Sunday, June 29, 2014

Slagle Autoformer Volume Control Modules And My First DIY

This is my first completed DIY project #I01 or I owe one. A while back I found a 1930's Phillips battery box and had refinished it for some project in the future. Ok I knew what I wanted it for as I was already a Slagle AVC fan. There are no power supplies or resistive parts which made it a good first project. Dave Slagle has cured me forever wanting or needing a traditional preamp. The AVC has been one of the biggest improvements I've made to my system.
I really dig the 80 years of attitude the box has picked up and glad it still shows. Problem is now I want to use this look again but I need bigger boxes for amp building.
This is the best shot I got of the  Slagle autoformer modules as I wanted to get them loaded ASAP.
These Autoformer modules operate in a slightly different manner than traditional linearly switched volume controls. Rather than using a single switch, two discrete switches are used to control the level. The switch on the left has 12 posiitons that are in 3.75dB increments. The switch on the right has 3 positions allowing +1.25dB, 0dB and -1.25dB modification of the overall level. By using this dual switch arrangement 1.25dB steps are possible. The total attenuation range goes from +1.25dB to -41.25 dB in 32 steps. The nature of the device skips the -3.75dB tap so the steps are +1.25, 0, -1.25, -2.5, -5, -6.25, -7.5...1.25db steps to -41.25 and off.

Q - Why use an autoformer volume control? I've been happy with a good quality potentiometer.
A - The simple answer is that most people find that the autoformer volume control sounds significantly better than even the best potentiometer or stepped attenuator. And it's not a subtle difference; most people report that the autoformer has such an open, effortless sound that they would not consider going back to a resistive device.
Exactly why they sound better is still under debate, but one theory is that it's because an autoformer doesn't attenuate by wasting energy. A fairly good analogy can be made to the transmission in a car. If you need to drive at a slow steady speed which method would you choose: (1) leave the transmission in high gear and apply the brakes to keep from going too fast, or (2) downshift into a lower gear that will allow the car to go the desired speed with minimum effort?
An autoformer is essentially an electronic gearbox that operates without wasting significant energy. Potentiometers and stepped attenuators adjust the signal level by literally turning the excess signal into heat. On the other hand, when an autoformer is adjusted for low volume level it actually makes things easier for the source, much like a low gear makes things easy for your car engine.
It becomes quickly apparent that the reflective load can be ignored in this case since it is many multiples of the inductance in parallel with it. Inductance gives you a impedance = 2*pi*Frequncy*L(inductance) or Z=2piFL. Its this simple formula that tells you what you need to know about the impedance presented ot the source.

Here you can see the acid burns from the old batteries that leaked  in the box. This was before and after wiring these up with magnet wire. I think the green wire sounds best ;-). Fortunately Dave's modules makes them very easy to install so even I couldn't screw it up.
Here are the left and right sides. 
 I tried many different new knobs on this box but they just didn't look right. After purchasing the wrong sized vintage knobs three times I finally got these and pulled the big selector from a Bud national radio I had. Lesson learned vintage box gets vintage knobs. 

There will be no labels. Perhaps that will keep party guests off my knobs.
Thank you Dave Slagle aka Intact Audio.

Saturday, June 28, 2014

TMBG - Don't Let's Start

This was my intro to They Might Be Giants back in the late 80's. TMBG was just what I needed at the time. I even called Dial-A-Song a few times. 

Friday, June 27, 2014

Wednesday, June 25, 2014

Power Amplification And The 245 Tube - Radio News 1929

I've been doing my homework researching the old triodes when I found this old article. It is just two pages but I also noticed the magazine was packed with info on the 245 and some on the 250. I included a few ads from the magazine as well.

I really like the simple utilitarian look of this amp. 225 245 and 280 tubes.

Monday, June 23, 2014

Zeiss Ikon - Ikovox CD

Here is something we don't see very often a trio of Zeiss Ikon Sound. 
What didn't Zeiss build anyway? 
Quality is high and they look superb. 
Does anyone have additional information on these?


Open baffle still baffles me.....Didn't Olson set that straight?

Sunday, June 22, 2014


Saturday, June 21, 2014

Motörhead Guts and Glory

This is a cool documentary about Motörhead and subtitled due to the English dialects. Great band and I'm not a big metal fan but you gotta love Motörhead.

Motörhead - GUTS AND GLORY 

Louie Louie
Perhaps my fave cover of this song. 


Ace Of Spades
Ok Rick Mayal died last week and without seeing this performance on The Young Ones I might not have been a Motorhead fan. 

Friday, June 20, 2014

Wednesday, June 18, 2014

Tuesday, June 17, 2014


Amen. "Only a big speaker system can authentically reproduce big instruments".

Sunday, June 15, 2014

The Bar-Kays - Soul Finger

Funk yeah! 
I didn't realize this was a STAX recording but I should have known all along. 

Saturday, June 14, 2014

$5 National Union NX 245

So Stacey made me go to the neighborhood boot sale but I said it was just a bunch of crap and couldn't we just have brunch instead.... Well no so we went and I scored a single tube for $5. If it works I'm in like Flint. My tube tester doesn't test old triodes so I'll add it to the list of things to pick up. 
If it works I guess I'll have to find a mate... Perhaps the tube hoarder will help me test it...
If only I had a schematic for 45 tubes ;-)

Friday, June 13, 2014

Thursday, June 12, 2014

Hi-Fi Stereo - Hang It All

I had this issue with three other turntables then I got a Garrard 301 with a TPA10 tonearm and the problem went away. I upgraded to a Jelco 12" and still no issues. I was about to go down this path of hanging my turntable but I'm glad I didn't since I have 12 ft ceilings.

Tuesday, June 10, 2014

1936 Presto Stationary Recorder

This would be one heavy beastie.

Sunday, June 8, 2014


A very early what would become the MC30 ad.

Friday, June 6, 2014

Thursday, June 5, 2014

1953 Bass Horn House

One this is a good sized bass horn.

Tuesday, June 3, 2014

Moondog - Viking Of Sixth Avenue - Kickstarter

This is very exciting. There is finally a serious evaluation of the life and times of Moondog.

If you love Moondog consider donating to the kickstarter.

Sunday, June 1, 2014

Cab Calloway

One of the masters.