New Foreplay build Questions

[mchurch]

Hi;

I am relatively new to the Bottlehead building community. I just finished my build of the Foreplay and Extended foreplay upgrade this weekend. The first thing I noticed was the volume after the first click blew me out of my room. I live in an apartment so this was not going to work, I tried the 360K padding resistor on just one input but it was still a little high  level for me. I change to 470K and this seems to be nice for low level control with still lots of room to open it up. My question is, does this amount of padding create any issues I should look for?

I am waiting for my Paramount kits to arrive so right now I am running the pre into a Hybrid Amp (Vincent SP-331) and I am not sure of its input impedance. I f necessary I will change back when using the Paramount. My speakers are 93db sensitivity.

Any info would be appreciated?

As far everything else is concerned the sound quality exceeds my previous Conrad Johnson pre. There is a very minute amount of hum on one input so I am going to trouble shoot that next.


Cheers,


Mike

 

[Grainger49]

There should be no problem with the padding you found to work.  You will need different padding for each source, probably less for a phono section.

What I foresee is that when changing amps you might need to change again.

 

[mchurch]

Thanks Grainger;

I fully expect to probably have to change again when I set up the Paramounts. I figure that most of the extra gain I am hearing was related to the Amp. I have discovered my selector switch is defective so when I get it replaced I am going lower the padding resistance on the input used for the Seduction.


Cheers

Mike

 

[Paul Joppa]

When you use the highest values of padding resistor, it's a sign that the amp and/or speaker are very sensitive. In that case, it is possible to get some hum and/or noise ("tube rush") that is audible. The best solution is to reduce the power amplifier sensitivity. That's not always practical - you may not want to modify the amp internally, for instance. For more information, including other options, I have a white paper on the subject linked off the Community page.

 

[mchurch]

Thanks for the input! Would the lower noise floor tweak mentioned by Doc work in this case to remove some of the "noise". I don't have the gain of the amp but I suspect it to high. Would this tweak have any adverse affect when switching to the Paramounts.


Cheers


Mike

 

[Paul Joppa]

If that's the tweak I am thinking of, it will work unless you have very noisy tubes - it addresses the noise originating in the shunt reg chip, not that originating in the tubes. I d am not aware of any downsides.

 

[mchurch]

Thanks Paul,

That is my next step before doing anything radical, change the tubes. I just received some NOS tubes from the Tube Store and I am going to see if they work out any better. If not then I will try the tweak.


Cheers

Mike

 

[Grainger49]

   .  .  .   There is a very minute amount of hum on one input so I am going to trouble shoot that next.


Cheers,

Just some basics.  Is it one or both channels?  To test if it is in the FP III substitute shorting plugs for the cables coming into the FP III. 

Does it still hum?  If not, the problem is the component or interconnects, but not the FP III. 

If it does hum you might try to rewet the solder joints at the offending RCA jack(s), at the terminal strip terminals where the cable goes from that/those jack(s) and the selector switch.  Those are the only connections that are isolated to one source.

 

[mchurch]

I solved the hum problem by going over every solder joint and re-flowing some that I thought might be suspect.  After which i installed a DACT  stereo attenuator. The hum was gone when I turned it on again.

I have another question; Why is there a resistor between the two outputs? If I want to run four mono blocs  2 for Bass and 2 for Treble can I remove the resistor and run a jumper between the outputs so each pair of amps sees the same input.


Cheers;


Mike

 

[Grainger49]

The resistor is there to keep one of your amplifier's input impedance from interacting with the other amplifier.  This configuration is specifically to feed a sub woofer and an full range amplifier.  

There is probably only a small amount of attenuation caused by that resistor.  You will probably need a volume control on one of your amplifiers to balance the outputs anyway whether the resistors were there or not.

 

[mchurch]

Thanks Grainger;

I figured there had to be some reason but I wasn't sure, partially because my old Conrad Johnson had 2 outputs that were just jumpered to each other. I guess the circuits are different. Like I said earlier this is all new to me.


Cheers Mike

 

[mchurch]

Another question:

Now that I have added the stereo attenuator I want to use the extra hole to add a power indicator light. Does anyone have any suggestions where I should connect this to so it has minimal impact on the audio quality. I want to add an LED unless someone has a better suggestion.


Thanks

Mike

 

[2wo]

You can probably connect an LED to the filament supply with a resistor in series to drop the voltage to what you need and the level of brightness you want...John

 

[mchurch]

Thanks John;

Thats kinda what I thought but it never hurts to get another opinion or idea. I have a bunch of LEDs so I will experiment with the resistors and see what happens.

Mike

 

[Grainger49]

Mike,

If any of the diodes you have tell you what current they draw we can calculate the series resistor easily.

 

[2wo]

I you still have the SW that you just replaced. You can use it as a 15K variable resistor to experiment with...John

 

[mchurch]

Mike,

If any of the diodes you have tell you what current they draw we can calculate the series resistor easily.

Grainger49, I am going to take a look a potential candidates for LED later this evening I will look for their current draw.

Thanks

Mike

 

[ajp]

Hi, I just completed the soldering potion of the build. But I notice that I never read, that I should solder the drain wires to 28U. Have I missed that in the instructions. That seems wrong, won,t they move around etc.

 

[Laudanum]

Hi, I just completed the soldering potion of the build. But I notice that I never read, that I should solder the drain wires to 28U. Have I missed that in the instructions. That seems wrong, won,t they move around etc.

If I recall, there were one or two minor misses in the FPIII manual.  That seems to be one of them, from memory.  Yes, they should be soldered. 

 

[ajp]

Thanks, that's what I though.