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Old 11th February 2011, 03:16 AM   #1
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Default Differential Input for Aikido Amp?

I'm waiting for an Aikido LV kit that I recently ordered, and I plan to have it follow a DAC with balanced outs. I'm familiar with the Broskie Cathode Follower, but I want some tube gain. To avoid using good transformers, which are quite expensive, I've been researching possibilities of modifying the Aikido the accept a differential input. I came across this page of Broskie's: Balanced-Ouput DACs and Tubes and Aikido

Half way through he takes the Aikido amp through four steps of modifications, eventually giving it a successful differential input with good CMRR. My main question is, has anyone had experience with this design? And, if not, do you believe it would be an effective method for giving it a balanced input?

Steve
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Old 14th March 2011, 06:03 PM   #2
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What is the impetus for your question? In other words, why do you need gain in the output stage of your DAC?

A decent DAC with differential current outputs such as the PCM1794 which can generate a differential signal of +/- 2.5V with passive current to voltage conversion using high quality 320 ohm resistors.

Coupled to a Broskie Cathode Follower it should have sufficient output to drive any amplifier into clipping.

I have this circuit in the prototype stage here:
EZDAC with differential outputs directly into a BCF running 12AU7s with a B+ voltage of 250V. B+ rectification is via a 6CA4. Filaments are powered by 12VDC through a voltage doubler.
Click the image to open in full size.

After only 8 hours of burn in this combination sounds awesome and doesn't need any further gain.
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Last edited by baldrick; 14th March 2011 at 06:06 PM. Reason: added photo
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Old 14th March 2011, 08:24 PM   #3
tomchr is offline tomchr  United States
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The Jensen JT-11P-1 will do the job nicely. You'll lose 3 dB in the transformer, but in most circuits this shouldn't be an issue. They're a bit spendy ($65~$100/ea depending on options) but their performance is stellar. I use them in my 300B amp.

~Tom
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Old 15th March 2011, 10:35 AM   #4
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I'm sure that you could cruise ebay and pick up a pair of Altec 15335A's which should also work for less than $100 for the pair. Altec 15095's should work also if memory is correct.
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Old 15th March 2011, 08:07 PM   #5
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Thanks for the transformer suggestions! But to be more specific, it's actually a balanced miniDSP that I want before Aikido LV line stage. I bought this line stage kit and thought it could be put to good use with a miniDSP because many people need line stage amps after them. And they could possibly share my H-PS-1 Glassware power supply .

I started this thread because I was hoping to take advantage of the optional balanced outputs for this miniDSP. Maybe cancel some noise from it, ect.

I just noticed on the datasheet that the balanced version has a much higher output than the unbalanced one (2Vrms vs. 0.9Vrms). So it looks like a line stage won't be needed . Maybe I'll order the unbalanced miniDSP...

I'll have to rethink the project. Above all, I'm just excited to build a tube preamp that runs on 24V!!
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Old 16th March 2011, 01:11 AM   #6
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If noise is not a big issue for you and the cable runs are short just connect pin 3 of the XLR to the centre pin of the RCA jack and pin 2 of the XLR to the ring of the RCA jack.

This only works if the source is balanced and the destination is unbalanced. In your case it would work.
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Old 16th March 2011, 02:05 PM   #7
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Quote:
Originally Posted by baldrick View Post
pin 3 of the XLR to the centre pin of the RCA jack and pin 2 of the XLR to the ring of the RCA jack.
Cold (-) lead of XLR to signal pin and hot (+) lead of XLR to shielding of RCA? Sound System Interconnection
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Old 16th March 2011, 02:21 PM   #8
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OOPS! That was a major typo on my part - sorry.
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