F5, Antek out, what transformer?

Starting a F5 build, if built chipamps w/smps and tube guitar amps but this will be my first big boy power amp build.

A few questions:

A) Antek is out of stock for a couple of months. I've got a baby due in May so I don't have much time to get this done before all free time and personal freedom will be lost. 18+18v, 400va-ish transfomers seem hard to find. I don't have the time or money for a custom job. US voltage, what's the next option other than Antek?

Two of these Avel 18+18, 250va might work. Didn't want to go dual mono but it could work. Looks like they would just fit side by side in the Diyaudio 4U case. But they would be awfully close to the heatsinks. I would rather use a single transformer.

Avel Y236651 250VA 18V+18V Toroidal Transformer 122-620

B) Is there any recommendation against using the diyaudio power supply board with the seperate diode board instead of the bridge rectifier like Pass uses?

C) This is a simple amp with few parts. Upgrading all the resistors from dale to PRP or something would be cheap. Is this a good idea? Money better spent elsewhere? Then where?

D) Pass states that the F5 is largely immune to input impedence mismatches. Why is everyone using a passive buffered preamp with this things? Seems that a single volume pot would be better if passive is your preference. Why the buffer?

E) Lots of people want more gain. Should I build it with stock resistors/gain or immediately bump up the gain with a resistor swap? I'll be using a passive preamp, possibly with a tube buffer.

Thanks.
 

AudioSan

Member
2009-02-12 7:47 pm
Starting a F5 build, if built chipamps w/smps and tube guitar amps but this will be my first big boy power amp build.

A few questions:

A) Antek is out of stock for a couple of months. I've got a baby due in May so I don't have much time to get this done before all free time and personal freedom will be lost. 18+18v, 400va-ish transfomers seem hard to find. I don't have the time or money for a custom job. US voltage, what's the next option other than Antek?

Two of these Avel 18+18, 250va might work. Didn't want to go dual mono but it could work. Looks like they would just fit side by side in the Diyaudio 4U case. But they would be awfully close to the heatsinks. I would rather use a single transformer.

Avel Y236651 250VA 18V+18V Toroidal Transformer 122-620

B) Is there any recommendation against using the diyaudio power supply board with the seperate diode board instead of the bridge rectifier like Pass uses?

C) This is a simple amp with few parts. Upgrading all the resistors from dale to PRP or something would be cheap. Is this a good idea? Money better spent elsewhere? Then where?

D) Pass states that the F5 is largely immune to input impedence mismatches. Why is everyone using a passive buffered preamp with this things? Seems that a single volume pot would be better if passive is your preference. Why the buffer?

E) Lots of people want more gain. Should I build it with stock resistors/gain or immediately bump up the gain with a resistor swap? I'll be using a passive preamp, possibly with a tube buffer.

Thanks.
you can almost fit 3 of those avel transformers side by side in that chassis(360mm internal with)

i would have increased the gain to 22db when used with a buffer.
 
Hipcheck: Thanks for the info...the ebay Antek has quad secondaries and is huge. It's in Seattle, I am in Seattle. That's good. What do you do w/the unused secondaries? Just tape em off? I'll look into that Plitron too. Not sure if 300va is enough though.

Bugz: Looks like the group by is gonna take another month to sort out and who knows how long to manufacture.

Audisan: Your right. Two of those Avels would fit. My math was wrong. I am a little scared of wiring for two transformers, and really is there that much benefit to going with two transformers and a single power board? I could see the benefit with seperate trannies and seperate boards but I am trying to keep it simple as this is my first build.

Thanks for the info guys. I appreciate it.
 

AudioSan

Member
2009-02-12 7:47 pm
Hipcheck: Thanks for the info...the ebay Antek has quad secondaries and is huge. It's in Seattle, I am in Seattle. That's good. What do you do w/the unused secondaries? Just tape em off? I'll look into that Plitron too. Not sure if 300va is enough though.

Bugz: Looks like the group by is gonna take another month to sort out and who knows how long to manufacture.

Audisan: Your right. Two of those Avels would fit. My math was wrong. I am a little scared of wiring for two transformers, and really is there that much benefit to going with two transformers and a single power board? I could see the benefit with seperate trannies and seperate boards but I am trying to keep it simple as this is my first build.

Thanks for the info guys. I appreciate it.

i would use 2 PSU boards if your using 2 trannsformers.
 
Amveco 600va 18v+18v.

Planned build is the following:

diyaudio 4U chassis
Fairchilds (maybe Toshibas)
PRP signal resistors
Panasonic (maybe Mills) power resistors
8 x 15,000 panasonic THSA power caps

Looking for matched 2SK170 jfets now if anyone has a source. Also looking for a pair of FQA12P20 and FQA19N20.

Planning on running a Thorens TD145 w/Denon 110 into a Jfet phone stage (boozehound) then a passive pre (25K ladder pot) and possibly into a Yaqin CD2 tube buffer before the F5. Speakers are Focal Chorus 714V's.

Currently I am using the same front end set up into a hotrodded Tripath 2050 amp with outboard 24V SMPS. It sounds very good I think. It will be interesting to see how the F5 compares. The only other amps I have had in this system are receivers and a Rotel integrated. Frankly, the tripath amp has sent all the other amps packing for home so far.