Line level preamp

[Firebottle]

Thinking as I often do about alternative circuits, I thought up a different approach to volume control implementation. Having built up a test preamplifier I found there was no mileage in it, in fact it was somewhat distorted at lower volumes.

That left me with a line level preamp built in the main from spares box parts. I have re configured it in a very traditional fashion, a low gain input stage, a conventional potentiometer volume control followed by a buffer output stage.
All stages include a CCS for best performance and the potentiometer is the TOCOS carbon pot. I have to say it sounds rather good.

The completed unit, in a home built case made many moons ago by a french enthusiast:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Line%20level%20preamp/P1040466.jpg

The inners are a bit untidy but it was only meant as a test bed originally:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Line%20level%20preamp/P1040467.jpg

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Line%20level%20preamp/P1040468.jpg

The valves used are 2 x 6J6 for the input stages, from stock and as cheap as chips at 50p each excluding delivery, followed by an ECC82 on output duties.
The only parts I had to buy were the output capacitors, the potentiometer and the HT board.
Gain is 13dB max with output impedance under 400 ohms.

A thank you is also due to Gordon for sending me an offcut of the 'carbon-fibre' stickon for the front panel :thumbsup:

:D Alan

[shane]

Never seen a pre-amp with a use-by date before!

[Gordon Steadman]

When is it going to stop working? I can't quite see the sell by date on that expensive cover to the right of the volume control.

Curses, someone beat me to it:lol:

[CageyH]

Have you given it the beans yet?

Does it sound a bit tinny?

[walpurgis]

A canny bit of work! :rolleyes:

[Paul Lange]

Hey, the tin is not made of mu metal but they work as a shield just fine. I have used tins before in the same way.

[Jimbo]

Nice to see you tinkering again Alan :)

[tubehunter]

Yes I too prefer an input tube before the potentiometer.
Audio Note have been doing it like that for awhile
http://www.ankaudiokits.com/PDF/Schematics/Kit2_AudioCircuit.pdf

Ok curiosity is raised what's in the and how do you go about getting your 170v?

Duncan

[Firebottle]

Loving the humour gents, keep it up :eyebrows:

Duncan, in the can is a regulated high frequency inverter, the important bit being it gives a well regulated output.
Who said it was 170V?

:cool: Alan

[CageyH]

Have you given it the beans yet?

Does it sound a bit tinny?

Alan has kindly sent me this pre amp for me to try in my system.
First impressions of the acoustic properties are rather good.

I hope it rains this weekend so that I have plenty of time to listen to this in my system.

[CageyH]

It's been plugged in for three hours now, and it sounds good so far.
Treble is clear, midrange is rich and the bass sounds very good. On George Ezra "Budapest", you can hear the fingers strumming the double bass.

I'll try some different material when Mrs H goes out.

[CageyH]

I really like the sound of this pre. It has a nice balanced sound, it brings out the detail well and gives nice definition to bass notes. The treble isn't too bright and the midrange sounds spot on. Really enjoyable, and all with 50p valves?
It's the first and only valve pre-amp I have listened to in my system, so I have nothing to compare it to, but I have spent the weekend enjoying it's performance.

The only thing I don't like is the lack of a "soft start" as my mono block amps are left powered on at the manufacturers recommendation. I just needed to power them down when connecting the amp. Not a big deal, and as it's a prototype, I can let Alan off this minor detail. I am sure he could fix it if he decides to develop this wonderful little amp further.

[DSJR]

Almost anything's better than that darned Arcam box you're using ;)

See, internal neatness says nothing about sound quality if the fundamentals are done right :)

[Firebottle]

An update on this thread.
After nicking the Tocos pot for other duties some time ago this pre was languishing doing nothing. I also had the power supply section from a 'failed' headphone amp going spare.

Now that I have developed my super linear circuit I thought I would rebuild this to provide me with a test bed for further work.
As luck would have it I had another home brew case the same size, so I have built the conventional power supply into that.

I've fitted a 1.2m umbilical to connect to the back of the power supply:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Line%20level%20preamp/P1050094.jpg

The pre now uses two 6J6 valves and is quite stunning. It seems strange that you can add a piece of gear into the system and it becomes more dynamic :D

Played some Paul Simon - Graceland and Tracie Chapman last night, wow such realism.

Internals for those that have the need:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Line%20level%20preamp/P1050095.jpg

:) :carrot:

[Macca]

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Line%20level%20preamp/P1050094.jpg

:

Even with my WAF-O-Meter on its most sensitive setting I am unable to get any reading at all. Is the 'Russian military equipment from the Cold War era' styling going to continue to be a feature of the Firebottle range?

I sort of hope so ;)

[Marco]

Hahahahaha.... Me, too! :D

My motto with hi-fi kit: spend the money on where it matters most!

Marco.