4P1L DHT Line Stage

[beardman]

Hi Ale

maybe i shall tell how my hifi is

i use a LS9 line Array speaker...

i same box i have my DDdac 1794..and Groundsound digital filter

the Groundsound give signal to my Groundsound bass amp

and the Groundsound give signal to my Encore amp who drive my Tweeter

from the DDdac the signal goes to the 4P1L

From the 4P1L signal goes to Groundsound filter

my sekundare winding have no connetion to ground (Lundahl 2745)

picture come later

best Bjarne

 

[michaelvv]

Hi Everyone..

Pictures from Bjarne, another dane with a 4P1L.

/Best Michael

 

[beardman]

Thanks Michael for upload the pictures of mine Pre

best Bjarne

 

[beardman]

Have try to messure with my voltmeter in 300mv area

out on Coleman reg about 3mv ac

out on Lundahl trafo 0.4mv

with my scop an can see something,,but do not know what to look at

 

[euro21]

out on Coleman reg about 3mv ac

???
It's too much.
At least one orders of magnitude greater, than what I measured in my #26 preamp R.C. regulator (1A heater current, -10V on the bias resistor).

 

[beardman]

Tomorrow i will use another voltmeter--in the firm i have a Agilent..will try and see if it gives the same result--as my Elma

 

[Rod Coleman]

Hi Bjarne,

Yes, Bela is right, 3mV is too much.

The rectifier and caps of filament supply must be near the transformer. This is important for low noise.

If they are moved to the transformer chassis (best), please add 1000uF 35V to the Regulator input - right on the PCB.

Cables to the output - maybe these need to be shielded too.

 

[beardman]

Hi Rod
have you seen the picture a little op in this tread...Michael has oploaded them for me

 

[beardman]

will try tomorrow to move the rectifier and caps to trafo,,

 

[Rod Coleman]

Yes - I think I can see the Filament supply rectifiers there. If they are far from the transformer, there will be some trouble with (radiated) noise.

 

[beardman]

let you know tomorrow if it help to remove the supply to trafo

 

[beardman]

Have remove rectifier and caps to trafo.. one resistor and caps near the Colman regulator

no change in noise

have messure ac on Coleman--my Agilator instrument show 0.4mv ac--the other instrument show 2.3mv ac---

have the noise something to do with the Lundahl trafo....i have once use a trafo on my kkdac ,,,there was hum ..

Best Bjarne

 

[Rod Coleman]

0,4mV - 2,3mV is probably just pickup on the meter leads.

The photo shows twisted, but unshielded cables to RCA (phono) connectors at the back.

Is this the volume control wiring? This will need to be shielded - it looks a long run.

 

[disco]

The input RCA plugs seem to be grounded to the case and not to star ground. The idea behind star grounding is to create a point that is considered to be at 0,000 volt. All small currents return to this point, all large currents and other noisy sources too. Sometimes (in a large build) one can combine certain routes that don't bite each other, like in this example:

An externally hosted image should be here but it was not working when we last tested it.

If you don't find a quick fix to the problem you're experiencing (was it humm?) I recommend starting all over again and beforehand think out the important placement of components. Filament supplies must be close (within 8cm), heat must not warm up nearby components. Do not combine 'busy' wires and signal wires in one cable etc etc.

 

[KevinC]

I keep a 10cm x 15cm piece of thin (~1mm) steel that is completely double wrapped with plastic packing tape around to test for magnetic induction hum in input and output transformers. With the piece of electronics in question powered and connected into an audio system I place the steel in between suspect power transformers or chokes and the audio transformer to see if the hum is reduced substantially. If it is, then I've found the problem and can devise a permanent magnetic shield or move one of the actors in the hum drama. The packing tape wrap keeps you from making unwanted sparks in a live circuit!

 

[beardman]

Thanks all for helping me
i will try all the latest idea

maybe it could be a ground loop----the hum is there ,,,but the buzz is more annoying

Best Bjarne

 

[beardman]

Have tried to move the Lundahl trafo just outside the cabinet...and wrap silver paper around,,,,,now is the hum very low

only thing now is the buzz in the tweeter region (from 900 hz and up )

where come buzz normally from ?

best Bjarne

 

[Rod Coleman]

Rectifier noise on the B+ supply, or possible oscillation of B+ regulator.

What value of Cap after High Voltage rectifier?

Double check B+ regulator connected just like its manual says?

 

[neskor]

Do you use two separate transformers for Rod regulators?

 

[beardman]

After rectifire on high volt--resistor...470uf ---resistor ..470uf...resistor ..68uf...and close to Maida regulator 0.33uf

i will check manual for Maida ones more....i have plus to Lundahl trafo,,,,and minus to star ground

I use only one trafo for Coleman regulator...seperate windings---is this very bad ??

best bjarne