3nity
Well-known member
the title says it all. it's it possible...any hint?? i was wondering how to do it in api configuration...
Electronic replacement for a Input transformer?
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NewYorkDave
Well-known member
The transformerless input stage is a topic that's been thrashed to death here and elsewhere. Have you tried a search yet?
[quote author="3nity"]the title says it all. it's it possible...any hint?? i was wondering how to do it in api configuration...[/quote]
I believe the answer is AC coupling.
Go to the THAT Corp website and find the data sheet for the 1500 line of their Op Amps. Open the data sheet and look at Figure 4. That should pretty much work, except I would omit D1-D4.
The problem lies in how do you want to deal with unbalancing the signal. You could something like the THAT 1240 Balanced Line Receiver, or you could just use the 'hot' side and send the other side to ground, after the 6.81k resistor and the filter cap.
I believe the answer is AC coupling.
Go to the THAT Corp website and find the data sheet for the 1500 line of their Op Amps. Open the data sheet and look at Figure 4. That should pretty much work, except I would omit D1-D4.
The problem lies in how do you want to deal with unbalancing the signal. You could something like the THAT 1240 Balanced Line Receiver, or you could just use the 'hot' side and send the other side to ground, after the 6.81k resistor and the filter cap.
3nity
Well-known member
maybe that question seemed stupid but actually i looked trough the meta....i am aware that something like this would fall into the transformless circuitry....but how does a IC change impedances...??
[quote author="3nity"]maybe that question seemed stupid but actually i looked trough the meta....i am aware that something like this would fall into the transformless circuitry....but how does a IC change impedances...??[/quote]
Nobody has bothered to mimic that particular characteristic of transformers (AFAIK). I for one am not sure what it would be useful for?
Please expand upon your application, that finds that particular aspect of transformers important.
JR
Nobody has bothered to mimic that particular characteristic of transformers (AFAIK). I for one am not sure what it would be useful for?
Please expand upon your application, that finds that particular aspect of transformers important.
JR
3nity
Well-known member
i would be mostly experimenting...maybe in an api 325 0r 312 configuration....line or mic input..
An APi without inout transformer?? is that alright..?
I'm not using tech words cuz my knowledge is very basic...
thank you.
An APi without inout transformer?? is that alright..?
I'm not using tech words cuz my knowledge is very basic...
thank you.
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Well we're even, because I don't have api models memorized...
JR
JR
[quote author="JohnRoberts"]Well we're even, because I don't have api models memorized...
JR[/quote]
312 is a mic pre, 325 is the line card.
Both are almost identical. The 312 has a transformer input, with the output going straight to the output iron. The 325 has no input iron and the output feeds the output iron via a cap.
JR[/quote]
312 is a mic pre, 325 is the line card.
Both are almost identical. The 312 has a transformer input, with the output going straight to the output iron. The 325 has no input iron and the output feeds the output iron via a cap.
[quote author="3nity"]the title says it all. it's it possible...any hint?? i was wondering how to do it in api configuration...[/quote]
Transformerless balanced inputs have been common since the late 1970's. The reason for a manufacturer not using a transformer is because good quality transformers costs significantly more than a transformerless solution that supposedly does the same thing. But it does not...
You average middle-of-the road console has about $2 worth of parts for the mic input, your inexpensive B*hringer < $1 and your high end console $4-5. Those are volume prices for a manufacturer of course.
You can maybe get a decent transformer for around $10 in China and twice that from a "brand name" in Europe/US - again manufacturing quantities.
Yes, a transformer colors the sound, it is not 100% transparent but sometime that's what you want. In my opinion, transformers solve more problems than they create and in an otherwise properly designed circuit, they can give stunning results.
Just my 2 cents of course, other may disagree...
Transformerless balanced inputs have been common since the late 1970's. The reason for a manufacturer not using a transformer is because good quality transformers costs significantly more than a transformerless solution that supposedly does the same thing. But it does not...
You average middle-of-the road console has about $2 worth of parts for the mic input, your inexpensive B*hringer < $1 and your high end console $4-5. Those are volume prices for a manufacturer of course.
You can maybe get a decent transformer for around $10 in China and twice that from a "brand name" in Europe/US - again manufacturing quantities.
Yes, a transformer colors the sound, it is not 100% transparent but sometime that's what you want. In my opinion, transformers solve more problems than they create and in an otherwise properly designed circuit, they can give stunning results.
Just my 2 cents of course, other may disagree...
rafafredd
Well-known member
http://www.groupdiy.com/index.php?topic=12480&start=0&postdays=0&postorder=asc&highlight=
barclaycon
Well-known member
I believe the standard as far as API desks were concerned was unbalanced input, transformer output. That is certainly how my API modules are (550 EQ, 525 Compressor).
Neve used to pad down the signal before it got to the line input transformer so they didn't have to have huge types.
There are some excellent designs for active balanced inputs. My favourite is MCI's line input which has passive bandwith limiting rather than the usual feedback caps.
Also worthy of note is Rupert Neve's design for some of the stuff he did for Amek which he described as a Transformer-like Amplifier (TLA).
Maybe somebody here could dig that circuit out so we can have a look at it.
SSLtech
Well-known member
[quote author="barclaycon"]Also worthy of note is Rupert Neve's design for some of the stuff he did for Amek which he described as a Transformer-like Amplifier (TLA).
Maybe somebody here could dig that circuit out so we can have a look at it.[/quote]
(ahem....)
Think "green", then think "Pre", and you may be onto something...
(ahem...)
Essentially the property which Rupert likes about the so-called 'TLA' design is that it has very HIGH impedances to ground, and a low impedance between the legs. Thus if a signal is sourced to one leg but not the other, it pretty much goes into common-mode, just like in a transformer input...
Keith
Maybe somebody here could dig that circuit out so we can have a look at it.[/quote]
(ahem....)
Think "green", then think "Pre", and you may be onto something...
(ahem...)
Essentially the property which Rupert likes about the so-called 'TLA' design is that it has very HIGH impedances to ground, and a low impedance between the legs. Thus if a signal is sourced to one leg but not the other, it pretty much goes into common-mode, just like in a transformer input...
Keith
Ok, if this thread is just asking about electronic balanced inputs that is indeed a mature technology.
There are some modern canned solutions (dedicated ICs) but nothing that can't be done with a handful of decent opamps and precision parts. The API products are most likely targeted at customers who prefer the sound of a "good" transformer to the less colored "good" electronic balanced.
Here's a link to a white paper about one from THAT, but there are simpler designs that work well in less demanding applications.
http://www.jensen-transformers.com/an/ingenaes.pdf
JR
There are some modern canned solutions (dedicated ICs) but nothing that can't be done with a handful of decent opamps and precision parts. The API products are most likely targeted at customers who prefer the sound of a "good" transformer to the less colored "good" electronic balanced.
Here's a link to a white paper about one from THAT, but there are simpler designs that work well in less demanding applications.
http://www.jensen-transformers.com/an/ingenaes.pdf
JR
SSLtech
Well-known member
API products were designed to go into API consoles. The API console frame is just a very wide lunchbox laying down on its back, with routing at the top, faders at the bottom, and aux sends and slots for EQs, Compressors etc in the middle.
People started using the modules stand-alone and that sustained the company when their console business started to drop off like most other manufacturers did... notice that now they are percieved more immediately as an outboard manufacturer, but I believe that ALL of their core products were initlally desgned solely to go into their consoles.
There's a rather nice pair of ORIGINAL APIs (about 30+ years old, I think) locally, which were joined together to make one rather larger console about 15 years ago... I engineered a couple of Deep Purple albums on them in fact. The owner is a good friend, in fact last week a +16V supply went belly-up, and I dropped round to repair it for him on the way home. it's really nice to stay in touch with the consoles as well as the outboard racks and lunchboxes that we have here at work...
Keith
People started using the modules stand-alone and that sustained the company when their console business started to drop off like most other manufacturers did... notice that now they are percieved more immediately as an outboard manufacturer, but I believe that ALL of their core products were initlally desgned solely to go into their consoles.
There's a rather nice pair of ORIGINAL APIs (about 30+ years old, I think) locally, which were joined together to make one rather larger console about 15 years ago... I engineered a couple of Deep Purple albums on them in fact. The owner is a good friend, in fact last week a +16V supply went belly-up, and I dropped round to repair it for him on the way home. it's really nice to stay in touch with the consoles as well as the outboard racks and lunchboxes that we have here at work...
Keith
I'm aware of the general history and yes, all early stuff was all console (Sol Walker, Dave Blackmer, etc?). The latter stuff after the more than one (?) hiccup, was Paul Wolff doing whatever it took to make customers happy. The lunch box module business was a better place to be at that point due to the flagging fortunes of the big console business... and customers were willing to exchange presidential portraits for them, so win-win. API is now in a post-Wolff chapter, but many of the classic designs deserve the respect they enjoy.
The large console business, like the music business, marches to a different percussion loop, these days.
JR
The large console business, like the music business, marches to a different percussion loop, these days.
JR
barclaycon
Well-known member
Ah before my time I think. Didn't know what that was all about. I only joined here 6 months ago.
Where's the circuit for that Keith ?
jdbakker
Well-known member
[quote author="barclaycon"]
Where's the circuit for that Keith ?[/quote]
http://www.groupdiy.com/index.php?topic=5150
Same topology as was discussed in the Cohen AES paper, similar to older pres by Valley People and others.
JDB.
Ah before my time I think. Didn't know what that was all about. I only joined here 6 months ago.
Where's the circuit for that Keith ?[/quote]
http://www.groupdiy.com/index.php?topic=5150
Same topology as was discussed in the Cohen AES paper, similar to older pres by Valley People and others.
JDB.
Samuel Groner
Well-known member
The green pre shows only half of the story (the input resistor bootstrapping). The interview which is presumably mentioned above talks about the input EMC filter which is not present in the GreenPre (which basic circuit was designed by AMEK before Rupert joined, I think). Part of the interview was posted by me here: www.groupdiy.com/index.php?topic=4317
Samuel
> I'm not using tech words cuz my knowledge is very basic...
And nobody is telling you what you need to know.
For several good reasons, microphones are normally wired for balanced 150-ohms.
When tubes/transistors were expensive, the best amplifier topology had an un-balanced higher-impedance input.
In that world, the best way to connect was a transformer. The windings are floating, and can be connected balanced or unbalanced. The windings can be different, giving voltage (impedance) transformation. And now that Phantom Power is common, transformers sweetly allow Phantom on the mike but not on the amplifier stage. Finally, a transformer needs zero DC power.
As transistors got much cheaper than iron, a more complicated amplifier appeared. It uses two transistors working at fairly high current, plus a bunch of other transistors or chips to combine and control the two signals. This has to be tarted-up with Phantom-blocking caps and protection diodes, radio-suppression caps and chokes, etc. But when you are done, you have a complete mike preamp, from mike to line output.
While it is complicated and has a lot of parts, the transformerless mike input today can be built a lot cheaper than a transformer. Also saves weight in large consoles: weight of transformers and weight of structure to support them in shipping or road-trips.
There isn't really any "rational" reason to do a good transformerless input and drop it into the input of a mike-amp which is missing its mike-input transformer.
If you run dynamic mikes on strong sources, wire them unbalanced into your line-card input. Gain and noise may be quite adequate.
For general best-performance use, while retaining your vintage amplifiers, drop a transformer on it. There really ISN'T a better way to do it.
If you are utterly broke, get small 120VAC:24VCT power transformers and wire them backward. Mike goes to 24V leads. Phantom 3K4 goes to CT lead. The 120VAC leads go to your card. Some iron will be as bad as 50-5KHz, but some small PTs worked this way will greatly exceed the essential musical range. (Find PTs with all windings in one lump; the two-lump winding improves power safety but does not couple the highs.) It'll pick up hum so you can't set it on top of power amps, but I've run PTs as mike transformers on lighting-infested catwalks and the hum was not obvious. Just do not tell anybody that you are using $5 "mike" transformers.
For the true API sound, you want the "right" iron of course.
And nobody is telling you what you need to know.
For several good reasons, microphones are normally wired for balanced 150-ohms.
When tubes/transistors were expensive, the best amplifier topology had an un-balanced higher-impedance input.
In that world, the best way to connect was a transformer. The windings are floating, and can be connected balanced or unbalanced. The windings can be different, giving voltage (impedance) transformation. And now that Phantom Power is common, transformers sweetly allow Phantom on the mike but not on the amplifier stage. Finally, a transformer needs zero DC power.
As transistors got much cheaper than iron, a more complicated amplifier appeared. It uses two transistors working at fairly high current, plus a bunch of other transistors or chips to combine and control the two signals. This has to be tarted-up with Phantom-blocking caps and protection diodes, radio-suppression caps and chokes, etc. But when you are done, you have a complete mike preamp, from mike to line output.
While it is complicated and has a lot of parts, the transformerless mike input today can be built a lot cheaper than a transformer. Also saves weight in large consoles: weight of transformers and weight of structure to support them in shipping or road-trips.
There isn't really any "rational" reason to do a good transformerless input and drop it into the input of a mike-amp which is missing its mike-input transformer.
If you run dynamic mikes on strong sources, wire them unbalanced into your line-card input. Gain and noise may be quite adequate.
For general best-performance use, while retaining your vintage amplifiers, drop a transformer on it. There really ISN'T a better way to do it.
If you are utterly broke, get small 120VAC:24VCT power transformers and wire them backward. Mike goes to 24V leads. Phantom 3K4 goes to CT lead. The 120VAC leads go to your card. Some iron will be as bad as 50-5KHz, but some small PTs worked this way will greatly exceed the essential musical range. (Find PTs with all windings in one lump; the two-lump winding improves power safety but does not couple the highs.) It'll pick up hum so you can't set it on top of power amps, but I've run PTs as mike transformers on lighting-infested catwalks and the hum was not obvious. Just do not tell anybody that you are using $5 "mike" transformers.
For the true API sound, you want the "right" iron of course.
3nity
Well-known member
Awesome PRR. that's wwhat i wanted to hear.....
So a transformer makes impedance conversion from primary to secondary to accomodate microphones to a given preamplifiers.....So a Transistor stage does that but not only that but a complete preamp???
I'm loving my Reliquias 312, i adore them....but i wanted to experiment DOAs in a transformless circuit...just like the green or Baby Animal Neutral...
That PT tips is cool.....i was wondering if i can do something good for a Neve 1272 output iron from a PT......By the way don't worry i can afford at least some OEP's
Thank you for making your point very clear.
So a transformer makes impedance conversion from primary to secondary to accomodate microphones to a given preamplifiers.....So a Transistor stage does that but not only that but a complete preamp???
I'm loving my Reliquias 312, i adore them....but i wanted to experiment DOAs in a transformless circuit...just like the green or Baby Animal Neutral...
That PT tips is cool.....i was wondering if i can do something good for a Neve 1272 output iron from a PT......By the way don't worry i can afford at least some OEP's
Thank you for making your point very clear.
