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Old 27th June 2010, 07:07 PM   #1611
Salas is offline Salas  Greece
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Quote:
Originally Posted by Dougie085 View Post
Is it possible to build one of these with balanced and S/E inputs and outputs? I have a few things in my system that are balanced like my DAC. My current amp is S/E though and I have some sources that are S/E as well.
You would need double builds to assign each phase to one I would suppose, but I haven't done it. My system is SE.
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Old 27th June 2010, 07:08 PM   #1612
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So one board for balanced connections, one for S/E? Or would the balanced section need 2 boards alone?
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Old 27th June 2010, 07:11 PM   #1613
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2 boards for balanced. XLR pin 2/1 to one, pin 3/1 to the other I would think, if I had to test such an option.
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Old 27th June 2010, 09:25 PM   #1614
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Might have to try that out.... I was thinking I could do the one with the source selection but, I've been eying the AC1 from twistedpear. So maybe I'll build the basic version.

I have quite a bit of PCB material so might just try etching finally lol.

What have you guys found the cost of parts to stuff the boards is?
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Old 27th June 2010, 09:44 PM   #1615
Salas is offline Salas  Greece
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Someone's looking to use XLR in the regular B1 thread too, made a schematic, I suppose it will interest you. B1 Buffer Preamp

As for cost, differs a lot with ''special'' parts or not, overspec trafos etc. Other members may give you some range, me I built the protos from existing components in my hobby stash, some recycled even, and I can't estimate.
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Old 27th June 2010, 10:02 PM   #1616
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Wow that will be a huge help, he made a very nice diagram there.
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Old 28th June 2010, 10:32 AM   #1617
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Hi Salas
P.S. I run what you did on LT Spice, it spends enough phase margin without a little ESR in the output cap if with film, so the Cdom is a necessity, and its a juggling act, so its trial n' error as you did. The Cdom eats closed loop gain of course on the other hand. Maybe a 0.33R in series with the 2.2u could save you the Cdom. Then again you have found a good tweak set subjectively and its stable on bench...
Nice to have feedback from a Spice simulation, it takes away my worries that there was something wrong in my B1.
I had a Vishay MKP1837 100nF on the output when I had the oscillation, seems it has very low ESR. I tried to put the elco in parallel, now I understand why it didn't help as the Vishay still kept ESR low.
I don't like a resistance in series with the output cap, as that would lower the buffer/impedance of the power supply, leaving more influence coming from the error-amp. I prefer to live with the lower closed loop gain. BTW, can you estimate the difference in bandwidth in Spice? Anyhow the end result is OK now, and that counts for me. Maybe I could put a resistor in series with this new cap, but I'm afraid that will result in unstable behaviour.

Yesterday I built the PCB in my preamp, bypassing everything but input-relais and pot. The result is astonishing. I didn't know my speakers went that low. And more important, it keeps an incredible control of the lows, this was not always the case with the tubes. Also voices and cymbals are great. My tube-amp never achieved this amount of details. And the same preamp completely passive (into 100KOhm input impedance of power amp) also didn't give the same power. Now music is in the room instead of coming from the speakers.

Great design, great thread !
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Old 28th June 2010, 03:42 PM   #1618
Salas is offline Salas  Greece
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Hello, nice results. Have a great time with it.

*ESR or technically added R in the output caps does not up reg's Zo because its a shunt capacitor. I could give you some cook ups of smaller Cdom and some added R for your 2u2 favorites, and I have seen the closed loop gain in Spice with the 10n huge Cdom from the start, but I will not tease you since you got the sound that you like. Its a PCB not a proto and too many experiments will destroy it.

Don't worry, be happy.
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Old 28th June 2010, 06:19 PM   #1619
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Oenboek, I specially like your idea of placing the relay out of the signal path, but still making and effective way for avoiding DC during startup.

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Regi
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Old 29th June 2010, 01:58 AM   #1620
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In this post from the Blue GB thread a 15-0-15 trasformer is reccomended.

As seen in my previous posts I've the Mezmerize board, I intend to apply the hi-current mod (10R Resistor) and I've ordered a 2x12V tranformer.

Any problem with it?
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