Good stuff. The only thing that may need thought is that some board houses want their own .extensions for individual board layers, or have limited drill sizes, so it's always best to add a text file with the drill sizes you have used and identifiers for each layer. I usually add a pdf of the complete board as well so they can check orientation and placement.

Slowly making progress on the top plate of the chassis. It's 16-gauge steel,and I still need to trim one end off. The plate is (going to be) 16.5 x 12inches. There will be another plate for the bottom cover of the chassis,and I'm going to build a wood (pine,probably) frame for everything,and stain it a nice color. (probably something light)

Kind of a tight fit for everything,but I think I can make it work.

Here's a couple quick snaps,while I was test-fitting the transformers.
http://i199.photobucket.com/albums/a...p/PICT0004.jpg
http://i199.photobucket.com/albums/a...p/PICT0001.jpg

Well I guess I should make an update regarding the FDNR on the lowpass. It's not working as well as I had hoped. It is basically oscillating, and I haven't found a solution as yet. I think I need to read up on Open Loop gain and phase margins to get my head around the problem and work out whether it is something that is fixable or whether it is simply not suitable for a crossover frequency this low.

Tony.

Hey Tony,

I'm thinking I'll make a thread about it sometime soon and see what kind of input everyone has. Right now the blog post is kind of for my own note-keeping/sanity,but comments are always welcome!

Hi DigitalJunkie I hope you start a thread as well! perhaps a summary and a link to your blog post? People seem timid when it comes to leaving comments on the blogs. I'm not sure why! I'm not a tube guy, but it certainly sounds like you have a plan!

My limited knowledge of tube amps tells me that at 50W / channel this will be somewhat of a beast!

Tony.

Joe-

This post is of the "food for thought" variety. I don't have any definite plans to build it.

Anyway, with a slightly different buffer topology 47 Labs has already "been there, done that, got the T-shirt."...

Hi rjm,
I'm currently starting a prototype for something very similar to this as a very long term amplifier project and have looked at that website previously. I'm not sure where it will end up if anywhere really but I'll be following with interest anything you do in relation to this!
Thanks,
Joe

That´s correct. I have a DCB1 hot rodded in my rig.

If the F5 doesn´t beat my 300B mono´s, i will use him for my next project, the Auridux.
It´s a direct coupled Tube Amp for my Stax SR-404 Ltd. headphone and here i need some voltage gain

The pcb is ready for month on my Harddisk:

Hello you two,

my new S1 double crowns gave a more three-dimensional sound with more microdynamics right out of the box.
Very fascinating!!

Let´s see if and how the sound change in the next few days.

The case... You are right... My new F5 amp project came in between...

But i swear, i will make the DAC case next

And once again you beat me to it.... I am planning (already for some months) to build an F5 as well. Actually I have decided to wait for F5Turbo as I don't have such sensitive speakers....

What made you decide to go F5 instead of F4 (I remember you have a B1 as preamp?) ?

Hi Oliver,
Got some S2's as well. How do you rate the different between normal and crowns?

By the way... isn't it time to put your dac in a case already... I remember the multiplex board from last year still! ;-)

Congratulations Oliver, you are really lucky man!

It would be fine if you share your experience with those S1 doublecrown's on Red Baron.

I have searched for S1 DoubleCrowns, but stopped after found S2 - those I have obtained two years ago from one guy on ebay.
S2 in my Philips CD960 (and in my friends Marantz CD94) at beginning played worse than regular TDA1541 (non-A), but after about 3-4 weeks of moderate play(2-3 hours/day) ones showed their power

I thought I'd post an update via the comments I finally breadboarded the highpass part of the circuit and tested, and I'm happy to report that it works!!!

The resistors used were for a 2nd order L/R crossover at 200Hz. Below is a target response (orange) generated in PCD, compared to the actual measured response of the crossover (red). The orange is the loopback response of the soundcard to show that the weird phase behaviour is actually the card and not the crossover (my holm is playing up and I can't currently calibrate it).

Note that I didn't have the exact resistor values I needed, so have compromised a bit for this prototype but it is still very close.



I've also managed to improve the LP in the sim, smoothing out the dip and rise after 20Khz. The solution was to put a 220pf cap across one of the resistors in the FDNR. I'm not sure why it works but it seems to help.


So for anyone who has wondered, I am still working on this, I'm just making very slow progress. However I would like to have the completed circuit done (on a board not breadboard) by the end of March, so stay tuned.

Tony.

Hi Nazar,
Maj I use these - ECHU1H104JC9 PPS Film Chip Capacitor 0.1uF @

Regards,
Ignat

Hey, sorry I did not see your message earlier. I have no idea about who could modify your K4040 in th UK. You may want to check these people, but I have no experience with them. I suggest that you collect information over time and do it yourself. It is not that difficult, you'll learn in the process, and will have fun!

The update:

The next day I went to measure the offsets and both were under 20 mV. It was no sweat to get them under 10 mV, where they stayed.

No hum, no noise, the amp plays music just fine! Go figure.

More on the sound and a comparison to my Gainclone in a follow up post.

Hi Teabag,
Is that a keratherm red in the picture? If so, it does not need any goo.

So I've spend some time over the weekend, comparing both. If I had to score it, and I am reluctant to, I'd say Sapphire 92, Treasure 87. That's not so much an accurate assessment as it is a starting point for the discussion.

Both amps are very good, and the subtle difference in sound is within spitting distance of the differences induced by changes in the volume, so level matching is crucial ... or to put it another way, at the end of the day the differences are probably not all that important. But since it interests me as a designer, I am insisting on drilling down on this as far as possible.

Ok, so the main difference, and the one that is immediately obvious I think to anyone even on casual listening, is the relative distance to the sound-stage. With the Treasure, it's a fairly traditional you-are-here-the-music-is-over-there affair, everything is arranged out in front of you. The Sapphire moves you right up to the edge, surrounding you with the musical events in every direction.

There are arguments in favor of both, but I generally preferred the more close up, enveloping presentation of the Sapphire.

Everything else I could discern in the way of differences were much further towards the limits of detect-ability.. and I am proportionately less confident in the claims.

Depending on how one decides to spin it, the Sapphire is either more extended in the bass and treble, or has some audible distortion in both extremes that can artificially accent transients. Is that extra shimmer and slam I hear in the Sapphire really on the recording or is it added glitter and rumble produced inside the amp itself? I'm honestly still not sure, and I'm not sure whether I'd call it a good thing or a bad thing either. Overall though I's say the Sapphire is more percussive, while the Treasure is clearly smoother.

Finally, there's a matter of what you might call "grain" or "haze". That last word in clarity that obstructs the perfect realization of the music. Here both the Treasure and Sapphire amps miss out by similar measures but in rather different ways. The Treasure has a slight cloudiness in the upper midrange, sounds seem to press together and details are lost or obscured. The Sapphire is resolutely three-dimensional, with wonderful blackness between the sounds, but perversely has a residual graininess over everything that means that sounds, while more realistically delineated, are not as cleanly reproduced as by the Treasure.

I've always thought that the Sapphire amp was still needing a couple of final tweaks, I haven't had the time to do the kind of sea-trials I did with the Phonoclone for example, trying out and comparing different versions - it was a "build it once, build it twice, done!" affair.

The events of the weekend has convinced me I need to go back and try out a couple of things with the Sapphire. First and foremost a quick op amp substitution, but there are a couple of other things I could try to reign in perceived instability or interference that might be adding grain.

That hammertone finish is hard to beat for good looks. Reminds me of a Hammarlund ham receiver I once had.

Hi,

I have just bought a bog standard k4040 from Ebay and this is my first valve amp or valve anything for that matter! Actualy I don't think the sound is too bad but their is still room for improvement and by the sound of the mods that you have made i think this amp has real potential! Do you know of anyone in the UK that could do these mods for me?

Many thanks

Steve