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Old 14th March 2005, 06:54 AM   #1
timos_t is offline timos_t  Greece
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Post The most simple tube preamp

Hello, everyone. I have designed a stereo power amp (2xLM3886), and no i need ideas about a siplest tube preamp join it. Any ideas? If you help me to finish this out, i'll publish my whole projecdt to net.

Cheers !!!

E.g. A qute ECC83 or a AU7 i prefer
100VDC or 250VDC plate voltage i prefer
No tube power rectifier, only pasive things
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Old 14th March 2005, 07:00 AM   #2
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Do you actually need preamplification or do your 3886s have sufficient signal gain?

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Old 14th March 2005, 07:23 AM   #3
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Why ECC83/12AX7 and ECC82/12AU7? There are better valves out there suited to line amplifier duty.

How much gain do you need (if any)?
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Old 14th March 2005, 11:09 AM   #4
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Very simple:

Click the image to open in full size.
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Old 14th March 2005, 11:17 AM   #5
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Regarding the triode-strapped EF86 schematic above:

You generally won't need a gain of 25. This just means you will have to have the volume turned waayyy down, and compromise noise performance.

The usually low-ish input impedance of a SS amp will likely load down the stage, causing gain to droop and distortion to rise. The high output Z might also cause some HF loss when driving a capacitive load.

Something along the lines of a simple grounded cathode 12B4 (as shown in some other threads) would be more appropriate for linestage duty.
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Old 14th March 2005, 02:33 PM   #6
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If you just want a tube buffer for the sole purpose of saying you have a tube buffer, use a CF. It kind of defeats the purpose of having a tube in the signal path, but people like to do irrational things like add stages they don't need.

If you actually need gain, anything from 12B4 to 6AU6 will provide gain. Higher gain tubes will need a buffer to match impedance to the amp.

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Old 15th March 2005, 07:31 AM   #7
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audionote m1 uses 5687.. very simple circuit, and yet very good.

Its designed to be used in SS gears to add so called 'warmth' effect.
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Old 15th March 2005, 08:53 PM   #8
Alkis is offline Alkis  Greece
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Hi Timos,
First of all:you don't need too much gain-what are you dealing with?
Second:try the schematic provided by Skyraider.5687 has a very good reputation and if you decide later to go for a tube amplifier,there is also an output transformer especially for this tube within you can drive anything.
You can also take a look at this schematic [URL=] which i have allready constructed and it's very good.
But from the other hand,in the first schematic only one triode is used(half tube) which makes it simplier.
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Old 7th May 2006, 05:46 PM   #9
Tyimo is offline Tyimo  Hungary
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Default EF86 line amp

Hi Simpleton!

Could you tell me where can I read more about the EF86 in triode connected line amp?? It is looking very interesting to me!!


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Old 7th May 2006, 05:56 PM   #10
phn is offline phn  Sweden
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I'm planning to build this EF86 pre using the low-noise E80F tube.

There are schematics on the page. The PSU is quite oversized and I'm considering other alternatives. It's my first ever tube project so I move forward slowly. Not to mention that my tube amp just quit on me.
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