Ohms, Wiring and Tube Amplifiers

[mydadslps]

Hey so I'm very much a beginner and not much of an electrician. I have a passion and love for vinyl (I do a radio program streaming and on FM playing my Dad's records) and recently bought two new components: an AudioTechnica LP-1240 direct drive turntable and a GemTune BL-02 tube amplifier with a 100w output. Now the table has a built-in phono pre-amp so the amp and table get along just fine.

My big problem currently is wiring the speakers. Now, I have two 8-ohm Infinity speakers but they've served me well in the past and it's what I've got at the moment and for now though I'd like to use what I have. Anyway I'd like to get this set-up at least on its feet with two speakers but I'm not sure how to do that and all of the articles on the internet are about stage amps, at least what I could find.

So the short question here is how do I get these two speakers hooked up and match the impedance so it doesn't blow the amp? I'd love to be able to enjoy this thing sooner than later and without having to do an immediate, expensive speaker upgrade.

Thanks a million, guys. Take me to school on this poop.

Specs:

Amplifier:

Input Voltage: 110V

Output Power: 10W*2

Frequency Response: 20Hz — 25kHz

Signal/Noise Ratio: 88dB

Output impedance: 8ohm or 4ohm

Input impedance: 100Kohm

Distortion: <=1% (kHz)

Input sensitivity: 500mV-2000mV

Tubes: 5Z3P*1; EL34-B*2; 6N9P*2

Turntable:

Direct Drive

Built-In Phono Pre-Amp (w/Phono-Line switch)

Shure M44-7 Cartridge/Needle

 

[markw]

I don't see the problem here. It's about as simple as they come.

Here's a link to the "owners manual", as it were. https://s3.amazonaws.com/Doctor-001/GemTune+Amp/Manual+for+Tube+Amplifier+BL-02.pdf

Study the "manual". It's one page.

From what I can fine about this amp, it has both four and eight ohm taps. One wire to the 8 ohm tap and the other to the common, which seems to show as a "0" in the drawing in the "manual". If you had four ohm speakers. you would connect one wire to the four ohm tap and the other to the common, or "0"

Or, to put it simply, look at step 4 in the one page "owners manual" and follow that.

BTW, that's NOT a 100 watt amp. That's the power it uses, not what it puts out.

IMNSHO, for what you spent on that toy*, you could have gotten a much better unit here : http://www.accessories4less.com/make-a-store/category/integratedamp/home-audio/receivers-amps/integrated-amps/1.html

* from an on-line review at Amazon: "In any case, the amp can't output more than 1 useful watts without distortion."

 

[mydadslps]

Thanks for the reply. When I did connect the speakers there was pretty significant buzz and I think it's because I hadn't connected a ground wire. Where would I connect the grounding wire on the amp to reduce that static?

Also thanks for the tip on the Marantz. My first setup so you live and learn i suppose. If this turns out to not work for me I'll definitely consider it. What about it makes it superior, in your not so humble opinion?

 

[Johnny2Bad]

As long as you have a load, which could be a resistor (test equipment) or a loudspeaker, connected to one of the vacuum tube amp's output terminals ... doesn't matter if it's the 4 ohm or 8 ohm taps ... you won't "blow" the amp.

Tube amps with output transformers (or some Solid State amps with output transformers, although rare today) deliver the same power to any load that matches the output transformer tap.

So 100w into 4 ohms via the 4 ohm tap, or 100w into 8 ohms via the 8 ohm tap. If the speaker impedance and the selected transformer tap are mismatched, less power will be delivered to the speaker.

I am curious, however, about your speakers. Infinity is well known for having low impedance, often dipping to 4 ohms or lower. You provide plenty of details about everything *except* the loudspeakers. They are more important than the turntable in so far as your question.

Exactly which model Infinities do you have, and are there any reviews / tests available on them? I very much suspect they may sound best connected to the 4 ohm taps on your amp. You won't damage your amp by connecting them to the 4 ohm tap.

Just a heads-up ... NEVER connect or dis-connect loudspeaker cables (either at the amp or the speaker) with the amp powered up. Turn it off first.

 

[mydadslps]

The speakers themselves are SAT750 speakers. I realize they're not ideal being satellite speakers but I've had success with them in the past. The 4ohm option makes sense since they were buzzing loudly on 8ohms.

 

[markw]

Thanks for the reply. When I did connect the speakers there was pretty significant buzz and I think it's because I hadn't connected a ground wire. Where would I connect the grounding wire on the amp to reduce that static?

Also thanks for the tip on the Marantz. My first setup so you live and learn i suppose. If this turns out to not work for me I'll definitely consider it. What about it makes it superior, in your not so humble opinion?

Any metal screw on the metal chassis. If that doesn't cure it, the amp has problems.

Why is it superior? Less distortion*, more power, more flexibility, more reliable.

* some people hear tube 2nd harmonic distortion as pleasing. Some don't.

 

[Johnny2Bad]

Just connect the two speaker leads to the two taps (per channel) on the amp ... 1 common and 1 4 ohm. DO NOT connect any speaker wire to a ground on the chassis. All speaker connections MUST pass only through the output transformer.

 

[markw]

OP, you WERE referring to the grounding wire on the turntable, weren't you?

 

[Johnny2Bad]

The speakers themselves are SAT750 speakers. I realize they're not ideal being satellite speakers but I've had success with them in the past. The 4ohm option makes sense since they were buzzing loudly on 8ohms.

I can't find any test data so the actual impedance curve is a guess. But I do know Infinity and they often dip to as low as 3 ohms in the lower area of the audioband, which is where you need the most power from the amplifier.

 

[Johnny2Bad]

OP, you WERE referring to the grounding wire on the turntable, weren't you?

The 'table has a built-in phono preamp, which is where you would normally connect a ground wire. You should not need a ground wire between a phono pre (output will be line level) and an integrated amp.

I suspect he's thinking of a speaker lead, which is why I replied the way I did. His answers don't make much sense, so it seems to be best to cover all bases.

 

[markw]

The TT does have a screw that is specifically labeled "GND" and the instructions say to ground it to the amp.

Speakers do not have a "grounding wire" and the speaker connection instructions are pretty clear, what between you, me and the manual itself.

 

[Johnny2Bad]

The TT does have a screw that is specifically labeled "GND" and the instructions say to ground it to the amp.

Speakers do not have a "grounding wire" and the speaker connection instructions are pretty clear, what between you, me and the manual itself.

Turntable grounds only work to reduce 60Hz hum, and connect to the phono preamp, whether separate or built-in to a preamp, integrated amp, or receiver. It is not a default connection; some cartridges hum with it, some without, you see how it works and hook it up, or not, accordingly.

The ground terminal on this table is there for when you disable the built-in preamp with the user-selectable switch. It should not be used if the built-in phono pre is enabled. you would actually be creating a ground loop because the phono pre would be also be grounded via the line level interconnects.

 

[markw]

Still, the only "grounding wire" in his entire system is on the turntable. Q.E.D.

Now, if that doesn't cure his problem then that overpriced POS amp should be returned ASAP and he better hope they will cheerfully refund his money.

 

[slipperybidness]

I'm in agreement with all the stuff that the AH regulars have been saying.

I will add that on my Dynaco ST-70, I originally set it up with 8 ohm taps (at the advice of Bob Latino, the designer of my kit). I came back later and upgraded to have the option of 4 or 8 taps.

In my experience, with my speakers (a couple of different brands), I found that the 4 ohm tap sounded better and delivered more power to my speakers.

Not much of a surprise, read up on the max power transfer theorem, Thevinin's equivalent circuit, etc.

I think the original advice from Bob was based on his thoughts that "most speakers today are 8 ohm". That was probably true 20 years ago, but today, not so much.