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Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum |
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#1 |
diyAudio Member
Join Date: Nov 2004
Location: Athens
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I'm thinking of building a current-source biased LTP line stage, to convert from SE to balanced and drive my electrocompaniet clone amp. What are your experiences with regards to the sound of this topology, also keeping in mind that it has to be done on the cheap?
Cheers. |
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#2 |
diyAudio Member
Join Date: Oct 2003
Location: San Jose
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If I could tag a similar question to the thread:
Are there good low power class A amp designs that have balanced input rather than using RCA with a phase splitter in the amp? -David |
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#3 |
diyAudio Member
Join Date: Nov 2004
Location: Athens
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From simulation it seems that gain balance in the two outputs requires an almost ideal current source. Even a current source impedance of 20K, which in practice does not seem easily attainable, leads to an amplitude imbalance as high as 0.5dB. The JFET current source has an even lower impedance. Any thoughts would be greatly appreciated...
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#4 |
diyAudio Moderator Emeritus
Join Date: Jan 2003
Location: Near London. UK
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20k is easily achieved - in fact, 20M is easily achieved. You need a couple of transistors to make a near-as-dammit perfect cascode CCS. It's been discussed before on this forum so a quick search should find it. What you will need, though, is a -15V (or so) quiet supply.
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The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference... |
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#5 | |
diyAudio Member
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Quote:
Are you looking for a push-pull or single ended amp? With a balanced input, your phase inversion has been done for you, and that is quite nice. For low power single ended amplifiers, this doesn't offer you a whole lot of favors (I still tend to build in a transformer coupled XLR jack onto my SE amplifiers). |
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#6 |
diyAudio Member
Join Date: Nov 2004
Location: Athens
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Thanks EC8010. I too saw the need for a negative supply when I started simulating possible topologies.
The cascode CCS you suggest seems to work very well; only 0.03dB differential imbalance is produced. But out of pseudoscience or just biased intuition, I was thinking of not using bipolar transistors in this design. Mosfets and jfets connected as simple CSs do not yield the required impedance. I'm thinking of cascoding a jfet and a mosfet. Cheers. |
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#7 |
On Hiatus
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I built such a preamp to drive the Pass F4 in balanced (The "ImPasse") and demo'd it at BAF '07. It can also be used to drive a balanced input of a power amp. The article was accepted by AudioXpress, but they've been sitting on it for nearly a year; we'll be posting it on diyAudio shortly. It will accept both single ended and balanced sources, and has a balanced output. Max gain of 20dB, with THD at under 0.05% at 20V out.
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"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is." |
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#8 |
diyAudio Member
Join Date: Nov 2004
Location: Athens
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Thanks SY, drop us a line in case we miss it!
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#9 |
On Hiatus
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You won't miss it, trust me.
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"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is." |
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#10 | |
diyAudio Member
Join Date: Oct 2003
Location: San Jose
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Quote:
I'm looking for a single ended balanced input amp. Although a good push-pull design would be OK. All my sources are balanced, seems a shame not to leverage them in balanced mode. -David |
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