1 Watt Single-Ended Output Stage

[FalderGuitars]

Good afternoon,

Like a lot of people I talk to, I'm struggling to get a decent guitar tone at home without upsetting the neighbours (or my wife). I'm currently down to an Epiphone Junior (rated around 6 watts), but even with a Bitmo attenuator between the head and speaker I can't get it down to a volume I feel comfortable playing at.

Long story short, having built a half dozen of so amps - first from kits, then from schematics - I thought the best solution might be to design a 1 Watt output stage for myself.

Here's the schematic:





Obviously, it's not the most complicated schematic ever drawn (), but since my experience of designing circuits has been limited to simple gain stages thus far, I'm not 100% sure I've got the maths correct.

According to my calculations, it should produce 1.2 Watts, but I've been wrong before!

I was hoping some of you good people out there might have the time to take a quick look and tell me if I'm at least on the right track. I've got all my calculations written down, so if there's any more data you'd like I'll be happy to supply it. If I can get my scanner to work, I'll scan a copy of my loadline

Thanks for looking,

Matt.

[Enzo]

The answer to low volume is rarely watts. 1 watt should be half as loud as 10 watts.

Apparently in your situation this needs to be at "mom" levels. The same level as the radio at my dentist waiting room. Really, consider just getting something with headphones, don't even try to get that eighth of a milliwatt output. The physics of your ear means the sound won't be the same at those low levels anyway.

[FalderGuitars]

Hi Enzo,

Thanks for your reply. I get what you're saying, but I'not sure it's relevant - in this situation at least. What I'm trying to do is not so much build an amp that's quiet enough to play at home, but to make one I can push to it's limits before it gets too loud to play at home. I like the sound the of power amp pushing the transformer and speaker hard. Master volume amps sadly don't cut it for me, or my problem would be easily solved. Headphones are a non-starter.

At this point, I've considered and rejected all other options, having tried the majority. I appreciate that a 1 Watt amp driven to the edge will not sound - or feel - the same as a 100,50,15 or even 4 Watt amp operating in the same region, but that's no reason - in my book - not to go ahead and make one anyway...

FWIW, I can get away with a good bit more than dentist waiting room levels, and no-ones actually complaining. It's just that at it's sweet spot, the Valve Junior makes a lot of noise for a relatively low wattage amp, and I worry my neighbours are silently grinding their teeth the whole time I'm playing, but are too polite to say so.

Do you have any thoughts on the circuit itself? I've seen a few deigned for 1W, but they're alll a little hazy on either voltage or transformer type. Or both.

Matt.

[J M Fahey]

Triodes are bland sounding as power tubes, why not try a small pentode instead?
It will sound much closer to what a typical tube amp does .

[Mike Sulzer]

Triodes are incapable of much current with low voltage across them. A quick look at the curves, and I would expect about .5 watt with both sections in parallel, but that could be a bit pessimistic.

According to my calculations, it should produce 1.2 Watts,

[nosaj]

Triodes are bland sounding as power tubes, why not try a small pentode instead?
It will sound much closer to what a typical tube amp does .

How about this one?
Low Power Vacuum Tube Guitar Amplifier
nosaj

[FalderGuitars]

Triodes are bland sounding as power tubes, why not try a small pentode instead?
It will sound much closer to what a typical tube amp does .

Thanks for the reply.

That's interesting, any recomendations for a suitable pentode? My knowledge of valves is more or less limited to what you'd find in a guitar amp. I know there are many more to choose from, but being no hi-fi enthusiast I wouldn't know where to start looking. Is an EF86 any good? That's the only small signal pentode in my bits box.

Matt.

[FalderGuitars]

Triodes are incapable of much current with low voltage across them. A quick look at the curves, and I would expect about .5 watt with both sections in parallel, but that could be a bit pessimistic.

Thanks for replying,

I expect you're more clued up than myself, but if I got my calculations correct I'm expecting 1.2W. When I get a miunte I'll consolidate my workings into a readable/logical form and post them here.

Matt.

[FalderGuitars]

How about this one?
Low Power Vacuum Tube Guitar Amplifier
nosaj

Thanks for the link,

I did see this circuit when I was doing my research, and was very interested. Unfortunately, the link that led me to it hadn't got the full gen on the valve choices, just the schematic.

It's getting late tonight, but I'll have a look at this over breakfast. It looks at first glance like I should be able to find a suitable circuit for my needs. Fingers crossed, although I'm a little loathe to abandon my own circuit, having forced my brain to concentrate long enough to design it - maths and I do not mix!

Matt.

[Justin Thomas]

When I looked, when I scrolled to the bottom to "Table 1," it had several potential power tubes, from 1 to 2.5 watts. Maybe a gadget malfunction? :P

Justin

[nosaj]

Thanks for replying,

I expect you're more clued up than myself, but if I got my calculations correct I'm expecting 1.2W. When I get a miunte I'll consolidate my workings into a readable/logical form and post them here.

Matt.

If you've already got an amp you like a less efficient speaker could be an answer. I took a 10inch field coil with some help from here and antiques radios forum built a speaker similar to a fluxtone Where you increase or decrease the speakers efficiency toned down a tweed deluxe from headphone level to pretty damn loud. It's not a master vol at all. Only thing I had to buy was the 50watt rheostat.

nosaj

[FalderGuitars]

Hi,

Yes, the link nosaj posted is working fine for me too. When I stumbled across the circuit a few weeks ago, the tables for valve choices wre missing - likely due to either a 'gadget malfunction' (nice phrase) or an old/dodgy link. I'll digest the options along with my porridge tomorrow morning ;-)

Matt.

[Justin Thomas]

Porridge? Are you from the UK or Ireland? Or IN the UK or Ireland? If so: you put your location in your profile, it may help to speed things along - not everyone reads whole threads before chiming in, and you don't want someone suggesting 120V primaries or other such stuff, right?

Justin

[nosaj]

Porridge? Are you from the UK or Ireland? Or IN the UK or Ireland? If so: you put your location in your profile, it may help to speed things along - not everyone reads whole threads before chiming in, and you don't want someone suggesting 120V primaries or other such stuff, right?

Justin

There sure are a lot of porridges
https://en.wikipedia.org/wiki/Porridge
jason

[Justin Thomas]

Just got off three weeks in Ireland. Never heard anybody say "porridge" anywhere else! :P
Either way, seems kind of "un-American" to me... paging Senator McCarthy...

Justin