ECH83 tube preamp

[tca]

This is my first attempt with tubes. It is a modified version of the Engel preamp with ECH83, btw which cost me 2.5Eur at a local store. Here is the schematic



There is a similar version here. My mods are in red.

I'm pretty happy with it, but there is always a hiss in the background. I've started with the triode part only and the hiss was initially there, and then coupled the heptode part. Is this hiss common or I'm using a broken tube? Any experience with this pre?

Thanks.

tca

[J0K3RX]

looks cool... have you built it already? Any sound clips?

[tca]

looks cool... have you built it already? Any sound clips?

Yes it is build just beside me... I'll post some sound samples tomorrow (is getting dark here now).

Here is the picture (didn't found any 9 pin socket for the tube)

[weasle76]

I made a dual version of this a couple of months ago, basically just the stock version with a fixed resistor replacing the 1M gain pot from V+ (I can't remember the value, but it was between 50k and 100k), the volume leaving the first preamp was the gain into the second. It ran from 12V so the heaters were wired in series.
There was a bit of a hiss, but nothing too distracting. I just thought it was due to the amount of gain it had. It went from nice breakup crunch to high gain thrashy sounds to full on extreme compressed fuzziness! And when I say extreme compressed fuzziness, the gain knob didn't increase the overall volume after about 11 o'clock, it was more like an auto volume limiter you find on camcorders and the like, but with more fuzzzzzz!

It's in bits at the moment, it was too much for me! I'm planning something else with it, but I won't be able to start on that little project until I've got my current projects out of the way...

[tca]

Hi Wayne thanks for your reply.

I made a dual version of this a couple of months ago...

I have an extra tube just waiting to be used!

There was a bit of a hiss, but nothing too distracting. I just thought it was due to the amount of gain it had. It went from nice breakup crunch to high gain thrashy sounds to full on extreme compressed fuzziness! And when I say extreme compressed fuzziness, the gain knob didn't increase the overall volume after about 11 o'clock, it was more like an auto volume limiter you find on camcorders and the like, but with more fuzzzzzz!

You are right, it has a lot of gain, not nice for playing at low volumes, it sounds lovely when overdriven and is very clean. I've to check that fuzz that you mention. Powering with 12v is a good idea.

I'm going to test it with other amps to see what happens to the hiss, probably is just my crappy SS amp!

Thanks again. Cheers.

P.S. edit

Just found your entries on this pre.

[weasle76]

No problem, glad I could contribute!

I've got everything ripped apart at the moment, re-building and modifying pretty much everything I've done (due to boredom and a few minor issues) including the twin tube noise monster! once I've got the stomps done, I'm planning on making a full tube pre to replace the current one in my all ss amp. That'll be fun, but I like a challenge!

The noise I was getting when not playing wasn't much worse than other dirt boxes, so I didn't think anything of it. But if you're thinking of running one into another, it'll need to be tamed a little because each stage is quite loud (something I would have discovered if I'd breadboarded first instead of just building it!)

Good luck with the rest of your build!

[tca]

Oh, and I forgot to mention where I saw it first: Mullard Reference Manual of Transistor Circuits, pg. 157



and then googled ECH83.

[weasle76]

When I started it, I just saw the post you linked to then hit up google and found the engel site. I liked the idea of using the TMB tonestack that he shows, but never got round to trying it. Once I get started with my full pre amp, I'll be abusing the breadboard!

[tca]

Just recorded some sound samples.

Cheers.

[kingswayguitar]

sounds nice to me!

[tca]

Just a few more comments, while the tube support doesn't arrive by mail.

Just replaced the 100k resistors with the 47k, less gain but ok, tone remains good. Just fix the hiss (bad connection to ground)!

The most amazing thing is that the circuit works fine with 6V, the same voltage as the heater... and now we have tube preamp that runs on 6V (as stated in the datasheet)!

Cheers.

[engels]

I'm happy my design catches some attention! That's really cool. If I was an American, I'd copyright it. But as far as I'm from Israel I don't care.

If you still have hiss problems I'd check two things:
1. Grid resistor of the triode (I've got 47K instead of 10M)
2. Connections, connections!

After all, although the preamp works and the most wonderful thing is the low voltage, I'm not really happy with the sound of the valve. It a bit mid-heavy, without too much bottom. Othervise I'd use it all the time.
I'm much more satisfied with the sound of american spacecharge tubes, like 12AJ6.

[Kesh]

Any reason for 9V not 12V?

[iccaros]

@Engel
I was trying a similar amp design (squirrel monkey) http://www.solorb.com/elect/musiccirc/squirrelmonkey1/ when I thought of putting it in a pedal, but the compactron did not play well with low voltage.
So here was what I came up with, http://www.diystompboxes.com/smfforum/index.php?topic=97383.0

I like your gain method though and may have to look into a mod.

[tca]

Any reason for 9V not 12V?

You can power it with 12v (it is a autoradio tube).

The datasheet says 6v for the heater, but I've tested it with 9V and it works. Probably it will reduce the life span of the tube.

[kingswayguitar]

very nice 
i'm hearing a lot of bass 

[rankot]

How much current is needed for heater? Would 78L06 be sufficient, or I have to use 7806?

[duck_arse]

heater is 6V3 at 300mA, from the datasheet I saw.

[rankot]

OK, thanks, that means that I can not use 78L06, since it has maximum of 100mA. 

[rankot]

Original design can be found here: http://meatexz.com/engel-sound/ECH83preamp.html