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Ultimate Twin TDA1541a Non-oversampling DAC with tube buffer & reclock set.......

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#363
Anybody has an idea how long this EZ80 valve in the tube buffer will last? Mine has turned into black colour quickly after a short time use. Does the capacitance after the EZ80 seem to large?

I intend to replace the power supply filter caps with 20uF or 30uF film caps (just basic MKT film caps). Will this result in any improvement?
 
#364
The 4u7 capacitor input is less then 10 times the maximum value that the ez80 should work into, and its being run at less then half its maximum current rating, its completely good in this circuit and should last a long time.

Discoloration should not be an reason for concern, but, check the heater voltage, and total current draw from the rectifier to confirm the circuit is operating as designed.

film caps in the supply.. sure, but you'd probably see more benefit from CCS loading the signal tube, or building out into a CCS fed shunt reg for the B supply.

shane.
 
#365
Hi quantran,

I noticed that there was a post earlier in this thread stating that the voltage provided to the EZ80 could be a little high.

I am running the tube buffer off 240V through the power transformers and get about 7.5V at the pins of the EZ80. This is higher than the 6.3V specified for the tube (OK for initial testing) but will follow the advice in the thread and use a 1R (or a bit bigger) in series to get this voltage down to about 6.3V for continuous usage.

Hope this helps,

Ian
 
#366
Ian and Shane

Thanks for your advices I have just chec the heater voltage. It is about 6V. Perhaps there is no need to worry as the DAC still sounds amazing.

I 've try another EZ80 tube made by Tungsram which sound loudsy. The Philips tube makes much better sound so it must be OK.

I still want to replace those 68uF Panasonic eletrolytic caps with film caps. Thomas specified 15 to 40uF at these positions and I may be able to fit 30uF film caps in. I saw that Conrad Johnson use all film caps in its preamp PS.
 
#367
Tube buffer supply

Hi,

Could somebody tell me what I have to connect to the AC-0-AC connection on the tube buffer?

Here in the Netherlands our power outlet is 230 - 0 - Grd. But it looks a bit strange to me to connect the phase to both sides.

Or do I only have to connect one phase and leave the other one open.

This question may look stupid, but this is the first time a work with tubes so please forgive me. 🙂 🙂

Thanks in advance,

Jeroen
 
#369
Output signal Too low

Hi,

Please help me with the folowing problem, any advise is appreciated.

When I Powered this DAC up for the first time I immediatly had the problem that music was only hearable when I turned the pre-amp almost to its limits.

So I checked the output power of the opamp buffer and this only 60 mV the output of the Dac board is 100 mV (with a sinus wave 1KHz at -10dB). So it seems like the opamp buffer is weakening the signal instead of amplifing it.

I am using single opamp setup (one opamp per channel, the AD797 type) and have checked the power supply levels before putting in the opamps. They were -15V and 15V at point 4 and 8

I have not done any of the modifications on the boards which were described in this topic.

Also when I turn up the volume on my preamp and get hearable music this sounds right so it does not look like a fase problem.

I have checked all AC and DC voltage levels before putting in the TDA1541 and AD797 and the all were within acceptable range.

I have not connected any groundwires to any of the boards yet, but as there is no ground in the diagram for the DAC and Opamp buffer I would not expect to find the problem there.

I you have any ideas what could be the cause of this or what I should check please let me know.

Thanks in advance,

Jeroen
 
#371
AD797

Hi Jeroen,

I notice in your last post you say that you are using one AD797 per channel in the opamp buffer, is that correct?

It is just that the opa2604 that comes with the board is a dual opamp, whereas the AD797 or opa627 types are just single opamps per chip.

This means that you need 2x AD797 per channel and they need to be attached to one of the single opamp -> dual opamp conversion boards that Thomas included with the kit. The opamp conversion boards enable 2 AD797 opamps to work with the same pin out as a single opa2604.

For reference have a look at the following:

opa2604
AD797

For a single solution that is already built using 2 opa627 to replace a dual opamp have a look at (under the opamps tab at the bottom):

dual SOIC opa627 assembly

Hope that helps,

Ian
 
#373
http://home.iprimus.com.au/sceglar/250306 012.jpg

hopefully the pic shows up.

Thomas' DAC board fed I2S by USB to I2S converter. Output stage B supply is 6CJ3 - 1uF PIO - 8H - 16uF PIO - DN2540 cascode CCS feeding 0B2 shunt regulators. Pimm plate load CCS, 6DJ8 voltage amp, 10ohm Rk for bias, with some caddock 30ohm grid leaks for I/V.

I2S IMHO is the way to go, significant step up from VRDS transport and SPDIF input. Sounds better than good.

Great DAC kit !!! Thanks Thomas.

shane
 
#374
I think you will also need to use the 82 ohm resistors (coming with the kit) to connect the DAC board to the opamp board. Without these, the opa2604 seems to be overloaded with two tda1541a. I am not sure about the ad797 though.

JeroenVl said:
Thanks Ian,

You are absolutly right. I did not receive the OPA2604 with the board and did not notice the difference between these two types

I will solder these boards tonight.

Again thank you very much.

Jeroen
Click to expand...
 
#376
Muchos gracias

Ian and Quan (and offcoarse Thomas),

Thanks to your help I have got a very nice sounding DAC. :clown:

And yes you also need the 82 Ohm resistor for the OPA 627 (and therefore probably also for the AD797).

Now first of couple of days listening to the opamp version then we start on the Tube buffer.

Again thank you very much.

Jeroen
 
#380
sceglar said:
http://home.iprimus.com.au/sceglar/250306 012.jpg

hopefully the pic shows up.

Thomas' DAC board fed I2S by USB to I2S converter. Output stage B supply is 6CJ3 - 1uF PIO - 8H - 16uF PIO - DN2540 cascode CCS feeding 0B2 shunt regulators. Pimm plate load CCS, 6DJ8 voltage amp, 10ohm Rk for bias, with some caddock 30ohm grid leaks for I/V.

shane
Click to expand...

Wow. that is super cool. Where did you get the board and how did you wire it? I really am interested in ordering Thomas's kit with a chassis and use a interface usb to i2s board like you have done. Does anyone know how much Thomas's kit is with a chassis?
 
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