Seduction.....need more gain w/ Foreplay and Dynaco 70

C

choff

New member
I just can't get enough juice out of most of the records I play with my fully modded Seduction.  I feel like at the loudest setting on my fully modded original Forplay,  I am about one to two steps away from a volume that will present the music the best.  Any suggestions?

FYI :  I have Rega speakers that I can't find documentation on their efficiency.  Cartridge is a Clearaudio "Virtuouso" MM rated at 3.6mv.

 
Do you have Sweet Whispers? If so, are they the -20dB version?

The Foreplay and the ST-70 both are fairly high gain, so this problem is surprising unless the FP has the -20dB mod.
 
very good question....i really can't remember off hand.  pretty sure i went for the higher gain but it's been about 4 years since i made that mod. 
 
choff said:
eegads.....looks like I installed the -20db version for some reason.  Why did I do this version?!?
Click to expand...

Because you have gobs of gain.  But just a little less than you need for your Seduction.
 
You are correct.....works great with my cd player but not so much with the Seduction.  So much work put into those Whispers I'm really on the fence as to whether I should tear them out and replace with the other resistors.  Do I have a choice?
 
I don't remember the -20dB modification.  Does it include a series resistor?  If so it can be easily changed.

I wouldn't tear out the resistors on a Sweet Whispers and change them for all the Tea in China.  If it came to that I would buy a Sweetest Whispers and build it as an S5 attenuator.

S5 Attenuator At VoltSecond's site

The instructions start at section 2.0.
 
IIRC the old -20dB version was a 10K attenuator with a 90K series resistor. You can reduce that 90K resistor to 20K which will present a 30K load to the Seduction, perfectly fine and that will provide 10dB more gain. You can even keep the 90K on one set of inputs and put the smaller resistor on another, so that the CD and phono match better. Just put the resistor between the RCAs and the selector switch input, instead of between the switch output and the tube input.

If you need more, you can go as low as 5K for that resistor and still keep Seduction happy; you may want to increase the 0.47uF output capacitor in Seduction to something like 1uF to give a bit more heft to the deep bass - but if your turntable has a bit of rumble, or your arm-cartridge resonance is a bit low, you might even prefer the subsonic rolloff provided by that lower load impedance.
 
Paul Joppa said:
IIRC the old -20dB version was a 10K attenuator with a 90K series resistor. You can reduce that 90K resistor to 20K which will present a 30K load to the Seduction, perfectly fine and that will provide 10dB more gain. You can even keep the 90K on one set of inputs and put the smaller resistor on another, so that the CD and phono match better. Just put the resistor between the RCAs and the selector switch input, instead of between the switch output and the tube input.

If you need more, you can go as low as 5K for that resistor and still keep Seduction happy; you may want to increase the 0.47uF output capacitor in Seduction to something like 1uF to give a bit more heft to the deep bass - but if your turntable has a bit of rumble, or your arm-cartridge resonance is a bit low, you might even prefer the subsonic rolloff provided by that lower load impedance.
Click to expand...

These seem like some fairly simple changes to solve my problem.  I imagine another 10db will get me where I want to be.  I'll have to check back once I get into these changes as I may have some questions.  Thanks so much for the help!!
 
Ok.....so just to be sure.....I need to purchase the following replacement parts : 

(2) 20k, 1/8 watt resistors

(2) 1uF 400V metalilized polypropylene capacitors

any recommended manufacturers for these parts and where I can purchase you can recommend?  Thank you.

Carl
 
Also,  I have attached an image and circled the (2) 90k resistors and their termination points with an orange pen.   I'm not clear on your directions for the changes,  am i removing both of these and replacing with the 20k resistors in the same place?  I like the idea of being able to get both cd player and phono at the same volume levels but i'm not clear on how this is achieved?  

Additional notes as i don't want anything to be missed with what i currently have : I reversed the last two resistors in each pot when building the Sweet Whispers per somebody's recommendation,  but I can't recall why this was done?  Also,  I have not put the Anticipation mod in yet but plan to do so shortly.

Thanks again for the assistance!!
 

Attachments

Edited:

You want metal film resistors.  Look at Parts ConneXion and you will find more than you want to.  The same goes for film capacitors.  Both resistors and capacitors are a matter of taste.  I can recommend what I like but that doesn't guarantee you will like it at all.  (I would recommend Caddock, Riken or Holco resistors; Auricap, Mundorf or Jensen capacitors for this use)

Replace the existing resistors with a wire.  Take the resistors that you removed and put them on the lugs on the selector switch where the CD player comes in.  Solder one end of the resistors to the selector switch and the other end to the wire you just removed.  You could now compare the CD player and Seduction (with no additional resistors).  But PJ mentions that it will be a low load for the Seduction to drive into.  But... you can still do it and you might get a rolled off low frequency range.

If the Seduction was too loud take the new 20k resistors and put them between the lug on the selector switch where the Seduction comes in and the wire that is there now.  If it isn't too loud bump up the size of the output capacitor in the Seduction.

You do the same with the third input to match its volume.
 
Great....this helps a ton.  It's kinda what I was thinking but wasn't completely sure. 

So,  IF the Seduction is good without the 20k in between,  then I add the 1uF.  But IF it is too loud,  add the 20k and NOT the 1uF to the Seduction??  correct??
 
Yes, you have it.

This is from the Seduction description, "The Seduction is designed to operate into line stages with 50K or higher input impedance through interconnects of 1M or shorter length."

Paul Joppa above says that a 20k resistor in series with the 10k attenuator (30k total) is a low end of the scale.  So if you need to try a 10k resistor or even a 5k resistor you will want to increase the 0.47uF output capacitor in the Seduction to a 1.0uF capacitor.
 
Well,  I made the initial changes with some very positive results.  The phono is now much louder and i sounds very different.  Is it too loud?  Perhaps, but I'm not sure yet.  I can comfortably get most of the lp's i have played to the 1 o'clock position. 

Just to be clear, I now have the 90k resistor in line with the cd player and no resistor for the phono.  No indication of a lack of bass with the phono (which i believe was noted as a possibility).  Phono is definitely louder (about 3 positions) than the cd player now.

Any idea what I should do now if anything??   
 
Carl,

If you have moved the resistor away from being the jumper between the selector switch and the SW, and added no other resistor you might have lost some bottom end from the Seduction since it isn't designed to work into a 20k load.  That could be the reason it "sounds very different."  But most of us can't hear anything below 50 or 40 Hz in our rooms anyway.  That takes a big room to get flat response down there.

Also the lowering of the noise floor that resulted from that change might also be the reason.

 
choff said:
ok.....do i need to also need to change out the .47uF to 1uF caps on the seduction?
Click to expand...
Into a 10K load (what you have without the 20K resistor), the extra bass rolloff is -3dB at 34Hz. Since most records already roll off at 50Hz, that is not usually very audible - and you said you did not hear a loss of bass. So, I do not see a need to change the capacitor.

Adding the 20K resistor would move the rolloff to 11Hz, where you will be much less likely to hear it. In that case there is absolutely no need to change the capacitor.

In both cases you can of course change the capacitor just to hear for yourself if it makes any difference, and whether you like the change if it is audible. I'm just saying that I see no technical or theoretical need to do so.
 
I added the 20k resistors and I am in a very happy place now.  I have plenty of gain with the records and they are very nearly matched to any cd's I may toggle to during a listening session.  Most importantly,  I feel like i am finally able to hear all that my vinyl has to offer.  I'm looking forward to revisiting many titles that were simply too quiet with my prior arrangement.

Thank you PJ and Grainger for your invaluable assistance!!
 
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