I understand the TVA-1 output transformer has a tap for 4 ohm speakers. However the published schematic diagrams I found so far are all wired for 8 ohm (see attached). Would appreciate to have suggestion on how to correctly modify it to 4 ohm.
Cheers
Cheers
Attachments
Thank you jazbo8, will do it and post the result.
I want to drive Anthony Gallo Strada 2 speakers and I understand their piezoelectric tweeter goes very low in impedance at high frequencies.
Now they sound ok (better than with my AVR), I want to see if with the 4 ohm winding they sound better.
I want to drive Anthony Gallo Strada 2 speakers and I understand their piezoelectric tweeter goes very low in impedance at high frequencies.
Now they sound ok (better than with my AVR), I want to see if with the 4 ohm winding they sound better.
Depends on how the ratios are exactly.
The number of windings from 4-8 and 0-16 are the same as these can be parallelled.
So either the secondary impedances are 4, 8 and 13,4 ohm, or 4, 9 and 16 ohm.
I got a reply by gingertube via email. Strangely I don't see it in the Forum..
Since it seems a good post to me I am posting it myself for further discussion within the Forum:
"Dear gorlando,
gingertube has just replied to a thread you have subscribed to entitled - M&A TVA-1: how to change the output transformer wiring for 4 ohm speakers? - in the Tubes / Valves forum of diyAudio.
This thread is located at:
http://www.diyaudio.com/forums/tube...ansformer-wiring-4-ohm-speakers-new-post.html
Here is the message that has just been posted:
***************
Fairly certain there is a better way:
A lot of Vintage HiFi Output Trannies came with 2 separate 4 Ohm secondaries.
You wire them in series for 16 Ohms and in parallel for 4 Ohms.
Important Note: that the top winding labelled 0 - 16 Ohms is actually a separate 4 Ohm winding.
When you put it in series with the bottom 4 Ohm winding (as shown on the diagram) you get at total of 16 Ohms.
For 4 Ohms output:
You should wire the top 4 Ohm winding in parallel with the bottom one.
That is:
connect the two taps labelled 0 together for the common output.
connect the taps labelled 4 and 16 ohms together for the 4 Ohm output.
Leave the tap labelled 8 Ohms unconnected.
Cheers,
Ian
***************"
This suggestion seems very valid to me, I can put in parallel 2 windings to extract more current to the loudspeakers.
I attach a hand sketch of the wiring suggested by Ian,
I have a residual question, though: what could be the drawback of leaving the 8 Ohm tap unconnected (if any)?
In fact, the 8 Ohm wiring doesn't leave any tap unconnected.
Thank you to all for their contribution, I'm learning a lot from these!!!
Cheers, Giovanni
Since it seems a good post to me I am posting it myself for further discussion within the Forum:
"Dear gorlando,
gingertube has just replied to a thread you have subscribed to entitled - M&A TVA-1: how to change the output transformer wiring for 4 ohm speakers? - in the Tubes / Valves forum of diyAudio.
This thread is located at:
http://www.diyaudio.com/forums/tube...ansformer-wiring-4-ohm-speakers-new-post.html
Here is the message that has just been posted:
***************
Fairly certain there is a better way:
A lot of Vintage HiFi Output Trannies came with 2 separate 4 Ohm secondaries.
You wire them in series for 16 Ohms and in parallel for 4 Ohms.
Important Note: that the top winding labelled 0 - 16 Ohms is actually a separate 4 Ohm winding.
When you put it in series with the bottom 4 Ohm winding (as shown on the diagram) you get at total of 16 Ohms.
For 4 Ohms output:
You should wire the top 4 Ohm winding in parallel with the bottom one.
That is:
connect the two taps labelled 0 together for the common output.
connect the taps labelled 4 and 16 ohms together for the 4 Ohm output.
Leave the tap labelled 8 Ohms unconnected.
Cheers,
Ian
***************"
This suggestion seems very valid to me, I can put in parallel 2 windings to extract more current to the loudspeakers.
I attach a hand sketch of the wiring suggested by Ian,
I have a residual question, though: what could be the drawback of leaving the 8 Ohm tap unconnected (if any)?
In fact, the 8 Ohm wiring doesn't leave any tap unconnected.
Thank you to all for their contribution, I'm learning a lot from these!!!
Cheers, Giovanni
I got the same reply by email.
Gingertube deleted the post because, I guess, he realized that he was wrong.
The top section (0-16) can not be a 4 ohm winding, as it can be parallelled with 4-8 of the lower section, and 4-8 is not a 4 ohm section.
Yes, the present wiring is as per schematic diagram and as per the sketch I drafted (8 Ohm wiring).
X turns is the bottom 4ohms winding.
Double that to 2X turns for the whole 16ohms winding.
Where there is an 8ohms windings it needs sqrt(2)X turns.
The extra turns added to the 4ohms winding for 8ohms is {sqrt(2)-1}X = 0.41X turns
The extra turns added to the 8ohms winding for 16ohms is X-0.41X = 0.59X
Thus the transformer has X, +0.41X, +0.59X for a total of 2X turns.
There is no 2/1/1, nor 2/0.83/0.83 ratios in there.
Double that to 2X turns for the whole 16ohms winding.
Where there is an 8ohms windings it needs sqrt(2)X turns.
The extra turns added to the 4ohms winding for 8ohms is {sqrt(2)-1}X = 0.41X turns
The extra turns added to the 8ohms winding for 16ohms is X-0.41X = 0.59X
Thus the transformer has X, +0.41X, +0.59X for a total of 2X turns.
There is no 2/1/1, nor 2/0.83/0.83 ratios in there.
You can't sucessfully connect two windings with a 0.41/0.59 turns ratio in parallel, do you?
Best regards!
I'm a bit confused now. Let's try to understand:
- The lower windings has 3 taps: 0-4-8 Ohm (0 to 4 has X turns, 4 to 8 has 0.41X turns);
- The upper winding has 2 taps: 0-16 Ohm (it should have 2X turns then);
- The present connection (which is the factory one and is working) connects tap0 to the
outlet negative post and tap8 to the outlet positive post. All clear so far.
- However, the outlet positive post is also connected to tap16 of the upper windings, while
Tap0 of the upper winding is connected to tap4 of the lower winding - This is tricky to
understand. The only way this could work is if the upper windings has 0.41X turns and not 2X turns (16 Ohm).
- If this is correct, the upper winding is 0.41X, and can be connected in parallel with tap4 to tap8 of the lower winding. Not sure what impedence the upper winding is then.
I am not an expert of transformers, am I missing something?
- The lower windings has 3 taps: 0-4-8 Ohm (0 to 4 has X turns, 4 to 8 has 0.41X turns);
- The upper winding has 2 taps: 0-16 Ohm (it should have 2X turns then);
- The present connection (which is the factory one and is working) connects tap0 to the
outlet negative post and tap8 to the outlet positive post. All clear so far.
- However, the outlet positive post is also connected to tap16 of the upper windings, while
Tap0 of the upper winding is connected to tap4 of the lower winding - This is tricky to
understand. The only way this could work is if the upper windings has 0.41X turns and not 2X turns (16 Ohm).
- If this is correct, the upper winding is 0.41X, and can be connected in parallel with tap4 to tap8 of the lower winding. Not sure what impedence the upper winding is then.
I am not an expert of transformers, am I missing something?
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That had been possible when the lower (0-4-8) ohm part would have had two terminals at the 4 ohm point instead of a single tap.
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