Antek OPT

[mr2racer]

I've found a few threads that mention Antek OPT's in the title but never seem to get around to mentioning them. Has anyone actually heard the Antek OPT's? I'm assuming the Plitrons sound better at four times the price. But has anyone actually heard the difference that can describe them?

[Shoog]

There was a thread a little while ago where someone actually tested one. The top end was very compromised from what I remember, They seem to have done something very wrong with the design.

Shoog

[whitelabrat]

I tested 35w and 100w older model numbers. The 35w was useless and the 100w may be acceptable. The newer models may be better. Just verify that they accept returns before buying and don't cut the leads in case you need to return them.

My Opinion: For the money, stick to Edcor.

[Jeb-D.]

I tested 35w and 100w older model numbers. The 35w was useless and the 100w may be acceptable. The newer models may be better. Just verify that they accept returns before buying and don't cut the leads in case you need to return them.

My Opinion: For the money, stick to Edcor.

Curious what test configuration was used and what were the results? I've got a pair of the 40W 4.8k in my closet that I was hoping to use some day, but you got me wondering if it's even worth a try.

The top end looks rolled off by the manufacture supplied curves, but the measurements were probably taken using a source with a Zout = the reflected impedance. I'd suspect that acceptable bandwidth may be attainable in circuit if driven by triodes with plate impedance in the 1/2-1/3rd range (typical triode loading) of the transformers primary Z. And/Or with use of NFB.

[Poindexter]

I talked to LeFevre about this awhile ago. His call was that, though toroids look cool to people due to the optimized iron circuit configuration, they cannot be made to have fine resolution due to the severely compromized copper circuit config. The winding and interleaving lay is very screwed up by the huge circumference difference in the outside and inside of the core. On the inside, the windings are piling up; on the outside, the windings are spaced apart, and the next (interleaved) layer is falling into the spaces.

In practice, this appears to be true. There is an earlier product designed by Van der Veen, which I have not tried either. I haven't heard much about them.

Aloha,

Poinz
AudioTropic

[kevinkr]

Originally Posted by Poindexter

There is an earlier product designed by Van der Veen, which I have not tried either. I haven't heard much about them.

Aloha,

Poinz
AudioTropic

Actually pretty widely used, and properly designed toroid OPTs are fine as long as you make sure there is no significant level of dc flux in the core.

Both Amplimo and Plitron make van der Veen designed toroidal OPTs.

Menno van der Veen, audio electronic research & consultancy

FWIW I think the winding argument stated in an above post is a bit specious - toroids are rather commonly used in non-audio specific applications where very wide bandwidth and good linearity are required. One can loosely make the same argument for the EI transformer, and what is often the case is that a toroid may offer much higher permeability in a given volume and much lower excitation losses as well. The big problem is it is hard to make toroids that can handle significant dc flux, I have seen this done with cut cores, but have not worked with or heard an amplifier based on such a core.

[jrenkin]

Originally Posted by kevinkr

Actually pretty widely used, and properly designed toroid OPTs are fine as long as you make sure there is no significant level of dc flux in the core.

Both Amplimo and Plitron make van der Veen designed toroidal OPTs.

Menno van der Veen, audio electronic research & consultancy

FWIW I think the winding argument stated in an above post is a bit specious - toroids are rather commonly used in non-audio specific applications where very wide bandwidth and good linearity are required. One can loosely make the same argument for the EI transformer, and what is often the case is that a toroid may offer much higher permeability in a given volume and much lower excitation losses as well. The big problem is it is hard to make toroids that can handle significant dc flux, I have seen this done with cut cores, but have not worked with or heard an amplifier based on such a core.

So how do I avoid DC flux in my toroid? Is push-pull topology enough?

[piano3]

Only if it is nearly perfectly balanced

[Shoog]

I have advocated and used power toroids in almost all of my amps as OT. They have always worked well with bandwidth from 10hz to at least 50khz. The theoretical critisms of toroidals as outputs just don't map to my experience. They win over EI on having clean bandwidth, and no hysterics losses which would tend to blur low level detail at crossover and low signal levels (ie almost all of the time).
This is for severely none optimized toroidals. The Piltron ones are highly optimized and are supposedly the most neutral OT available. The Antek ones seem to be very badly designed, they probably tried interleaving, which boosts up the already high interwinding capacitance.

My toroidals will tolerate little more than 1mA of imbalance and because of this I use carefully matched CCS (simple LM317 type) to impose DC balance. Alternatively Garter bias will balances things adequately.

Shoog

[piano3]

Hello Shoog,

I was wondering what would be the highest B+ you would risk using with these toroids; after all,if you parallel the secondaries that would seem to allow the use of a range of tubes and not only the low impedance type?

Best wishes, N.A.