McIntosh MC-30...Balanced Input Feasible?

[Wayniac]

I spend many hours reading these forums and up-front, I would like to thank the contributors and moderators for these excellent forums. 🙂

I own a pair of McIntosh MC-30s. The amplifiers are functional, having been restored by me about two years ago.

I am exploring the feasibility of replacing the octal preamp input socket with an XLR connection and rewiring the amplifier to take advantage of the unused half of V1 (12AX7).

All guidance and comments are welcome. Thanks!

 

[Eli Duttman]

While it can be done, it's a major engineering change to activate that 'X7 section. Please notice the GNFB loop. Why is switching to balanced so important? Should balanced interconnect wiring really be needed, a simple solution is to install a transformer that "sits" between the balanced cabling and the I/P RCA jack.

 

[Wayniac]

Thanks for the reply.

Switching to balanced operation isn't that important to me. Both of my DACs have balanced outputs and I thought I would like to try it. The feedback loop had me scratching my head, as I am not as astute as most contributers here. If the results are likely not worth the effort, so be it. 🙂

 

[HpW]

Both of my DACs have balanced outputs and I thought I would like to try it.

Well, I have the same question in my head since month... while would like the Wadia 27 balanced output to my Cary SLM-100.

What I have seen so far from Cary for balanced support:

- switchable balanced on/off
- no over all NFB
- a symple differential input pair with cathode current tube

What I do not like to add is some input balancer transformators, while no space available.

Other designs for full balanced where the required balanced NFB connections from the output trani.

Any other input is welcome. 😀

Hp

 

[Kay Pirinha]

I'd go, as aready suggested, for a pair of good (i.e. studio quality) input transformers ("baluns") and leave the circuitry as it is.

Best regards!

 

[bear]

Unless your pair is more or less in sorry condition (like badly pitted chassis, and paint peeling off the iron) I would not modify it. Today these amps are worth a boatload of $$, and changes to the chassis will more or less destroy the value of the amps...

Plus as noted, there's no simple way to do this without some major changes to the input section.

You can buy Octal plugs, plug into the Preamp input that way and use a small transformer hanging off that, but it doesn't buy you anything in terms of sonics unfortunately.

 

[MelB]

Easy way to get a good pair of balanced input connections:
JENSEN TRANSFORMERS, INC. - ISO-MAX® PC-2XR Stereo "Pro" to "Consumer" Converter / Isolator
If you are looking to remove ground loop or RF interference.

 

[DavesNotHere]

it could be like this.

feedback isn't necessary if the circuit is set up correctly.

first is balancing the positive and negative signal stages by making sure the resistors match in the mirrored circuit.

all tubes must have matching sections. outputs of course are matched pairs.

a 12au7 could be substituted in the first position and the grid resistor can be reduced in value accordingly.

 

[Loren42]

Easy way to get a good pair of balanced input connections:
JENSEN TRANSFORMERS, INC. - ISO-MAX® PC-2XR Stereo "Pro" to "Consumer" Converter / Isolator
If you are looking to remove ground loop or RF interference.

+1

I have two sets of those sitting around on a desk, but they do work well for that.

I ended up buying two Cinemag transformers and installing those inside my amp and replacing the RCA connectors with XLR chassis mount connectors.

My amp is not a McIntosh, but something I built myself that I required balanced inputs for.