The No.1 Website for Pro Audio
 Search This Thread  Search This Forum  Search Reviews  Search Gear Database  Search Gear for sale  Search Gearslutz Go Advanced
can I drive transformer coupled outboard through Amek Angela inserts? Consoles
Old 1 week ago
  #1
Gear Head
 

can I drive transformer coupled outboard through Amek Angela inserts?

Hello,
I have few external mic preamps with transformer coupled outputs.
When I connecting the preamp output to the Angela insert return I'm suffering from unmatched impedance between the low impedance output transformer to the high impedance input (the insert return driven by a quarter of a tl074).
What would be the best way to solve this issue?
There's a quad op amp with lower input impedance that I can sweep in without changing too many components on the A10 module?
Old 1 week ago
  #2
Lives for gear
 
Richard Crowley's Avatar
 

There should be no problem with low source impedance and higher load impedance. In fact, that is the ideal connection.
It is unlikely you problem has anything to do with impedance.

The major issue here is HOW you are connecting to the insert return?
If we assume that your console has a standard TRS connector with send on ring and return on tip,
you should be using a TS plug which isolates you from the "send" signal.

If you are using a TRS plug to connect to the console insert, then you probably are connecting it wrong.
Please tell us what kind of connection is coming from the source (your mic preamp)?
And what kind of cable and connector you are using to plug into the Amek console?
Old 1 week ago
  #3
Gear Head
 

My console have a patchbay with different insert input / output sockets with bantam TT connectors, both of them unbalanced.
The output of my external mic preamp is balanced.
When I connected the preamp output to the insert return I'm getting a thinner tone with lot's of hum comparing to the signal that I'm getting by connecting the preamp output directly to the input of my Motu 16A audio interface.
So a TS cable will solve this issue?
Old 1 week ago
  #4
Lives for gear
Add to Richard's summary:

There are different ways to connect a balanced output to an unbalanced input, depending on how the output is built. This can get very complicated for transformerless devices (I know it's not the OP, but others read these forums).

But even a transformer can get dicey.
Does it have a center-tap on the output? A few devices seem to want that grounded.
I've come across one that, for some reason, was happier with only half a center-tapped secondary connected.
I've never come across a transformer output that cared which side went to ground, but can imagine a circuit where it's critical (think a feedback loop that tries to compensate for transformer).

And one that argues against Richard's advice: early in my career I tried to install a used Scully 280 to unbalanced inputs on an A&H consolette. The 280's output transistors were hiss city when the tape was parked, and the deck was much too bright when it was playing.
I called the seller to complain, and he told me to try putting 680 ohm resistors across the output. Quieted it right down, and the machine met spec.
Apparently, at least some transformers care about having a near upward match rather than a very high one.
This might apply to the OP. YMMV.
Old 1 week ago
  #5
Lives for gear
 
nosebleedaudio's Avatar
 

Quote:
Originally Posted by smilan View Post
My console have a patchbay with different insert input / output sockets with bantam TT connectors, both of them unbalanced.
The output of my external mic preamp is balanced.
When I connected the preamp output to the insert return I'm getting a thinner tone with lot's of hum comparing to the signal that I'm getting by connecting the preamp output directly to the input of my Motu 16A audio interface.
So a TS cable will solve this issue?
Its probably because the pre output is electronic balanced out (Not transformer) which does NOT like one leg (Pin 3) grounded.
I would try lifting pin 3, or use a transformer box that will float the signal..
I prefer using a transformer..
Old 1 week ago
  #6
Lives for gear
Ah. As I said, transformerless is different. There seems to be an almost infinite way to design those circuits. If you can find a manual, take its advice. Otherwise, try different things: Almost all transformerless boxes want pin1 (XLR) to circuit ground. Some also want pin 3 to ground; others don't.
Old 1 week ago
  #7
Lives for gear
 
nosebleedaudio's Avatar
 

Quote:
Originally Posted by Jay Rose View Post
Ah. As I said, transformerless is different. There seems to be an almost infinite way to design those circuits. If you can find a manual, take its advice. Otherwise, try different things: Almost all transformerless boxes want pin1 (XLR) to circuit ground. Some also want pin 3 to ground; others don't.
He said it was balanced, so don't connect pin3 to ground..
There are only about 3 basic types outputs;
1:Electronic balanced out.
2: Unbalanced out.
3: Transformer balanced out.
You can ground one side of a transformer output with no problems 99% of the time.
Old 1 week ago
  #8
Lives for gear
It also appears that, despite the subject line, the OP's device might be transformerless. Sometimes those ciurcuits work better with pin 3 to ground, and leaving pin 1 floating. See the Rane note on this, if you haven't yet actually experienced it in a hookup.

Or see this Eventide manual, which I picked at random because I wrote the processing software for it. (I'm not responsible for its circuit design or hardware manual. A lot of similar classic Eventide has the same configuration).

From p8 of the manual:
Quote:
Analog Audio Outputs
To “unbalance” the jack, use pins #1 and #3 as ground and use
Pin #2 as “hot.” If either pins #2 or #3 are unconnected, you
will get more distortion than signal !
Best advice, always: RTFM.

------

I guess I've been involved with enough gear over my career that "99% of the time" also leaves room for a few exceptions.
Old 1 week ago
  #9
Lives for gear
 

longtime amek angela owner here: as far as i remember, the inserts are indeed unbalanced - i therefore had (tascam) un-/balancing units in use for interfacing with some balanced gear (although i inserted most standard dynamic processors to each side of the desk through unbalanced lines). on rare occasions (and if available), i mis-used the balanced aux sends/efx returns for 'inserts' or the subgroups (through the tascams again) as insert sends.

see whether i can still find a pic - lovely desk for the price! got replaced with an amek recall though...
Old 1 week ago
  #10
Gear Head
 

Thanks guys,
I've double checked myself one more time, what I found is that I didn't took in consideration that the bus output in my console contains another amplification stage that affecting the output signal.
After calibrating the bus amp levels in a way that I was getting the same output level when connecting the preamp output directly to the motu input and when connecting it to the insert return with fader at 0db and from the bus out to the motu input I made a simultaneously recording (using a Y split) of the preamp output directly to the motu input on one channel and the preamp output connected to the insert return and assigned to the bus output and from ther to the motu input on the other channel.
The difference was very minor referring the frequency response and the noise level so it seems like now everything works fine.
Old 1 week ago
  #11
07x opamps have no problems with inputs as they are very high impedance and will accept any load the design is compensated for. The problem is usually outputs. 07x opamp cannot drive a load below 2k ohms without increasing THD and level losses. Replace them with 600 ohm load capable opamps and that issue is solved.
Old 1 week ago
  #12
Gear Maniac
 

Quote:
Originally Posted by Jim Williams View Post
.... The problem is usually outputs. 07x opamp cannot drive a load below 2k ohms without increasing THD and level losses. Replace them with 600 ohm load capable opamps and that issue is solved.
Haaaa ? I thought that the OP was:
Quote:
Originally Posted by smilan View Post
.... suffering from unmatched impedance between the low impedance output transformer (of the external mic preamps) to the the high impedance input (the insert return (of the Amek Angela) "driven" by a quarter of a tl074).
.....

Last edited by analogguru; 1 week ago at 10:03 PM..
Old 1 week ago
  #13
Lives for gear
 

Hi
The Angela inserts are unbalanced as said. The return would be no issue as they are at least 10K input impedance, but the insert send would not be happy driving a 600 Ohm 'load' as they use a TL0 series chip.
Almost all AMEK balanced outputs are a cross coupled design where if you want to run it into an unbalanced input then you MUST ground the 'cold' side otherwise the level will be a bit low and more noisy. Some desks use a NE5532 and some use a SSM2142 or equivalent, essentially the same circuit but in 'integrated' form.
Matt S
Old 1 week ago
  #14
Gear Maniac
 

Quote:
Originally Posted by Matt Syson View Post
Hi
The Angela inserts are unbalanced as said. The return would be no issue as they are at least 10K input impedance, but the insert send would not be happy driving a 600 Ohm 'load' as they use a TL0 series chip.
.....
I suspect that the assumed 600 Ohm load (= microphone preamplifier) would also not be happy to see a (line) signal of the insert send of an Amek Angela..... but this was not the problem/question of the OP. (As far as I unterstand it, he wants to use the insert returns as line inputs for his external mic preamps).
Old 1 week ago
  #15
Lives for gear
 

Hi
The original problem was a combination of the wiring not being the correct way to get from a balanced mic amp out to the Angela unbalanced in, and the other possibilities for gain or loss elsewhere in the channel path.

The comments by Jim, myself and others about the send of the insert were not specifically for the OP but as a note for others who may use the send to feed into a Pultec EQ for example which is a 600 Ohm INPUT impedance. If this is what you are doing then unless the send amplifier chip is changed it will be more distorted than it could be. Of course 'normal' line level gear will be 10K input impedance or more and no problem.
Matt S
Top Mentioned Products
Topic:
Post Reply

Welcome to the Gearslutz Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…
Thread Tools
Search this Thread
Search this Thread:

Advanced Search
Similar Threads
Thread
Thread Starter / Forum
Replies
johndykstra / Electronic Music Instruments and Electronic Music Production
0
sctt_stone / High end
13
alex / High end
4

Forum Jump
Forum Jump