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Old 4th June 2008, 02:09 AM   #1
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Default I/V after amplification using current amp?

Hello Nelson and all,

I am buying a Twisted Pear Buffalo DAC and need an I/V stage before the 24V Aikido I am building. I will be driving a pair of HD650 cans and in the future, biamped open baffle full range and stereo subs.
The guys a TP have me excited about something other than women again! I need an I/V stage to go with the Buffalo. I know that they have used some of the opamps you designed in their IVY but they are still opamps, right? It outputs +/- 2.112 mA in current mode and I would like to avoid transistor like harmonics, I love clean SE tube sound. I have seen the Lampizator dude's page and I like the concept but don't tubes have a fairly high input impedance in genereral and we are trying for low imp, right? Transformers are an option too. How about amplifying the current from the DAC and then doing the I/V after the signal is amplified?

I am looking for the closest to unrestrained SET sound with 2volts out or there abouts. A circuit that does both SE and balanced is nice, but I can settle for either. I was even thinking Pass F4 as a buffer, unity gain, or something like that. I am thinking DAC(current)->Buffer/current amp(current)->Passive I/V(voltage)->Preamp(voltage)->Active Xover(voltage)->current amp->speakers.

Idea time!
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Old 4th June 2008, 03:21 AM   #2
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How is it possible for springtime to arrive in Canada and Thailand
simultaneously?

Oh, wait a minute - you must be in Thailand at the moment...

The I/V from the PL D1 is really pretty ideal. I think there's enough
stuff on this forum, and it's a very simple circuit anyway.

I always smile when I think of the company offered licensing on
that I/V converter. The leading DAC company at the time looked
at it and their technical expert said, "I don't see how that could
work" (He couldn't find the op amp).
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Old 4th June 2008, 04:24 AM   #3
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Quote:
Originally posted by Nelson Pass

I always smile when I think of the company offered licensing on
that I/V converter. The leading DAC company at the time looked
at it and their technical expert said, "I don't see how that could
work" (He couldn't find the op amp).

I almost fell out of my chair laughing.

-David
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Old 4th June 2008, 05:29 AM   #4
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I am in Canada at the moment, hence the immediate need for fantastic sound to keep me distracted from how much I miss Thailand. Well Thailand and my pseudo wife, who is my other true love.

PL D1? I will search, but what is this PL D1 thingy? Hmmm, PL? Oh! Pass Labs D1! Ok then, I had read in a thread somewhere that the IVY from Twisted Pear is based on your D1's I/V stage, am on the right page here? If the D1 has a close to an ideal I/V stage that means the TP IVY is very good and the boys at TP have done well. This will likely be the route I will go. It is just that it has always been easy for me dislike transistors and opamps because of the previous products and designs that hurt my ears at any cost! I love music and when I was introduced to SET amps and tubes I fell in love again.

What first made me look into tubes more closely what a tubed ouput CD player, Jolida JD100, as the source for the speakers I was auditioning. Listened to a tube amp and a very good ss amp with this player and was impressed with both. Listened to the same amps with a Cambridge player and found the expensive SS amp unlistenable and the tube sounded much less involving. While it maintained a similar sound it was lifeless. I found that the old saying about garbage in/garbage out makde a lot of sense. I though this had everything to do with tubes! Later I heard a discrete design with no tubes and I was impressed! It was then that I had to take a more inquisitive look at the product i was buying. So for me, the quest for high end on a low end budget had begun.

So it's requirements for me are that it must be able to make music! Not just sound. I don't need tubey sound, nor do I want it. I like SET magic with tight, full bass and glorious midrange that is not bloated. I liked the discrete mosfet one that I heard. It conveyed the dynamics and close to the soundstage of the better tube ones I have heard, but the highs were harsher and midrange was a little dry. FETs sound better than MOSFETs I have read. I have never listened to a transformer coupled I/V, so I cannot say either way. What I will not have however is the flat, lifeless, harsh, fatiguing sound that almost every opamp CD player is too me!(that I haveheard)

So, if the TP IVY is going to be close to yours Nelson, I will Likley go that route unless you can see improvements on what they have done at little expense... I have to get back to Thailand and the way the airfare is getting hit with fuel surcharges I will have to resort to hooking to buy these toys!
So is my idea about the current amp and then passive I/V idea silly? Nelson, what is your take on transformer output?
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Old 4th June 2008, 07:22 AM   #5
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Quote:
Originally posted by khundude
Ok then, I had read in a thread somewhere that the IVY from Twisted Pear is based on your D1's I/V stage, am on the right page here?

Read where? Isn't the IVY just a silly opamp thingie?
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Old 4th June 2008, 09:37 AM   #6
KSTR is offline KSTR  Germany
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Quote:
Originally posted by Nelson Pass
The I/V from the PL D1 is really pretty ideal. I think there's enough
stuff on this forum, and it's a very simple circuit anyway.

I always smile when I think of the company offered licensing on
that I/V converter. The leading DAC company at the time looked
at it and their technical expert said, "I don't see how that could
work" (He couldn't find the op amp).
Your bad, Nelson!
You should've drawn the conceptual schematic this way:
Attached Images
File Type: gif i-v.gif (1.4 KB, 1145 views)
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Old 4th June 2008, 10:11 AM   #7
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I have the RAKK-DAC, which seems to have a DC offset at the output ( I was reading http://www.borbelyaudio.com/pics/Web435DAC.pdf )...so I am wondering: How can I apply the D1-output stage to the pcm 1794 ?
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Old 5th June 2008, 10:56 PM   #8
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Quote:
Originally posted by Blitz
How can I apply the D1-output stage to the pcm 1794 ?

Perhaps this thread could be helpful.Anyone built a Pass D1 I/V for a TI1794 or TI1794 DAC?

-David
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Old 8th June 2008, 02:43 PM   #9
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Default current amp

Nelson and the rest,

I had just thought that using a passive resistor I/V would be the purest way to do it. However, the get enough voltage to drive the preamp or amp with a passive stage the bandwidth and dynamics suffer, don't they? If the current was amped first, the resistor value needed to achieve a certain voltage can be different allowing higher voltage out and wider bandwidth, right? I am only guessing here but it seems logical to me. In the current domain, tubes could be used without having the resistor do the I/V first and then have input impedance problems with the tubes. This impedance problem would affect sound in a negative way. Current amp with tubes is the only way I can see that one could use tubes and still offer a low input impedance for the active I/V.

I have not ruled out transformers like Sowter yet since they will mate well with almost anything.
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Old 8th June 2008, 04:20 PM   #10
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Default Re: current amp

Quote:
Originally posted by khundude
In the current domain, tubes could be used without having the resistor do the I/V first and then have input impedance problems with the tubes. This impedance problem would affect sound in a negative way. Current amp with tubes is the only way I can see that one could use tubes and still offer a low input impedance for the active I/V.


Dunno if this is just a poor translation from Thai, but it makes no sense whatsoever.
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