Phono stage

murray johnson said:
If the design has passive eq it relies on the o/p impedance of the 83's combined with the following filtering to get the right curves. Sustituting with a different valve may well make the eq inacurate.
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Hi Murray,

There was some discussion of this on WD forum with most feeling that any effect on the curve would be extremely small, however the stage does sound different with 5751s substituted into the gain and EQ sections so this could be due to EQ errors. The final tube is simply wired as cathode follower output so that is the place to experiment.
 
Considering the tolerances of the standard WAD resistors I wouldn't think its going to matter that much.
 
murray johnson said:
I'll have to try to get to hear one of these. Most CF's I've listened to or tried building have sounded very poor.
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Where you based?
Pop over for a listen :)
 
Having disabled the dc servos and fitted the dc blocking caps to the phono, I am just letting it warm up but it has made an enormous difference - suddenly the bass guitar and drums have much more weight definition and attack. Timing is massively improved. The hum that I attributed to the transformer has also gone - so it must have been an affect of the servo as well presumably. Also the treble has improved and got cleaner. I am wondering if the bandwidth limiting affect of the cap has prevented some ringing in the TVC preamp...

Its warming up at the moment and I still need to experiment tonight with cap loading on the stepup primary. Currently it is unloaded and the emt needs about 500 pf min cap loading inc leads. Will keep you posted!
 
murray johnson said:
Hi Rob,

Way out west I'm afraid although thanks for the offer.
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The circuit is worth a go, I assume it is still on the website. If not I have the pdf's if you wanted a look, and Nick G's excellent variation of it using CCS. Sounds a little less soulful to me with the solid state CCS in but spade loads more information and generally better all round. I'd like to try an all tube CCS at some point but I've been saying that for ages :)
 
BBV,

You know perfectly well that the TVC's don't ring and that I and my scope were just imagining it.

Encouraging news on your mod though.:)
 
Cap loading should help further - as it will bring up the mid and increase the subjective speed of the bass.

I just mentioned it as a possibility ;)
 
Considering Robs findings with putting a filter on his pre-amps transformers mainly being noticeable on vinyl I'd say it is quite possible. I mean, look at that cutter ringing! Second, from what others have said to me removing DC servos in power-amps normally affects the treble making it sweeter and cleaner, not much affect at all on the bass.

Anyway, very good news Nick! I look forward to this bake-off :D Are you going to bake anything?
 
The servos are fine!

330 pf dialed in for the time being - seems like a big improvement! Will experiment over the next few days.
 
brizonbiovizier said:
The servos are fine!

330 pf dialed in for the time being - seems like a big improvement! Will experiment over the next few days.
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Welcome back - that was a short trip!
 
You missed all the fun at the weekend Nick.
Thanks to some help from Simon I now have active H2s and have become a worshiper at the church of the TVC :)
 
Ahh yes whats going on with the active H2's? I'll have to pop over to PFM in a min...

Welcome back Nick! I look forward to the bake-off but I can't make it any day this week. Late next week is good though. Sunday 27th maybe?
 
Active H2s? You now prefer tvc???

Need to liase with family first ... have to visit home some time.
 
brizonbiovizier said:
Active H2s? You now prefer tvc???

Need to liase with family first ... have to visit home some time.
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Yes active with huge f**k off heatsinks on the back :D
Pics tomorrow.

Not sure that I prefer the TVC but having heard a pair in my own system I found that my concerns over the slight lack of drive and pace were so small as to be insignificant - certainly didn't stand in the way of the enjoyment.

Oh, my valve phono drove Simon's S&Bs perfectly well - so I need to think on why it wouldn't drive yours. One thought is that the PSU has been rebuilt since you heard it.

Anyway, did you enjoy your break?
 


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