Aleph 3? Project.

[Zen Mod]

ref to schm in post #1 - increase 1K (situated on inner IRF9610 gate , in series with 220uF) to 2K , and you'll have half gain (-6db vs. original , overall 5x , which is 14db)

no sonic penalty vs. original

 

[Zoef]

Zen, thank you VERY much.!

 

[Zoef]

Zen Mod. To be absolutely sure, this is the resistor i need to change?
In all the revisions this resistor and the one on the input stay the same. Would that mean it works on all revisions?
If so, I could build the "latest" version and if i ever change speakers i could simply swap back the original resistor.

I tried to google what this means, changing the gain. To be honoust i'm a bit lost. If gain changes, does the power output change also?
Or does power output stay the same only it has a "weaker" signal to amplifie

 

[Zen Mod]

yup , that's it

ratio of 1k:22K on left and 1K:10K on right is already different and nobody objected

in this case , not much difference , at least not to care ....

 

[Zoef]

Ah... i just updated my post

 

[Zen Mod]

keep googling ........


power is in function of many things , but mostly of PSU rails and ability of circuit to use voltage and current potential of PSU

gain is ratio of input/output voltage

so , when you decrease gain , you need to shovel more volts in amps input to push full power in spk

changing the gain , you didn't change power of amp

pic of the day :

 

[Zoef]

[emoji14]

 

[Zoef]

Thanks

 

[chelg2012]

Mr Pass posted a revision of the aleph 3 schematic. Now using some Toshiba 2sj313's. And some other changes are made. I took a long stare at the schematic and compared it with the kk schematic i got with the boards ( first post in this thread) . If i am correct the kk is exactly the same as the aleph 3 schematic of 1995. No.: pl40r02.501
On this schematic r113 is 47K and R114 750r. The revision shows 56k and 680r. Would it be a good idea to replace these as well?

Dear friends,
Could someone provide this scheme with the original revision from Nelson Pass ?

 

[Zen Mod]

http://www.diyaudio.com/forums/pass-labs/267857-aleph-design-reloaded.html#post4184920

 

[rif]

I believe this is related so I'll post here. Should the output of the PS drop once it is hooked up to the amp circuit? Input is around 20Vac, something like +- 27 Vdc before connecting it, +-22Vdc when connected to the amp pcb?

 

[chelg2012]

I believe this is related so I'll post here. Should the output of the PS drop once it is hooked up to the amp circuit? Input is around 20Vac, something like +- 27 Vdc before connecting it, +-22Vdc when connected to the amp pcb?

You are absolutely right! Initially, the amplifier contained one 300 VA toroidal transformer. AC input was around 20Vac. DC output was about +- 26 Vdc without connection to a board and +- 22.8Vdc under the loading. Toroidal trans was very hot.After addition the second tor(dual mono) the DC voltage under the loading become exactly +-25 volts. As a result the decline in HF was gone! Thanks for the reply.

 

[6L6]

rif - Yep. Completely normal. The 27V is no-load, and the Aleph is a big draw, so it seems a bit less than you are expecting under load.

 

[koja]

that's why you should always check the regulation number for the transformer. basically a percentage drop under full load to have an idea where it will end up on the amp rails.

 

[rif]

that's why you should always check the regulation number for the transformer. basically a percentage drop under full load to have an idea where it will end up on the amp rails.

Thanks, I've been trying to get some specs from antek. Its an an-8238, with 2x 38V secondaries plus 2x 12V sec. If it follows typical antek nomenclature its 800VA. They won't/ can't send me a datasheet. I run the primaries in series to get about 20Vac.

 

[nr12]

Thanks, I've been trying to get some specs from antek. Its an an-8238, with 2x 38V secondaries plus 2x 12V sec. If it follows typical antek nomenclature its 800VA. They won't/ can't send me a datasheet. I run the primaries in series to get about 20Vac.

Did you ever think about using a 300VA, 2x18VAC transformer?
That should be suitable for Aleph 3.

Ulf

 

[rif]

Did you ever think about using a 300VA, 2x18VAC transformer?
That should be suitable for Aleph 3.

Ulf

Well its actually for an aleph 30, its what i had on hand, and i have aspirations of eventually turning it into an aleph 60.

If 18Vac is suitable, so should 19Vac. 800 VA may be overkill, but shouldn't be an issue either.

 

[Dennis Hui]

If you are using a CRC power supply, how much resistance do you have for R and
what voltage drop are you seeing?

 

[Zen Mod]

Thanks, I've been trying to get some specs from antek. Its an an-8238, with 2x 38V secondaries plus 2x 12V sec. If it follows typical antek nomenclature its 800VA. They won't/ can't send me a datasheet. I run the primaries in series to get about 20Vac.

it isn't 800VA anymore

wire in primary is dimensioned for 400VA per winding , plus some leeway

so , connecting two primaries in series , while still on 110Vac , current capacity of wire is weakest link in chain

result - it'll be 400VA plus that leeway

however , if you're cheapskate ( as I am often , by choice ...... but most often erring to overkill side) , use it , having on mind real/resulting power

 

[rif]

I think im using 16gauge wire for all power connections. I guess i could go to 14 gauge, but then im likely to use some speaker wire scraps i have,.

Here's what im seeing, no signal input.

PS not connected to amp input 20Vac, output 27.3 Vdc
PS connected, Cold : input 17.8 Vac, output 18.14 Vdc
PS connected, Warm: input 18.0 Vac, output 18.8 Vdc

Other notes: the thermistor on the transformer primaries gets hot. The thermistor between the PS and ground is cold. The rectifier diodes get hot.

The PS and amp boards are BrianGT. The PS is CRC with 44,000uF, then 3x 1 ohm, then 22,000uF all per rail.