• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

First tube project.

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dome406

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Joined 2004
#1
I recently built a gainclone amplifier, the one from audiosector lm3875. I am very pleased with the sound. I have always been interested in tubes so think that I will make one as my next project.

I dont want to make an amplifier I would prefer just to introduce and get a feel of what tube amps sound like, e.g. warm musical sound. Would building a tube preamp do this and would the preamp kit from bottlehead.com be good for this.

Thanks very much
 
#2
As I have never heard a Bottlehead amp I cannot speak from personal experience. However, general consensus seems to be that their are better, cheeper kits.

The Gainclone is a fun project but there are few tube projects that are "done for you" as much as the gainclone. Would you be willing to build something from a schematic? or do you want a kit that has a building manual?

Check headwize.com for some project amps that have schematics and parts lists. Or just go all out and find a schematic somewhere and build from there. One thing to keep in mind though is that building from a schematic and sourcing all needed parts is a deal harder then building from a project, which is a deal harder then building a kit.

Milo

EDIT: This is a good start. Lots of people build it, its cheep, fun, and likes the senns. Also if you build it small then its good for the bedside which opens up room for a new tube preamp for the living-room 🙂.

http://headwize.com/projects/showfile.php?file=cmoy5_prj.htm
 
#3
dome406 said:
I dont want to make an amplifier I would prefer just to introduce and get a feel of what tube amps sound like, e.g. warm musical sound. Would building a tube preamp do this and would the preamp kit from bottlehead.com be good for this.

Thanks very much
Click to expand...

I'm inexperienced myself, but I have some tube amps and have built one. I see no reason you can't make a tube amp sound pretty much any way you want - warm, cold, good or bad. Depends on the design and execution. Building a preamp will allow you to hear what that preamp sounds like in your system, nothing more.


Sheldon
 
#4
A3rd.Zero said:
As I have never heard a Bottlehead amp I cannot speak from personal experience. However, general consensus seems to be that their are better, cheeper kits.
Click to expand...

Consensus among whom? I think the actual consensus is that Bottlehead kits represent excellent value for money. I have never heard anyone who has built one of their kits say anything negative. Indeed, judging from the bottlehead furum, most people that build one end up building a bunch.

A3rd.Zero said:
The Gainclone is a fun project but there are few tube projects that are "done for you" as much as the gainclone. Would you be willing to build something from a schematic? or do you want a kit that has a building manual?
Click to expand...

There are actually tons of tube projects that are "done for you". The Bottlehead is a good one. Welborne Labs makes a low voltage preamp kit that is supposed to be very nice and quite a bit safer than some of the others. Hagtech (Jim is a member here) makes a preamp kit. DIY HiFi Supply makes a kit. Audio Note UK makes highly regarded kits. There are also a few others, but these are probably the most popular.
 
#6
Hey-Hey!!!,
I'll second the idea that there others than Bottlehead to consider. That said, I bought a manual from Doc and found it very educational. The issues I have with the Foreplay have largely been resolved with the revsiion III, but it isn't a $150 kit anymore either.

There are far simpler circuits and Far, *FAR* better pre-amp tubes than the 12AU7.

I'd also suggest looking at system requirements before getting something as high-gain as a Foreplay. A low gain or buffer circuit is probably a better idea.

On buffers, a pentode cathode follower is hard to beat. For a reasonable parts bill, and literally $10 of tubes you can do the whole thing. Tube rectifier included.

Power Iron is simple and cheap too. Set yourself up a means to deliver ~200V and you're off to the races. Even even less is OK too.

There is not much to it( says me after building a half dozen or so ). If you can deal with a schematic and bill of material, with construction notes...you've come to the right place.

You'll need some tools, pen and paper, DuncanAmp's PSUDii power supply simulator, and Frank Philipse's page of tube data sheets, and of course a calculator for working out the various forms of Ohm's Law.
cheers,
Douglas
 
#7
Thanks for all of the replies, I could work off just a schematic so it doesn't necessarily have to be a kit.

What do you recommend the specifcations I use for the tube preamplifier because I dont really know, or what I need for optimum performance. The gainclone I have built is the LM3875 non-inverted using dual 18v transformers and would like a 'warm musical tone'.

Thanks very much
 
#8
Hey-Hey!!!,
Let's start with some measurements. A test-tone CD and a load resistor, or loudspeaker should be able to tell you how much input signal your amp needs.

You'll compare this to the output voltage of your CD player and see if you ever need gain. Be aware you'll have some variation between CD levels( and perhaps later speakers and amps ).

Do you have any measurement gear? volt-Ohm meter, O-scope?
cheers,
Douglas
 
#9
Bandersnatch said:
Hey-Hey!!!,
Let's start with some measurements. A test-tone CD and a load resistor, or loudspeaker should be able to tell you how much input signal your amp needs.

You'll compare this to the output voltage of your CD player and see if you ever need gain. Be aware you'll have some variation between CD levels( and perhaps later speakers and amps ).

Do you have any measurement gear? volt-Ohm meter, O-scope?
cheers,
Douglas
Click to expand...
I second this idea. Most systems have too much gain and preamps are often of little benefit for non-phono systems apart from the switching and volume facilities. No point in making a preamp with lots of gain to just throw it away again in the VC.

Why build a preamp at all? Why not a poweramp with a VC and some switching all in the same box?
 
#11
dome406 said:
I would prefer just to introduce and get a feel of what tube amps sound like, e.g. warm musical sound. Would building a tube preamp do this
Click to expand...


dome406 said:
i just use a cd walkman as input at the moment.
Click to expand...

You cannot, as they say, polish a turd. With just a cd walkman, you are likely not hearing what the GC can do, and if a tube preamp is doing its job it will simply reveal to you what that walkman sounds like. Instead, you might be better served by building a DAC, perhaps one with a tube output stage. This will introduce tubes into your system as well as improve the source which I would bet will do more good for less money than a new preamp.
 
#13
I would seriously echo this point about too much gain, especially if there is a volume control later in the circuit. What with the very large variation in the output of both CD players and CDs, I have often traced folks' problems to instantaneous overload, i.e. too little 'headroom". Especially with popular op-amps of the +/- 18V variety, there can be as little as 12 dB headroom. Some struggle up to 15 dB. I am not going to join the subjective debate about "tube sound", but often the main reason why tube pre-amps have the edge is the odd 250V supply voltage available for signal swing.

While on this subject, may I throw in another cent's worth of comment: Beware of poorly filtered dc heater supplies (apology to members who read similar comments by me on other threads). It sounds very pious to boast "dc heater voltage", but just earlier tonight I struggled with just such a feature in someone's amplifier, with too much ripple - the sharp capacitor charging current peaks caused more noise in the end than a balanced 6V ac supply. Use dc for pre-amp heaters by all means, but save yourself anguish by smoothing properly. One of the many LM..... regulator chips does a whole lot of good.
 
#14
to echo the DC thing, I suggest one step firther, L-C or choke input filter. The rectificationnoise is best not created in the first place. The charging spikes so characteristic of cap input filters is usually not easy to get rid of once you have created it. Regulate afterwards, and from a farily smooth raw voltage will yeild better results than more careless methods.

Of course, all my amps are all AC. Even the 12.0 volt DH finals. Same when I decide to run 6.0v on the DH finals, or 2.5 in the previous edition. With PP, they are spooky quiet.

One of the many reasons I feel that PP is simpler than SE. Certainly the additional power side-effect canbe useful...
cheers,
Douglas
 
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