Hi Salas,
I'm loving the preamp, but since it's driving a Pass M2I'm finding that I need a little more gain. So I'm going to bump it from 3X to 4X, but while I've got it apart to do that I'm wondering if there is any upside to increasing the bias (~ 112 mA now). I still have the proper resistors from Teabags kit so it would be simple. I runs very cool right now, it is heat sinked to the entire case.
Paul
I'm loving the preamp, but since it's driving a Pass M2I'm finding that I need a little more gain. So I'm going to bump it from 3X to 4X, but while I've got it apart to do that I'm wondering if there is any upside to increasing the bias (~ 112 mA now). I still have the proper resistors from Teabags kit so it would be simple. I runs very cool right now, it is heat sinked to the entire case.
Paul
It would make better THD if ever used with under 70 Ohm headphones is one objective thing with high bias. As it runs very cool now in your build try the heat with high bias and have its extra "traction" there just in case. I don't think I could hear anything better with that when in line mode though. But maybe in your system and to your ears you can. You tell us. Just don't estimate the higher gain better suited result as partially due to the high bias. To really say it would take doing the new gain first, the new bias next.
I meassured it with 230R and got 21.65V and 21,72V respectively. But I will leave them for now. Hopefully they will come to use some other time... =)
I will get the proper transformer anyway, no point in saving on that. I've seen all kinds of transformers beeing used here, so maybe it's not that important, but what would you recomend for a dual mono build? I will use it as both a preamp and for my headphones (AKG 7xx at 62Ω).
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They look like high for what's on their labels. Which brings extra heat at the supplies sinks. A couple of 18V-0-18V 50VA transformers will be good for you. Also aim to circa 150mA bias which is better for the 7xx.
The goal with the trafos is not to have less than 22V DC at the smoothing capacitors when the mains are at their anticipated lowest but not to bring too much extra wasted in heat when the mains are at their average either.
The goal with the trafos is not to have less than 22V DC at the smoothing capacitors when the mains are at their anticipated lowest but not to bring too much extra wasted in heat when the mains are at their average either.
I had a quick shop around for 50VA 18+18V toroid transformers and started wondering about the differences between the different makes. Two of them are 50% heavier, and the Hammond is twice the price. It's natural that there are prize and manufacture differences, but theese are quite significant, so I wonder if there might be something that I'm missing?
I noticed that shielding is an extra $15 on the Airlink, which adds up to $36.-
Toroidy (Poland) 0,5kg (potted) $25.-
Airlink (GB) 0,75kg (21 + 15 =) $36.-
Hammond/Mouser (EU) 0.7kg $51.-
Any thoughts on this?
//Ronny
I noticed that shielding is an extra $15 on the Airlink, which adds up to $36.-
Toroidy (Poland) 0,5kg (potted) $25.-
Airlink (GB) 0,75kg (21 + 15 =) $36.-
Hammond/Mouser (EU) 0.7kg $51.-
Any thoughts on this?
//Ronny
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Since you are in Europe, then I suggest you look at Toroidy.
he offers a number of add-ons for potentially increasing the audio quality of his basic transformers.
His prices on a like for like comparison are very competitive. Not as cheap as the USA based retailers. But their postage costs become uneconomic for EU customers.
I forgott to write that the Toroidy 50VA is their "Audio Grade"; potted and with double shieldings. So the price is very competitive, unless there is something else I'm missing...
I notice that we are "on the same piece of ground", so where did you get yours? The Noratels are manufactured not to far away from where I live, but that that does not allways mean that they are easy to find...
Since you live in Sweden 
https://www.elfa.se/sv/toroidtransf...r_Buyable=1&page=15&origPageSize=50&simi=97.5
https://www.elfa.se/sv/toroidtransf...r_Buyable=1&page=15&origPageSize=50&simi=97.5
It would be interesting to get some comments! I'm not really worried about any of these trannies quality. I'd guess they're quite comparable, but there is obviously things for me to learn...
Since you live in Sweden
https://www.elfa.se/sv/toroidtransf...r_Buyable=1&page=15&origPageSize=50&simi=97.5
Thanks! That was a bit too obvious!
There was a ELFA shop here in town a few years ago, but they cosed it. I've never bought anything from them on-line.
Works just fine
What seems obvious isn't allways the best...
From ELFA, with free shipping, two Noratel 50VA 18+18V are $95.-
From Toroidy, with shipping from Poland, they charge $77.-
The shielded ones you linked to, but in 50VA, would be $71.- from ELFA. The question is which ones are best: Toroidy Audio Grade, or the Sri Lankan made Noratels?
Toroidy seems very competitive indeed!
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I used toroidy transformers for a diy power amp (amb beta 24). I did never measure the specs but I was impressed by the apparent quality of the product in its steel casing. I had a customized transformer made with four secondaries in the top audio quality (they have if I remember correctly three different qualities) , the price was very fair and they were very professional to deal with. I can recommend them but YMMV, of course.