dgatwood
is out. Leave a message.
that might work
but i'd use a 7824
F*ck. Yeah, that's what I meant. Home sick with a cold today, so it makes the mind a little fuzzy.
Negative 24V, positive 24V... what's the difference? 
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F*ck. Yeah, that's what I meant. Home sick with a cold today, so it makes the mind a little fuzzy.
Negative 24V, positive 24V... what's the difference?
R
rodabod
New member
I'm pleased you've taken some time to contribute investigative work here. I'm still waiting for my preamps from someone else and am keen to start testing and figuring out a solution.
I'm not completely sure what you are saying can be rulked-out here. Can you elaborate at all?
Seems most likely.
Here's where having a 'scope would help. You could potentially be seeing oscillation on the supply rails here. Could you disconnect the boards one-by-one while measuring and see if this level changes noticeably at any point? Also, does this ripple value change if you set the knobs to make the preamp hum the most?
Interesting. Some people have reported that rotating the transformers helped though.
Since you have more than one preamp, you could jumper the transformer secondaries to another unit over a few feet of wire to see if an external PSU definitely doesn't help.
The PSU schematic looks ok to me. Like I suggested before, you could disconnect the boards and then test the PSU alone with a dummy load. If the 7824 option is easy to swap, then go for it.
The one thing that doesn't seem to have been mentioned much in this thread is ground loops; there are several boards and this could be a potential problem. As I said though, I don't have a unit myself to look over.
Cheers,
Roddy
I'm not completely sure what you are saying can be rulked-out here. Can you elaborate at all?
Seems most likely.
Here's where having a 'scope would help. You could potentially be seeing oscillation on the supply rails here. Could you disconnect the boards one-by-one while measuring and see if this level changes noticeably at any point? Also, does this ripple value change if you set the knobs to make the preamp hum the most?
Interesting. Some people have reported that rotating the transformers helped though.
Since you have more than one preamp, you could jumper the transformer secondaries to another unit over a few feet of wire to see if an external PSU definitely doesn't help.
The PSU schematic looks ok to me. Like I suggested before, you could disconnect the boards and then test the PSU alone with a dummy load. If the 7824 option is easy to swap, then go for it.
The one thing that doesn't seem to have been mentioned much in this thread is ground loops; there are several boards and this could be a potential problem. As I said though, I don't have a unit myself to look over.
Cheers,
Roddy
cannabis
New member
great idea
especially if you
brought over dc from
the regulated outputs
then there would be
no ac in the unit
and if the hum weren't
significantly decreased
(by inverse square)
you will have ruled out
the psu transformer
as the source
nuemes
Be Here Now
Yup yup. Excellent on kick & snare for rock.
Bill: I've never used API's. How would you compare the ACMP's to API's (as far as pre's only)? I gather they're different animals but curious to get a better idea of the API sound.
I
ittam
New member
I might act like a shithead to this gb ( or have to ) :
Is there someone wanting 2 81´s and near Chance
I can´t wait anymore ( hold the money ).
If so contact me at ittamletti@gmail.com
I´m tired and out of money, why send these to europe if the cure
is in California?
Matti
P.S. Seriously
Is there someone wanting 2 81´s and near Chance
I can´t wait anymore ( hold the money ).
If so contact me at ittamletti@gmail.com
I´m tired and out of money, why send these to europe if the cure
is in California?
Matti
P.S. Seriously
Last edited:
D
drBill
New member
More forward. Fast. More aggressive. Muscular. Brash. ???
Hard to put into words. Great for rock. Really, great for anything. Not as heavy as a neve. Never got anywhere near the cool kick sound on the API's that I'm getting with the ACMP's. Did that help??
jasonbmerrill
the end of unreality
some have experienced problems with these but mine works perfectly...
however i have a question. In reaper, i am seeing - 55 db on the meters when monitoring the preamp @ MAX gain (80db) and MAX output... (firepod line in trim @ 12 o clock which i assume is neutral)
is that normal?
lowering the gain to 70 gets rid of the noise floor almost entirely.
jasonbmerrill
the end of unreality
hmm im getting this @ max settings:
also i am using an adapter to get into the firepod... i need a true cable for it.... (even though the adapter is balanceD)
it could be that...
also i am using an adapter to get into the firepod... i need a true cable for it.... (even though the adapter is balanceD)
it could be that...
mshilarious
Banned
That's your basic 60Hz hum with the broadband noise floor below it, but it's a meaningless number without calibrating it to an input level. I mean, 80dB is a stupid amount of gain--let's take a near-perfect input noise level of -135dBV, that +80dB = -55dBV.
But I don't know what your interface is doing at its 12:00 position. Attenuating a little? Also, what is plugged into the ACMP? It should have a 150 ohm resistor between pins 2 and 3 for a proper test. If you have an inline pad, you can use that, it should be close enough. The difference in terminated and unterminated inputs can be significant.
nuemes
Be Here Now
Yes - thank you! Interesting to hear that they're faster than API's. Yes, brash is right on track for describing the ACMP's. They are big sounding pre's.
There were two spots where I felt my pre's where lacking prior to getting the ACMP's and it happened to be in bass DI and kick/snare - exactly the ACMP strong points that I've gathered so far, and that's not a case of GAS. They are solid pre's for those purposes.
Considering the cost of API's (which I would have gotten if the ACMP's weren't avail) I feel very fortunate.
RightOnMusic
asshat
i had an opportunity to use a friend's acmp73 and 84s on kick and snare last saturday (acm 3 on kick two feet back, angled down at bottom of drum > acmp73, audix d6 inside kick > acmp84, sm57 top snare > acmp84) and they really brought that big fat sound that i've been looking for in kick and snare. the d6 had all the smacking attack and the acm3 had all that bottom end girth... snare's an early 70s deep wood ludwig, so it sounds big and ballsy to begin with. acmp84 really allowed that huge sound to pass through and the eq was really helpful in accentuating the sweet spots. really happy with these for drums.
kojdogg
bollocks redux!
some have experienced problems with these but mine works perfectly...
Glad to read that Jason!
kojdogg
bollocks redux!
RightOnMusic
asshat
Those are some nice drums too
koj got to use the same setup at the same studio the day before me. he had other fancier preamps, but i had that ludwig snare...
kojdogg
bollocks redux!
koj got to use the same setup at the same studio the day before me. he had other fancier preamps, but i had that ludwig snare...
sweet-- what kind?
is your acm3 stock?
D
drBill
New member
No you read me wrong. 100% out of phase....
The API's are brash and faster and more agressive than the ACMP's, which I would describe as big, heavy, a little syrupy, and slower.
dgatwood
is out. Leave a message.
First error on the schematic thus far: they numbered the pins wrong. Pin 2 is the output on a 317. (This means that subbing in an alternate part is a major board rework....)
Okay, I've finished swapping out the part, and it made no difference. *sigh*
That said, I just found the problem, though I'm not sure why it is happening. I started bridging across boards with hackish jumper cables, and the hum went away when I disabled the demifinal (second from right) board.
Next, on a hunch, I said "I wonder what happens if I skip the next to the last board instead. I got hum, but noticed that wiggling part of the wire could make the hum disappear completely (with a pop), i.e. my cable wasn't quite solid on one contact.
Long story short, pushing sideways on connector 5C21 made the hum almost completely disappear. (I think it completely disappeared at one point, but I can't reproduce that.)
I checked the connectors to make sure that none of them were failing to make good contact when the board was used. I didn't find any problems.
That leaves two possibilities that I can think of:
1. The placement of the board lines in parallel (and or in proximity to the transformer) is responsible.
2. Adding a negligible amount of resistance (a few inches of wire) between these two boards keeps some part of the circuit from oscillating.
Yikes. Anyway, with a set of wires in place of that board, it no longer makes any change to the sound when I move wires around inside the case, and there is no longer that bizarre behavior where the hum gets suddenly louder near either end of a pot. At this point, all I have is a small amount of... probably induced hum. If I touch the top of one of the inductors (the farther one from the transformer), it gets louder, which leads me to suspect that the remainder of the fix involves shielding the inductors, though why the "upper" board would have problems and not the much closer "lower" board, I couldn't say.
I'll experiment more and see if replacing the other jumper board with a wire harness improves the hum further. I'll have to get more parts, though, before I can do that, and I'm not feeling well today, so it may be this weekend before I make much more progress.
thajeremy
registered abuser
what software are you guys using to test your pre's and come up with these graphs? Is there anything in AA1.5 or PT 7.3 that will let me check mine???
I guess I should know this...but...I dont....
P
P. Glaser
New member
I ran the 310 through the 73 last night and it sounded great again. Haven't figured what was wrong previously. I had the input at the 9 o'clock position and the output max. Played around with the EQ and was able to get some really good stringy rhythm sounds out of my Taylor 614. BTW, I have rotated the power transformer and the humming is much reduced.I tested out my 310 after a 24 hour burn-in and it sounded great. I set it up tonight to record with it and it sounds like it's breaking up when I get on it a bit.
Two questions. I'm going to open it up so what should I look for and what should I be careful of? Also, does anyone know if the power supplies and the multi-pin cables for the 310 and the 900 are the same? They look like they are. If so, I can check that as a possible source of the problem. Thanks.
Paul
Paul
nuemes
Be Here Now
No you read me wrong. 100% out of phase....
Doh! That makes sense as I've heard API's are fast and a Neve inspired design would be slower. So... when will the ACMP Quad Eight inspired Group Buy begin?
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