Telemark said:
I am looking for ways to quiet down my YBA-1 while hopefully getting a bit of poweramp grind out of it.
Does anyone have experience or comments on either option?
Any other suggestsion are welcome. thanx.
Mark.
I use a 'bridged attenuator' with my epi valve junior and pignose gt40.
I run the Vjr wide open.
After the attenuator I have an L-pad, which is really just a 8ohm variable resistor and I've put a 2.2uf non-polarized capacitor as a high frequency bypass across the L-pad.
The 'bridged attenuator' is described here;
http://www.18watt.com/modules.php?name=Downloads&d_op=viewdownload&cid=38
schematic is;
http://www.18watt.com/storage/bridged_t_schematic.gif
R3 and R4 are always equal to your speaker impediance, so in my case both are 8 ohm ten watt resistors. ( about 1.80 each ).
Currently I'm using a 76ohm R2 and a .68ohm R1 both ten watts.
I would describe this as loud-ish, suitable for daytime, not suitable for nighttime.
So the L-Pad makes for the final adjustment from silent to loud-ish.
Last week-end I bought a few more resistors and a switch so I am going to find three settings that I like.
Here is a spreadsheet of the required values for different dB reductions for 8ohms.
db R2 R1
10 17.30 3.70
11 20.39 3.14
12 23.85 2.68
13 27.73 2.31
14 32.09 1.99
15 36.99 1.73
16 42.48 1.51
17 48.64 1.32
18 55.55 1.15
19 63.30 1.01
20 72.00 0.89
21 81.76 0.78
22 92.71 0.69
23 105.00 0.61
24 118.79 0.54
25 134.26 0.48
You can see that I'm around the 20db mark.
I'm quite happy with it.
I can bring back the highs so I'm ok on that.
Really it is for late night playing and it works great for that.
With the Valve Jr un-modded the resistors stayed cool.
With the Valve Jr modded the resistors get warm.
With the 40watt Pignose the resistors get hot.
I would like to try a minimass as well, I havent found a used one yet.