I'm researching a Tubelab SSE build using a pair of NOS 6P3S-Es, which I've found locally at a good price. The design of the SSE calls for a 5K OPT and I had been thinking of going with the Edcor GXSE10-8-5K, but given that I live in the EU, I though it might be preferable to go with a Toroidy toroidal OPT. Now their model for EL34, 6L6, 6P3S, etc. tubes is the TTG-EL34SE [1] which has a primary impedance of 3.2K. (My guess is, it's meant to be used at lower B+ voltage and higher currents, since it's also gapped for 100mA nominal anode current.)
This would cost about as much as the Edcor and it seems to be better, at least in terms of specification (seemingly larger core, going by the weight and 51H primary inductance vs 6H for the Edcor, hence more extended frequency BW, etc.), so I've been thinking I might use that and simply connect my 8 Ohm speakers to the 4 Ohm taps, to get a 6.4K primary impedance which ought to work fine for my application. As far as I can tell (and that's not very far) this should work ok, since most of the specifications (perhaps with the exception of leakage inductance) seem to primarily determined by the core and primary windings, which won't change.
Now, I can also get a custom version of the TTG-EL34SE wound for 5K primary impedance, albeit at about 50% higher price. Would that be worth it? What could be the difference of the custom version, in terms of design and operation, with respect to using the 4 Ohm taps on the default version?
This would cost about as much as the Edcor and it seems to be better, at least in terms of specification (seemingly larger core, going by the weight and 51H primary inductance vs 6H for the Edcor, hence more extended frequency BW, etc.), so I've been thinking I might use that and simply connect my 8 Ohm speakers to the 4 Ohm taps, to get a 6.4K primary impedance which ought to work fine for my application. As far as I can tell (and that's not very far) this should work ok, since most of the specifications (perhaps with the exception of leakage inductance) seem to primarily determined by the core and primary windings, which won't change.
Now, I can also get a custom version of the TTG-EL34SE wound for 5K primary impedance, albeit at about 50% higher price. Would that be worth it? What could be the difference of the custom version, in terms of design and operation, with respect to using the 4 Ohm taps on the default version?
Consider that a lot of "8 Ohm" speakers have output impedances that vary from 6 Ohms to over 30 Ohms versus frequency . . .
And you are good to go.
Good to go perhaps, but perhaps not the Best to go.
Contrary to some opinions, loudspeakers are anything other than: an ideal non inductive load resistor (and non capacitive too).
Impedance matching is a compromise.
Output tube(s); output transformer; loudspeaker
Common tradeoffs are output power; distortion; damping factor; primary inductance, DCRs, primary to secondary Leakage inductance versus the load, and difficulty of getting global negative feedback to work well (if there is GNF).
And you are good to go.
Good to go perhaps, but perhaps not the Best to go.
Contrary to some opinions, loudspeakers are anything other than: an ideal non inductive load resistor (and non capacitive too).
Impedance matching is a compromise.
Output tube(s); output transformer; loudspeaker
Common tradeoffs are output power; distortion; damping factor; primary inductance, DCRs, primary to secondary Leakage inductance versus the load, and difficulty of getting global negative feedback to work well (if there is GNF).
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I am afraid it will saturate at 20 Hz at the same voltage, so maximal power would be lower. Another concern is primary inductance. If you can live with that, it is fine.
I recently tried transformers from Ali Express, rated 15W from 20 Hz, and found that at 20 Hz they already saturate at 6W. If I wanted to use it for twice higher primary impedance, it would deliver even less power.
From the other hand, losing 3 dB of maximal sound pressure is not a big deal.
I recently tried transformers from Ali Express, rated 15W from 20 Hz, and found that at 20 Hz they already saturate at 6W. If I wanted to use it for twice higher primary impedance, it would deliver even less power.
From the other hand, losing 3 dB of maximal sound pressure is not a big deal.
I have considered that too, but this is apparently designed for different tubes, that operate at larger currents (and lower voltages I suppose), so I wonder whether it would be a better choice than the TTG-EL34SE, operated trought the 4 Ohm taps. If the answes is "yes", I wonder why exactly and in what way.
Stated differently I could ask the question in two ways:
- Suppose I use the TTG-EL34SE, what would differ in its operation, what parameter change, apart from the doubled primary impedance, which is desirable? How would that affect the operation of the device and hence the sound?
- Suppose I redesign the TTG-EL34SE as the manufacturer proposes, at increased cost. What would change in its design, apart from using fewer turns in the secondary winding, which is the same as simply using a tap midway along a longer secondary winding? How would that affect the operation of the device and hence the sound?
Can you explain how the primary inductance, saturation and damping factor would be affected? Remeber, I'm not considering the difference in using the 4 Ohm vs the 8 Ohm taps on the same transformer. What I'm considering is the difference in using the 4 Ohm taps of a 3.2K transformer vs using the 8 Ohm taps of a 6.4K transformer.
In the end, what I'm trying to decide on, is whether to go for the 5K TTG-EL84SE, gapped for 150 mA (where I'll probably be drawing about 50 mA), or the TTG-EL34SE through the 4 Ohm taps, which is only slightly more expensive, but has double the primary impedance and is gapped for only 100 mA, or whether going for a custom wound 5K TTG-EL34SE at substantially higher cost would be worth it.
I understand that, but that doesn't answer my questions
.I believe you are asking about the performance differences of different output transformers, when they are applied to specific output tubes and a specific circuit.
The answer requires either building and testing with each transformer type; or simulation software; or doing all those calculations in longhand (plate curves and load lines, etc. and additional calculations (slide rule or calculator).
Without the specifics of each transformers factors (impedance ratios, DCRs, inductance, saturation power versus frequency, etc., the only way is by building and measuring the different transformers. To get the optimum out of the transformer, tube, and circuit will require adjustment of B+ voltage, plate current, etc.
Most transformer manufacturers do not list all the characteristics of the transformer.
A primary that is rated for 100mA, for example, does not tell you how much power before saturation at 40Hz, 30Hz, or 20Hz, those are all different answers.
(simulation software does not work with incorrect or missing data; and longhand calculations have that problem too).
Perhaps someone has built that circuit, and used different transformers, and has some performance information.
If not, I am not sure where this thread can go from here.
Wavebourn's post is a good example.
Trust but Verify . . . the performance of an output transformer.
The "proof of the pudding, is in building, and measuring, and listening".
The answer requires either building and testing with each transformer type; or simulation software; or doing all those calculations in longhand (plate curves and load lines, etc. and additional calculations (slide rule or calculator).
Without the specifics of each transformers factors (impedance ratios, DCRs, inductance, saturation power versus frequency, etc., the only way is by building and measuring the different transformers. To get the optimum out of the transformer, tube, and circuit will require adjustment of B+ voltage, plate current, etc.
Most transformer manufacturers do not list all the characteristics of the transformer.
A primary that is rated for 100mA, for example, does not tell you how much power before saturation at 40Hz, 30Hz, or 20Hz, those are all different answers.
(simulation software does not work with incorrect or missing data; and longhand calculations have that problem too).
Perhaps someone has built that circuit, and used different transformers, and has some performance information.
If not, I am not sure where this thread can go from here.
Wavebourn's post is a good example.
Trust but Verify . . . the performance of an output transformer.
The "proof of the pudding, is in building, and measuring, and listening".
Be aware that afaik neither manufacturer provides the test conditions for their primary inductance spec value.
Not only would primary inductance significantly vary with the DC idle current for SE operation (where it can only be assumed that the manufacturer measures at the nominal/max DC current rating, eg. 80mA for Edcor, and 100mA for Toroidy), but also with the test VAC across the primary, and there is no consistency or indication of what that test level is and so different manufacturers may 'bias' their testing to maximise that parameter, or not.
Also, the consideration of what is nominal, or max, DC idle current, and why they chose that spec level is undisclosed. It could be a spec level related to internal power dissipation, or related to droop of AC inductance for the peak of a sinewave where the B-H point is pushed furthermost into the saturation region which could then show up as increasing signal asymmetry/distortion (and hence interrelated to the Vac signal level being applied for that DC idle condition), or related to marketing hype/advantage against competitive products.
There are just so many performance parameters that are not presented by manufacturers that it comes down to you making the effort to also buy a competing product and to be able to sufficiently test their performance, to come up with a confident comparison of two parts. Very few people are going to make that effort, as 6A3sUMMER has indicated, so imho its up to you when buying parts that are poorly speced.
Can you explain how the primary inductance, saturation and damping factor would be affected? Remeber, I'm not considering the difference in using the 4 Ohm vs the 8 Ohm taps on the same transformer. What I'm considering is the difference in using the 4 Ohm taps of a 3.2K transformer vs using the 8 Ohm taps of a 6.4K transformer.
Looking at my comment vs your question & comment, I have missed the point and wrote 'Off Topic'. Sorry
Generalizations:
1. Saturation:
With specific numbers of: the core's volume of laminations, the air gap distance, the area of the air gap, and the number of primary turns:
The current times the number of turns is called amp x turns.
The core saturation due to DC is according to the DC current times the primary turns, and the above details of the core.
As the DC current is increased, eventually the core will saturate.
Suppose the DC current is less than the amount to saturate the core;
But then a signal is applied that has an additional peak current which is 70% of the quiescent DC current.
At some low frequency, the quiescent DC current plus 70% more current (A total current that is 170% of DC current) causes core saturation.
The lower the frequency, the more effect the extra 70% signal current is likely to cause core saturation.
A lead guitar note of 84Hz, is less likely to cause saturation, versus a bass guitar note of 42Hz.
2. Damping Factor:
Given a specific plate impedance, rp:
A 6.4k primary with 320 Ohms DCR, and 8 Ohms secondary with 0.4 Ohm DCR,
And,
A 3.2k primary with 160 Ohms DCR, and 4 Ohms secondary with 0.4 Ohm DCR . . .
Then those two combinations of tube and output transformers will have the same damping factor.
3. Primary Inductance:
When the core is not saturated, the primary inductance depends on our old friends . . .
Specific numbers of: the core's volume of laminations, the air gap distance, the area of the air gap, and the number of primary turns.
And, DC current in the primary will affect the inductance.
4. The various transformers that are being discussed do not have the same:
Specific numbers of: the core's volume of laminations, the air gap distance, the area of the air gap, and the number of primary turns.
I conclude that we need to test each of the transformers at a moderate DC current, then apply signal, and then measure the performance of a complete output stage . . . at different combinations of power levels at different frequencies.
Then increase the DC current, and test again.
5. Make a decision, select a transformer model, and build.
Be prepared to make a change, perhaps a different transformer model, a different output tube, a different circuit.
One of the best teachers is designing, building, and then making changes.
Please, just do not ask me how many times I have done that.
A few of my designs were not even passable, they quickly got one or more of the changes in 5. above; but many of the other designs were good as soon as they were built.
Have Fun!
1. Saturation:
With specific numbers of: the core's volume of laminations, the air gap distance, the area of the air gap, and the number of primary turns:
The current times the number of turns is called amp x turns.
The core saturation due to DC is according to the DC current times the primary turns, and the above details of the core.
As the DC current is increased, eventually the core will saturate.
Suppose the DC current is less than the amount to saturate the core;
But then a signal is applied that has an additional peak current which is 70% of the quiescent DC current.
At some low frequency, the quiescent DC current plus 70% more current (A total current that is 170% of DC current) causes core saturation.
The lower the frequency, the more effect the extra 70% signal current is likely to cause core saturation.
A lead guitar note of 84Hz, is less likely to cause saturation, versus a bass guitar note of 42Hz.
2. Damping Factor:
Given a specific plate impedance, rp:
A 6.4k primary with 320 Ohms DCR, and 8 Ohms secondary with 0.4 Ohm DCR,
And,
A 3.2k primary with 160 Ohms DCR, and 4 Ohms secondary with 0.4 Ohm DCR . . .
Then those two combinations of tube and output transformers will have the same damping factor.
3. Primary Inductance:
When the core is not saturated, the primary inductance depends on our old friends . . .
Specific numbers of: the core's volume of laminations, the air gap distance, the area of the air gap, and the number of primary turns.
And, DC current in the primary will affect the inductance.
4. The various transformers that are being discussed do not have the same:
Specific numbers of: the core's volume of laminations, the air gap distance, the area of the air gap, and the number of primary turns.
I conclude that we need to test each of the transformers at a moderate DC current, then apply signal, and then measure the performance of a complete output stage . . . at different combinations of power levels at different frequencies.
Then increase the DC current, and test again.
5. Make a decision, select a transformer model, and build.
Be prepared to make a change, perhaps a different transformer model, a different output tube, a different circuit.
One of the best teachers is designing, building, and then making changes.
Please, just do not ask me how many times I have done that.
A few of my designs were not even passable, they quickly got one or more of the changes in 5. above; but many of the other designs were good as soon as they were built.
Have Fun!
It seems quite a bit of concern is focused on the top few dB of peak excursion in the speaker bass region, where some non-linearity around the peak of one polarity of excursion may be perceived to be noticeable. I'd suggest that may well be below the OP's speaker LF corner, and may depend much on the speaker enclosure tuning and room modes, and the distortion being produced by the speaker unit. If the OP hasn't got that all under tight measured control then much of the concern is imho ill-founded, especially as we have no clue as to the amplifier format being proposed, and whether any global feedback is going to be applied (and if there would still be some feedback in play at the frequency range of concern), or whether the speaker unit is reflecting its nominal impedance in that frequency range or is highly variable due to enclosure/speaker tuning.
Given a specific circuit, and two output transformer models . . .
One very important variable is how well each one will work if Global Negative Feedback includes the output transformer secondary.
That just Adds to the complexity, or should I say Multiplies the complexity.
To a lesser extent, the local negative feedback of the Ultra Linear circuit complicates things, versus 2 different output transformer models.
When it comes to the discussion of an Air Gap . . . For a Toroid output transformer.
Are they putting a thin insulating tape on one side of the metal, to act as a predictable and consistent Air Gap all along the toroid core, for each and every turn of the core?
Without proper pressure, as current varies, so will the Air Gap spacing.
Help us help you . . .
Please post a complete and accurate schematic of the proposed amplifier that will use one or another model of output transformers.
If you can not nail down the complete design of an amplifier . . .
Isn't that like forgetting to put the nails in the vampires coffin?
One very important variable is how well each one will work if Global Negative Feedback includes the output transformer secondary.
That just Adds to the complexity, or should I say Multiplies the complexity.
To a lesser extent, the local negative feedback of the Ultra Linear circuit complicates things, versus 2 different output transformer models.
When it comes to the discussion of an Air Gap . . . For a Toroid output transformer.
Are they putting a thin insulating tape on one side of the metal, to act as a predictable and consistent Air Gap all along the toroid core, for each and every turn of the core?
Without proper pressure, as current varies, so will the Air Gap spacing.
Help us help you . . .
Please post a complete and accurate schematic of the proposed amplifier that will use one or another model of output transformers.
If you can not nail down the complete design of an amplifier . . .
Isn't that like forgetting to put the nails in the vampires coffin?
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Buy the proper transformer.
Pay what they ask for it.
Enjoy.
What's the point of going way outside mainstream, building a wild offbeat amplifier (DHT triodes were king of the hill ... In 1940), big, clunky, expensive (given it's power), low power, expensive, etc. and then NOT build it, using the wrong tubes, wrong transformer, etc
If not clear, also use the proper tubes.
Pay what they ask for it.
Enjoy.
What's the point of going way outside mainstream, building a wild offbeat amplifier (DHT triodes were king of the hill ... In 1940), big, clunky, expensive (given it's power), low power, expensive, etc. and then NOT build it, using the wrong tubes, wrong transformer, etc
If not clear, also use the proper tubes.
Sorry, I though I had mentioned it. I am planning to build a Tubelab SSE so you can find a complete schematic here. My only changes concern different bias resistors for different tubes (12AY7/6P3S-E) as well as a different R13/R23, to set an appropriate current for the 12AY7. I'm also considering dropping the cathode bias bypass capacitors, as I don't need the gain (I have a DAC with a 2VRMS output) and get better results in terms of THD without them in my simulations (since they implement a sort of local NFB). I'm concentrating on triode operation for now, without cathode feedback, but might try UL and other forms of feedback later. For our present discussion though, we can assume triode operation with no UL or GNFB.
Good question. For me, the primary benefit of building a tube amplifier, is that the circuits can be relatively simple, that is simpler than modern Hi Fi designs, so that I can hope to understand them wihtout more effort than I can spare. In other words, building the amplifier is more an excuse for me, in order to study the underlying physics and engineering. That's, in part, why I'm trying to understand how a custom-wound OPT would differ from using the 4 Ohm taps of a similar half-impedance OPT. It's not about saving a few bucks, although that is of course welcome. An other reason is that going to the effort of building a custom part, when an off the shelf part will do just as well, is just bad engineering.
So I'm trying to understand what would make the custom-wound transformer more "proper". Again I'm wondering: the proposal is to rewind the existing TTG-EL34SE for 5K primary impedance. How could the design be altered? Let's assume the published specs remain more or less the same for the custom part (although they haven't mentioned what those specs will be, and I'll have to ask). It's a rewinding of the TTG-EL34SE, so that seems to imply the core won't change, but instead only the windings will change. In particular the secondary winding of the custom OPT can become smaller, instead of just using part of a larger winding through the 4 Ohm tap, which might in turn allow for a larger primary winding or better geometry in some way, but since the turns ratios are about 28:1 vs 20:1, I imagine the difference couldn't be very large. If e.g. the primary is 1000 turns the secondaries would be 35 and 50 turns respectively. I can't see how the space saved by these 15 turns could be used to make much of a differnce in the custom design.
That's because the reflected primary resistance, which would add to rp would be the same in both cases, correct? By my above argument, I'd expect the DCR of the primary to be about the same in the off-the-shelf TTG-EL34SE vs the rewound one, so the DF woudn't change much by the rewinding, no? The same would seem to hold for primary inductance and saturation characteristics, as far as I can tell. Assuming the same core and a target of 6.4K primary impedance, how could the rewound part differ in terms of design and implementation, to make any substantial difference compared to the 4 Ohm tap of the off-the-shelf part?
I wholeheartedly agree that this is the proper approach. Budgetary concerns do not allow me to apply it but, even if I end up doing it, there's no harm in using theoretical reasoning to hope to get closer to a good choice on the first (and each successive) attempt. That's my intent here. I do not expect a definite answer.
Oh, nothing too complicated.
Here "proper" means "whatever Amp Designer" specified, no more no less.
Transformers sadly are always a compromise, so designer optimizes it the best he can, deviating from that doesn't help.
As I see it there is a mere $40 or so difference between proper Edcor and iffy Toroid.
Pocket money compared to whole project cost I guess.
Your project your choice of course.
Keep us updated with your build 👍🏻
.
This is sound advice, no question abou that, but, and forgive me if I'm wrong, you seem intent to assume that I'm trying to make a better amp for less money, by buying questionable part with impressive spec sheets for a less than "proper" parts. As I've explained above, the stock Toroidy OPTs are about the same as the Edcor GXSE (and this although the Edcor has to be ultimately imported and shipped from the US). It is the custom-wound Toroidy that is 40$ more. For two pieces, thats 80$ and, while not pocket money, it is true that it is not a substantial part of the project cost. But as I've explained before, it is not about saving money.
Deciding what OPT to use, is a good reason to learn about OPT design and the engineering and physics associated with it. If I can buy a better part for the same price, by saving on shipping and customs, I wouldn't be averse to that and if (if, not when) it turns out that a set o custom wound parts would essentially perform similarly to taking the output out of the 4 Ohm tap of an existing part, I'd rather do the latter too. Not for the money difference (well for that too), but because it's bad engineering to get a custom part, where something off-the-shelf would do just as well.
Furthermore, the designer has only specified a 5K OPT, that is, unless you happen to have a 3K OPT sitting around, which will work, but not as well. Apart from that, a couple of Edcor and Hammond models are mentioned as tried parts that work well, in the builds he's done, so I suppose these are safer bets.
The only way to determine what your changes will sound like is to build both "designs" and listen to the differences. Things like removing the cathode bypass cap doesn't just impact gain, that can change the whole sound signature of an amp. If I have learned anything, dwelling on theory will only get you so far. Many times what something should do, even on computer simulations and applying information from the data sheets, might not happen in the actual built amp.
I publish details on all the amps I build. If you build it just like mine, it's going to sound good and work properly. Once you start substituting parts, no one can accurately guess what the result will be sonically.
As far as your transformer question, I would be asking this question to the folks who make transformers. I personally can see how using a transformer 2X outside of it's intended impedance rating could create unforeseen problems. If it's simply about turns ratio, all output transformers would sound the same and we could use power transformers with the correct turns ratio instead as well!
Imagine you have 2 transformers of the same size, for the same output power. One is wound for 4K, another one is wound for 8K drive. That means, the second one supposed to be driven by 1.412 times higher voltage before the saturation at the specified lower frequency. You aright, your transformer supposed to work at lower voltage and higher current. It's inductance will be lower, so there will be lower the ratio between it's reactance on the lower frequency and the output resistance of the amp stage that drives it. And it will saturate at 1.4 times lower swing at the same frequency, and that is your 3 dB of sound pressure loss if you want the same frequency range. Or, the same power, but higher lower frequency limit. Your choice. I used 80W guitar transformers made by Chumakher for Ada Depot in very nice 30 and 40W per channel amps.
I thought that while we were discussing it back and forth you had plenty of time to breadboard and check for yourself.
Speaking of damping factor, it is a marketing term that has almost no meaning since speakers at their resonant frequency see the sum of output resistance of the amp plus their own DCR that actually dissipates the power doing it's damping thingy.
I thought that while we were discussing it back and forth you had plenty of time to breadboard and check for yourself.
Speaking of damping factor, it is a marketing term that has almost no meaning since speakers at their resonant frequency see the sum of output resistance of the amp plus their own DCR that actually dissipates the power doing it's damping thingy.
Given a specific set of laminations, weight, volume, air gap cross section area, and windings that fit just right . . .
A 3k primary has a certain number of turns; and a specific wire size.
A 6k primary has 1.414 times the turns of the 3k primary, and it has 0.707 smaller wire diameter to fit in the same space as the larger 3k wires.
That means the ratio of 3k to its DCR . . .
Is the same as the ratio of the 6k to its higher DCR.
And, the inductance of the 6k primary is 2 x the inductance of the 3k primary.
With output tubes that have rp = 1/3 of the primary impedances (rp = 2k for the 6k primary; 1k for the 3k primary)
The -3dB low frequency will be the same for both transformers.
If the 3k primary is driven by a tube with an rp = 1k
And the 6k secondary is driven by a tube with an rp = 2k . . .
The damping factor will be the same for both output stages.
For the same power output, the 6k primary will have 1.414 x more voltage swing, and 0.707 x the current swing . . .
Versus the 3k primary voltage swing and current swing.
How about that?
A 3k primary has a certain number of turns; and a specific wire size.
A 6k primary has 1.414 times the turns of the 3k primary, and it has 0.707 smaller wire diameter to fit in the same space as the larger 3k wires.
That means the ratio of 3k to its DCR . . .
Is the same as the ratio of the 6k to its higher DCR.
And, the inductance of the 6k primary is 2 x the inductance of the 3k primary.
With output tubes that have rp = 1/3 of the primary impedances (rp = 2k for the 6k primary; 1k for the 3k primary)
The -3dB low frequency will be the same for both transformers.
If the 3k primary is driven by a tube with an rp = 1k
And the 6k secondary is driven by a tube with an rp = 2k . . .
The damping factor will be the same for both output stages.
For the same power output, the 6k primary will have 1.414 x more voltage swing, and 0.707 x the current swing . . .
Versus the 3k primary voltage swing and current swing.
How about that?