Yet another output stage for TDA1541

[mevangel]

Kuei and others,
I have built some output stages for my non-OS TDA1541A based dac. IMHO the most natural and involving is the one used in T. Loesch's "Adagio" (others are 1. passive with 8347 sowter trafo and 2. TNT) Now I find intriguing the following idea posted by KYW some time ago:

Best is direct coupled, filterless (but use Anti Sin(x)/(x) Filter), transformerless 7308 (Common Cathode stage per channel), biased directly from the -2mA offset of the DAC at a few 100mV, low anode voltage, choke or CCS load. Watch linearity though, this arrangement is a bit critical, the Valve operates near zero bias. But the short chain of: Chip -> Resistor -> Grid (cathode direct to ground) -> Cap from Anode to output works best from where I stand.

It is not clear to me if KYW talks about a gridleak biasing stage (as the one in his phono pre) or he means a direct DC connection between the current output of the TDA1541 and the grid of the 7308, omitting the series capacitor and the gridleak resistor. I'd like to know something more. Can you help me?
Best regards to you all.
Marco

P.S. I have not tried the solid state rbroer's "Less simple I/V". Does anyone offers a board or a kit for it?

[zygibajt]

P.S. I have not tried the solid state rbroer's "Less simple I/V". Does anyone offers a board or a kit for it?

It would be nice if you would try this and Super Pair one and compare it to the tube ones.I'm curious.

That is what Thorsten recommended on his Yahoo forum to one of the members:

"Try the following:

I/V Resistor = 47R

RLC parallel "Anti Sinc Filter" circuit (130uH, 27R, 330n, 33n) in
series with the 47R Resistor

Lowpass Cap = 56nF in parallel to R + RLC section

Valve Stage E88CC/6922/7308 et al with a 10 ohm Cathode resistor and
a Choke (like the S&B 120H/12mA Anode Load Choke) and around 50V +B
or a 12..15mA CCS with around 100V +B.

The grid bias is fixed at around -0.1V from the DAC's offset and
around 0.15V from the 10 Ohm Cathode Resistor, Output Coupling
Capacitor 2.2uF. Output Impedance is around 3k, minimal load
impedance > 20K.

Let me know what you think."


Bartek

[mevangel]

Hi Bartek,
thank you for reply. The schematic of the sinc filter is a little "obscure"... I guess it is similar to what appeared in this forum some time ago and to the one for TDA1543 found on T.L. forum (with scaled values to adapt it to TDA1541). In this case why two condensers (330n and 33n) ? Do they go in parallel?
About the gain stage: the grid of the E88CC is directly connected to pin 6 and 25 of the TDA1541? Is there a gridstop resistor?
Sorry for "ingenuity" of my questions.
Thank you again.
Marco

[zygibajt]

Hi Bartek,
thank you for reply. The schematic of the sinc filter is a little "obscure"... I guess it is similar to what appeared in this forum some time ago and to the one for TDA1543 found on T.L. forum (with scaled values to adapt it to TDA1541). In this case why two condensers (330n and 33n) ? Do they go in parallel?
About the gain stage: the grid of the E88CC is directly connected to pin 6 and 25 of the TDA1541? Is there a gridstop resistor?
Sorry for "ingenuity" of my questions.
Thank you again.
Marco

I think they go in parallel ,together with resistor and choke and as said then in series with resistor.
I don't really have much expirence in tubes,so can't answer to you questions.But I'm also interested in ultimate analog stage for TDA1541A.Maybe Thorsten himself will help.

All Best

Bartek

[GaryB]

Originally posted by mevangel
Kuei and others,
I have built some output stages for my non-OS TDA1541A based dac. IMHO the most natural and involving is the one used in T. Loesch's "Adagio" (others are 1. passive with 8347 sowter trafo and 2. TNT)

I'm curious if you built the Adagio with the 8347 transformers or if you used the exact transformers that Thorsten suggested, the TM-3s from Amplimo?
I've got some 8347 transformers on hand and I"m interested in playing with output stages for my TDA1541a non-OS dac and I 'm curious if I can try the Adagio circuit with these. In his Adagio article, Thorsten makes some remarks about tuning his filter for the particular response of the TM-3s.

---Gary

[mevangel]

Hi GaryB,
The digital board and the power supply were common for all versions of the DAC.
The digital circuit was the one presented by Thorsten Loesch.
The power supply was the one presented by Klaus Bohem.
I have built a tube output stage based on T.L. Adagio: 22 ohm resistor + Amplimo TM3 transformer + RLC T-filter + E182CC SRPP.
You can certainly use the Sowter 8347 but, as T.L. observed, you have to trim some values of the T-Filter to obtain the peak at the correct frequency in order to compensate the non-OS losses at high frequences. With the 8347 you will also obtain a little more gain.
The passive output stage I have built uses only a 22 ohm resitor and a Sowter 8347.
I definitely prefer the tube active stage, but some listeners, among my hi-end-addictioned friends, preferred the passive one.

These days I am experimenting with Rudolf's "less simple I-V" and will report as soon as possible.

Marco

[GaryB]

Marco,
Thanks for the feedback. Since I have the Sowters, I'll probably just try the E182CC output stage without the sinc filter. I can always compensate for the slightly higher step up with lower I-V resistors. If I like the sound but find it missing a bit of air then I might spring for the TM-3s.

Please keep up posted on your progress with different output stages.
Thanks,
---Gary