Tube pre-amp

[jaaasgoed]

Hi,

I'm new to tube amps (not new to electronincs) and I found this forum. Been reading the massages for some time now and I thought I'd ask a question myself. I am looking for a schematic of a tube pre amp, but since I'm new I'm having trouble finding sites about the topic. You peolple know some good sites? You would realy help me out!

Thanks !!

Roel Dirks
The Netherlands

[Asen]

The Internet is full of schems of tube preamps. The problem is what are you looking for.
Try this link:
http://www.1388.com/articles/ampdesi...ish/index.html
There are several preamps comparred. I own the McIntosh C22 and the SRPP preamp. Both work fine. The original C22 has tone controls, which are made perfect. They have nothing to do with all the other I've seen so far. May be something similar is just the tilt control of Quad.
The SRPP circuit is quite simple, the sound is great, there is no need for global feedback. The THD are very low because of the circuit configuration.
My own oppinion is that if you use a solid state amp, the tube preamp will help you overcome the transistor sounding of your system.
Note that both preamps have pretty high gain. If you don't need high output swing, I suggest a resistor in series with the pot. Lets say 150K and 100K pot after it. I personaly use 226K resistor plus 10K pot. This way my SRPP preamp works like a follower. The input equals the output.
The tubes in the SRPP will last less then these in the McIntosh.
Note that the input and the output of the SRPP preamp are out of phase.

Success

Asen

[Edited by Asen on 05-06-2001 at 09:07 AM]

[jaaasgoed]

Thanks. Lots of information here. But since I have little experience, are there things I need to look at when building the preamp? On the site it reads: "However, some experience is required or it will end up as an impressive noise generator"
So how do you prevent this?

Also found this site:
http://www.diyaudio.8m.com/lpsh.html
It is a preamp a lot like the one on the site you mentioned and it uses the E88CC. I have some of these tubes so it would be nice if this would work.

Thanks again.

Roel

[Asen]

Don't be afraid - there's no noise. According to my experience tubes are times quieter than anything else. My preamp has 2mV output noise - there are not any special measures taken.
I'll find time these days and will send you more detailed information. For being with not enough experience I sugest you build a simple preamp, like the SRPP. There are loads of information about this circuit in the net. I'll send you details for the PSU, which is nothing special - 3 RC groups, 400uF is enough for both channels.
To be continued...

Asen

[Edited by Asen on 05-07-2001 at 05:15 PM]

[GRollins]

Roel,
Two questions:
1) Are you planning on a phono stage, or just line?
2) How much gain are you shooting for? If you're using a CD player, you won't need much gain...perhaps only 6-12 dB. Some tuners would require more. If you're planning on a phono stage, then it's nice to have some extra gain on hand (perhaps 18-24 dB) in case you get a low-output cartridge and need to take up slack from a phono stage that's a few dB shy. Anything over high twenties is overkill.

Grey

[jaaasgoed]

Thanks Asen, looking forward to your information, and thank you in advence for your time.

Hi Grey,

It's just for a cd player, no phono. So about 6 to 10 dB will do fine i think. And it is just like Asen said, I am HOPING to overcome some of the solid state sound of my amp without having to build a full tube amp.

I also might add that I am planning on using it also as a pre amp on my Pass ZEN amp, if this is possible.

Any info you can offer me is well noted.

Roel

[hifi]

http://www.diyaudio.8m.com/lpsh.html


Im figuring to build this preamp can i use one tube per chanel or should i use one tube for the "upper" and another for the "lower" ?? in the SRPP pair

/micke

[jaaasgoed]

Hi Micke,

Look at: http://www.diyaudio.8m.com/srpp.html

It says something about not exceding the heater to catode voltage. Not sure what it means but it says that in a stereo version you use one tube for both upper parts of the schematic and one tube for both lower parts of the schematic. Can someone else clear some thins up?

Also take a look at: http://www.infomaniak.ch/~bonavolt/lindesrp.htm

Roel

[Edited by jaaasgoed on 05-07-2001 at 09:39 AM]

[GRollins]

Roel,
If you're planning on using it with a Zen, then you might need more gain, as the Zen is not the most sensitive of amps. Perhaps 18-24 dB would be in order.
Micke,
The heater to cathode voltage limit is a number not to be taken lightly. The heater, usually a folded wire, and the cathode, usually a rectangular metal shell, are in close physical proximity to one another, generally touching (they're insulated). While the cathodes are separate, the heater is shared between the two sections of most twin triodes, so you can't run one cathode at a drastically different voltage from the other. If you exceed the rating, you're likely to get an arc between the two, with unfortunate consequences. In a circuit such as the one you are discussing, it's general practice to use one tube for the lower sections, and another for the upper. In this case the heater voltage for the tube handling the upper sections should be lifted to something approximately equal to the cathode voltage (somewhere within the heater/cathode rating--it's not critical). A voltage divider from B+ to ground, tied to one side of a *separate* filament transformer (or a separate winding, if you've got more than one on your power transformer) will do the trick.
You're on the right track.

Grey

[jaaasgoed]

So would using 2 separate tubes for upper and lower part (so 4 tubes for stereo) fix this problem 2?

Roel