Yes done. I can only remember this link...
Diego Barone MAD
not sure you will undestand italian BTW. He is using a CCS loaded 2A3 AC coupled to a torroidal power tranny (look at Audio HI FI/MAD link). Other examles must be somewhere else on the net.
Ciao
Gianluca
Diego Barone MAD
not sure you will undestand italian BTW. He is using a CCS loaded 2A3 AC coupled to a torroidal power tranny (look at Audio HI FI/MAD link). Other examles must be somewhere else on the net.
Ciao
Gianluca
Yes I have done it with excellent results. Forget about using an EI type, only toroidals will work well. Mine is in a 807 ultra linear arrangement (using the 110V tap on the dual primary for the UL) this works because the 807 draws little screen current as it is a specially designed tetrode. Try to have no unused secondary windings as they will spike the response. You need to specify at least 4x the required output power as the VA rating to get decent bass, though in parafeed you can boost the bass by correct specification of the parafeed cap (a black art indeed). I used plate to plate feedback to lower the effective output impedence of the 807's so that they were better able to drive the inductance and capacitance of the toroidals, this was based on the RH807 design, though the feedback resistor was increased from 100K to 130K to stop suggested bass boost. I used a 110+110 : 18V+18V with the secondaries in parallel. I unwound about two thirds of the secondaries to get the correct ratio.
Don't believe anyone who tells you it won't work or will sound rubbish - they are wrong - wrong - wrong !!!
I am currently experiementing with toroidals as PP outputs as well.
If you are at all interested I can supply the schematic of the design.
Shoog
Don't believe anyone who tells you it won't work or will sound rubbish - they are wrong - wrong - wrong !!!
I am currently experiementing with toroidals as PP outputs as well.
If you are at all interested I can supply the schematic of the design.
Shoog
I tried a parafeed with toroidal too.
I built a parafeed with 2 KT88 connected in parallel, loaded with a solid state CCS (150mA).
I used a 150W, 230/9V main toroidal transformer (with a 4 Ohm load this is a 2500 Ohm primary inductance).
It sounded GREAT!
Shoog:
Please let me know how your experiment with toroidal on push-pull are going, I'm thinking to realize a KT88 PP with a toroidal output transformer (115+115V primary, 9+9V secondary - to be rewound).
Ciao,
Giovanni
I built a parafeed with 2 KT88 connected in parallel, loaded with a solid state CCS (150mA).
I used a 150W, 230/9V main toroidal transformer (with a 4 Ohm load this is a 2500 Ohm primary inductance).
It sounded GREAT!
Shoog:
Please let me know how your experiment with toroidal on push-pull are going, I'm thinking to realize a KT88 PP with a toroidal output transformer (115+115V primary, 9+9V secondary - to be rewound).
Ciao,
Giovanni
I'm also thinking of using toroidals for PP output, what I've on my bench is an EL36 triode PP amp. I will experiment and make measurements, and post here and on my site.
Shoog, and other people experienced with this: I live in 220V country, I need 8k load, so I need a 7V secondary. Since 7V isn't standard, and most of the toroids have 2 secondaries (or one centertapped), what is the best way to go? 7Vct doesn't exist, but 2 x 15V (to be paralleled) is a standard value, am I right?
What's the best in terms of audio performance, put secondaries in series or in parallel (given the same impedance ratio)?
Shoog, and other people experienced with this: I live in 220V country, I need 8k load, so I need a 7V secondary. Since 7V isn't standard, and most of the toroids have 2 secondaries (or one centertapped), what is the best way to go? 7Vct doesn't exist, but 2 x 15V (to be paralleled) is a standard value, am I right?
What's the best in terms of audio performance, put secondaries in series or in parallel (given the same impedance ratio)?
Giaime:
The main voltage standard in Italy is not anymore 220V, but 230V.
The main voltage value has been increased some years ago.
For this reason the primary/secondary ratio of transformers has been slighty modified (230/15V is different than 220/15V).
If you parallel 2 secondary eindings at 15V, you still have a 15V secondary, but with a double current capability: this means the primary inductance will not change at all.
As you know, the primary inductance can be calculated with a the formula:
Primary inductance = (Primary/secondary ratio)^2 * (secondary inductance)
For example, with a 230/15V we have (for a 4Ohm load):
Primary Inductance = (230/15)^2 * 4 = 900 Ohm
If you want to have a 8K load, with a 230V primary winding, you need a secondary winding of:
4 Ohm = 5V secondary
8 Ohm = 7V secondary (your request in your post)
The best way to obtain it is to completely unwound the secondary winding, counting the turns while unwounding it.
At the end, you can reuse the wire to wound a different secondary with the right turns.
For example, let's suppose you have a 230/15 toroidal transformer.
Unwounding the secondary gives you a 200 secondary turns count.
At this point you have a 15V/200 = 0,075 V per turn.
If you need a 5V secondary, simply calculate how many turns you need with:
5V secondary = 5V / 0.075V_per_turn = 66 turns
7V secondary = 7V / 0.075V_per_turn = 93 turns
Hope this is clear.
If you need, please contact me, I can explain everything better in our italian language.
Ciao,
Giovanni
The main voltage standard in Italy is not anymore 220V, but 230V.
The main voltage value has been increased some years ago.
For this reason the primary/secondary ratio of transformers has been slighty modified (230/15V is different than 220/15V).
If you parallel 2 secondary eindings at 15V, you still have a 15V secondary, but with a double current capability: this means the primary inductance will not change at all.
As you know, the primary inductance can be calculated with a the formula:
Primary inductance = (Primary/secondary ratio)^2 * (secondary inductance)
For example, with a 230/15V we have (for a 4Ohm load):
Primary Inductance = (230/15)^2 * 4 = 900 Ohm
If you want to have a 8K load, with a 230V primary winding, you need a secondary winding of:
4 Ohm = 5V secondary
8 Ohm = 7V secondary (your request in your post)
The best way to obtain it is to completely unwound the secondary winding, counting the turns while unwounding it.
At the end, you can reuse the wire to wound a different secondary with the right turns.
For example, let's suppose you have a 230/15 toroidal transformer.
Unwounding the secondary gives you a 200 secondary turns count.
At this point you have a 15V/200 = 0,075 V per turn.
If you need a 5V secondary, simply calculate how many turns you need with:
5V secondary = 5V / 0.075V_per_turn = 66 turns
7V secondary = 7V / 0.075V_per_turn = 93 turns
Hope this is clear.
If you need, please contact me, I can explain everything better in our italian language.
Ciao,
Giovanni
Well,
I do not know of any company selling a toroidal transformer with a 5 or 7V standard output.
your choices are:
1. To find a company that would prepare a customized toroidal transformer for you, with a primary of 230V and a secondary of 5V or 7V.
This is really hard, cause such companies are really rare.
2. Unwind and rewind your transformer on your own.
I sugest this second alternative, it is really really easy.
You have only to remove the secondary winding (that is the first on top) and then rewind a new one, using the same wire, all around the transformer (spreading it all along the toro).
My sugestion is to wind two or three secondary, with exactly the same turns, and then connect them in parallel.
Speaking about current: if you have more than one secondary winding, place them in parallel, the total resistance (in series with the loudspeaker) will be reduced and, thus, the dynamic should encrease.
Ciao,
Giovanni
I do not know of any company selling a toroidal transformer with a 5 or 7V standard output.
your choices are:
1. To find a company that would prepare a customized toroidal transformer for you, with a primary of 230V and a secondary of 5V or 7V.
This is really hard, cause such companies are really rare.
2. Unwind and rewind your transformer on your own.
I sugest this second alternative, it is really really easy.
You have only to remove the secondary winding (that is the first on top) and then rewind a new one, using the same wire, all around the transformer (spreading it all along the toro).
My sugestion is to wind two or three secondary, with exactly the same turns, and then connect them in parallel.
Speaking about current: if you have more than one secondary winding, place them in parallel, the total resistance (in series with the loudspeaker) will be reduced and, thus, the dynamic should encrease.
Ciao,
Giovanni
I will report on my finding on PP when I have some satisfactory results.
An alternative to completely unwinding the secondary is to partially unwind as I did.
The procedure is;
Hook transformer up to a AC voltage source
Take a voltage reading on the unmodified secondaries.
Unwind 10 turns from each of the secondaries
Take another voltage reading.
Decide on what reduction you are seeking and divide it by the voltage drop produced by by removing the 10 turns. Multiply this number by 10 to get the number of turns you need to remove.
The secondary will be loose so wind insulating tape over the whole.
Start with a 10V secondary.
It sounds frightening but is surprisingly easy - if a little tedious. Its a little more complicated than it sounds because the winding will tuck under itself in places.
If you want 10Watts of output go for a 120VA transformer.
Good luck.
Shoog
An alternative to completely unwinding the secondary is to partially unwind as I did.
The procedure is;
Hook transformer up to a AC voltage source
Take a voltage reading on the unmodified secondaries.
Unwind 10 turns from each of the secondaries
Take another voltage reading.
Decide on what reduction you are seeking and divide it by the voltage drop produced by by removing the 10 turns. Multiply this number by 10 to get the number of turns you need to remove.
The secondary will be loose so wind insulating tape over the whole.
Start with a 10V secondary.
It sounds frightening but is surprisingly easy - if a little tedious. Its a little more complicated than it sounds because the winding will tuck under itself in places.
If you want 10Watts of output go for a 120VA transformer.
Good luck.
Shoog
the one important thing to realize when doing this is the power ouput is going to be limited by the maximum flux on the core.
Most toroids are designed to operate at a flux just under saturation so the most voltage you can put across the prmary is 230V@ the line frequency. Say you wanted a 5K ratio and sized the secondary to deliver 9V. This means you max voltage inot an 8 ohm load would be 9V or 10W at the line frequency. Cutting the frequency in half to get 25-30hz power you can only deliver 4.5V or 2.5W!
a good way to start this is to figure the power you need at 1/2 the line frequency and then work backwards to determine the load the transformer will provide and choose an appropriate tube.
Lets say you want 24w @ 30hz into 8 ohms (i'm in the us) This means you need 14V@ 30hz or 28V @ 60hz which translates to a 240:28 transformer or an 8.5:1 turns ratio. When you plug the 8 ohm load back inot this you get a primary impedance of 575 ohms which suggests the tube to use is a 6C33.
dave
Most toroids are designed to operate at a flux just under saturation so the most voltage you can put across the prmary is 230V@ the line frequency. Say you wanted a 5K ratio and sized the secondary to deliver 9V. This means you max voltage inot an 8 ohm load would be 9V or 10W at the line frequency. Cutting the frequency in half to get 25-30hz power you can only deliver 4.5V or 2.5W!
a good way to start this is to figure the power you need at 1/2 the line frequency and then work backwards to determine the load the transformer will provide and choose an appropriate tube.
Lets say you want 24w @ 30hz into 8 ohms (i'm in the us) This means you need 14V@ 30hz or 28V @ 60hz which translates to a 240:28 transformer or an 8.5:1 turns ratio. When you plug the 8 ohm load back inot this you get a primary impedance of 575 ohms which suggests the tube to use is a 6C33.
dave
He may not have the expertise to do that for you.
You would need a really large core, with a high number of primary turns. If inter winding capacitance isn't going to be a significant issue, then he will need to interleave the primary and secondary windings. He may not be set up to do this as usually the primary winding is wound on the core before the secondary. This, I suppose, is why these transformers cost more !
Shoog
You would need a really large core, with a high number of primary turns. If inter winding capacitance isn't going to be a significant issue, then he will need to interleave the primary and secondary windings. He may not be set up to do this as usually the primary winding is wound on the core before the secondary. This, I suppose, is why these transformers cost more !
Shoog
Elettronica Novarria is downtown Milano, so really near where I live.
My question was also about materials and so on.
If a parafeed transformer is conceptually the same as a PP transformer, primary-secondary interleaving should not be a problem
Thanks
My question was also about materials and so on.
If a parafeed transformer is conceptually the same as a PP transformer, primary-secondary interleaving should not be a problem
Thanks
Look like they could do it.
You need to decide what low and high level response is acceptable, what power you need at the average and lowest level. Then take that information to them and they should have computer models to do all the rest for you. If your going to get one custom wound don't waist your time reinventing the wheel.
Useful primary information can be got from the www.bottlehead.com
Good luck
Shoog
You need to decide what low and high level response is acceptable, what power you need at the average and lowest level. Then take that information to them and they should have computer models to do all the rest for you. If your going to get one custom wound don't waist your time reinventing the wheel.
Useful primary information can be got from the www.bottlehead.com
Good luck
Shoog
LC-OPT ...
... I'm lost !
What do you mean ?
Let me ask again the same (unanswered) question: if I ask for a (parafeed) transformer to my local manifacturer what are the characteristics I should ask ?
1. no gap
2. high primary inductance
3. low parasitic capacitances (i.e. pri-sec interleaving)
...
What else ?
Thanks
... I'm lost !
What do you mean ?
Let me ask again the same (unanswered) question: if I ask for a (parafeed) transformer to my local manifacturer what are the characteristics I should ask ?
1. no gap
2. high primary inductance
3. low parasitic capacitances (i.e. pri-sec interleaving)
...
What else ?
Thanks
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