Buffalo II & transformers

[Angelm]

Originally Posted by Marek

Last days i tried this BuffaloII output stage configurations:
1. passive stage using Jensen JT-11P-1
2. Jensen -> SRPP based on 6N30P supertube
3. DAC directly to SRPP
4. DAC directly to tube diffirential preamplifier (PP->SE on 2 triodes+ current cource in cathodes a than cathode follower to lower output impedance)

Marek, the next step is to try tube output stage,
could you share simplified scheme of point 3 and 4 ?

[Marek]

3. SRPP -> The Valve Wizard- SRPP
4. diff preamp http://rapidshare.com/files/448854915/ls60_balance.pdf

ofcourse for you should modify circuit for tube you choose.

and one more thing. If you want to connect DAC directly without caps you have to recalculate cathode resistors to compensate DAC DC offset.

[pirastro]

I am in the interim tried using a step up with 28dB gain. The primary is 1.5R and secondary is 400R, with good results, appreciate some advise if this is safe for longterm usage?

Do you reckon if any of these could be adapted to work with B-II, which would be ideal?
a) 6SN7 SRPP by diyhttp://analogmetric.com/ebay/6SN7%20Preamp%20schematic.JPG
b) ebayer raindrop_hui's SRPP tube output module coupling transformer

Thank you

[pirastro]

Originally Posted by pirastro

I am in the interim tried using a step up with 28dB gain. The primary is 1.5R and secondary is 400R, with good results, appreciate some advise if this is safe for longterm usage?

Do you reckon if any of these could be adapted to work with B-II, which would be ideal?
a) 6SN7 SRPP by diyhttp://analogmetric.com/ebay/6SN7%20Preamp%20schematic.JPG
b) ebayer raindrop_hui's SRPP tube output module coupling transformer

Thank you

Appreciate any advise on this, thanks in advance

[Marek]

Step up trafo you use is ok for long term use.
You should load secondaries with a proper resistance (as low as possible) to allow DAC see low impedance (to put Sabre outputs to work in near current mode).

From my experience step up trafo is not the best choice with Sabre32 chip - it is not typical current out DAC and it seems working better in voltage mode with 1:1 trafo (like Jensen JT-11P-1).

If you plan to use tube output the best choice is leave trafos and put positive DAC output DIRECTLY to tube grid without any capacitor (you should recalculate cathode resistor to compensate Sabre DC offset)
SRPP is good choice but that one form analogmetric is based on 6SN7 tube which has definetely to much gain for voltage mode Sabre and to high output impedance.

[WDYSUN]

Originally Posted by Marek

Step up trafo you use is ok for long term use.

What do you mean by "long term use"?

You should load secondaries with a proper resistance (as low as possible) to allow DAC see low impedance (to put Sabre outputs to work in near current mode).

Originally Posted by Marek

From my experience step up trafo is not the best choice with Sabre32 chip - it is not typical current out DAC and it seems working better in voltage mode with 1:1 trafo (like Jensen JT-11P-1).

how did you load the trafo?

Best
Pietro

[Marek]

Every trafo is safe to use with Sabre DAC, but not every will work as you wish.

If you use 1:1 trafo you do not have to load secondaries with any resistance - just connect it directly to you amp/preamp.

[WDYSUN]

Originally Posted by Marek

Every trafo is safe to use with Sabre DAC, but not every will work as you wish.

If you use 1:1 trafo you do not have to load secondaries with any resistance - just connect it directly to you amp/preamp.

yes but you said something about "long-term" use which to me is quite strange, can you tell us what did you mean?

Pietro

[markusA]

I'm running a 2:1 trafo and it's working perfectly. I haven't even had the time to fine tune the load for the transformer and it's still kicking *ss.

[WDYSUN]

Originally Posted by markusA

I'm running a 2:1 trafo and it's working perfectly. I haven't even had the time to fine tune the load for the transformer and it's still kicking *ss.

What I understood is that you need to know the preamp/linestage input impedence in order to match the trafo's load.

I use a Lundhal trafo, so I wrote to Per Lundhal with preamp specs and he gave me the right resistor to load the trafo... it works very good, and I don't undesrtand this "long-term use" thing mentioned previously.

ciao
Pietro