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"The Wire" Headphone Amp GB
BAL-BAL - SOLD OUT
SE-SE - SOLD OUT
PSU - SOLD OUT
BAL-SE - SOLD OUT
Following the success of the first group buy for the original version of "The Wire", this is the reference page for the second run of amplifier boards and kits.
The philosophy of "The Wire" is to offer a headphone amplifier to the DIY community that makes absolutely no compromises in its effort to achieve perfection in the intended application. The circuits are simple and well implemented, and do away with much of the fluff which generally embellishes circuits of this type. There are no limiting elements to roll off the high frequencies or to block DC. Series elements have been kept to a bare minimum, and all three amplifiers have only a single series resistor and the two active elements in the signal chain. This results in perfectly flat frequency and phase response, and extremely low noise and distortion. I don't expect you to take my word for it either, so each variant has extensive measurements of all these characteristics using a $30,000 Audio Precision APx585.
There are three variants of the amplifier on offer here, along with a power supply which will work with each. Each variant uses the same LME49600 as an output buffer, but each variant differs in output and input configuration. These variants are as follows:
This variant is specifically configured to take a balanced input from any balanced source and provides a standard "single ended" output which is compatible with almost any type of headphone having a 3-pin connector. The outputs are driven directly from a single LME49600 per channel and both channels share a common ground return. An instrumentation style front end is realized with three LME49990 single op-amps. The result is high input impedance, very low noise, excellent CMRR, extremely low distortion and a ruler flat frequency response from DC up to well over 100kHz at full output swing.
This is the most basic implementation of "The Wire" having a single ended input and output. It is essentially the same as the BAL-SE version, except is does not have an instrumentation style front end, and does not accept balanced inputs. There is a single LME49990 in a non-inverting configuration with a single LME49600 nested in the feedback loop. It shares all the positive attributes of the BAL-SE version with the exception of balanced inputs.
This is a fully balanced version of "The Wire" which offers a true differential input and a bridged output using a pair of LME49600 buffers nested in the feedback loop of an OPA1632. As a result of this configuration, the BAL-BAL amplifier requires a dedicated connection to both the positive and negative terminals of each transducer in a pair of headphones, and does not share a common ground like the other two variants. Running this configuration will likely require modification of the headphones to eliminate the 3 pin connector and replace it with a 4 pin connector, giving access to each transducer's terminals separately, and breaking the shared ground connection. This configuration offers two significant benefits:
1. Eliminating the shared ground return between channels significantly improves channel separation.
2. The bridged output offers twice the voltage swing of an SE output, and can provide 4 times the power into certain loads.
Because of the above, this is the only version which can be used with dual mono power supplies for even greater channel separation if desired. The board maintains completely separate ground planes for each channel. It should also be noted that this amplifier will perform equally well with a single ended input by simply tying the unused input to ground. This negates the need for an SE-BAL version since the BAL-BAL accomplishes both in one design.
I (Owen Columbus"opc") will organize and execute the group buy.
I am offering:
Please see the attached documents below for the most up to date list!
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