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OLD THREAD DAC End by Andrea Ciuffoli

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#1,641
Nikon1975 said:
I have a small problem in the protection circuit of the I/V. When the voltage approaches the opening of the relays, I have a strong oscillation, like the relays opening and closing very quickly. This happens only if both the tubes are installed, and only on one I/V (I have two). Now I have a BC550 instead of a BC337 installed (I could not find the right one), but on one board works OK. Is it just a faulty relays ? I hope not, it's a nightmare to unsolder it 🙂. I am not very familiar with this circuit, any hint to stabilize it ?

Thanks,

Davide
Click to expand...

Hi Nikon1975,
Can you please tell me how you solved the problem with relays oscillation?
 
#1,643
I experienced this (see waaaaaay back in the thread). It is due to intitial poor regulation of the 6.3v and slow start up.

To solve i dropped the 2.2r resistors to 1r, i also changed the rc cap to 100uf.

The combination led to an oscillation free relay.
 
#1,649
Nikon1975 said:
Hotzman, for me increasing the ac voltage that feeds the regulator fixed the problem. Try a 7.5 transformer.

Davide
Click to expand...

Thank you! I used 10V AC and the problem was solved! But now from time to time the output signal is interrupted. The buffer running a time (listening to music) and are moments(some seconds) when the relay does not work!
And I have to solve another problem: analog signal after buffer is noisy
( hum)!
 
#1,650
Hotzman,

Check the temperature of the regulator (the filament one, do NOT touch the sink of the HV). I do not know how the temperature protection works for the 1084, but I think that what happen is that the filament voltage goes down from time to time. With 10 V you dissipate at least 5 W in the heatsink.

Check also for cold soldering joints.

For the noise, do you have noise when the DAC is not connected to the I/V ? Check for residual AC in the B+ (DMM in AC mode) or bad tubes. Mine is dead quiet. I have to say that I do not have any ground connected, as the things are mounted on a piece of wood now.

D.
 
#1,652
My Dac-ends has sung for a couple of days now with very nice sound and spectacular mids. Attached are some photos after it was housed in a chassis.

I use 8.15 volt AC and lm338T for the filament regulator. It's too hot inside the chassis even with a 2" heatsink with a BGA heatsink sitting on its top! 😱

I'll be cutting traces of the filament PCB and install a 0.68R 10W between the 4700UF caps to lower down the dissipation. Of course, I'll use lt1084CP in lieu of the 338. Unfortunately I only have the TO-3P version so some modification to the leads of the IC is required.
 

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#1,654
housing said:
My Dac-ends has sung for a couple of days now with very nice sound and spectacular mids. Attached are some photos after it was housed in a chassis.

I use 8.15 volt AC and lm338T for the filament regulator. It's too hot inside the chassis even with a 2" heatsink with a BGA heatsink sitting on its top! 😱

I'll be cutting traces of the filament PCB and install a 0.68R 10W between the 4700UF caps to lower down the dissipation. Of course, I'll use lt1084CP in lieu of the 338. Unfortunately I only have the TO-3P version so some modification to the leads of the IC is required.
Click to expand...

Nice work!

What chassi did you use?

Did you compare the original powersupply to the the shunt psu you use now?

David
 
#1,655
Yunick said:
Nice work!

What chassis did you use?

Did you compare the original powersupply to the the shunt psu you use now?

David
Click to expand...

Hello David,

Thanks.

I have the chassis from a local diy shop costing me about USD70.- It just fits all pcbs of the DAC-end and the 2 trafos.

I do not have the pcb of the original power supply and thus I can't compare its sound with that produced with the shunt supply. Sorry.
 
#1,660
Is there a builder's thread for the "END 2" DAC project?
Also, any suggestions on sourcing the Os Con's? Would the Black Gate variety of caps work as good here? I have been having a hard time coming up with any Os Con's of the values shown to build this project.
Thanks,
Jeff
 
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