Using BH headphone amps as preamps - any models where this is inadvisable?

[twofires]

Hi there,

I've seen a couple of instances on this forum where people have asked about converting this or that Bottlehead headphone amp to work as a preamp. The answer typically given has been to use a 1/4" TRS to RCA adaptor. I'm just wondering if this can be done with all the headphone amps, or just the OTL ones, or if there are any other concerns? I don't know enough to know what kind of load an output transformer needs to see to be happy and not burn my house down.

If someone wanted to be fancy I'm guessing they could drill another two RCA socket holes and wire them up off the switched side of a switching TRS jack as is done with the speaker posts on the SEX (providing they don't try and hotswap between the two while the amp is on)?

Thanks in advance!

 

[Paul Birkeland]

You can hot swap all you want with our amps and they won't be bothered.  The SEX is certainly quiet enough to use as a preamp, and you could probably find some oddball RCA jacks that would fill the holes of the speaker binding posts.  The Stereomour and Kiaju are not really as well suited to this application as the SEX amp is.

 

[twofires]

Thanks for that, Paul. I meant more whether the speakers would be bothered by the hotswapping of pre and headphone (loud thumps and whatnot), but it's good to know that the amp itself won't be bothered.

Is the SEX the best candidate of the headphone amps for a pre due to the power it can deliver, or will they all do well enough? I'm sort of eyeing off that last Crackatwoa unit that keeps popping back onto the store. I don't need yet another headphone amp (only just finished my SEX), but if I could whack it into a system as a pre if needed (in addition to using it as a headphone amp) I might well drop the cash on it. I had the thought of changing the 3 input selector to a two input and repurposing the third set of RCAs as a pre out (providing I can route the signal back there without introducing too much noise).

 

[Paul Birkeland]

The Mainline will also work nicely in this duty.  It's more about low noise floor rather than power or even output impedance in this application.  The Crack-a-two-a will also work nicely as a preamp.  You could just add a pair of RCA output jacks to the back of the wood base. As a bonus, the C2A doesn't use the shorting jack, so you don't need to defeat that or leave an adapter plugged in to keep the outputs active.