Upgrade Path from PhonoII to Phono III

[david.rogers]

Looking at the recent article from Peter in HFW and the schematic provided, it's pretty obvious that this latest design is a refinement of the earlier one. Upgrading from one to t'other without major surgery should not therefore be too much of a problem. I understand that Peter and his team will want to protect their commercial designs and ensure they don't get cloned and manufactured elsewhere, but for those of us who subscribed to, invested and suffered under WAD, it would be nice to think it would be possible to manage the upgrade without purchasing a new case, new socketry, switches etc. Has anyone thought about this? I understand that mods to the RIAA compensation circuitry were discussed in this forum and I would be grateful if someone could point me at the relevant posts. What about other component changes? Are these published anywhere? (Perhaps I missed the posts on this, if so, I apologise for going over old ground).

Thanks in advance!

[prince of darkness]

This is from the FAQ section.

http://www.wduk.worldomain.net/forum...read.php?t=145

[Ianm2]

unofficially, the changes are

3 selectable coupling caps for bass rollof
2x RC decouplers in the power rail
and of course, the time constant mod.

I think that's it, all very useful mods. , its about as good as a stock design can be, all the weak areas have been sorted, if the riaa curve is accurate, I think NickG alluded it MAY not be spot on, but I worked it out and it seemed fine if I got it right, its quite involved.

may be difficult to do as the volt rail may mean cutting tracks, and the switchable caps a bit fiddly methinks.

perhaps peter will sell the new pcb.

oh you have seen the schematic....

[david.rogers]

Thanks POD and IanM2. I would probably breadboard the switchable cap arrangements, do some listening tests, and hardwire in what sounded best to me. I am slightly bothered by the HT rail decoupling additions, and would like to include them if possible. Looking at the new schematic, V3 anode is fed by a resistor (R31/32) and decoupled by C15/16. An additional resistor (R29/30) sits on the HT rail feeding the anodes of V1a/2a and 1b/2b via anode resistors (100k and 330k respectively in Phono2, but presumably changed by the addition of the HT rail resistor). have these values been published anywhere? Anyone know what they are?

(Please don't flame me, I'm not a well man....)

David

[Ianm2]

flame? why would people do that for that inquiry,

no idea what they are, but they won't drop an awful lot of volts, as the ecc83s only run on a milliamp each, probably less than 10k, perhpas even 1k and around 10-22uf

there is a rough recommendation about the frequency/time constants of RC decup circuits, but not sure what they should be

for the coupling caps, its a little easier, you have your std value, and it may be as simple as doubling for one and halving, I think you may have to take valve impedances into accout, its been so long since I did calcs. so can't remember

and the cathodes are unbypassed, but you won't be far out by doubling and halving. the higher cutoff is only if you get problems with flapping cones so they aren't strictly ness. but useful

for ecc83 bypassed, the output impedance is the load resistor, parallel with the ecc83s ra, which is 62500 according to spec. but this varies with the bias point, it could be anything from 20k to 500k perhaps

and sometimes also the whole lot b4 in parallel with the grid resistor,

just had a look, std is 20hz, low is 12hz, higher 30hz, so someone can do the calcs. if the stock is 0.22,

0.1/ 0.15 and 0.33/0.47 will be v. close

personally, the most worthwhile additions are the psu filters, it was a weak point not to include them originally

[NickG]

I think NickG alluded it MAY not be spot on

In my sym's and building a clone, I found the HF was slightly more rolled off than it had to be, but it seemed to be the result of the 3.18us mod, it looked to me that there was a slight effect on the other TC on that leg that could be fixed by altering the other R.

However WD have access to better test kit than I have, so I am not making any claims either way.

[Phil Y]

Hi all,
Sorry to hijack the thread slightly, but i wonder if someone could put my mind at rest. Would it cause any problem having the first 2 anodes of the Phono II at different supply voltages. The reason i ask is that when i built my Phono II last year i added a CR filter to the first stage only. Mine is non-standard as i used an existing chassis/power-supply for ease/cheepness reasons. I assumed that as the equalisation is an "AC signal" thing that altering the supply voltage slightly would not have any adverse effects. Am i correct or is this a case of a little knowledge being a dangerous thing? The first anode supply is at 250 volts where as the second and third stages are at about 280 volts.

Regard, Phil.

P.S. I have circuit diagrams done in Paint but they are too big to add and i'm afraid i don't know how to change them.