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Old 16th July 2008, 04:45 PM   #101
Cappy is offline Cappy  United States
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The idea to stick in the oil cap as the first transitional cap came from some posts I read from Dave Slagle.

That worked out well, so I went looking for other Slagle power supply ideas. On Dave's forum I read a post where he suggested to a DIYer to remove his final LC cell. And on his index page, he says "We have had great results with CLCLC power supplies with the first choke being Amorphous and the second choke being Nickel."

So even though I had to move around some alligator clips, I decided to make the two minute herculean effort to pull out my last LC stage and make it a CLCLC.

This turned out to be a good win. There were noticeable gains in tonality, frequency extension, and dynamics. Obvious gains, not requiring any back and forth checking at all. Definitely a bandwidth bottleneck removed.

Plus the power supply is smaller and cheaper by removing a big capacitor and a small inductor. I did end up using the 70 uF Oil Obbligato Oil/Film as the last cap instead of the 47 uF Obbligato Film as I thought it sounded better in my circuit.

So the new CLCLC supply with the current Soviet Special Aikido is "Configuration D". As usual, I'm following the Swenson methodology for getting a good impulse response.

Ripple is higher, of course. PSUD simulated ripple is 20+ mV. Interestingly, actual measured ripple is only 12 mV and steady on the scope. This is higher than the previous supply's 3-4 mV but sounds subjectively ok to me on horns.

The only downside, other than a touch more hum, is a bit of sizzle in the treble but I believe this is the class-d amp showing it's true colors. I'll revert back to my 300b amp soon.

Given that Dave's first two suggestions worked well, I'm guessing using an Amorphous core first inductor and Nickel core second inductor would be good too, but that is $$$ and must wait.

When I get my courage up I'll try running some FFTs.

Here is the new supply showing the 10% change in current. Note impulse response is quicker than the previous supply.
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Old 17th July 2008, 04:41 AM   #102
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Hi Cappy
I was hoping you could answer a slightly off topic question for me.

I am planning to build a TP DAC, but am trying to decide which one. Wondering if I should build a Buffalo, COD or Opus, and I noticed you had replaced the COD with the Buffalo.

How would you compare the two?

I was leaning towards a Opus, in dual mono config, with two Ivy's, although I may wait for the in development discrete IV module. Source is a squeezebox into the metronome.

TIA
Randy
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Old 17th July 2008, 06:46 AM   #103
Cappy is offline Cappy  United States
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Randy,

I prefer the Buffalo, at least with SPDIF.

I did about 20 minutes of listening with the COD via the I2S of the Pace Car and it was very good. I had a grounding problem -- too many different boxes I think -- and there was some hum but I didn't get around to debugging that. Now the COD has swum up the Willamette River to Portland - a friend is enjoying it with a headphone setup.

In SPDIF mode I just like the resolution and accurate tone of the Buffalo. The COD sounded a bit fuzzier.

Your post got me to reinstall the Buffalo with Configuration "D" tonight. Nickel Creek is sounding quite fine as I write this. I can say with some relief the bass is good too -- it sounded a bit "porous" previously. This is with passive I/V of 15 ohms through one half of the differential output. Nothing at all changed with the Buffalo, just the 6n6p swap and the major power supply changes. I'm going to have to do some measurements with the Buffalo with the new and old power supply to see if I can figure out what was going on.
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Old 17th July 2008, 11:37 AM   #104
SY is offline SY  United States
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The FFT plots with no signal, was the input shorted or left open?

I also use a 192 with AudioTester, and can't seem to get the zero dB level where I want it. It's excellent software but has some odd blind spots. The card input should be buffered (I use a BUF03 for that), and for high level measurement (>2V), you can use a 10x scope probe to knock down the levels. Set the buffer input resistor to 1M and whatever your scope's input capacitance is.
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Old 17th July 2008, 04:49 PM   #105
Cappy is offline Cappy  United States
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Sy,

They were open. Should I short them for the next batch of measurements?

Regarding the zero dB level. Is it perhaps because you can't run the calibration routine? I can't get that to work. I need to email the developer on that possible bug. It's a pretty big issue, methinks.

Good idea on the scope probe, thanks.

Regarding buffering of the the card input. I will do that. What will that accomplish? Is it for safety or will it also change the measurements because it normalizes impedance?

Regards,

Bill
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Old 17th July 2008, 04:52 PM   #106
regal is offline regal  United States
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Most sound cards have a rediculously low input impedance that makes it tough to measure tube equipment. You can build a pair of JISBOS buffers for impedance matching.
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Old 17th July 2008, 04:57 PM   #107
Cappy is offline Cappy  United States
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Regal,

I remember you saying that previously but I didn't make the connection to impedance issues when measuring, thanks.
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Old 17th July 2008, 07:06 PM   #108
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Quote:
Originally posted by Cappy
Randy,

I prefer the Buffalo, at least with SPDIF.

I did about 20 minutes of listening with the COD via the I2S of the Pace Car and it was very good. I had a grounding problem -- too many different boxes I think -- and there was some hum but I didn't get around to debugging that. Now the COD has swum up the Willamette River to Portland - a friend is enjoying it with a headphone setup.

In SPDIF mode I just like the resolution and accurate tone of the Buffalo. The COD sounded a bit fuzzier.

Your post got me to reinstall the Buffalo with Configuration "D" tonight. Nickel Creek is sounding quite fine as I write this. I can say with some relief the bass is good too -- it sounded a bit "porous" previously. This is with passive I/V of 15 ohms through one half of the differential output. Nothing at all changed with the Buffalo, just the 6n6p swap and the major power supply changes. I'm going to have to do some measurements with the Buffalo with the new and old power supply to see if I can figure out what was going on.
Thanks for the info.
I think I am going to give the Buffalo a try, when they start taking orders again.

Randy
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Old 22nd July 2008, 11:19 PM   #109
boudy is offline boudy  United States
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Default Buffalo - Aikido Interface

Hi Cappy and others,

I'd like to hear the details in how you interfaced the Buffalo's output to the Aikido. Cappy it seems like you are running singled ended, did you use both (+/-) DAC outputs for each channel?

I've been considering either going the balanced Aikido route or implementing a Broskie Cathode Follower.

Thanks.

-Eric
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Old 23rd July 2008, 05:46 PM   #110
Cappy is offline Cappy  United States
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Eric,

Right, I'm running single ended.

So far I've just pulled the signal from the + differential output.

From the + and ground outputs, the dac output goes directly into the grid of the first Aikido stage. I did not find a post-dac analog filter necessary with the Aikido (other than the implicit one), which is nice.

The balanced Aikido would be cool if one has a balanced preamp/amp.

Looking at the schematic for the Broskie Cathode Follower, if I understand it correctly, it looks like a circuit for voltage out DACs. I believe the Sabre supports voltage out, but does the Buffalo?
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