Output Impedance Missmatch...

[PageyNT]

Hi guys.

I have a pair of floor standing speakers that are rated as input impedance 6ohms.
I am currently finalising the build of a small DIY Tube Amp, EL84 Push Pull as per the Dynaco schematic just as a way of easing in to things.

As far as I can see there are no output transformers available for 6ohm speakers. Am I able to use the 4ohm or 8ohm tap or is this a very bad idea? Are there any work arounds that don't involve buying new speakers?

Thanks!

 

[TonyTecson]

connect that speaker to the 8 ohm tap and be done with it.....

fyi, the output impedance of any amp ought to as low as possible, closer to zero...

 

[6A3sUMMER]

The rated input impedance of loudspeakers is nominal.

Many 8 Ohm loudspeakers have a minimum impedance of about 6, or even 4 Ohms at one or more frequency ranges.

Many 4 Ohm loudspeakers have a minimum impedance of about 3 or even 2 Ohms at one or more frequency ranges.

Many 6 Ohm loudspeakers have the same kind of minimum impedance effects that are less than 6 Ohms.
Connect your speakers to the 8 Ohm tap.
Then connect them to the 4 Ohm tap.
Decide which connection you think sounds better, and leave them connected that way.

 

[Diabolical Artificer]

The 6 ohms impedance - Z , quoted on your speakers is a nominal Z, meaning it is 6r at one frequency, at others it will go up or down, so when playing music it will change a bit.

As others have said, connect to the 8r tap. BTW don't forget to ground the "0" or C tap of your OPT.

Andy.

 

[PageyNT]

I was really hoping there would be an answer that did not involve me finding an OPT with a 6ohm tap!!
Thanks very much.
And no I won't forget to ground the C of the OPT. Cheers!

 

[DF96]

Connect your speakers to the 8 Ohm tap.
Then connect them to the 4 Ohm tap.
Decide which connection you think sounds better, and leave them connected that way.

Yes.

BTW don't forget to ground the "0" or C tap of your OPT.

But be careful where you ground it. Any difference between the OPT secondary ground and the input signal ground becomes part of the feedback signal. Best to ground to the input signal reference, whatever that is.

 

[Yvesm]

Beware, on the schemo there is a link between the negative of the filter caps and the upper side of the valve heather that should not exist or you will blow the valve rectifier

 

[artosalo]

How about the short circuit of 5 V secondary ?
Well, the reason is the primitive style to draw circuit diagrams (without a "dot" at connections).

 

[rayma]

Beware, on the schemo there is a link between the negative of the filter caps and the upper side of the valve heather that should not exist or you will blow the valve rectifier

PageyNT:
This is a very bad error, you should post your corrected schematic here for checking before completing the wiring.

 

[6A3sUMMER]

PageyNT,

Use a DMM to read the DCR of your loudspeaker.
The DCR Ohms is the minimum impedance at the low frequency to mid frequency ranges of your woofer.

Suppose your '6' Ohm loudspeaker has a DCR of 5, or 4, or 3 Ohms.
In that case, use the 4 Ohm tap of the output transformer.
The 4 Ohm tap will give lower distortion and better damping factor (but perhaps a Very little less power) than the 8 Ohm tap.

 

[baudouin0]

The 6 ohms can come about by using two 8 ohm bass drivers in parallel. When you include the bass resonance peaks it sort of averages about 6 ohms. The mid-range and treble will be 8 ohms. You may be a little low on watts maybe EL34 push-pull might be better.

 

[6A3sUMMER]

Without knowing more about PageyNT's loudspeakers, we are getting off the subject.
He wants to build the amp in Post # 1.

1). We do not know the speaker model, room size, music selections; desired sound level, etc., and the other requirements that PageyNT has.

2). We do not know his budget, nor how big or small the amp will be to fit in a tight spot, or how much complexity he will accept in an amplifier that he will build.

He has selected a circuit (that admittedly needs some connection corrections).

Now, suddenly, without knowing 1). or 2). above, are we going to recommend that he build an EL34 amplifier?
Huh?

And . . . since when is the Average Impedance of a loudspeaker the factor that you use to design or select an amplifier?

Think of music signal source, amplifier, loudspeaker, and room as a playback system.
Each part has to properly match the input and output characteristics of the system parts that interfaces before and after it, respectively.

 

[baudouin0]

You're quite right - it's not the place to offer advise.