That’s interesting. This is a bit above my head at the moment, as I’m not so familiar with transformer windings etc and not so technical, but if the “8 ohm” setting is actually 10 ohms, then that would explain the results I got with these amps with 8 ohm speakers. Something didn’t sound right. A bit too heavy and slightly recessed in the top end. I switched to the 4 ohm setting (by resoldering the wires) and used that with 8 ohm speakers instead. That gives no recession in the top end but the sound is slightly too bright and lacking in weight. Something more in between those would be better.
Sorry if this is a question that is obvious but could there be a different way to wire (other than the combinations in the manual) to get a proper 8 ohms? (For example could you cut out the parallel middle part in the “8 ohm” diagram for example)
Or could you wire for 6 ohms? Not sure if either of these is possible without more knowledge of the windings etc, but if it was possible then either would be more desireable for me than a 10 or 4 ohm output (when I’m using 8 ohm speakers)
Sorry if this is a question that is obvious but could there be a different way to wire (other than the combinations in the manual) to get a proper 8 ohms? (For example could you cut out the parallel middle part in the “8 ohm” diagram for example)
Or could you wire for 6 ohms? Not sure if either of these is possible without more knowledge of the windings etc, but if it was possible then either would be more desireable for me than a 10 or 4 ohm output (when I’m using 8 ohm speakers)
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I doubt that it could be detected - at least not because it’s changing by 2 Ohms. It’s more to do with how well the winding are magnetically coupled. If two segments are well coupled then they will have higher bandwidth. But this also depends very much on how the transformer is wound - it’s a technique called interleaving.
Stop over thinking things if you just want to enjoy music 😆 As a technical question you could work out all the combinations of four segments - that would give you options, then do it for 3, 2 etc
But as I said above I doubt you will beat the data sheet, it’s more complicated than just an impedance value. You might even get the perfect impedance matching and decide you don’t like the top end, and you prefer it with a different combination. You be are just playing with a low-pass and high-pass filter connected from the amplifier to your speaker - it’s not that wow.
I'm quite sure that for 4 Ω the related winding part also could be connected in a way that the BW wire can be grounded. If that weren't possible, this winding would need to be wired out of phase, which wouldn't make sense at all. Or it is one of both upper ones in the drawing, which could easily be swapped with a lower one.
Best regards!
Best regards!
Thanks for the info and explanation of how it’s more complicated than just the impedance ratings
I have quite a bit of experience with many different tube amps on various speakers and generally find that if the impedance rating of the amp is too high for the speaker, you get a fuller top end and heavier sound. For example if you connected an 4 or 6 ohm speaker with an 8 ohm tap from an amp, an 8 ohm speaker connected to a 16 ohm tap from an amp.
That’s what I experience with these monoblocks using the 8 ohm tap on various 8 ohm speakers. The sound isn’t right, the FR is off - too bloated and lacking in top end.
When I first got these amps I had initially suspected they was set to the 16 ohms setting, based on the way they sounded with 8 ohm speakers. When I checked internally I was surprised to see they were set on 8 ohms.
So something doesn’t seem right with the 8 ohm setting on these amps IMO. I have tried many different pairs of 8 ohm speakers. Appreciate there is some subjectivity here but the 8 ohm setting setting is too full and muted at the top end for me with 8 ohm speakers. The 4 ohm setting goes a bit too far the other way unfortunately (when using 8 ohm speakers). Much better top end detail and extension but a bit too thin and bright.
If I was to go about working out all the combos for the segments (as you suggest) then how would I go about doing that and then transpose it to the wiring? Would appreciate some help and appreciate (that as you say) its more complicated than that. It might not ultimately give me what I like, but I would like to try if it’s possible.
You can wire the secondaries in series, instead of connect the output terminal to red wire (16Ω output impedance), connect the output terminal to the green and white wire joint will provide a 8Ω output impedance. However, it might not give you the sound that you prefer.
Wouldn't that tap be effectively 4 Ohms? Not that it really matters - speakers aren't resistors.
All good fortune,
Chris
All good fortune,
Chris
Thanks a lot for that info. I was going to try to work on the combos myself but didn’t get too far as didn’t have time.
So my understanding is that each winding is 4 ohms, so what you suggest will give 8 ohms. I can see that by doing that you aren’t using all of the windings. I assume that would give slightly less output?
Appreciate it might not give me what I want as it’s more complicated as explained by Boyfarell, but it’s worth trying.
I don’t like the sound of these monoblocks with the stock 8 ohm setting when using 8 ohm speakers, as explained before.
The other obvious combo I saw using three windings (instead of four or two) is to take the stock 8 ohm wiring (that’s 10 ohms total) and miss out one of the top or bottom series windings. Then you get 6 ohms. Might also be worth trying.
Thanks a lot for your help.
As Tom has said several times, each winding is 1 Ohm (I was wrong saying it was 2 Ohms). That means it has a turns ratio appropriate to a 1 Ohm load if any one of the windings was used by itself, or if all were paralleled. Remember that these "Ohms" numbers are just another way of stating the turns ratio. They have no other meaning, none.
From the standpoint of the best possible coupling performance within the transformer, we'd want to use all of the secondary windings equally, so all in series, or all in parallel, or all in series-parallel. Thus, 16, 1, or 4 Ohms configuration.
From the standpoint of the output valves driving a loudspeaker load, we have to choose between lighter loading for lowest distortion and best speaker damping and heavier loading for most peak output (up to a point). There is no magic bullet but there are balanced decisions.
All good fortune,
Chris
From the standpoint of the best possible coupling performance within the transformer, we'd want to use all of the secondary windings equally, so all in series, or all in parallel, or all in series-parallel. Thus, 16, 1, or 4 Ohms configuration.
From the standpoint of the output valves driving a loudspeaker load, we have to choose between lighter loading for lowest distortion and best speaker damping and heavier loading for most peak output (up to a point). There is no magic bullet but there are balanced decisions.
All good fortune,
Chris
W. r. t. the drawing in #46, the tap definitively is 4 Ω instead of 8 Ω.
Anyway, other than for convenience I don't see any reason to wire like that, as the transformer's efficiency will be compromised. Tube output power is expensive and doesn't need to be transformed into heat more than necessary. Better do it as shown in #37 (and see that the 8 Ω wiring numerically transforms to 9 Ω).
Best regards!
Anyway, other than for convenience I don't see any reason to wire like that, as the transformer's efficiency will be compromised. Tube output power is expensive and doesn't need to be transformed into heat more than necessary. Better do it as shown in #37 (and see that the 8 Ω wiring numerically transforms to 9 Ω).
Best regards!
Are the output impedances of the 4 windings identical? 1R?
P.S. Yes, they are, I misread.
Note that high frequency performance might vary depending on the connection of the secondaries and the transformer geometry.
For example in the 4R and 9R configuration, you have two connection options
P.S. Yes, they are, I misread.
Note that high frequency performance might vary depending on the connection of the secondaries and the transformer geometry.
For example in the 4R and 9R configuration, you have two connection options
Thanks for this, getting my head around it a bit better now.
As I say, my problem, using the secondaires wired up for a turns ratio optimised for 9 ohms doesn’t sound right to me with 8 ohm speakers, and using the 4 ohm option has other different issues with 8 ohm speakers.
If I don’t like the results of these amps from either the 4 ohm or 8 ohm taps I suppose another option might be to replace the transformers with some others that have ratios and windings more suited to my particular 8 ohm speakers, but I suspect it’s probably more complicated than that and the trannies are very matched to the particular amp circuit..
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Thanks for the info. That’s interesting about HF performance.
If I’m understanding you coreccrly, do you mean for the 9R config there are two different ways to connect up the windings? If so would the second option be having the parallel two windings not in the middle and at one of the ends instead?
Can’t see it for the 4R config.
Apologies if I’ve misunderstood you.
If we have four identical windings of 1R and we label them as A, B, C, D
You can get 4R by the following connections: ( // stands for parallel connection, = stands for series connection)
A // B = C //D
or
A = B // C =D
or even cross coupling like
A = C // B = D
You can get 9R by the following
A // B = C =D
or A = B = C // D
You can get 4R by the following connections: ( // stands for parallel connection, = stands for series connection)
A // B = C //D
or
A = B // C =D
or even cross coupling like
A = C // B = D
You can get 9R by the following
A // B = C =D
or A = B = C // D
Connecting an 8 Ω speaker to an output transformer wired for 9 Ω won't harm at all, I'd say. Plate to plate impedance would be decreased by just 11 %. But do we know exactly which load impedance matches best with the power tubes at their given operating conditions? And by which criteria would we decide? What's the dimension of tube manufacturing tolerances? There are several ways to skin a cat...
Best regards!
Best regards!
@Tubelover25 do you have an oscilloscope? You might enjoy measuring the transformer throughout (Vout/Vin) as a function of frequency. You will see a flat band in the middle (e.g. 50Hz-10,000Hz) but the throughput will roll off at the low end and the high end.
This might let you home-in on the particular sound you like.
You could do that for the different combinations of windings.
This might let you home-in on the particular sound you like.
You could do that for the different combinations of windings.
Thanks for this. Many speakers stated of 8 ohms have lower impedance at some frequencies or the overall is lower than stated. My main speakers (Proac 3.5s) are probably more like 6 or 7 ohms overall, so in between 4 and 8.
I’ve had some trouble with 8 ohm taps on other tube amps in the past (same thing of HF being a bit too rolled off and bass too prominent). However some 8 ohm taps from other tube amps were fine.
The best match I’ve had with these speakers was from a power amp that had a single OT tap optimised for 6 ohms (Art Audio Quintet mk1 EL34/PP amp). Very well balanced. No top end recession)
The bass not quite being balanced is less of a problem for me, but I’m pretty bothered to the top end being too rolled off.
So with these 300B amps, perhaps a transformer tap optimised for 9 ohms is slightly too high and 4 too low, but I’d like to try the different combos for each.
My Proacs are not as sensitive as speakers usually used with 300B SE amps but it’s just fine with most material in the smaller room I’m in (apart from when playing dynamic classical).
These Welborne labs 300B DRD monoblocks have a very pure sound. DC coupled, use few parts and only 2 stages instead of the typical 3. They would of course be more suited to high efficiency horns etc and I’m planning to move to those (or similar high efficiency speakers) eventually. The 2 stages (vs the typical 3) gives low input sensitivity but extremely low background noise at the speakers, which is nice. I really hate any background hum at the speakers
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Thanks for this. I don’t have an oscilloscope but had been planning to get one. Would be well worth trying that and seeing the results.
Although this thread has gone on a bit of a diversion, thanks for all the helpful info on this from everyone so far. Optimising the OP transformers to my speakers better would be more useful at this stage than installing a selector switch to change between the 4 stock settings.
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