Signal path, gain and/or volume?

[Hopstretch]

Audio theory question. If you have two components with separate volume controls in your signal chain (in my particular case a passive pre-amp and a headphone amp), what would be the preferred method of setting the playback level: Max out pre, use amp pot; max out amp, use pre pot; half and half (or whatever other proportion you fancy)?

In practice, using an SPL meter to crudely level match, I can't discern any particular difference in sound quality. But I'd be interested to know if there's a rule of thumb.

[Pars]

I assume the passive pre is for your 2 channel rig? How about a pass-thru for the headphone amp to sit off of, taken before the passive's volume control? Or would this muck with impedances, etc.?

[Dusty Chalk]

Impedance match.

Yeah yeah, I know, easier said than done, but I've been able to do it by ear, so it's not impossible. (Admittedly -- not in as complex a scenario as you have -- in my case, it was simply raising the level on the mixer [as a pre], and lowering the input sensitivity on active monitors.)

[Hopstretch]

It's the continuing desktop clusterfuck. Like an arse, I decided to add an analogue source as well, so I needed a preamp. Thought I'd run it active with the headphone amp on the tape out and the powered monitors on the pre out. But it turns out there's a wicked hum in the speakers that way.

Passive, though, it's beautifully quiet and transparent -- so the bodge setup right now is both sources into the pre, line out to the headamp and loop through that to the speakers. This appears to work fine from a SQ perspective, but still begs the original question about where to be setting the levels.

The simple answer, I guess, would be to sell the lot and buy a Zana and be done.

[Dusty Chalk]

Well, if it sounds the same with pre at max vs. with the speakers at max (and then volume matched in both cases), then I wouldn't worry about it.

Remind me -- what's the setup? I'd say, set it so that it's easier to adjust the level on the one that's easier. (My quad 12L's are rather difficult to adjust -- I think I am going to take the advice to mod them to bypass their volume control, and then put a "real pre" in front of them.)

[digger945]

Can't remember or find it now, so don't hold me to it, but I think I remember Ti explaining to someone that you should run everything as hot as it will go to the amp, at which point the amp attenuator will do it's thing.

I've played around with it both ways and there isn't a lot of difference to me, other than the amp maybe making a little noise at full volume if the source isn't perfect.

I do run the monitors with the attenuation on the back at 0db.

[Dusty Chalk]

That's a good point about noise -- I actually had to "gain stage" my Mac/Duet/Singlepower amp in order to reduce distortion (I.E. the Duet was running too hot for the singlepower).

Another thing to try is to turn both up to full and see if you can hear any noise by pressing your ear up against the speaker (be careful not to accidentally play anything while doing this). Then turn one down and then the other to see which has a bigger contribution to the noise floor.

[n_maher]

I wouldn't stress too much about it Stretch, I'd just do whatever is most convenient till you get the Zana.

[Hopstretch]

See below for current setup, complete with some castoffs from Mike that just arrived today.

I'd be interested to hear more about this mod for the 12Ls, Dusty.

[mulveling]

I don't believe there would be an "audiophile speak" sound quality differential of any significance (within range of reasonable settings), but here's what I've determined from using a tube pre with a tube power amp (each with their own level controls):

* Cut down amp gain and use higher level on preamp to minimize the effect of preamp tube microphonics (which is the likely source of such problems), which is independent of the preamp level setting.

* Also cut down amp gain and use higher level on preamp to mitigate the risks of preamp tube failure - a "firecracker" preamp tube feeding unattenuated into your power amp could be bad news for your tweeters. Nothing you can do about a gain/driver tube in the amp itself going bad, of course.

* Also cut amp gain down to mitigate noise floor from preamp

Basically, make the amp as insensitive as you can comfortably (with ample headroom for soft records) get away with. Different situation then yours, though

[jinp6301]

See below for current setup, complete with some castoffs from Mike that just arrived today.

I'd be interested to hear more about this mod for the 12Ls, Dusty.

Your rig turns me on

[Dusty Chalk]

I'd be interested to hear more about this mod for the 12Ls, Dusty.

The suggestion was to just snip the attenuator out of the circuit, then solder the two ends together, that's all.

[swt61]

Your rig turns me on

Careful, that desk has just been wiped down!

[Hopstretch]

Careful, that desk has just been wiped down!

Nah, I just hose it off occasionally. Fnarr fnarr.

Thanks Mike. Food for thought there. Made me wonder if it's a good idea to run the tube amp maxed out at all. Presumably that's going to be stressing the magic bottles more than having them loafing along while the SS pre works harder?

[Voltron]

This thread makes my head hurt. No, wait, that's from the 3 gallons of beer, whisk(e)y and the best gin ever I drank last night. Wish you guys were here.

[luvdunhill]

What about running everything at unity gain until the headphone amplifier, and use it's passive attenuation?

(note: this is a slightly different recommendation than digger945, because I'm assuming it's possible that you might have a active preamp than can actually give the signal some gain (For example, my BAT VK-3i could do this, and unity gain was at around 65% or so on the volume display), but I really have no idea)

If you have a 1kHz test signal and a DMM, I think you could just adjust each component until the AC volt reading on the input is the same as the AC volt reading on the output.