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timos_t 14th March 2005 06:54 AM

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

Steve Eddy 14th March 2005 07:00 AM

Do you actually need preamplification or do your 3886s have sufficient signal gain?


audiousername 14th March 2005 07:23 AM

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)?

Simpleton 14th March 2005 11:09 AM

Very simple:

audiousername 14th March 2005 11:17 AM

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.

Sch3mat1c 14th March 2005 02:33 PM

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.


skyraider 15th March 2005 07:31 AM

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.

Alkis 15th March 2005 08:53 PM

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.

Tyimo 7th May 2006 05:46 PM

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!!



phn 7th May 2006 05:56 PM

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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