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RE: SRPP/5687 - love it or hate it ?

79.75.11.18

richardcooper2k

In Reply to: RE: SRPP/5687 - love it or hate it ? posted by RhythMick on December 07, 2007 at 01:43:16

have you tried 7119 instead of 5687 - this gives a different sound which some people like ?

mixing up topologies like srpp and set often gives a better sound as the associated sound artifacts are different so the don't add up if you see what i mean. if you follow one stage with another of the same topology and they have similar distortion spectra, etc then you increse colouration whereas if they're different they can cancel to a degree. this is why you don't always get improvements by using more of the same ( including using all the same coupling caps). to get an improvement often requires thinking out side the box and coming up with something new.

i have heard more criticism of the 6ns7 part of the kit circuit. for example look at http://diyparadiso.com/teksten/issue1-2/ANkit1mod1.htm. other people have just bypass the 6sn7 and taken the input straight to the volune pot, but not everyone liked the sound of that one.

you could also look at http://db.audioasylum.com/cgi/m.mpl?forum=audionotekits&n=154&highlight=6sn7&r=&ses
where thorsten also suggests trying an ultrapath capacitor ( i think thats what its called)

Follow Ups:

7044 should sub for 5687, too (nt) - SteveBrown 06:37:24 12/12/07 (0)
nt
RE: SRPP/5687 - love it or hate it ? - RhythMick 03:29:31 12/09/07 (2)
the link to the article is interesting but slightly confusing. The circuit diagram doesn't say what the valves are (I'm assuming the second is the 300B), apart from the rectifier (GZ37 which I like). What the H is that big yellow thing - is that the Panasonic volume pot ?

He says he hated the sound. That I differ on, after the mods I've already made I think it sounds superb.

The only reason I was considering trying a change was a) from what I've heard and read push-pull is to be avoided at all costs and b) I like to experiment and improve. I loved my sound 3 weeks ago, but I'm really glad I decided to change the driver board for hard-wired with better components.

Perhaps the biggest lesson is to trust my ears more than articles. I'm still interested to hear what others have tried though.

I'm going to focus my efforts on the power supply next. I'm going to convert it to choke-regulated. I've ordered a new AudioNote Choke and am going to make it LCLC with 47 & 100 as a pi-filter. Only question is where to fit the second choke !
- RE: SRPP/5687 - love it or hate it ? - GTCharlie 17:35:34 12/09/07 (1)
  Hi Mick. A choke input filter could bring great improvements, BUT do you have enough voltage out of the 2ndary? and/or the rectifier? Supply for input and driver can be adjusted via the dropping resistors, but B+ to the OPT could be iffy (and this could change load-lines). One way to accommodate all that is to locate the power supply (mains transformer, rectification, chokes/caps) in a box separate from the electronics. Another option is to use a choke (say 10Hy/100mA) to decouple the pre/driver from the final stage (instead of the 2k2 or 2k7 dropping resistor). Yet another mod would be to use another transformer to supply the filaments (the 6SN7, the 5687 and the 300B), and unwinding the 2ndary of the present AN transformer (I suspect over 200 DCR), and re-winding for (1) higher voltage to allow choke input filter, and (2) lower DCR for more dynamic response. You can tinker with the 5687 ... but SRPP is a complicated animal, (balancing the push and the pull, and matching impedance) and I'd rather leave it as it is, unless you want to explore parallel or cascaded, etc.... (a note : in a later design, Andy Grove used a parallel 5687, cathode, to 300B). 90 percent of the fun is in the "doing" ...
  - RE: SRPP/5687 - love it or hate it ? - RhythMick 00:59:02 12/10/07 (0)
    Thanks Charlie, all good food for thought there. We had a concern about the voltage after the LCLC filter but actually I had to go through a process of reducing my voltage to get it all right. I have 246V at the wall socket, the mains Tx was wired for 230V and all in all I was measuring 529V at the 300B Anode ! I re-wired the Mains TX for 240V and used a 200R dropper resistor on the leg of the rectifier. I'm going to move to LCLC and remove that dropper then remeasure and rethink. When it's right I'll drill the holes to mount the chokes (and move the rectifier valve base across towards the 300Bs).
    
    Of course I could rewire and remeasure and find (as you indicate) that I'm down on voltage. I'm running my 300Bs gently as well at 58mA which takes a bit less out of the power supply. If I need more I'll look a your suggestions, all of which I'm VERY grateful for - thanks !
    
    If needed I'd be inclined to use a separate Tx for the filament supplies.
    
    How would moving the power supply into a separate box help ? It's something I plan to do anyway, but not to gain voltage ? I must have misunderstood.

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