Yes. Some circuits a transformer is used. Other circuits, the differential input that is grounded is lifted brought out as the inverting input , normally called "signal -"
I converted my sub to XLR input by redoing the balanced input of the consumer subwoofer called the speaker input. That is just a 30db attenuator in front of a balanced line input.
On the amp that I have, could I do what you say and connect the inverting input to the inverted side of the circuit? I'm smart enough to see the symmetrical nature of the design, but dumb enough to not know how/where the SE signal is split. Is it just before V2(3), starting at R8/R9?
(Schematic re-attached for convenience)
(Schematic re-attached for convenience)
You would open the connection between 96 &97. Then take a wire from point 97 to pin 3 of an XLR. The other input would go to pin 2. Then you install a 10K resistor between the two signal lines to terminate the input transmission line and set up the +4 electrically balanced input line standard.
That’s encouraging, and would make my life easier.
Could the 10k resistor go anywhere? Like could it go between the pins on the input jack?
EDIT: Do you know what “L.C. only” means?
Could the 10k resistor go anywhere? Like could it go between the pins on the input jack?
EDIT: Do you know what “L.C. only” means?
across pins 2&3 of the XLR is ok for the 10K resistor.
I don't know what L.C stands for. That's an Dynaco term.It could be a kit version as far as I know.
The first Audio Research projects were modifications to the ST-70, so maybe he picked it up there?
With this balanced mod, is there a way to retain the SE jacks?
With this balanced mod, is there a way to retain the SE jacks?
to do it cleanly you would have to use a switch to relink pin 3 back into the circuit. But you couldn't use both at the same time. Other way would be to put a matching transformer in the input circuit and go RCA-> transformer-> xlr input.
Some plate amps' RCA + xlr combos when they combine them with the same op amp on they often have issues compared to some that use a separate op amp and combine them afterwards.
One would think that would work, but the amp's signal common in unbalanced is a virtual ground from a constant current sink.
And the feedback is not set up to provide the inverted signal without a constant current sink. Hence that is why the input switch.
You could redesign the amp. but the two solutions I came up with will be the cleanest without having to do a lot of modifications.
I just checked the amp, and separating 96 and 97 is dead simple. Thank your for your suggestions!
@thisusername I think LC Only means Left Channel only! Those points aren’t mirrored on the other channel, like 42(43)
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Obviously this schematic is incomplete. Usually when someone prints a schematic, If the both channels are the same they print only one channel. Strange that isn't the case.
I will dig for a complete print. But its quite odd they are not exactly the same.
On the other schematic, I overlooked R1, so you would have to add another resistor. I guess you could cut the land, but if you going that far might as well delete V1 circuit and go totally XLR and ditch RCA or change out the RCA jack to an isolated RCA jack and wire pin 2&3.
Here is another one from Audio Reaserch version, but the resistance values in the front end are different.
I find it quite dumb there are things with the same name and model # , yet they have different circuits.
Here is another one from Audio Reaserch version, but the resistance values in the front end are different.
I find it quite dumb there are things with the same name and model # , yet they have different circuits.
If the 4 ohm tap is the common one, then what is the name of the tap that the other speaker wire is connected to?
I'd like to minimize change, and retain the RCA jacks. If the method is to connect the second phase of the balanced signal topping 97, wouldn't it just be a matter of adding a 39.2k resistor in series with it?
I dont understand the Stereo 70 schematic you linked. What relation does it have to the D70?
I've attached the original Mk1 schematic for the D70, as well as the full schematic for the MkII, including the power supply. As far as I can tell, there has never been a two-channel schematic published.
Attachments
yes, but you would have to lift the 96-97 link for XLR operation and link it when you want to use the RCA jacks like they did long ago.
You can run an RCA in the XLR But you have to change the RCA jack and isolate it from the chassis. But at the price of half the volume.
Another way would be to use little matching transformers and convert the RCA into XLR.
Wouldn't the 0 ohms contact be called the common one, as in, common to the 4, 8 & 16 ohm connections?
O ohms is just a label, pairing with the selected 4/8/16 tap.
If the 0 ohm tap is not a signal ground (and it isn't, since it has half of the output signal),
what else would you call it? It isn't "common" since that is frequently used for signal "grounds".
The confusion arises because the secondary is not symmetrically tapped.
If it were, there would be -16/-8/-4/+4/+8/+16 outputs provided instead,
Then an 8 ohm load would be connected between -8 and +8, for example.
But ARC decided to design a standard secondary with only 0/4/8/16 taps.
If the 0 ohm tap is not a signal ground (and it isn't, since it has half of the output signal),
what else would you call it? It isn't "common" since that is frequently used for signal "grounds".
The confusion arises because the secondary is not symmetrically tapped.
If it were, there would be -16/-8/-4/+4/+8/+16 outputs provided instead,
Then an 8 ohm load would be connected between -8 and +8, for example.
But ARC decided to design a standard secondary with only 0/4/8/16 taps.
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