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Using the AD844 as an I/V
Using the AD844 as an I/V
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Old 21st February 2017, 02:44 PM   #2141
Torchwood421 is offline Torchwood421  United States
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Thumbs up Sparkos Discrete Op Amp Review

I had a chance to hear my version of the PCM1704 DAC in my cousins system yesterday. He has the Alon `4 loudspeakers. So has a lower bass frequency response then I can get with my ribbon planar MG2.5R based Magnepan system. Listening impressions: Bass. Has a clean powerful low end. Even more so then the BUF03. A sense of limitless power. Kick drums have weight and a just correct quality. Midrange is clear and vocals are absolutely defined in space a "you are there" quality. Treble is clean and absolutely real sounding. Good recordings leave one to just close your eyes and listen. The SS3601 clearly out performs the OPA627 and OPA1641. The transparency and holographic presentation betters these op amps. Extra detail is also heard. I'd recommend this discrete op amp in critical applications. It's cost is more then the venerable OPA627. However not by that much all things considered. PCM1704 DAC... It is my DIY reference which all others must be compared with. I don't plan to modify or change this going forward. I am fortunate that I have another pair of PCM1704's that are ungraded. So I can experiment with those in the future. The best testament I can give... I am more interested in listening to music then rolling op amps in the reference DAC.
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Old 21st February 2017, 03:01 PM   #2142
batteryman is offline batteryman  United Kingdom
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Using the AD844 as an I/V
Quote:
Originally Posted by Torchwood421 View Post
I tend to prefer the transformer approach over the active filter one. Adding additional active devices in my experience does more harm then a quality transformer does. My experience might not be typical.
Its been my experience too. I definitely want to minimise active devices in the audio chain.

I had an Audio Note Dac1 a few years ago - AD1865 in nos mode, no filtering, tube output stage. I couldn't live with the aliasing and birdies until I tried my Sowter transformers.
What an improvement with no loss of treble or any other side effect. Not perfect of course, but the benefits far outweighed the cost.

I had the same results with a pair of parallel 1541s and hope for an even better result when I have them differentially connected (due to cancellation of common mode noise), initially with just passive I/V and then with single or stacked 844s.

I will even try the transformers between the + & - Tz resistors.

The transformers have 5:1 step up (+20db) so there is no need for Tz resistors of more than 100R (same value I used when I had passive I/V).
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Old 21st February 2017, 07:21 PM   #2143
georgehifi is offline georgehifi  Australia
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Quote:
Originally Posted by Torchwood421 View Post
Adding additional active devices in my experience does more harm then a quality transformer does. My experience might not be typical.
I was more thinking to use the existing stages to add filtering to, not add an additional one.

Cheers George
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Old 21st February 2017, 07:32 PM   #2144
Torchwood421 is offline Torchwood421  United States
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Exclamation Sallen Key

Quote:
Originally Posted by georgehifi View Post
I was more thinking to use the existing stages to add filtering to, not add an additional one.

Cheers George
In that case it starts to look like a non-inverting Sallen-Key filter. A better option is a GIC filter assuming the DDNF can drive it and the load is high enough going into the Buffer. The GIC gyrator configuration places the filter function in a shunt with the signal. The quality of the op amp is less an issue. However you likely would need 2 parallel sections to equal what the Lundahl is actually doing. I suppose that is a good area to explore.
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Old 21st February 2017, 07:39 PM   #2145
Torchwood421 is offline Torchwood421  United States
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Thumbs up Transformers and parallel DAC's

Quote:
Originally Posted by batteryman View Post
Its been my experience too. I definitely want to minimise active devices in the audio chain.

I had an Audio Note Dac1 a few years ago - AD1865 in nos mode, no filtering, tube output stage. I couldn't live with the aliasing and birdies until I tried my Sowter transformers.
What an improvement with no loss of treble or any other side effect. Not perfect of course, but the benefits far outweighed the cost.

I had the same results with a pair of parallel 1541s and hope for an even better result when I have them differentially connected (due to cancellation of common mode noise), initially with just passive I/V and then with single or stacked 844s.

I will even try the transformers between the + & - Tz resistors.

The transformers have 5:1 step up (+20db) so there is no need for Tz resistors of more than 100R (same value I used when I had passive I/V).
Hi Ian, Sounds like we are on the same page. Although your well ahead of me on the I/V conversion using transformers as a step up device. That actually should work very well. I have a Cinemag microphone transformer that was sent to me by mistake. I'd need a second one to make an attempt. I'll have to look at that and see what the turn ratios might be.
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Old 21st February 2017, 07:50 PM   #2146
Torchwood421 is offline Torchwood421  United States
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Default Cinemag

I have a CMMI-10B 1:10 ratio. Might be useable... 150 Ohm primary.
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Old 21st February 2017, 09:26 PM   #2147
kazap is offline kazap
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Has any one tried these transformers on eBay claimed to be made for DAC outputs?



Click the image to open in full size.
  • For Passive I/V of DAC
  • Low Copper Resistance
  • Low Distortion
  • High Level Capability
  • Nickel Permalloy Core
  • Mu-Metal Shield
1. 20 Ω : 600 Ω (CT 150Ω) 1:5.48(2.74)
2. Distortion (THD) : <0.001% @1KHz
3. Frequency Response : 5 ~ 100KHz(-3db)
4. Power Level : MAX +24dBu @20Hz
5. Transformer Size : 30 x 24 x 18(W x D x H : mm)
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Old 21st February 2017, 09:52 PM   #2148
Mike Gergen is offline Mike Gergen  United States
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I'd try an Edcor for under $20, just 'cause it's cheap enough to try it.
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Old 22nd February 2017, 03:49 AM   #2149
Torchwood421 is offline Torchwood421  United States
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Thumbs up EDCOR

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Originally Posted by Mike Gergen View Post
I'd try an Edcor for under $20, just 'cause it's cheap enough to try it.
I have used those. Good stuff. Standard EI type with Nickel Iron. Good performance.
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Old 22nd February 2017, 07:40 AM   #2150
samoloko is offline samoloko  Bulgaria
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Torchwood421,
thank you for tell us your Impression with Sparkos Lab discrete op amps - It Is on my list to try
I guess you are using 3 x AD844 for I/V and then Sparkos as a buffer ?
but why there Is a transformer In your set up
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