

This is a sincere attempt to help the OP understand the choices he can make while considering phantom power... which was the nature of the original question.

I readily acknowledge that this is really silly stuff considering the amp/appliance in question is a one man band coffee house gigging machine... which implies that absolute sound quality is just part of the requirements to make it a satisfactory product.

I hope the discussion will provide long term benefit rather than just helping with a present buying decision.

I hope I'm not too frustrating!

all the best,
mike


PS Bill (wst3) please stop by and school me if I've misrepresented anything. :-)

Hi Kriz, that's why I said:

mike wrote: "I readily acknowledge that this is really silly stuff considering the amp/appliance in question is a one man band coffee house gigging machine... which implies that absolute sound quality is just part of the requirements to make it a satisfactory product."



Kriz wrote: "15V specification... could be an issue down the road that we haven't considered."

But, I just considered it in great detail... and tried to share my thoughts. :-(
I guess it's just that I think the big picture stuff is useful info and that the OP might find it useful. I also like to imagine everyone can reach for the stars. It's my hope the info will help down the road. I just don't think in terms of... it's only a $699 amp... who's gonna notice.

Rodar6 is already suspicious of the 15vDC rating... it's my hope that now he knows why his suspicions were well founded.



"Maybe call Marshall and discuss it with them and see what they have to say."

I suggest calling a microphone company to see what they say.



What I'm saying is that a $69 (I don't know why Kriz thinks this is only about expensive microphones...) condenser mic rated at 9vDC thru 52vDC will sound best at the highest voltage... period.

I don't know why anyone would knowingly hook up gear that they suspected/knew was not an ideal match... unless they had too... (and I have had too many times) but Rodar6 still has choices.

Which brings me to:

I recommend to Rodar6 that you consider a dynamic mic which I expect will work VERY well with this amp. The Heil P35, for example, is an excellent mic and in my humble opinion will outperform a condenser in this instance. I also think a SM57/58 would be a great mic to use.

all the best,
mike

Thanks George!

:-)

You just made it worth all the effort... I do enjoy reminding myself of this stuff.
best regards,
mike

Your welcome Rodar,

I hope you have fun with the gigs!

best,
mike

ah ha,

So are you're suggesting that the power supply we typically enjoy in a guitar amp is much dirtier than we would ever accept in a dedicated preamp design?

I had not thought of that... most of us, whether we know it or not, seem to enjoy a little dirt in a guitar amps power supply and guitar amps have historically been designed to not be as clean as high fi standards. Some guitar amps have been designed as such... they are called Bass amps. :-)

This would be a great question for Marshall.

Is this new breed of *acoustic guitar* amplifier equipped with a really clean power supply or is it fairly standard for an electric guitar amp?

Just in case anyone is thinking this is over kill and hyperbole... let me clarify... what we are saying is that NONE of this is a problem with a dynamic mic... but should be a concern when using a condenser mic because the side effects of any dirt on that power supply will be AMPLIFIED by the FET amplifier housed within the microphones body and sent back to the amp for further amplification.

That's a real good point Gary!

best regards,
mike