Good small valve amp for keyboards?

[Arpangel]

I'm trimming down my gear, and I need a good small valve amp for one keyboard and my i Pad playing live. I like the sound of a valve amp, the tone and overdrive, they always seem to sound more interesting than solid state equivalents. Trouble is, I don't want to spend money on something that just has a token valve in it, I'm prepared to budget for something a bit decent.
I'm looking for something along the size of a Roland Cube, orbmaybe a bit bigger, 10/15 watts maybe. Any ideas much appreciated...

[Sam Spoons]

Fender Blues Junior? I'm assuming you are not looking for faithful reproduction of grand piano samples then?

[Drew Stephenson]

Or if you are after something full range you might consider a Yamaha THR10 - surprisingly capable little bit of kit.

[Arpangel]

Thanks, good suggestions, the Blues Junior ticks the valve box, but only one input, I could get around that with a mixer, I've got one of those little Behringer mono jobs, but how do these amps cope and respond to a line level output? The Yamaha looks interesting, but does it have "the sound"? It does have an extra stereo input though, which would take my i Pad, and a seperate volume control.
You're right, I'm not after clean piano, If anything the dirtier the better, I'll be using it in our free-improv duo, so a bit of valve noise and grit should be exactly what's needed.

[Sam Spoons]

Is your keyboard a master keyboard or does it have sounds? Guitar amps expect an 'instrument level' signal which falls between line and mic level (obviously that varies somewhat). A live synth/piano output is usually somewhere around that of an electric guitar but a line output would be a bit hot for a guitar amp.

[Drew Stephenson]

Lord knows I'm no guitar expert but the guitarist in our band was very impressed (and he's a lot more picky than me). Personally I find that it plays like a 'proper' amp and allows me to play around with tones that I'd expect from my Peavey valve amp.
But the stereo input is completely clean so might not be what you're after.

[ore_terra]

the THR10 sounds ok, but of course it's not "the sound", and above all its 10W have nothing to do in terms of loudness with a 10W valve amp.

if you want stereo, maybe the best option is 2 valve amps instead of 1. that what guitar players wanting to stick to small valve amps will typically do if they want their stereo effects not to come back to mono in the amp.

regarding signal levels, you could do it with reamp boxes. they've designed to turn line levels acceptable for guitar amps, so they should be fit for the task.

something like this: https://www.palmer-germany.com/en/products/di-boxes/5093/daccapo

[The Elf]

...and all of these points are the reason why I strategically run my keys through a Line 6 Helix!

[Arpangel]

...and all of these points are the reason why I strategically run my keys through a Line 6 Helix!

Yes, a preamp is a good solution, but I need a speaker in a box, I'm traveling quite a bit at the moment, with no access to sound equipment, lots of bits and pieces start to become a pain. I have a Music Easel, that's just a suitcase basically, another little amp is all I need, just two boxes to deal with. I could use a pair of headphones and a preamp I suppose, but I have a problem with my right ear and don't like to wear phones, I prefer the sound of speakers anyway.

[Arpangel]

I bought a Roland Street Cube, it's not valve I know, but the sound is quite "big" for its size and output, plus it's got all the inputs I need, and the price was right. If it doesn't work out I'll get the Fender B J but TBQH, I think this Cube will be fine.

[ore_terra]

that's a fuill range amp, so nothing to do with valve amp sound

good amp though

[Arpangel]

I need a re-amp box, I can hear things in my synth, not nice things, simply because the gain is way too high, I just have to breath on the volume knob it's ridiculous. Keeping everything way down is the only option, I need to match the impedences.
I'm having a great time though, I've got this amp, my synth, and a handy recorder, some headphones, and a few leads and adaptors, I recorded a 40 min piece yesterday, this little set-up is more productive than being at home in my studio. .

[Chimera]

I have a Laney Lionheart Studio. It’s a wonderfully flexible amp. There are combo versions too.

[Drew Stephenson]

Orchid do a re-amp box for £56, reviewed in these pages but frustratingly i can't get a link to the review here on my phone.
Just search for Orchid Electronics and it's the second result.

[Sam Spoons]

A simple attenuator would almost certainly do the job, or a transformer DI? Reamp boxes are designed to present the correct load to a guitar amp's input where all you need is a level match.

[Arpangel]

A simple attenuator would almost certainly do the job, or a transformer DI? Reamp boxes are designed to present the correct load to a guitar amp's input where all you need is a level match.

Thanks Sam, logic prevails! Once someone suggests something it's easy to get get blinded to the obvious. Of course, I have my little Behringer mono mixer, problem solved, and no money spent!

[Hugh Robjohns]

I need a re-amp box

The Orchid Amp Interface is my stock recommendation these days:
https://www.soundonsound.com/reviews/orchid-electronics-amp-interface
http://orchid-electronics.co.uk/Amp_Interface.htm

This device will accept either balanced (from a console or interface) or unbalanced (from a keyboard etc) inputs and applies a minimum of 20dB attenuation -- more if you turn down the output level knob. It also allows the source and destination grounds to be separated if necessary to cure ground-loops (via a transformer).

It's a very useful and cost-effective box... but as has been said, all you probably need is a simple 20dB L-pad unbalanced attenuator. 10 minutes work with a soldering iron and a couple of resistors to modify a standard cable if you're handy enough...

I need to match the impedences.

No... you just need to match the signal levels. We don't use matched impedances in most analogue audio interfaces these days... haven't since the early 1970s... In almost all modern analogue audio interfaces the source has a very low output impedance (of around 100-200 Ohms) and the destination has a high input impedance (typically somewhere between 1.5k and 50k Ohms). As long as the destination input impedance is at least 5 times the source output impedance, all will be well.

The obvious exception to the above is an electric guitar which has an output impedance of maybe 5k-10K Ohms, and needs to see an input of 500k-1M Ohms or so. This interface is complicated because it is highly reactive and forms a resonant circuit in which small changes of impedance can have an audible effect. Thankfully, this is not the case with more sensibly designed electronic outputs from keyboards etc!

[ef37a]

Yes Hugh, this idea that guitar amplifiers need to "see" a particular, usually high impedance is a common one and hard to shift!

The idea may have started from the practice of using two passive DI boxes to run a guitar in a control room out to the studio floor. In fact you are of course just using the over a century's idea of unbalanced middling impedance to balanced low impedance and back to middling unbalanced to get a low noise connection.

"Ah but" someone countered a few years ago on an American forum, "you are matching the guitar's impedance at the amp end!" I replied that, although in theory two very good transformers would reflect the remote impedance, DI box transformers are usually so poor in terms of coupling and inter-winding capacitance that in practice not much of the guitars electrical characteristics would very faithfully preserved.

My protagonist eventually conceded when I pointed out that transistorized pedals had been used for decades straight into the "magic meg" of countless guitar amps and they had an output Z of around 1k or less.

As you say, it is almost always The Volts (mV) that matter. Impedance generally takes care of itself.

Dave.

[Arpangel]

Hugh! That's fine, I can make up a lead, but can I be a pain and ask you the value of the resistors I would need?

[ef37a]

Hugh! That's fine, I can make up a lead, but can I be a pain and ask you the value of the resistors I would need?

Phoarrr! How long is a piece of string, or wire in this case! Not knowing the actual output level of the kbd and the input sensitivity of the amp? Pretty d difficult. But...

Ten k Ohms (10,000) in the hot wire and 1k2 (1200 Ohms) from the junction of the hot pin and 10k to earth, jack sleeve will give just under 20dB of attenuation, i.e. a reduction of about 10 times. Making both resistors 10k will halve the signal, -6dB.

Ideally the resistors should be at the destination plug not the source but if the cables are short, under 3m not really a problem.

N very B. If you make the attenuator up as a jack to jack cable LABEL it! Otherwise in a years time you will pull it out the bag and wonder WTF's gone wrong with sommat!

Dave.

[Arpangel]

Hugh! That's fine, I can make up a lead, but can I be a pain and ask you the value of the resistors I would need?

Phoarrr! How long is a piece of string, or wire in this case! Not knowing the actual output level of the kbd and the input sensitivity of the amp? Pretty d difficult. But...

Ten k Ohms (10,000) in the hot wire and 1k2 (1200 Ohms) from the junction of the hot pin and 10k to earth, jack sleeve will give just under 20dB of attenuation, i.e. a reduction of about 10 times. Making both resistors 10k will halve the signal, -6dB.

Ideally the resistors should be at the destination plug not the source but if the cables are short, under 3m not really a problem.

N very B. If you make the attenuator up as a jack to jack cable LABEL it! Otherwise in a years time you will pull it out the bag and wonder WTF's gone wrong with sommat!

Dave.

Thanks a lot Dave, Ok, a 10k in-line to the hot pin, and a 1/2k plus a 10k from hot to the screen terminal? I've looked for a circuit diagram for this but can't find one..?

[ef37a]

https://www.google.co.uk/search?q=atten ... 8262550571

You want the first circuit on the left, the L pad. R1 is the 10k and R2 the 1k2, can you visualize putting them in a plug? If not I am sure someone here can do you a drawing? I am not that PC cute!

The resistors are necessarily going to have to be very wee, does not matter HOW wee, they consume no power to speak of. The sadly missed Maplin used to do a Lucky Bag of Rs and you would have found something in there to use. The values can be widely varied. Don't make R1 less than 10 k but 12, 16, 18, 22k are all possible then keep R2 such that the ratio is about 9/10:1 for about 20dB loss. 20dB might be a bit much actually so I would fix on a value for R1 then "tack in" a guesstimate and give it a blow.

(btw, if you want to get technical, the loss is given by..R2/R1+R2 then log the result and times by 20 to get it in dBs)

Dave

[Arpangel]

https://www.google.co.uk/search?q=atten ... 8262550571

You want the first circuit on the left, the L pad. R1 is the 10k and R2 the 1k2, can you visualize putting them in a plug? If not I am sure someone here can do you a drawing? I am not that PC cute!

The resistors are necessarily going to have to be very wee, does not matter HOW wee, they consume no power to speak of. The sadly missed Maplin used to do a Lucky Bag of Rs and you would have found something in there to use. The values can be widely varied. Don't make R1 less than 10 k but 12, 16, 18, 22k are all possible then keep R2 such that the ratio is about 9/10:1 for about 20dB loss. 20dB might be a bit much actually so I would fix on a value for R1 then "tack in" a guesstimate and give it a blow.

(btw, if you want to get technical, the loss is given by..R2/R1+R2 then log the result and times by 20 to get it in dBs)

Dave

Dave, much appreciated, I'm OK at soldering, no problem, but my maths especially relating to electronics is virtually non existent! But, the way I see that diagram is this, there is a resistor R1 connected "in line" to hot or tip of the plug, then R2 goes between cable screen and shield on the plug.
I think I may have some 10k resistors in my toolbox, I'll experiment with values for R2.
Alternatively, I may just use my Behringer mono MiniMix, it'll enable me to match levels, and also have control over the balance between my i Pad and my Buchla into the Cube.

[ef37a]

"then R2 goes between cable screen and shield on the plug. "

No. R2 goes between the hot pin of the jack to screen pin on the plug. I.e the JUNCTION of the hot pin and R1.

Dave.

[Arpangel]

"then R2 goes between cable screen and shield on the plug. "

No. R2 goes between the hot pin of the jack to screen pin on the plug. I.e the JUNCTION of the hot pin and R1.

Dave.

All is now clear!

I'll have a go I've got nothing to loose but a few mins rummaging around for bits!