Foreplay III Upgrade Advice

[skippy1416]

Hello,

Now that my Foreplay III has been in the system for a few months and I have settled on tubes (Raytheon 12AU7s and a CBS Hytron 0D3) I am looking to do some upgrading.  I am still a newbie (I learnt to solder just for the kit) and I have to admit that I don't completely understand how the kit works - but that doesn't mean that I don't want it to sound better.

I know that the old forum had a lot of information about upgrades but there doesn't seem to be a lot on the new forum.  So please forgive me if this has been covered in the past but I am hoping that it will be valuable to others (as well as myself).

If I wanted to make one or two simple and inexpensive changes to a Foreplay III what would you recommend.  I'm not ruling out the Extended upgrade but right now it isn't in the budget since I am planning to order a Seduction very soon.  Ideally any recommended upgrade would complement the Extended if I was to go that way in the future.

I am guessing that the volume switches and/or the input selector might be a good place to start. Or should I go straight into caps?  Or something else entirely?

Any ideas would be greatly appreciated.

Thanks

 

[Paul Joppa]

I'd do the output caps (2.2uF/250v) first. It's easy, it's non-critical (250v or greater voltage rating, but anything from 1uF to 10uF will work fine), and there are many choices.

The switches are more of a long-term thing - the stock units sound fine, it's a matter of longevity and resolution. Google for switched attenuators and you'll see why this kit does not include 24-position $hallco attenuators!

Many of the upgrades for the Foreplay I and II are incorporated into the III, which is one reason there are fewer posts.

 

[ssssly]

And once you are done replacing all of the caps then you can start replacing all of the resistors. Most people talk about caps all the time but few ever get into the resistors. The resistors in many places can make as big a difference in sound as some of the caps (with the exception of output caps and the last power supply cap, these always seem to change the sound the most to my ears at least).

 

[skippy1416]

Many thanks for the replies.  That is some great information.

I have picked out some Auricaps from the partsconnexion website - I am planning to change the 2.2uF caps and the 0.1uF.  Since I am going to be placing an order I thought that the resistor upgrade sounds interesting as well but I am unsure as to which ones might be the best candidates for replacement.  What are the best couple of spots to make a switch?

Thanks again.

 

[Grainger49]

Doc or PJ once posted that they had upgraded the Cbypass capacitor (0.1uF@630V at the OD3) with a USSR Military Surplus Teflon.  (This assumes you haven't gone to the Extended Foreplay upgrade)  You can get those pretty cheap.  I just saw 2 for $19 on ebay.  If I were you I would buy 3 from a seller since you will want to try these in a signal path position too.  

Teflon caps are considered to be much better sounding than PP film like the Auricaps, which I have used often as well.  But the surplus caps make Teflon more affordable.  Teflon also takes a while to break in.  That is they don't sound their best at first but then the door opens.  So... Look here for a fast burn in method:

http://www.bottlehead.com/smf/index.php/topic,80.msg286.html#msg286

BTW, all film caps have a burn in time.  The Auricaps should burn in too.  4 days should be enough for them.  Teflon, well I have started burning them in for 10 days to really get them there.

 

[ssssly]

For resistors I would suggest starting with those directly in the signal path. Then high voltage stuff. Have been a couple of threads on this here. Can also experiment with replacing resistors with inductors. Would start with the last power supply resistors if going that route. Just have to make sure you mount them where they won't induce hum. Can also replace some of the larger resistors with LEDs or LEDs and smaller resistors, often bias resistors.

I myself like Shinkoh tantalum for high voltage and Texas Components bulk foil for low voltages. Power supply resistors like to be replaced with chokes.

Have fun and be well

 

[Paul Joppa]

The shunt-regulated power supply serves to isolate the last power supply capacitor so its quality becomes less important, but that bypass cap across the gas regulator tube is important at the higher audible frequencies. We used 0.056uF teflon across the 0D3 with good audible results. However, I will caution that we have run across teflon caps that never sounded good, even after more than 500 hours of burn in. You still have to use your ears!

For a stock Foreplay III, the plate and cathode load resistors (22.1K 1 watt) are probably the most important in the circuit. We use metal film where there is significant current because most carbon is noisy; quality carbon film can be better than carbon composition but I still avoid it. The traditional gold standard for this application is non-inductive wirewound; I imagine the Shinkoh tantalums would work pretty well.

Of course the input attenuator is made of resistors and they are significant. We use nice quiet metal films; among the best of these (too expensive for a cheap kit!) has been the Dale RN series which have copper leads. Goldpoint, which makes good relatively inexpensive switched attenuators, say they have had good results with certain surface-mount resistors. I have a set of them but they are not yet installed so I can't yet report what my own ears hear. For an inexpensive test, you could just replace the gain-setting series resistor and see what you hear.

 

[skippy1416]

Once again thanks again for the replies - they all contain excellent information.

I have now settled on Mundorf ZN M-Caps and Takman resistors.  Partsconnexion doesn't have any Shinkoh 22K 1W so I will go for the metal film Takmans.  I am looking forward to trying these out - although right now the Foreplay is grooving pretty good (GEMA copy of The Doors 'Greatest Hits' - I have never had any greatest hits album that sounds as good as this one).  I am really looking forward to building the Seduction.

Thanks again

 

[ssssly]

I use the Takmans for places that the larger tantalums won't fit. I enjoy them. Not as good as the tants but very nice. Have a pair of 24 step attenuators that are all Takman and they have stayed in without desire to mess with them.

Wire-wounds sound great as well, but I have found that you have to order tons of them to match them. For some reason the tolerances don't seem as tight. If you don't mind measuring piles of resistors is hard to go wrong with a good wire-wound though. 

Have fun tweaking. And try to fight the urge to do everything at once. That way you get the most out of each tweak and know what did what.