Output Transformer Question?

[Cloth Ears]

Hi,

I was just looking at the Miniblok SET amp on Fred Nachbaur's site. I noticed that the +/- 3dB points for the amp were 40Hz and 9kHz. And then I remembered reading (somewhere - possibly here in this forum) about how you could raise or lower this frequency range by changing the output transformer.

How does this work? I'd assume that by altering (or replacing) the transformer that you could get this amp to shift its' range to (say) 100Hz to 22.5kHz (or possibly 20Hz to 4.5kHz) by using a different transformer. Have I been reading fairy tales (or did I forget my little blue pills this morning), or is this a real possibility?

If it is real ("Toto, I've got a feeling we're not in Kansas anymore"), is there a thread (or other info somewhere) that I can read? I've had a look at some transformer sites, and they seem to offer wider range transformers (for more money, of course), but not specifically higher or lower frequency range items.

I'm asking as I'm looking at maybe trying to put together a tweeter amp (active 4-way) as a project...sometime.

[BudP]

Cloth Ears,

You can indeed tailor an E/I SE output transformers frequency response, though it is not usual to do so.

The only site I know of where that has been discussed and implemented is over at Romy the Cats hidey hole. In his Meliquides threads he tells about using dedicated SE amps (DSET's) for specific frequency ranges.

If you haven't been there, be ready for some true Russian intellectual expressionism, filtered through a relatively recent and still incomplete understanding of American English. Quite a hoot most of the time.

http://www.goodsoundclub.com/

Iwill be happy to help as you post.

Bud

[Tweeker]

Try Edcor for nice budget SE OPTs.

The Edcor meets the 6AV5.

Cheap SE OPTs.

The $19 Edcor XSE 15-8-5K may be your ticket, though it might not be suited for the Miniblock.

[tubelab.com]

The $19 Edcor XSE 15-8-5K may be your ticket, though it might not be suited for the Miniblock.

I breadboarded an amp very similar to the Miniblock. I used a 6EM7 and a variable power supply. The Edcor XSE 15-8-5K works very well in this design. The frequency response goes up to about 40 KHz. At the power level that this amp makes (just over 1 watt) saturation should not be a problem either. You should get full power down to near 30 Hz.

[kevinkr]

Originally posted by tubelab.com


I breadboarded an amp very similar to the Miniblock. I used a 6EM7 and a variable power supply. The Edcor XSE 15-8-5K works very well in this design. The frequency response goes up to about 40 KHz. At the power level that this amp makes (just over 1 watt) saturation should not be a problem either. You should get full power down to near 30 Hz.

Hi George,
Do you think these transformers (or the 16 ohm version) would perform adequately as a headphone amplifier output transformer? I'm planning on using 71A as outputs and I am having a little trouble finding something suitable, cost isn't the issue, but I'd like something with a reasonably sized core for the low power involved, and something I can get in the very immediate future.. Do you have any other suggestions?

[Cloth Ears]

Originally posted by BudP
The only site I know of where that has been discussed and implemented is over at Romy the Cats hidey hole. In his Meliquides threads he tells about using dedicated SE amps (DSET's) for specific frequency ranges.

Bud,

I had a bit more of a search and found a post where EC8010 had mentioned it.

I had a look a Romy the Cats site - I can see I'm going to have to spend Easter going through that looking for gems.

Bear in mind this is more an 'interest question' - as I may never get around to building anything more complicated (electrically) than a passive crossover. I work with computers that run on 3-phase power, and it has left me somewhat in awe of the speed at which the magic smoke can come out.

The plan was that once I had my active up and running, that I might experiment in building an amp for the tweeter. Or possibly use it for a 'full-range' FLH/BLH that I dreamed up a couple of months ago.

P.S. the tweeter in question is an AuruM Cantus unit (G3, I think). Fairly flat impedance at around 7.7 to 8 ohms in the range I intend to use it (above 5k).

[tubelab.com]

Do you think these transformers (or the 16 ohm version) would perform adequately as a headphone amplifier output transformer?

Unfortunately I am not the right person to ask about a headphone amp. I am not much of a headphone person (my head sweats too much). I built a TubelabSE based headphone amp for a customer who drove 500 miles on 3 consecutive weekends to listen to all of the possible tube - transformer - headphone (he had 3 pairs) combinations.

He listened to every transformer that I had in my lab with 01A's, 30's, 31's and 45's. I did not have any Edcors at the time since I had not heard of them yet. We did try some Hammond 125CSE's and he did not like them at all. What did he like? The situation was made more complicated by the fact that one set of his headphones were high impedance. After trying about 30 transformers I tried a pair of vintage UTC LS57 push pull transformers (not bothered by 10 mA of current). The customer was thrilled with these transformers and 31 type tubes. I was unwilling to part with my set, so he got a pair from Ebay. He paid more for those transformers than I do for entire amplifiers. In fact he paid more to have the cabinet made than I pay for amplifiers.

I can't say what the Edcors would do with headphones since the only headphones that I have came from WalMart!

[dsavitsk]

Originally posted by kevinkr
Do you think these transformers (or the 16 ohm version) would perform adequately as a headphone amplifier output transformer?

In my headphone amp, I tried the 8 ohm version of the edcors with 32ohm phones (with and without a resistor in parallel) and the edcors were clearly bettered by some James which were in turn clearly bettered by some custom wound electra-prints. The EPs were only $160 or so for the pair.

[BudP]

Keninkr,

I will have a pair of SE 3200 ohm primary reactive impedance, to match driver tube (1/Rp + 1/Ra) + OPT primary DCR, in about 3 weeks. They have a 1:.875 turns ratio with the secondary CT'd and a separate winding tapped for 12, 24, 48 and 196 ohms for headphones. One for each channel is needed and due to Nickel core, not cheap at all.... though, with micro gapped core that will tolerate 40ma DC without caving and 16vac drive level tolerance, yes for a preamp and Cathode coupled without a blocking capacitor at that, you can use them for a very wide range of tubes.

If interested email me and I will shiver your timbers with a number..... actually, I use the things and would not ever go back to a capacitor output preamp, even without my bias...

Bud

[kevinkr]

Thanks Budp,
I need something in the 5K range and am planning on a conventional SE common cathode output stage, so this doesn't sound quite like what I need this time around.

Doug, thanks for the tip on the Electra-Prints, I think I will contact Jack and see what he can do. The price you mention is well within the acceptable range.