Transformer to lower Foreplay III gain

T

triode

New member
Hi,
I just finish building Extended Foreplay III.
All good, but my system has too much gain : FP3->Paramount (12AT7 driver)-> front horn loaded Lowther (I believe >100dB/W sensitivity)
I hear hiss if FP3 directly connected to Paramount.
But with my passive TVC in between and attenuate by 14-20dB the noise is low enough. Also volume control has more usable range now.

Could I use Edcor 8.2:1 (-18dB) matching transformer right on the FP3 output?
Which one should I pick : the 1/2w (http://www.edcorusa.com/p/146/wsm10k-150) or the 2-1/2w version (http://www.edcorusa.com/p/159/xsm10k-150)

Any one has tried these transformer?

Thank you in advance
 
I am certainly not the expert here, but I would guess that it is a safer bet to modify the volume control itself, rather than to spending money on a transformer for the same purpose.  To correct at the volume control will only add resistance, whereas a transformer will add resistance AND inductance, not to mention capacitance.  This is only from my limited knowledge here, but that would be my feeling aboout your issue. I have the same trouble with my integrated amp(sensitivity too high), and the volume control was the easiest fix.
 
Thanks for the reply, but this noise is heard even when the FP3 volume turn all the way down.
It's the noise from FP3 (after its volume control) which heard in the sepaker due to gain of power amp and speaker are too high.
I read in other posts that I can pad the power amp input (change the input resistor in to voltage divider), but I do not want to modified my Paramounts. Hence the question of step down transformer between FP3 and Paramounts

Cheers
 
Triode,

The gain can not be changed. 

Is the problem on both channels?  If so, your problem might be the tubes.  Try rolling one in on one channel. 

More later, less sooner,
 
Based on the information you provided about your situation (which is pleasantly comprehensive), I would attenuate the input of the amplifier.

15dB of attenuation is about a voltage step down of 5:1.  There is a 470K resistor at the input of the Paramount, you can remove that resistor, then replace it with a 120K resistor.  Retain the 470K resistor and put it in series with the signal coming out of the RCA jack (remove the red wire at the center pin of the RCA jack and install the 470K resistor between the center pin and the red wire).

You can also pad the inputs of the Foreplay down, but I would only recommend this if you can turn the level controls all the way down and the hiss goes away in your speakers.

-PB

(I really wouldn't advise using the transformers)
 
Resistors are 17 cents apiece.  When you decide on a ratio, you buy $4 each resistors, a whopping $16 and you are done with it.  Very simple and cheap.
 
The Extended  Foreplay is noisier that the stock version, because of the hybrid shunt regulator. There is a fix - it's a sticky on the FP-III board. You still need the resistor changes to get the volume control into a good range, but if the fix makes it quiet enough, it will sound better without the transformer.

A smaller improvement would result from the "soft-start_ board using a 5670 driver, which has nearly half the gain of the 12AT7. That's about 6dB lower gain, but would affect both the noise floor and the volume control setting.
 
Thanks PJ, I will install the caps and see if they reduce the hiss. But I think I still need the pad to make volume control usable
 
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