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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

Cheap and upgradable preamp

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C

camelator

Member
Joined 2013
M

MrCurwen

Member
Joined 2010
If you want really upgradeable (and I don't mean just swapping caps and stuff) you better not go with a PCB.

Have soldering strips on the chassis and go point to point. Pick a common enough socket for the tubes (octal or noval) and have one tube socket per channel - that way you can go balanced at some point, with dual triodes.

Leave a lot of room, so you can add different plate loads, CCS tails for balanced, and source follower output buffers at some point.

Then begin with a simple all resistors and capacitors and tubes kind of a setup, and get experimenting!

The single most significant thing in a preamp is not the tubes you use, not the capacitors you use but the topology. Leave room to change that (most significantly, to go balanced).
 
C

camelator

Member
Joined 2013
MrCurwen said:
If you want really upgradeable (and I don't mean just swapping caps and stuff) you better not go with a PCB.

Have soldering strips on the chassis and go point to point. Pick a common enough socket for the tubes (octal or noval) and have one tube socket per channel - that way you can go balanced at some point, with dual triodes.
Click to expand...

Thanks for answer,
what kind of schema do I use? Do you have some links and advertise?

Thanks!
 
fdegrove

fdegrove

diyAudio Senior Member
Joined 2002
Hi,

First of all I don't understand why anyone would want a preamp where all it takes is a source selector, a volume control and, if you need to drive long capacitive cables, a well designed buffer stage?

Anything else thrown in only just degrades the sound further, surely?

So, O.K. you want a preamp to add some even harmonics to that sterile digital sound......:D

Anywho, of the two I'd rather put my beans on the Aikido than on a dubious clone of a circuit that sounds like someone has pulled a sock over your ears.....

@McCurwen: you make leaps and bounds but from what the TS expresses I'm not sure he's still with you....:p

Ciao, ;)
 
artosalo

artosalo

Member
Joined 2010
How about this ?

6J4 6P6P 6Z5P Class A HiFi Tube Preamp 110V 220V Vacuum Tube Preamp Kit 1set | eBay

$_12.JPG
 
kevinkr

kevinkr

Administrator
Joined 2004
kta-hifi.net
Paid Member
Watch out for the 220V primary, the web is legion with stories of transformers that cooked on the "nominal" 230V mains found in the EU which in some places at some time of the day might be as high as 240V.

My advice would be if possible to find someone local who can guide you through the process of designing and building your first pre-amp.

Kits are well and good, but what if you cannot get it to work properly or worse, like so many these days it turns out to be a very badly designed circuit that someone nonetheless decided to commercialize?
 
G

grogger

Member
Joined 2013
Douk Audio 6j4+6p6p Class A preamp

Hi
I am a complete novice and beginner into valve technology. At the risk of
being laughed out of the park by the guys out there who really know their
stuff, can I add the following:-
A friend gave me a pair of Hacker speakers which were being thrown out,
they were knocked about a bit and looked in need of a little TLC. I spent
some time refurbishing the cabinets and crossovers and I am very pleased with the result. Surely then these speakers in all their vintage splendour
deserved to be paired with a valve amplifier?
As a retirement present my wife bought me an Icon Audio ST25 valve amp.
This opened up a whole new interest, such a gorgeous sound !

If I haven't bored anyone to sleep yet, this is where it started.

I wanted a remote volume control for the system, but didn't want to start carving up my Icon Audio amp. Also my listening room isn't perfect and I always could perceive an imbalance between the speakers. I tried various
things to remedy this, but nothing worked. So, I thought maybe a balance
control!

OK, so maybe a remote volume and balance control doesn't really warrant
building a preamp. But the problem is, I've been bitten by the valve bug.

So to cut a long story short (are you still there ! ) I purchased the Douk Audio 6j4+6p6p preamp in an attempt to enter the wonderful world of valves. I found a motorised volume control complete with remote in kit form on E-Bay for only £19.99p.
Both kits have been built and are working beautifully. I found that using the preamp between my Cyrus CD player and Icon amp opened up the sound stage somewhat and increased separation between instruments.
For the price I am very pleased, there was a very small amount of hum
when connected to the main amp. I cured this by splitting the mains earth
and OV rail, then reconnecting via a 100R resistor and 220nf capacitor.
The system is now noiseless. I solved the sound imbalance problem by
mounting two 47k pots on the front panel of the preamp and wiring them
between the input jacks and the stereo motorised pot. It's given the desired result, but I'm not sure whether this is good practice.

I think the Douk preamp is excellent value for money, it has given me a real insight into the construction of valve audio equipment and because of the "point to point" wiring, can be modified as I learn more.
 
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