At last, My Aleph 2+

[Brian Donaldson]

I was refering to the homemade coils on the smaller caps. They have too low R and H. I need to dump around 6 v to bring the rails down a bit.

 

[Mark A. Gulbrandsen]

Nice Job! My 2's are running with about +- 42 volts due to availability of surplus toroids. First thing I did was pull the bias resistor completely out and man what a difference..... Now to add a couple more devices and make the changes to go to 5 amps.....Thats gotta sound great and will greatly reduce my GAS bill costs this winter. My 2's will be one year old this xmas!
Mark

 

[Panelhead]

Now that my darling bride is out of town, I've been hard at work. The first of my Alephs is up and running. I let a little magic smoke out before I bought a variac. I must admit, I was worried that I sunk $700 into a project that may never get finished. I replaced 5 shorted fets (yes they failed shorting drain to source) and a few source resistors and powered up slowly.
First was some 60 hrz hum , then sound. I inched it up and it became clearer and the line on the scope sharpened.
I worked the voltages up to +- 40 then cranked the bias to 5 amps total and the line on the scope became razor sharp and dead straight. And the sound! Beautiful clear and focused.

Thanks to everyone
Hardvarian and BrianGT for the boards
Damon for the new soldering station
Mark for the insperation
And the countless other posters (I've read them all over and over)

Looks great. I wish my projects looked near as nice. My wife and children are leaving Wednesday for a month. There are several projects I hope to finish with that much time.
Also, we have that same table and chairs from World Market. But my wife does not let me work on it.
I could not live here in Houston with the Aleph 2's. My Zen V4 generates just about all I can handle. But it gives up a lot in bass and punch to those power hungry 2's.
I guess you have been there, but Ace Electronics has the chokes you need. Big muthers for 15.00 to 25.00 each. You should find 6 mH 15 amps ones that have 0.2 - 0.3 ohm DCR.

George

George

 

[jam]

Mark,

When you say you pulled out the bias resistor what do you mean,
and what improvements in sound quality did you get?

Regards,
Jam

 

[Mark A. Gulbrandsen]

Thats easy, just pull R-19 the 56k resistir and the amp goes wide open... as based on other preset component values.

The soundstage went much deeper and wider. Distortion also goes down lower although they sounded really nice with R-19 in circuit...things just got even better. I also had to increase the line fuse to 5 amps. The specified fuse would blow after a week and a half.
Mark

 

[jam]

Mark,

Have you tried pulling R21 thusbdefeating the dynamic current source?

Regards,
Jam

 

[Mark A. Gulbrandsen]

Nope, Haven't tried that as of yet. Does anyting else have to be changed to be able to do that and what is the overall effect of doing it?
Thanks!
Mark

 

[Eric]

Brian, Great looking work! I'm a little confused about your power supply configuration, would you be able to describe it in a little more detail for me?

It looks like you are building a stereo Aleph 2 using a single transformer (with a single secondary) feeding your two large caps, and then tap individual + and - rails for each channel (the four smaller caps) from the two large caps. This would mean that the toroid and two large caps are shared by both channels. Is this correct?

 

[jleaman]

Congrats another aleph 2.. Mine to come soon now..

One thing you shuold do is make sure you have no metal shaveing near or in the amp. would hate to see you power it up and see a nice spark or clowd of smoke..!

 

[Brian Donaldson]

Eric
Actually this is only one channel. I added 2 extra output fets to each rail and decreased source resistor to .89ohm to raise bias.
The toriod feeds fred diodes to 2 huge caps (68000uf100v) to 6mh air inductors to 2 pairs of 17000uf75v caps. Sims showed .05v ripple(if I remember right) at 5A load.
I haven't got it all back together, but I'm expecting 50v at 5A bias.
I'm going to include a pot and bias meter so I can turn it down for non-critical listening. I'm also including a temp meter and output meter and variable speed fan so I can keep an eye on everything and try to not burn down the house.
Before I tore back in to it, I was running both channels from a 22A variac at around 180v in to get 50V rails and it sounded great. But it ran at 170 deg without the fan. I'm hoping the fan can keep it down around 155 without making niose. I wish I had 20 hours to finish tham instead of only sneaking a few minutes here and there to talk and dream.

 

[Brian Donaldson]

Jason
I'm now a veteran. I let some smoke out of the first one and debuged a incorrect resistor in the second one that wouldn't bet the bias up. Now I fear nothing.

 

[Eric]

Thanks for the details, Brian! Sorry if I missed it earlier. Great work - I think I'll try using a metal chassis when I get around to my Aleph-X. My first amp was made with a wooden chassis and it was very easy to work with.

 

[MikeZ]

Brian,

I think I want to put a pot for r19 and a bias meter on the front panel

I have seen several post on a meter. I like the idea of a meter. How would it be connected so as not to degrade the sound?

Mike

 

[Brian Donaldson]

I'm putting one meter across a source fet. My source fets are less than one ohm, and the meter impedance is around 50Kohm, so I don't see how it could be audible. The second will be hooked up through a NTC varistor / voltage divider to be a sink temp gauge. The third will be hooked to the output through a resistor, small signal bridge rectifier, and cap to be show output. No scales or gradients, just ballpark indicators. Bias indicator will be 3/4 scale = 5A total bias, Temp indicator will be 170 degF will be 3/4 scale. I may put in a switch for dual sensitivities for the output.

 

[jleaman]

I have a great idea for my amplifiers. it is for temp status. it will be 5 green Small led's and one blue.

The blue is power on. and the 5 green leds are going to show me starting from bottom mildly warm and the top will be peak temp.

i cant wait.

Parts are on there way so should be able to start Alephs very quickly

 

[Kermit]

JasonL, that sounds interesting do you care to elaborate?

 

[Brian Donaldson]

Ah at last. It's starting to look like a amp I'll be proud to say I built it myself.

 

[Brian Donaldson]

Check it out. Hinged standoffs. A tweakers delight.

 

[jleaman]

Hey you mounted your resisters just like mine : O)

 

[Brian Donaldson]

The buss bars are made out of 3/16" x 2" copper bars I found on ebay. I'm a little worried that my coils may go up in flames. They'll be dissapating 20 watts+ each and I'm not sure how hot that'll make 'em. If they smoke, I'll just replace with a larger one. I potted the inside with polyurethane, nylon bolt, and a cpu type heat sink. (I may have ****ed away $50.00 and 2 hours. we'll see)