I had some Lundahl LL1540 which I was using in 1:2. Didn't like them at all. A Hammond 124B was better in 1:3. Smooth and musical but not as transparent as the Hammond 1140-LN-C, plus the treble is a little down on the 124B.
Yes, that one. Don audio is €45 each. That's very good value. It's a studio quality transformer containing nickel.
This 1:4 SUT opened the doors for me to 2 stage all-DHT amps. I'm never going back - this is the end game. Ale Moglia uses a similar setup - Lundahl LL7903 into 47 into 300b. The 1140-LN-C is considerably cheaper and may well be of a similar quality - I haven't compared them. But I'm happy with the Hammond.
https://www.bartola.co.uk/valves/2020/07/25/300b-se-amp-47-driver/
This 1:4 SUT opened the doors for me to 2 stage all-DHT amps. I'm never going back - this is the end game. Ale Moglia uses a similar setup - Lundahl LL7903 into 47 into 300b. The 1140-LN-C is considerably cheaper and may well be of a similar quality - I haven't compared them. But I'm happy with the Hammond.
https://www.bartola.co.uk/valves/2020/07/25/300b-se-amp-47-driver/
I asked because there is a couple of 1:4 Lundahl LL1676 for sale https://www.diyaudio.com/community/...676-x-2-lundahl-for-sale.395971/#post-7273145 but looking for at the specs it seems Hammond is better?
I own these 15K-300R double c-core amorphous so 7:1 and sounds very very good the primary inductance is 54H
I own these 15K-300R double c-core amorphous so 7:1 and sounds very very good the primary inductance is 54H
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The downside of using random x:1/1:x transformer as stepup is the source impedance.
If you want to use it to "gain" the input signal and use it with "any" source (not dedicated "own" DAC->amplifier), the most of these transformers are useless.
The used sources output impedance usually in kOhm range (most of them -mainly SS ones- has few hundred Ohms, but others even 1-5k).
If you choose such 1:x transformer which developed for large/r/ source impedance the result would be satisfactory.
If you select such transformer which has -for example- 600R as recommended source impedance and use it with some kOhm source, the result will be unpredictable.
If you want to use it to "gain" the input signal and use it with "any" source (not dedicated "own" DAC->amplifier), the most of these transformers are useless.
The used sources output impedance usually in kOhm range (most of them -mainly SS ones- has few hundred Ohms, but others even 1-5k).
If you choose such 1:x transformer which developed for large/r/ source impedance the result would be satisfactory.
If you select such transformer which has -for example- 600R as recommended source impedance and use it with some kOhm source, the result will be unpredictable.
I load the 15KΩ primary with 50Ω source impedance & the secondary 300Ω with 100KΩ or more, so no problem.
Felipe, that's what you're talking about is -line- output (7:1) transformer.
I wrote about stepup -for example 1:4- transformer choosing problems at the input of the amplifier.
I wrote about stepup -for example 1:4- transformer choosing problems at the input of the amplifier.
Yes step up at the input could be problematic because you are decreasing the input impedance of the amplifier.
Strangely, I can order Hammond 1140-LN-C from Europe or the UK for about half the price as in the US, even with shipping and foreign transaction fees. I've written KGA in the UK to ask whether I would need to pay VAT. Shipping from a German or Italian retailer would be 29 euro.
Andy or anyone else: have you tried/compared the Sowter 1:4 input transformers, which cost about 70 GPB excl. VAT? I have a pair of Sowter MC step-up transformers in front of a phono preamp and love them. The 8540 are center-tapped on the secondary side to allow for use in PP applications (not necessary in this case), while the 4383 are center-tapped on the primary side for phantom powering of microphones, etc.
https://www.sowter.co.uk/specs/8540.htm
https://www.sowter.co.uk/specs/4383.php
The Cinemag CMLI-10/600 might be a good product, too. I've inquired about pricing and will let you know when I hear back.
https://cinemag.biz/line_input/PDF/CMLI-10-600.pdf
Indeed. The Cinemag mentioned is made for a 600 ohm source impedance.
I haven't tried Sowter, Cinemag, Jensen or any of the usual suspects. I have a pair of Lundahl LL1554 but that also looks like 600R source. I've seen UTC A-20 listed a few times - that looks like a good unit that can work in 1:3. I think there's a thread on all these SUT choices somewhere here.
On that subject, has anybody tried permalloy transformers from Aliexpress? Are those any good for step-up?
Nothing "wrong". Just depends on what your source is. If it's a DAC it could be OK. If it's a preamp it would need a low output impedance, so not a valve preamp unless it had a mu stage or cathode follower or step-down or the like.
https://www.canford.co.uk/TechZone/Article/CableImpedance
Interesting read on the origins of the 600 ohm convention in early telecommunications systems and later broadcast studio installations. 600 ohms derives from long cable runs (many kilometres) using telegraph posts, which ended up at around that figure. But while studios initially worked on a 600 ohm standard for cable runs (more than was typically the case), this was then reduced to a more typical 100 ohms which also suited digital transmission.
https://www.canford.co.uk/TechZone/Article/CableImpedance
Interesting read on the origins of the 600 ohm convention in early telecommunications systems and later broadcast studio installations. 600 ohms derives from long cable runs (many kilometres) using telegraph posts, which ended up at around that figure. But while studios initially worked on a 600 ohm standard for cable runs (more than was typically the case), this was then reduced to a more typical 100 ohms which also suited digital transmission.
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600 ohm is high but if you use tubes surely no problems, almost always high input impedance....
The issue isn't driving the following stage, as you say tubes have a high input impedance. The issue with a step-up where the primary is rated for 600 ohms is what is connected to the primary, since it may not have enough inductance. This is assuming I'm understanding these kind of transformers correctly. For example, in 1:4 my LL1554 has all 4 primaries connected in parallel.
Well primary impedance depends how secondary is loaded, but your are right could be problematic depending the source impedance connected to the 1:4 step up. I'm not sure about the role of inductance if higher is better.