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

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#623
Any luck with good Dig IC match for NOS Dac?

Wondering if anyone has achieved noticeably better resolution and/or improved soundstage by experimenting with different digital ICs for the NOS dac? I'm currently using a diy Belden 1505a IC...the cable that came with the kit. Striving for better resolution! I'll post my mods to the V2 project shortly.
 
#625
Quan Tran, I'm using my CD player as the transport. It's a Njoe Tjoeb (24/192 upsampled as a DAC). I did switch the position of two brands of analog ICs. I now have VHAudio Pulsar betw Dac and preamp, and Swiss wire between Pre and Amp (flip flop). Improved highs. Percussive brushwork is more open and slightly less distant in the sound stage. However, the overall soundstage is still slightly diffuse compared to using the Tjoeb for d-to-a conversion. I only notice this in an A B comparison of the same tracks. On the positive end, vocals are relaxed with no sense of glare on the NOS Dac. Trade offs. I'm going to try a different digital IC.
 
#627
Some pics and my mods

Well, I think I was the last to assemble Thomas's version 2. It was my first component-level DIY project. Many thanks to everyone who helped along the way, and a special thank you to Quan Tran, JeroenVI, Shane and Jarthel for helping me get it to play music. It's been in a temporary chassis while I finished the mahogany wood one in the pic below. Here's the mods that I've completed, all suggestions posted on this board.

DAC board:

1. replaced the digital input cap with Blackgate NX
2. replaced the digital input resistor with Caddock 75R
3. replaced the I/V resistors with Mills wirewound (tried 22R and 44R)

Op-amp Stage - never used

Tube board (have only used 6dj8/6922/7308 tubes):

1. removed cathode bypass cap
2. replaced inductor (L3/L4) on input with mills wirewound 20 ohm
3. replaced first cap on input with 1nF polystyrene & tin foil
4. removed caps C24 and C42
5. replaced 6800R resistors on B+ line with 20K (my voltage was too high)
6. replaced output coupling caps with Mundorf Supreme 2.2uF (because the next stage is TVC)

Wiring and AC:

1. Fururtech IEC inlet
2. chassis mount fuse
3. 2-pos rotary switch and ebony wood knob (source: thingamaknob)
4. VH Audio AC internal wire
5. VH Audio pulsar mini coax for LED, and Digital input wire
6. Audio Consulting silver wire in cotton sleeves for all analog wire
7. Inserted 1.2ohm resistors after 6.3V secondaries before board (voltage too high)

USB Input
1. Doede's USB board with Tent clock will be connected via I2S (waiting to arrive)
2. USB type-B female socket on chassis

Chassis and resonance control:
1. Custom African Mahogany Chassis
2. All transformers shock-mounted on microsorb and EAR C-1002 paper (Percy Audio)
3. Both pcb's mounted on EAR isoloss grommets (Percy Audio)
4. Brass bolts and hardware used throughout
 

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#628
OK, Tube-Lover, I'm new and I didn't read all the posts here but I would like to buy your dac kit. So, please tell me how much it costs. Right now I using an Audionemesis DC-1 dac wich is a nonoversampling dac but it has a precice clock( asincron!).

Thanks !
 
#631
I just connected (for the first time) the TDA1541 DAC and is sounds pretty nice 🙂

I do have the DAC board rev 1.2 and the opamp board rev 1.0 using OPA2134 opamps.

I do have some questions though:
1. When I remove the I/V resistors from the DAC board the sound is distorted, how is this possible? When I put them back in it sounds good. Is the opamp board supposed to do I/V conversion or not?
2. Where van I find the schematic of the opamp board?

If anyone could answer my questions it would be very much appreciated (couldn't find the answers in this very long thread..).

Best regards,

Ronald
 
#634
I only tried the opamp board once a long time ago. I remember that it sounded normal when I removed the I/V resistors.

It did not work without the 82 ohm resistors in series between 2 board.

It sounds much better with the tube buffer so I did not bother much with the opamp board.
 
#635
Hello Quan,

After reading your post I was starting to doubt, did I tried the DAC without I/V resistors before or after I read about the 82 Ohm resistors.

So I removed the I/V resistors again and tried (with the 82 Ohm resistors in series in place) and got again very distorted sound.

To make sure (I used a different opamp then most) I replaced the 82 Ohm by 2K2. Still the same distorted sound (at much lower volume of course).

So this seems kind of weird to me. I would like to try different opamps before going the tube route.

Maybe this opamp board revision I got does not do I/V conversion ? On the other hand there is "opamp I/V convertor" printed on the opamp board so this does not sound very likely.

Since the sound is fine when keeping the I/V resistors in place I do not think there is anything wrong with the DAC itself.

Hopefully Thomas can shed some light on this issue and maybe has an idea what is going on here?

Best regards,

Ronald
 
#637
Hi all,

Yesterday I tried AD797 opamps (using the convertor board). But when I removed the I/V resistors there was again this mega-big distortion.

Then I removed one TDA1545 from the board and the distortion was gone, the sound was fine! To make sure that I did not had one defect TDA1545 I took the 1545 out and did put in the other one. Still perfect sound!

I also switched the 1545 to the other socket (still using only one) and still perfect sound.

So it looks like the problem is in paralleling the dac outputs when using no I/V resistors.

Does anyone have the same experience?
Does anyone had the opamp board playing with good sound without the I/V resistors and using two TDA1545 ?

Hopefully somebody can shed some light on this issue.

Regard,

Ronald
 
#639
It seems like the 3K3 I/V resistors on the opamp board are way too high in value.

2 dacs give a full scale current of 2x4=8mA. An I/V resistor of 3k3, results in a voltage of 26.4 Volt which is larger then the 15V power supply voltage and thus distortion. An of course the amplifier the DAC is connected to won't like this either.

For a 2Vtt output a resistor of 680 Ohm is suited.

After searching again in this thread Thomas actually mentions somewhere that these resistors should be changed to 820 Ohm.

So I am going to try this this evening which will probably solve my problem 😛
 
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