• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

? about powering a sub with a Fisher 30a mono amp.

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I apologize in advance if this question makes little or no sense. I am running a Creek CD 60, to a Creek DAC 60, to a Fisher 400 tube receiver, to a pair of Kef Q1 bookshelf speakers. I needed the bookshelf speakers because of space limitations and because they were a great deal, $250 for the pair. So here is the part that will probably out me as someone who has no idea what they are talking about.
I have a very clean 30a fisher mono amp. Can I run the center channel out to the 30a and power a subwoofer?

P.s. I was not sure weather to post this in the tube or subwoofer sections, I apologize if I put it in the wrong place.

Thanks for taking the time to read this.

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Valve amps can have all sorts of problems with bass which SS amps don't have (or don't suffer to the same degree) such as output transformer saturation, high output impedance leading to poor cone control, and limited power output.

This is not to say that valve amp bass is subjectively bad, but those are some of the technical problems. In my opinion, the best place for valves is the midrange and highs, and not as sub amps. Unless you have an efficient sub, like maybe a horn sub (but I highly doubt this, real ones are freakin' huge!) 15W from the PP EL84s wouldn't be enough.

But of course it will work (as in producing some sounds, not necessarily working well) - why not just try and see if you like it?
 
I think there is something we are missing here, generally in a 5.1 surround system they have the "center" channel as a standard box which sits ontop of your television set or wherever and that has it's own full-range drivers, so this channel is not for bass speakers.

Now you said you used the Creek Audio DAC 60 for your analog outputs, I don't know wether this is a full-blown 5.1 decoder or if it's simply 2.1 so I'm going to assume it's for 5.1 operation.

In a 5.1 system you have two front two rear, that makes four and one extra to make five, this extra one is a full-range channel as described above, where 5.1 systems get their bass channel from is generally from a dedicated analog RCA socket on the back of the receiver which goes directly to the subwoofer "speaker" which most people don't know, has a rather powerful but cheap and nasty amplifier inside.

So what I think you're trying to say is you've got a mono tube based amp hooked up to the output of your /CENTRE/ channel output on your decoder and NOT your bass output, Then what you want to do is run a line off the tube amplifier output to make a sort-of 2-way speaker system but with the bass driver on the floor and the mid-tweeter in the centre box.

This can not be done with a tube based amplifier, there simply isn't anywhere near enough power to drive a cheap and cheerful 8" 10" 12" or 15" bass speaker and actually make a sound let alone try to run a midrange with it's own set of tweeters alongside.

You can use slightly insane commercial bass speakers but only if you build a PP 6L6 or PP KT88 for a seperate dedicated bass amplifier and hook this new amp to your decoder and then an efficient bass speaker, But you need to do your research on the output transformers, speakers and crossovers so that it all performs efficiently.

Efficient bass speaker
Google search of Efficient bass speakers

Now from what I've read a tube bass amplifier is nearly the same as an ordinary hi-fi amp, just a bit more dirty in it's design, so by the sounds of it nearly any standard KT88 amp design will do.

The cheap way out is to simply have every channel a valve based amplifier but use a nice sounding MOSFET transistor setup for bass.

Personally I'd love the challenge of a tube bass head with plenty of grunt at 30-50 watts with KT88 tubes, 100watts is doable but as you increase power so does unreliability and cost, as someone said once for a bedroom or living room 30 watts is plenty even for low frequency reproduction.:cool:
 
Layberinthius said:
Efficient bass speaker

Now from what I've read a tube bass amplifier is nearly the same as an ordinary hi-fi amp, just a bit more dirty in it's design, so by the sounds of it nearly any standard KT88 amp design will do.
Using a low Q pro speaker in a reasonable size box with an amp that has an output Z of a few ohms can actually get good performance as the tube amps output Z will raise the effective Q of the system and allow you to bring the box size down if you design it as a system.. The E140 is a good speaker for bass guitar: my rig uses K140's (it's modular).

As for BG amps being a 'bit dirtier' that's about true, but it depends on the design. Some get their distortion from the pre and some from both. A couple I've heard are very clean (poweramps).
Personally I'd love the challenge of a tube bass head with plenty of grunt at 30-50 watts with KT88 tubes, 100watts is doable but as you increase power so does unreliability and cost, as someone said once for a bedroom or living room 30 watts is plenty even for low frequency reproduction.:cool:
Use a 50W AB1 hifi design and add a second set of output tubes and halve the Za-a of the OPT. If everthing else is up to the task, and there's plenty of airflow, it won't be any less reliable than the 50W version. But, 100W is a lot for a bedroom amp, and not quite enough even for most smaller (RnR) gigs where you're not running through the house PA. And tube bass heads are heavy.
 
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