Foreplay 2.1

amioutaline?

New member
a.k.a. Parts Box Foreplay.

I came across my original manual from 2001 last month. When I  saw how simple the schematic was and  figured out I had everything but the transformer, I decided to go for it. First time around I just soldered tab "A" in slot "B" and hadn't a clue what was going on. In the intervening years I learned enough to at least ask the right questions.

Working for the first time ever completely from the schematic and without a net (net's name is Steve Brown), I've got a functioning pre-amp.

A little early to think about tone and texture but the initial very favorable impression is all about bass weight and soundstage.

Niels (that's Niels on Upright Bass) likes it too, especially a Jo Jones drum solo which was the first thing I played. Great whacks and shimmers!

It's a 2.1 because I used a CLC power supply and star ground. I installed CBs recommended attenuation but took it out before playing to judge whether it was needed with 1.8 Watts to the 97dB speakers. Turns out 9 O'clock is where the VC is for average listening with 10 getting kind of loud. I have a pair of 18 Watt KT-88 mono blocks nearing completion and that will be a different story.

I've used a passive switch and attenuator for over 6 years and forgot how bass weight often trumps clean and clear. Voices are a little sweeter, too which is likely the 3.0 uF Auricaps, not my first choice, but what I had.

There's a bit of hum that may be coming from the Cinemags which were displaced from alongside to behind the Caravaggio. I'll get to that eventually; the hum level at my chair is non-existent.

Voltages are  right in line with 126 line volts (189 B+) but the H+ which is 6.9, probably should be lowered. Sounds great, though and I've got a ton of AU7s.

When you're too old to get in (much)  trouble, few things are better than hearing a new component that came off your own bench!

 

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Thanks, Paul.

Now let me get stupid after I mention that I had to repeat a Math Course every Summer  of High School.

I want to drop the voltage 0.6 so I divide that by the 15mA secondary current and get a 4 Ohm resistor?

BTW, after a couple of hours today the little bit of hum became no hum. Nada, but I know how voltage can effect the sound so I'll give it a try.
 
Well it would be 150ma for a 12V Filament. I get 2 ohm at 300ma to drop 0.6V from 6.9V. I would order an assortment from 1 to 3 ohm and cut and try. Dropping such a small voltage, a small variable can throw off the calculation...John   
 
The odd thing, on the surface, it that the heater voltage is not linear.  As John suggests get a number of caps, I suggest using jumpers to start with.

Have fun!
 
I dug around and found a 2 Ohm, 5 Watt WW so that goes in tomorrow morning. Developing a routine: solder in the morning, listen all day.

This A.M. I  bypassed  the muddy midrange Auricaps with .1 Soviet FT-3 teflons. Now they sound like Obbligato Coppers!

Binging right now on Clifford Brown and Max Roach.
 
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