Is it balanced?? I need help and kinda pronto-like...

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sweetbeats

sweetbeats

Reel deep thoughts...
I'm trying to figure out if the output of my Ampex 440 electronics modules are balanced or not...these are the same modules as are installed in my MM-1000 as well.

The inputs are balanced because I have the optional bridging trannies installed, but the manual simply states that the outputs are balanced OR unbalanced at 600ohms. Looking at the schematic I can't figure out if the output is truly balanced...the output is on the right hand side of the schematic. There is an output transformer there, but I'm not savvy enough to understand if the output is balanced by default all the time and becomes unbalanced automatically if an unbalanced cable is connected (i.e. an XLR cable with pins 1 & 2 strapped together), or if there is something special needed for the output to be balanced.

I want to know because I have an opportunity to pick up a Tascam LA-80 and an LA-81 for a good deal, but I'm trying to decide if I need the LA-81 at all. They would be going between my Tascam mixer and the Ampex MM-1000 if needed. I don't need to run balanced because my cable lengths are short enough and I can just unplug the input transformers on the Ampex to run unbalanced inputs, but I'd like to maintain the option to run fully balanced if I like the coloration of the input transformers and/or if in the future the MM-1000 needs to be located in a different area from the mixer and monitors since it is a noisy beast...but what of the outputs?? If they aren't balanced then I don't need the LA-81 and I'll have to get creative if I need to relocate the MM-1000. If they ARE balanced then I don't need the LA-81 but it would be good to get it in the package that's being offered in the event that down the road I need to run balanced on the output side.

The deal on the LA-80 and 81 is limited time...HELP! :eek:
 
-Is it balanced??


-YES.
:)

that is to say so, in short, so to squeeze the deal of the answer into "limited time".
 
Thanks guys...I was studying the schematic some more...I can start to see how/where signal flows...it get's confusing because in the Theory of Operation section it refers to transformer 8T2 as the "headphone transformer", but that's the output transformer right? And I was trying to understand what happens when you connect the output to an unbalanced load and does that just shunt the output of 8T2 to ground and then the output comes straight off the repro amp prior to the primary winding of 8T2 (and post output select switch of course)? Again, Its just sort of a fuzzy dance right now as I look at the schematic but that is the picture that's sort of clearing for me.

Jinn, I'm using my prototype Tascam mixer: https://homerecording.com/bbs/showthread.php?t=270992. All the line level inputs are unbalanced on RCA's but tests have demonstrated that those line level inputs do really well handling +8 nominal sources, so +4 should be just fine. I have the option to use the mic inputs with a -30dB pad switched in but I'd rather not and keep those open for mics and not have to repatch.

Thanks for the link to that .pdf too.

I live in a pin 3 hot world... :D
 
sweetbeats said:
Thanks guys...I was studying the schematic some more...I can start to see how/where signal flows...it get's confusing because in the Theory of Operation section it refers to transformer 8T2 as the "headphone transformer", but that's the output transformer right? And I was trying to understand what happens when you connect the output to an unbalanced load and does that just shunt the output of 8T2 to ground and then the output comes straight off the repro amp prior to the primary winding of 8T2 (and post output select switch of course)? Again, Its just sort of a fuzzy dance right now as I look at the schematic but that is the picture that's sort of clearing for me.

Jinn, I'm using my prototype Tascam mixer: https://homerecording.com/bbs/showthread.php?t=270992. All the line level inputs are unbalanced on RCA's but tests have demonstrated that those line level inputs do really well handling +8 nominal sources, so +4 should be just fine. I have the option to use the mic inputs with a -30dB pad switched in but I'd rather not and keep those open for mics and not have to repatch.

Thanks for the link to that .pdf too.

I live in a pin 3 hot world... :D
Click to expand...

If the board outs are rated @ -10, you might find it runs out of suds trying to send signal to the Ampex. That's why bump boxes were built.

Just a thought.
 
sweetbeats said:
...I was studying the schematic some more......"
Click to expand...
I thought you have very little time. hmmmm, I guess not. :cool:

sweetbeats said:
...in the Theory of Operation section it refers to transformer 8T2 as the "headphone transformer", but that's the output transformer right?
Click to expand...
I can't see "SHEET 2", but I'd imagine that Reproduce Amplifier is THE Output Amplifier, one can call it what he wants :), and that's all that is there.... And so it is The "headphone amplifier" as well.
5C15 must be the coupling capacitor of The Amplifier's output (?).
From there - Over 8R32 - to Headphone Jack.
From the same point -to the "top" of the transformer's primary winding.
The "botom" of the transformer's primary is Ground (The Ground of The Amplifier Circuit, that is).
The secondary of the transformer provides you with "transformer coupled output" ... (or you can say - transformer isolated).
It's not balanced neither unbalanced ..heh heh, (at this point) it is what it is - a pair of terminals of the secondary winding of the transformer. You can choose what you want to do with them (to use them for).
BUT! - The output XLR jack is configured for Balanced Line interconnection.
Switchable Line termination is provided.
Makes sense? :D

sweetbeats said:
...what happens when you connect the output to an unbalanced load and does that just shunt the output of 8T2 to ground and then the output comes straight off the repro amp prior to the primary winding of 8T2 (and post output select switch of course)?
Click to expand...
Not sure what you are saying.
In short.
If you connect that output to unbalanced device input - you do it by connecting Pin3 (Blue of the Transformer's secondary) with The Signal Input of the Unbalanced Device, and you connect Pin2 (black of the Transformer's secondary) with Ground of the Unbalanced Device (this also will be the shield of unbalanced cable). I'd say you need to try-experiment to tie or not to tie Pin 1 and 2 of that special XLR plug of that "special cable" you are going to use (I assume you'll be using some custom XLR-RCA cables for this, are you???).
************
p.s.
if you want to get more confused about "balanced things" check out couple animations I've made-up for demonstration at my "tech archive", here: http://www.mzentertainment.com/studio_workshop_technical_archive.html, see on the left side of the page there, click on them - things will start moving ... and may freak you out a bit :D:p:D
 
Dr ZEE said:
Not sure what you are saying.
In short.
If you connect that output to unbalanced device input - you do it by connecting Pin3 (Blue of the Transformer's secondary) with The Signal Input of the Unbalanced Device, and you connect Pin2 (black of the Transformer's secondary) with Ground of the Unbalanced Device (this also will be the shield of unbalanced cable). I'd say you need to try-experiment to tie or not to tie Pin 1 and 2 of that special XLR plug of that "special cable" you are going to use (I assume you'll be using some custom XLR-RCA cables for this, are you???).
************
p.s.
if you want to get more confused about "balanced things" check out couple animations I've made-up for demonstration at my "tech archive", here: http://www.mzentertainment.com/studio_workshop_technical_archive.html, see on the left side of the page there, click on them - things will start moving ... and may freak you out a bit :D:p:D
Click to expand...


Thanks Zee. Oh, wait.... this is to Sweetbeats... never mind. :D ;)
 
Funny, I've tried going to both balanced and unbalanced inputs and not really noticed anything wierd. And I don't think my balanced to unbalanced cables are pin 3 hot. I'll have to check them but both ways it sounded good.
 
SteveM said:
...both ways it sounded good.
Click to expand...
Steve, remember?, I had a project idea with transformers. Well, I was testing/experimenting/comparing yad yada yada...
So at the end I tossed the "project" , sold the transformers.
Guess why? huh huh ;) :D

And I needed cash to fix brakes and other things on my Jeep.
 
Dr ZEE said:
Steve, remember?, I had a project idea with transformers. Well, I was testing/experimenting/comparing yad yada yada...
So at the end I tossed the "project" , sold the transformers.
Guess why? huh huh ;) :D

And I needed cash to fix brakes and other things on my Jeep.
Click to expand...

Yes, I remember. With all the xlr jacks? No big diff?

So if I were going out to a balanced input, technically I still should have the hot pin swapped to pin 3 on the Ampex side?

Also ideally if I was going into a balanced mixer I would want the inputs to be line level? no mic amps right? Or what level is it that a balanced input is.
 
Pin 3 "hot" vs Pin 2 wasn't always standardized until (EIA Standard RS-297-A according to Wiki) don't know what year. I have a Sony DAT deck from 1988 or so that is pin 2 hot. I have Fostex and Tascam and even some digital gear (Creamware) of the same vintage that is pin 3 hot. (The Creamware is TRS with the ring +)
 
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SteveM said:
Yes, I remember. .... No big diff?
.
Click to expand...
No little one either :)


SteveM said:
... if I were going out to a balanced input, technically I still should have the hot pin swapped to pin 3 on the Ampex side?
.
Click to expand...
Generally (technically) speaking, as I understand, in a one single interconnection between two devices it does not matter. But in a complex world and various devices involved you wish to set-up and follow a rule, so you keep the polarity checked and don't run into problems when trying interconnect bal/unbal gear with diffrent jacks/plugs types.


SteveM said:
Also ideally if I was going into a balanced mixer I would want the inputs to be line level? no mic amps right? Or what level is it that a balanced input is.
Click to expand...
"Ideally", I guess:
Line outputs to line inputs.
Mics to Mic inputs.
:D
If the balanced "mic input" on the device (mixer) is equipt with "facility" to attenuate the signal level, you may be able to use it. I don't know practically, as I have never had a such device.
Any signal level can be easyly attenuated if needed, but you know that :)
*************
Blue Jinn said:
Check this out too:

http://www.sdds.com/PDFS/technotes/TN99060401.pdf
Click to expand...
Thanks Blue Jinn! This is a good one :cool:
 
I have to add this, to avoid confusions:
Dr ZEE said:
If you connect that output to unbalanced device input - you do it by connecting Pin3 (Blue of the Transformer's secondary) with The Signal Input of the Unbalanced Device, and you connect Pin2 (black of the Transformer's secondary) with Ground of the Unbalanced Device (this also will be the shield of unbalanced cable).
Click to expand...

OR! (and maybe is the batter way!) is to use balanced cable (or a cable with two twisted wires inside the shield), and you connect:
- Pin 3 to one wire in the cable, that will go to Tip of the RCA plug on the "unbalanced side".
-Pin2 to another wire in the cable, that will go to the sleeve of the RCA plug on the unbalanced side
-Pin 1 to the shield of the cable, the shield will not be connected at all on the unbalanced side (as the shield will be "grounded" on the Balanced side via Pin1, that is)
 
Cory:

Looks like you have it sorted out. Just to confirm that yes, at least for my experiences with AG-440Bs, electronics are balanced, transformered both input and output, and you can tie the minus side (pin 2!) to ground to unbalance and it should not reduce the signal level nor diminish the quality of sound. I'm pretty sure earlier generations of AG-440 were the same.

Cheers,

Otto
 
Everybody, thank you. This has been really helpful:

Otto:

AG-440Bs, electronics are balanced, transformered both input and output
Click to expand...

But only on the input side if using the plugin transformer in the accessory octal socket yes?

ZEE:

I thought you have very little time. hmmmm, I guess not.
Click to expand...

I did. I took the quick answers and jumped on the deal, and then wanted to edumacate mythelf.

check out couple animations I've made-up for demonstration at my "tech archive"...click on them - things will start moving ... and may freak you out a bit
Click to expand...

I popped some popcorn and watched for awhile. Very relaxing. And seriously, those are really great. Another opportunity to promote your website. Everybody, roam around Mike's website when you have a chance if you haven't, or even if you have, do it again...it is really great. Prepare to take some time.

Rick:

If the board outs are rated @ -10, you might find it runs out of suds trying to send signal to the Ampex. That's why bump boxes were built.
Click to expand...

Right. Fortunately the BUSS outs (the 8 PGM groups and AUX 1 ~ 4 outs) are switcheable -10 or +4...STEREO outs are either fixed -10dBv on RCA pin jacks or are switcheable 0, +4 or +8 dBu on balanced XLR's.
 
sweetbeats said:
Everybody, thank you. This has been really helpful:

Otto:



But only on the input side if using the plugin transformer in the accessory octal socket yes?
Click to expand...

My recollection is that the inputs are transformer balanced, even without the plug in transformer. As I recall, the accessory plugin unit was a transformer for plugging a microphone directly into the unit. I got one of those from Dave Dintenfass and used it once or twice, just for fun, when I had mono heads on my AG-440B. I/O was transformer balanced on the AG-440 without that optional module.

Cheers,

Otto
 
I got one of those preamp plug ins with mine too. But the signal from the mic is very weak. I don't know if it's a bad one or what.

Otto, do you know anything about those "dummy plugs" they mention in the manual, to use when calibrating? What exactly is that?
 
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