[dayneger]

I've finally gotten my AKSA 100W together and it seems to be running well.  However, I've discovered that my Foreplay has a really high gain, and combined with the high-gain AKSA we're talking about that extreme hair-trigger feeling!

As for the future outlook, the Foreplay is going to stay in the system until funds and time recover enough to make a GK-1, while the AKSA's here to stay.  Until I Nirvana it!

I've read about various ways of reducing the Foreplay gain, including padding the inputs or the outputs, with various pros and cons.  Some say it's better to pad the amp input rather than the preamp output to reduce impedance issues driving the cable (or something like that).  Another possibility would be to reduce the AKSA gain, but only if it doesn't have a negative impact on the sonics.

Unfortunately I'm massively lacking the background knowledge needed to evaluate these options.

Anyone have suggestions?

Thanks!

[PSP]

The Foreplay, since it was designed to be used for very low-powered tube amps, has something like 19db of gain (if I remember right), and in stock form is IMO way too hot for the majority of SS amps.  

I have implemented VoltSecond's recommended T-pad on the Foreplay input.   http:// http://www.siteswithstyle.com/VoltSecond/12_posistion_shunt/12_Position_Pure_Shunt.html  

There is an Excel spreadsheet on this page that you can use to determine which resistors you need; simply decide how many db reduction you need (if I remember right, I padded mine down by 9db and if I did it again, I'd pad it down by maybe 12 db) and plug that value into the spreadsheet.  This is an extremely easy and effective tweak (without negative sonics that I could detect, assuming that you use good metal film resistors for the T-pad), and it's what I would strongly recommend.  If you go ahead and pad down the Foreplay, you will have a preamp that you can use with essentially any SS amp you will own in the future and you will leave your 100w AKSA in an "as-designed" configuration (which all agree sounds fantastic).

Peter

[dayneger]

Thanks, Peter!

I'll probably try a couple of versions to see how they go.  Someone else emailed me this link as another possibility:

http://db.audioasylum.com/cgi/m.pl?forum=set&n=11011&highlight=series+double+shunt+mod&r=&session=

The idea of reducing the sonic impact of the pots is an interesting one.  Can't say I understand how it works, though!  

[PSP]

The basic idea is that you control volume by shunting a variable portion of the signal to ground.  In this way, the pot is removed from the direct signal path.

[AKSA]

Peter's technique reduces the adverse influence of the pot on the sonics, and thus is a great mod for any preamp with excessive gain.

The Foreplay uses a 12AU7 at very low current with a 120K plate resistor to give very high gain, approaching the mu of the tube.  This circuit supplies a gain of around 15, then follows it with a cathode follower as a buffer, giving around 23dB, way too much gain in most situations with sensitive hifi amplifiers.  It is preferable to scale this down with padder resistors at the input rather than alter the gain of the AKSA, which can be done, but which has repercussions down the line for damping factor and amp sonics.

Cheers,

Hugh

[dayneger]

23db?  No wonder I was having problems!

Last night I tried a simple L-pad on the input using 100K to signal and 10K to ground.  The attenuation worked but the nasty buzzing problem I'm having with the Foreplay got even worse, except at very high volumes with no signal.

Then I tried an output pad like Doc B suggested, 100K to output, 2.2K to ground.  This yielded optimal attenuation and dramatically killed the buzzing.  I'm not sure how great it sounds, I'd have to put in better resistors I'd imagine.

Soon I'll try some of the other possibilities.  Anyone know where to order Riken resistors in Switzerland or the rest of Europe?