Quick clarification. The AVC's are functioning as both output autoformers and volume controls. Since I didn't need the LL1676's as output transformers as I originally intended to use them, I put them on the preamp input as noted above. It's totally silent, no hum, buzz, or hiss. I'm very happy with the sound so far.
I'm using battery grid bias so that I can run the autoformer return back to the tube cathode since it is at ground potential. The autoformer cannot handle the DC which would be present in a cathode biasing arrangement. I've found from experience that returning the current to the cathode in a parafeed setup sounds better than returning it to ground.
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Yum Yum, good taste is always cost high!
Following OPTs available used Finemet core.
Andix audio: RT20K600
Noguchi : FM20K600CT FM24K600CT
What would be a good transformer readily available to buy online to start building one of these pre-amps?
There are so many schematics, and I am still trying to pick one. I have a friend I can call out for help and advice and of course all 205 pages of this amazing "thread", though this seems much to informative to be just a thread...
Thanks
Mark
P.S I haven't gone thru all of the pages yet, but I am working on it.
There are so many schematics, and I am still trying to pick one. I have a friend I can call out for help and advice and of course all 205 pages of this amazing "thread", though this seems much to informative to be just a thread...
Thanks
Mark
P.S I haven't gone thru all of the pages yet, but I am working on it.
Hi!
Balanced outputs would help to reduce noise pick up in the interconnect from preamp to power amp, but only if the power amp has a balanced input. With an output transformer you can have both. PN me if you are interested to give the Lundahl LL2745 a try, which has been developed for the 26
Best regards
Thomas
Balanced outputs would help to reduce noise pick up in the interconnect from preamp to power amp, but only if the power amp has a balanced input. With an output transformer you can have both. PN me if you are interested to give the Lundahl LL2745 a try, which has been developed for the 26
Best regards
Thomas
Hello Mark! Welcome to the thread.
Thomas is one of the Big Daddies in this and he's a safe bet to sort you out - he started us all off with filament bias, and what a pleasure that has been. You'll need a couple of Rod Coleman's boards for the supply, and they are cheap and very effective and come with comprehensive instructions, including filament bias use.
Thanks to this thread, we've evolved this design into a real building option which can scare off multi thousand dollar commercial products. We've got quite a big pool of users now.
I remember reading in a post at least 5 years ago that "the 26 was the king of preamp tubes" and now we have the proof!
There's a rogue break-off group including myself who've gone over to the 4P1L, and most of the theory and practice applies to that as well, including filament bias. I use a Lundahl LL1660/18mA for that, which I got from Thomas. He's the guy for the transformers.
Andy
Thomas is one of the Big Daddies in this and he's a safe bet to sort you out - he started us all off with filament bias, and what a pleasure that has been. You'll need a couple of Rod Coleman's boards for the supply, and they are cheap and very effective and come with comprehensive instructions, including filament bias use.
Thanks to this thread, we've evolved this design into a real building option which can scare off multi thousand dollar commercial products. We've got quite a big pool of users now.
I remember reading in a post at least 5 years ago that "the 26 was the king of preamp tubes" and now we have the proof!
There's a rogue break-off group including myself who've gone over to the 4P1L, and most of the theory and practice applies to that as well, including filament bias. I use a Lundahl LL1660/18mA for that, which I got from Thomas. He's the guy for the transformers.
Andy
Hi Mark,
I recently built my third incarnation of the 26 preamp using the LL2745 provided by Thomas. I'm very happy so far with its sound and overall tone. Starving filaments slightly can eliminate microphonics (if you have any globe ones) and also rubber suspension on the sockets.
Rod Coleman boards are invaluable if you are looking to have a hum free preamp using DC and avoid capacitors using filament bias.
I don't have my latest diagram at hand as an away from home. Can post it when back if there is any interest
Thanks
Ale
I recently built my third incarnation of the 26 preamp using the LL2745 provided by Thomas. I'm very happy so far with its sound and overall tone. Starving filaments slightly can eliminate microphonics (if you have any globe ones) and also rubber suspension on the sockets.
Rod Coleman boards are invaluable if you are looking to have a hum free preamp using DC and avoid capacitors using filament bias.
I don't have my latest diagram at hand as an away from home. Can post it when back if there is any interest
Thanks
Ale
Yes, and me being a promoter of a great tube blamed to be very microphonic. 4p1L as a preamp is fantastic if properly used. Needs care on microphonics though. Filaments in parallel and starved at 500mA and easier for filament bias. 4P1L doesn't like currents below 20mA (check curves) so either the Hammond gapped for 30mA or the LL1660/20mA should work best. I just ordered from Thomas an LL1660/20mA so will report results soon
There is a multi-tapped secondary OT from Pieter which can provide dual function (OT and Volume control) in one. Apparently has had great feedback.
Thomas, can you share your experience with The tribute's OT?
Thanks
Ale
Hi Ale & All
earlier this year I discussed a lineoutput transformer with Pieter which should have it's secondary tapped as volume control. He initially wound a pair for me for a 10Y linestage runnign at 20mA. The ratio is 1:1 with 24 2dB taps.
Here are some photos:
VinylSavor: The Modular Preamplifier, Part 11: 10Y linestage
I will write a more detailed report about it within the next weeks
Obviously a integrated transformer/TVC has the advanatge of less parts in the signal path, while with separate transformer and AVC each can be optimized separately for it's task.
I borrowed both versions to a customer. He found that the tribute TVC has more dynamics compared to a spearate solutions, while the latter showed a better depth in teh soundstage. Both versions sound very good. The Tribute solution has teh dadvantage of less parts and a bit easier wiring.
I personally would prefer the tribute but will continue to have both variants in my offering.
Anybody interested in these can also contact me. I have an agreement with Pieter regarding sale of these. I will have several pairs by end of November. I can offer a pair for free trial to DIYaudio members. (Sorry for the commercial plug)
Best regards
Thomas
earlier this year I discussed a lineoutput transformer with Pieter which should have it's secondary tapped as volume control. He initially wound a pair for me for a 10Y linestage runnign at 20mA. The ratio is 1:1 with 24 2dB taps.
Here are some photos:
VinylSavor: The Modular Preamplifier, Part 11: 10Y linestage
I will write a more detailed report about it within the next weeks
Obviously a integrated transformer/TVC has the advanatge of less parts in the signal path, while with separate transformer and AVC each can be optimized separately for it's task.
I borrowed both versions to a customer. He found that the tribute TVC has more dynamics compared to a spearate solutions, while the latter showed a better depth in teh soundstage. Both versions sound very good. The Tribute solution has teh dadvantage of less parts and a bit easier wiring.
I personally would prefer the tribute but will continue to have both variants in my offering.
Anybody interested in these can also contact me. I have an agreement with Pieter regarding sale of these. I will have several pairs by end of November. I can offer a pair for free trial to DIYaudio members. (Sorry for the commercial plug)
Best regards
Thomas
I would be very interested in trying one - what will be the price for a pair?
Ale,
Does starving filaments (in general) influence tube characteristics? I take it for granted the power limit goes down because of the diminished space charge...
Rgds, Jaap
Hi!
rp goes up when starving filaments. How much depends on the tube.
Best regards
Thomas
rp goes up when starving filaments. How much depends on the tube.
Best regards
Thomas
I think there are various preferences for how much to starve the filaments. A colleague in London here uses 3.7v in series, and he says also Pearl tube coolers help cut down on microphonics. I haven't done any really detailed listening - I'm using 1.9v and 600mA generally. That would translate as 3.8v in series. Somewhere around 1.85-1.9v in parallel seems OK. Ale has been experimenting.
Hi Thomas
discussed this with Pieter (Tribute) around a decade ago when he told me about his idea to combine the TVC/AVC with the output transformer. Cool that you did it
The disadvantage is that you have no constant output impedance because it increases with increasing of the volume. In your configuration with ratio 1:1 you have the max. output impedance of tubes plate resistance - assume the source input from the next stage is large. So with high plate resistance of the 10Y you deal with high output imedances ...
Anyway, with short cables to the power amp you can ignore it - more or less.
You mentioned it and as manufacturer it would be helpful to discuss technology only and not brands.
BR, Joao