EH 12ay7 + LDC = Low gain

Recording Techniques, People Skills, Gear, Recording Spaces, Computers, and DIY

Moderators: drumsound, tomb

Murphdasurf
ass engineer
Posts: 46
Joined: Fri Dec 30, 2005 2:38 pm

EH 12ay7 + LDC = Low gain

Post by Murphdasurf » Tue Jan 31, 2006 1:47 pm

I just noticed today how much of a dropout in the
gain of the 12ay7 occurs when I try to use the phantom
power with a Shure KSM 32. The blue power light goes
completely out and there is a good amount of gain for
about 5 seconds and then a slow fade to almost nothing.
When I patch in an outboard phantom p.s. everything
is fine. Am I right to assume that the lost gain is from
the mic's end? As opposed the pre itself?

Analoghacker wrote on another thread:
"yes the blue LED goes dim or out with certain condensor mics (the marshall, for example...). this does not effect the operation of the pre. it does show you how much sag the wallwart has when you add the draw of the phantom supply. this is the one area where the economy of the unit is apparent. i accept the responsibilty completely. if you can replace the 12VAC 1A wall wart with a 12VAC 2AMP supply, this will "fix" the lamp and the bass will be punchier too. "


I've done a quick google search and so far zero luck trying to track
down the 2amp supply. Any comments or suggestions?


thanks,

Murphy
next to me, Hodor is a genius

analoghacker
alignin' 24-trk
Posts: 67
Joined: Mon Jun 14, 2004 9:02 am
Location: malm?, sweden
Contact:

Post by analoghacker » Tue Jan 31, 2006 2:17 pm

murph, i don't know the supply requirements of the mic you mention... you should google it and find out. there is 10mA of phantom supply (48V) available in the 12AY7 mic pre. if the BLUE LED goes out, you are drawing more than 10mA. 10mA is standard... most mixing board phantom supplies are calculated for 10mA per channel, so they have alot more available for one hungry mic and who would know otherwise. older mics use much less current than newer ones, why i don't know. there may be some kind of preamp in the shure? i don't know. but the polarizing current needed for any known capsule is micro Amps, not milli Amps. so there must be some sort of preamp or other conditioning circuitry in the mic you have. does it normally come with a power supply?
jc

Murphdasurf
ass engineer
Posts: 46
Joined: Fri Dec 30, 2005 2:38 pm

Post by Murphdasurf » Tue Jan 31, 2006 3:16 pm

JC

shure KSM 32 SPECIFICATIONS

Phantom Power 48 Vdc ?4 Vdc (IEC-268-15/DIN 45 596),
positive pins 2 and 3
Current Drain 4.65 mA typical at 48 Vdc

does this help?

Murphy
next to me, Hodor is a genius

KennyLusk
dead but not forgotten
Posts: 2037
Joined: Wed Sep 22, 2004 10:22 am
Location: Ramah, New Mexico

Post by KennyLusk » Tue Jan 31, 2006 3:19 pm

4.65 mA
"The mushroom states its own position very clearly. It says, "I require the nervous system of a mammal. Do you have one handy?" Terrence McKenna

analoghacker
alignin' 24-trk
Posts: 67
Joined: Mon Jun 14, 2004 9:02 am
Location: malm?, sweden
Contact:

Post by analoghacker » Tue Jan 31, 2006 5:18 pm

are you sure the phantom is on? the green LED should be on and will not go out.

Murphdasurf
ass engineer
Posts: 46
Joined: Fri Dec 30, 2005 2:38 pm

Post by Murphdasurf » Tue Jan 31, 2006 6:04 pm

Yup

tried a: sm58 with no phantom=good

sm94 (SDC) with phantom on: green light on,
blue light (weak)on,
= good (current drain 1.0-1.2 mA)

KSM 32 ... refer to opening post.

I think the reason I didn't notice sooner is I was in the middle of
updating software and until last night had not tried to run the signal to "tape"
I've only been monitoring the mic pre with the headphone amp
on a presonus firebox, which has been described as criminal in terms of output gain.
I've tried the mic with other pre's and it works fine.
Like I said, at first rush the gain is fine, then a slow fade out.


Murphy
next to me, Hodor is a genius

rodabod
takin' a dinner break
Posts: 151
Joined: Wed Nov 02, 2005 5:39 am
Location: London

Post by rodabod » Wed Feb 01, 2006 9:12 am

Have you measured the current drain when the KSM32 is plugged in?

I don't always trust specs.

analoghacker
alignin' 24-trk
Posts: 67
Joined: Mon Jun 14, 2004 9:02 am
Location: malm?, sweden
Contact:

Post by analoghacker » Wed Feb 01, 2006 9:27 am

hey murph,
try removing the 12AU7 and put the 12AY7 in instead... or a 12AX7 if you have one. you are using a 5751 in the first stage, right? in any case, that will reduce the current draw in the pre, because the 12AU7 draws the most current. if the phantom still goes out, something else is drawing current. let me know what happens.
jc

User avatar
Ben Logan
takin' a dinner break
Posts: 166
Joined: Wed Jun 02, 2004 10:01 pm
Location: Chico, CA.

Post by Ben Logan » Wed Feb 01, 2006 11:06 am

Are you using the XLR out, or the buffered 1/4 inch out? The XLR one seems a decent amount hotter.

Murphdasurf
ass engineer
Posts: 46
Joined: Fri Dec 30, 2005 2:38 pm

Post by Murphdasurf » Wed Feb 01, 2006 12:03 pm

JC

tried a AKG C-1000 and it seemed to work fine.

here's the tubes I tried with your suggestion. (ksm-32)

EH 12ay7 and 12au7
GT 7025
chinese 12ax7a
RCA 5751 old stock
RCA 12au7 clear top old stock

The results: no change as per the topic of this thread.

with one exception: Agent 5751 at yur service.
The only one (driver socket) where the level stayed
the same after a few seconds.
The most initial level came from the 12au7's in the driver.
As for the slow ramp phantom....OUCH!
It almost clips the meters in cubase.

Ben
Are you using the XLR out, or the buffered 1/4 inch out? The XLR one seems a decent amount hotter.
XLR, I've never even tried the 1/4 out. maybe I should.

Murphy
next to me, Hodor is a genius

dgrieser
steve albini likes it
Posts: 327
Joined: Tue Feb 15, 2005 11:34 am
Location: New Mexico

Post by dgrieser » Thu Feb 02, 2006 7:49 am

I just got my EH12ay7 last night and tried it out with a few mics. With a MC-012 the power light stayed on and I had plenty of gain. I've never heard this mic sound so good. With the KSM 32, the power light went on and the gain was lower but was still usable. I tried an external phantom power supply for the KSM 32 but didn't notice an appreciable gain in the pre's output.

I'm running the pre into a Tascam 788. With my Symetrix SX202 (no mods) I can keep the gain all the way down on the 788 and still get plenty on the meters. With the EH12ay7 I had to turn the gain up just a little on the 788 to get the same level on the meters.

Soundwise, there's no comparison--the SX202 sounds brittle/extra crispy compared to the EH. Someone loaned me some NOS tubes to try. I'm seriously hooked. Can't wait for a rack mount version but hope it has a little more output. I didn't really notice any difference in level from the knob turned from about 1/3 to all the way up. Is that normal?

Murphdasurf
ass engineer
Posts: 46
Joined: Fri Dec 30, 2005 2:38 pm

Post by Murphdasurf » Thu Feb 02, 2006 8:20 am

dgrieser
With the KSM 32, the power light went on
With your '32 the blue power light stayed on?

Let us know how the tube rolling goes.
next to me, Hodor is a genius

User avatar
;ivlunsdystf
ghost haunting audio students
Posts: 3290
Joined: Mon Oct 18, 2004 7:15 am
Location: The Great Frontier of the Southern Anoka Sand Plain
Contact:

Post by ;ivlunsdystf » Thu Feb 02, 2006 8:22 am

Wannabe William Safire here: Why do we call it tube "rolling"? Just curious.

dgrieser
steve albini likes it
Posts: 327
Joined: Tue Feb 15, 2005 11:34 am
Location: New Mexico

Post by dgrieser » Thu Feb 02, 2006 8:34 am

Sorry, the power light went out with the KSM 32. It stayed on with the MC-012.

There was one GE 12AU7 tube was really outstanding with the KSM 32 recording my mandolin. It was a real ear opener. There was a richness and dimensional quality to the sound I hadn't heard with the SX202. I think by that time I was using the external phantom power supply too.

I gave the tubes back today--it kinda made me nervous swapping them, so now I need to order some. Any recommendations?

And thanks to llamajammer for getting the good deal on these pre's.

Murphdasurf
ass engineer
Posts: 46
Joined: Fri Dec 30, 2005 2:38 pm

Post by Murphdasurf » Thu Feb 02, 2006 9:10 am

Tater
Wannabe William Safire here: Why do we call it tube "rolling"? Just curious.
When you have all your tubes lined up and ready to try,
if you bump into them they fall over and "roll" everywhere.
They're trickey little bastards.


dgrieser

you might try doing a google search on "Joe's tube lore"

I like http://www.audiotubes.com/
at least for a quick reference for how a tube "might" sound
and for general price and availibility.

If you haven't already looked through analoghacker's posts
on the "stupid questions regarding 12ay7" thread on this forum,
I recomend that you do.

There seems to be equal parts wheat and chaff when it comes
to NOS tubes. You really never know what you'll get.
The 12ay7 really seems to be very responsive to different tubes.
even the crappiest tube I have sounds pretty good.

Murphy
next to me, Hodor is a genius

Post Reply

Who is online

Users browsing this forum: No registered users and 55 guests