New phono project – valve of course

[Firebottle]

After the great success of my first valve phono amp using unconventional design for the circuitry, I thought I would build one along more conventional lines.

This one is all triode, 2 x ECC83 plus ECC82, with traditional mains transformer PSU.
In order to provide ventilation and to show the valves I opted for a perforated front panel.

http://i601.photobucket.com/albums/tt97/Paramotorpilot/MM%20Preamp/Triode%20MM%20preamp/Newkit.jpg

The components used are all from ‘stock’ including the case, which I had forgotten I had.
Front and rear views:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/MM%20Preamp/Triode%20MM%20preamp/Frontview.jpghttp://i601.photobucket.com/albums/tt97/Paramotorpilot/MM%20Preamp/Triode%20MM%20preamp/Rearview.jpg

Lots of space to build in, the one worry I had was possible hum induced from the mains transformer. Internals of the amp section:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/MM%20Preamp/Triode%20MM%20preamp/Ampsection.jpg

The power supply is very straightforward, but the mains tranny is somewhat large, it was the only one I had with the correct voltages :doh:
The heaters are powered via a 12V regulator.

http://i601.photobucket.com/albums/tt97/Paramotorpilot/MM%20Preamp/Triode%20MM%20preamp/Powersupply.jpg

My worry about hum was unfounded; the amp is really quiet and sounds good. I am going to check the response on the test bench and confirm the accuracy of the RIAA network. I have adjusted the component values based on what I had available that had the necessary voltage rating, not what I originally drew out on the circuit.

What fun to be had,
:cool: Alan

[Firebottle]

I've now checked it on the bench and my suspicions were confirmed.
The first listen yesterday didn't sound quite right with the bass response. I had made a mis-calculation on the cathode bypass capacitors.

I have added two more and response down to 20Hz is ensured.

I have been listening to vinyl this morning and it has never sounded so good. I had on Roberta Flack 'The first time I ever saw your face', stunning clarity and depth.

Woo hoo ;)

[Frankyc2003]

Looking good Alan!

:stalks::stalks::stalks:

[Audio Al]

I've now checked it on the bench and my suspicions were confirmed.
The first listen yesterday didn't sound quite right with the bass response. I had made a mis-calculation on the cathode bypass capacitors.

I have added two more and response down to 20Hz is ensured.

I have been listening to vinyl this morning and it has never sounded so good. I had on Roberta Flack 'The first time I ever saw your face', stunning clarity and depth.

Woo hoo ;)

Alan , I envy people like you good self :respect:

O to be able to design and build a amp ( In my dreams :( )

Good luck to you and what a classic track to be able to listen to your new amp , wonderful :D

[Firebottle]

Thanks for the good words Al :)

[Firebottle]

:wow: Isn't vinyl playback great. I know, I know I'm talking to the totally converted, but .....

The previously used transistor preamp isn't a patch on the new valve pre.
This latest one did have rather high gain, I had the volume at about 9 o'clock, so I have replaced the second ECC83 with another '82, with suitable adjustments of circuit conditions to match.

I have also bootstrapped this stage to improve linearity and lower distortion :eek:.

I never realised that there is a fantastically low bass line on 'Arnold Lane', time now for a better TT I think.

:cool:Alan

[6L6]

Fabulous! Wonderful!

Do you have a schematic? Or is this based on a different project? It looks fantastic, and I have much of what is needed on hand as well.

[Firebottle]

Hi Jim, thanks. I do like the user name :)

I have stopped a*seing about with preamp so I do have a finalised schematic.

http://i601.photobucket.com/albums/tt97/Paramotorpilot/MM%20Preamp/Triode%20MM%20preamp/Schematic.jpg

If your voltages are a little different adjust the 82K resistor to give around 80V on the ECC83 anode. This will give the correct output impedance to drive the passive RIAA network for accurate response.

For more gain substitute an ECC81 for the middle ECC82. I haven't tried this because I don't have an '81 :doh:
The output will drive into 50K admirably. That is the I/P resistance of my OuTLaw valve amp.

The power supply is very simple:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/MM%20Preamp/Triode%20MM%20preamp/PSUcct-1.jpg

If you build it let us know what you think,

:cool:Alan

[Firebottle]

I've since sourced a 12AT7 (ECC81) and tried it out in the pre.

When first fitted I checked the voltages around the circuit and was a bit alarmed as they didn't seem correct. Once I had the scope on it I found shed loads of oscillation on the '81 stage :scratch:

A quick thought that the '81 is designed for much higher frequencies and it clicked; need to fit grid stoppers.
I fitted a 6K8 resistor to each grid on the valve base and problem solved. I used that value as I have a lot of them :eyebrows:

The gain at 1KHz is now x180, just what I was after. The pre has now got the full set, ECC83 / ECC82 / ECC81 :mental:

Jim 6L6 any thoughts? Are you going to build it?

:cool: Alan

[Firebottle]

I've forgotten to switch this preamp off on occasions because the only indication it is on is the glow from the heaters.
Much as I don't really do 'bling' I knew I had a couple of spare blue LEDs in the drawer. So here it is all blinged up:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/MM%20Preamp/Triode%20MM%20preamp/P1030655.jpg

Not much chance of not noticing I've left it on now:eyebrows:

:cool: Alan

[Macca]

lol I forgot to mention that the blue LED on my FB phono stage (we are all sorted btw) is brighter than the Death Star exploding. Can't see it from where I sit, though.

[Firebottle]

Good positioning Martin I think.
If I'd put the usual sort of current level through the LED it would light the street.
For those in the know it is incredibly efficient, it is being run on 0.1mA; not a lot.

Cheers, Alan

[Oldpinkman]

So how does this compare with the current firebottle I have on the shelf to listen to? Which do you prefer ?:cool:

[Firebottle]

This particular one is all triode (ECC83, 81, 82) so built to a different circuit. It still uses passive RIAA equalisation but doesn't have a regulated HT supply.

I have only done a quick comparison and at the time couldn't tell them apart; lack of aural memory:scratch:
So can't give you an answer to your question. I am more pleased with the design of the current one from a technical viewpoint as it is more left field.

Cheers, Alan

[Firebottle]

I have swapped out some of the equalisation components this morning> I have fitted some very well matched polystyrene capacitors and it has improved the image focus, it's now up to Firebottle Phono standard :thumbsup:

:cool: Alan

[struth]

a year and 4 months later;) thats quick Alan :lol: