Question about replacing specific resistors in the Foreplay III

[Mr. Lin]

I'm currently in the midst of buying and installing a number of boutique passive parts in my new Foreplay III.  So far, so good.  

The next one's I'd like to replace are the 22.1k ohm 3/4 watt resistors on the right and left 12AU7 tube sockets.  I can't really find any of the brands/types of resistors that I would want to try that offer 22.1k ohms.  Is it ok to use 22k ohms in those four places instead?

And one other thing while we're on this topic: Would it be ok to replace the stock 22.1k ohm resistors with something like Riken carbon comp. ones?  Or perhaps the carbon film versions that a number of companies offer?  I've just replaced the 220 ohm carbon comp. resistors at the tube sockets with Riken resistors, which is why I have them in mind specifically.

 

[Grainger49]

Try these in the 22k 2W version.  They were recommended by PB (CaucasianBlackplate) for Eros plate load resistors.

http://www.partsconnexion.com/resistors_amtrans_amrg_two_watt.html

Carbon comp are noisier and can drift value with time and heat.  The 220 shouldn't make any difference.  I would be interested if you heard an improvement.  Search Grid Stopper.

 

[Mr. Lin]

I'm starting to think you're going to be my new best friend on this forum.

I replaced those 220 resistors with the Rikens because I was already placing an order with Parts ConneXion for some other things, so I just threw them in.  Worst case scenario, they really look cool!  I've been listening all night and couldn't tell you for sure whether there was an improvement.  It sure sounds sweet though.  The Riken resistors are actually carbon film and the tolerance is alleged to be 1%.

I've also replaced the 470k ohm resistors with Kiwame 470k 2 watts.  Any other places in the circuit where replacing stock resistors may improve the sound?  I was considering the 2.7k ohm in the power supply, but I don't know if that would help at all.  

I'm sorry but I'm not clear on what you were suggesting in the post above, specifically what they're called.  Was there supposed to be a link?

When I finish my Paramours (which I just started a few days ago) I'm going to have to pick your brain on those as well.  Just studying the schematic and manual I see a bunch of things begging to be experimented with.

 

[Grainger49]

I hope the Rikkens are the big blue ones.  I've always thought they were cool!  

I will put the link back in.  Somehow I forgot to "paste."

The Dropping resistor, 33k, is in the audio path.  Every resistor on the Sweetest Whispers up to your maximum volume level is also in the audio path, somewhat.  Those go to ground but might affect the sound.  Not nearly as much as the 33k.  But don't buy a hand full of 33k ohm resistors now.  Find what padding resistor gives you the best match in sources.  Then buy some nice $4 resistors to replace those.

 

[Mr. Lin]

You mean the six 33k resistors on the middle switch?  That's something I thought about after your last post.

And yes those Rikens are bright blue!  I'll post a picture later on, don't have time now. 

 

[Paul Joppa]

22K +/-5% is fine. Those are load resistors, carrying DC current. The "gold standard" would be non-inductive wirewound resistors. I would avoid even the best carbon composition, and certainly any metal oxide, the all ave bad reputations for noise and nonlinearity when there is a substantial DC voltage drop. There are some new thick film metal glaze resistors from IRC, the GS-3 series, that are reported to sound good. I have not listened to them; I like them for the robust 3-watt rating and especially for the high 1000v maximum operating voltage. Mouser has them for less than a dollar, so it might be worth an experiment.

 

[Paul Birkeland]

The clear upgrade here would be to upgrade those to C4S loads.

A 22.0k resistor will work just fine in place of the 22.1k, the resulting voltage change is in the tenths of a volt and well within the variance one would expect when swapping tubes.

As far as parts selection goes, tantalum resistors make nice plate loads.  Parts Connexion has 22k 1 watt Audionote Tantalum resistors for about $10 each.

-PB

 

[Mr. Lin]

22K +/-5% is fine. Those are load resistors, carrying DC current. The "gold standard" would be non-inductive wirewound resistors. I would avoid even the best carbon composition, and certainly any metal oxide, the all ave bad reputations for noise and nonlinearity when there is a substantial DC voltage drop. There are some new thick film metal glaze resistors from IRC, the GS-3 series, that are reported to sound good. I have not listened to them; I like them for the robust 3-watt rating and especially for the high 1000v maximum operating voltage. Mouser has them for less than a dollar, so it might be worth an experiment.

Thank you Paul, I'll look into those GS-3 resistors.  Glad I asked before I put the wrong kind in there, it's a bit of a hassle to work in those tight spaces without damaging anything with the soldering iron.

 

[Mr. Lin]

The clear upgrade here would be to upgrade those to C4S loads.

A 22.0k resistor will work just fine in place of the 22.1k, the resulting voltage change is in the tenths of a volt and well within the variance one would expect when swapping tubes.

As far as parts selection goes, tantalum resistors make nice plate loads.  Parts Connexion has 22k 1 watt Audionote Tantalum resistors for about $10 each.

-PB

Since I'm very new to the FP III, I have to ask - By C4S loads do you mean the six from the center switch that go to ground? 

The Audionote idea is certainly intriguing, but I don't know if I'm going to be able to afford a $60 + resistor upgrade at the moment.  Perhaps the Shinkohs? 

 

[Paul Joppa]

The C4S (Camille Cascode Constant Current Source) are part of the Extended upgrade package. They are constant-current sources (obviously!) which replace those four resistors. (The Extended Foreplay package also includes dual-mono power supplies and active hybrid shunt regulators.)

 

[Grainger49]

You mean the six 33k resistors on the middle switch?  That's something I thought about after your last post.

And yes those Rikens are bright blue!  I'll post a picture later on, don't have time now. 

Sorry, I'm out of town and not online much.  Yes, those are the ones, I forgot there is one for each input.  Post some pictures in the Gallery folder.  I'm going to post some of my Eros when I get home.

 

[Laudanum]

Since I'm very new to the FP III, I have to ask - By C4S loads do you mean the six from the center switch that go to ground?  

The Audionote idea is certainly intriguing, but I don't know if I'm going to be able to afford a $60 + resistor upgrade at the moment.  Perhaps the Shinkohs?  

Mr Linn,  PJ and PB are referring to the 4 22.1K plate resistors located at the tube sockets, two on each 12AU7 (tan with red stripes).  Unless Im missing something.  

 

[Mr. Lin]

Grainger I will post the pictures soon.  I've done something heretical and installed a pair of Takman carbon film resistors in the input two channels.  I did this because they're the only ones among the boutique resistors I've recently purchased with a proper value, and I just wanted to hear what would happen.  One thing I can say at the moment is that I do not hear any more noise than there is on input one where the original metal film 33k resistors are still installed - by which I mean, no noise at all, it's completely silent aside from a right channel noise issue I have that's on and off, which I think I've narrowed down to RFI.  It's not the Foreplay in any case.  But if that changes, I'll just pull them out and put something else in there. 

Mr Linn,  PJ and PB are referring to the 4 22.1K plate resistors located at the tube sockets, two on each 12AU7 (tan with red stripes).  Unless Im missing something.  

No you've got it right Laudanum.  Those plate resistors are the ones I was originally asking about when I started this thread, and now I've sort of confused things by asking about something different. 

 

[ajp]

Hi, I'm in the process of building a Foreplay III and have also bought the upgrade kit. How can I add the upgrades without first building the Foreplay and disassembling it to add the up grades? Are the instructions somewhere to follow? This is my second build so maybe I'm missing something.

 

[richmi]

Hello,

The Foreplay is somewhat complex, with lots of connexions.

It is always recommended that one builds the kit without the upgrade first.

On the one hand, you get to know how it sounds stock. On the other hand, if something goes wrong, it is easier to troubleshoot.

Once you know that everything is working right and you are familiar with the sound, you can add the upgrade and see what it does.

The manual for the Extended kit contains all the instructions for the changes you have to do to the Foreplay before installing it.

Richard

 

[Grainger49]

Hi, I'm in the process of building a Foreplay III and have also bought the upgrade kit. How can I add the upgrades without first building the Foreplay and disassembling it to add the up grades? Are the instructions somewhere to follow? This is my second build so maybe I'm missing something.

The answer to this is that it is difficult.  The VERY STRONG suggestion by all at Bottlehead and most of us here on the forum is not to do that.  If there is a problem finding the solution is that much more difficult.

It is up to you. 

 

[ajp]

Makes sense. Thanks.

Al

 

[epistaxsis]

As Grainger said that resistor in the input selector is ripe for replacement - I am bunging some Shinko tantalums in there to see what happens

Now I am going to disagree with Grainger the volume control(s) is also fresh for fiddling.

However I wouldn't recommend just changing resistors here.

What you need to do is to change it over to a proper ladder attenuator.

This requires new switches and a *lot* of soldering - basically you are now dealing with at least twice the quantity of resistors which also at least doubles the cost of your boutique components!

But it is worth it as a ladder gives you a fixed input impedance (which things like valve based phonostages prefer).

Hopefully my new attenuator will arrive before the fat bloke goes charging around interfering with childeren...