Newbie question about amps and sound cards

Posted: 10/29/2010 12:47:22 PM

From: A Coruña, Spain

Joined: 9/26/2010


I have been playing a B3 theremin for six weeks or so. Until yesterday, my setup was the following: the theremin's output went to my PC soundcard's line in jack, and the PC soundcard's output was connected to speakers that are internally amplified.

I know that this is *very* far for the ideal setup, but it sounded OK enough for me, until today. Today I got a new PC, and if I do the same I was doing before, I get the high tones right but an unpleasant distortion in the lower tones. I fiddled with all the options in the sound card but I couldn't get rid of it (disabling bass boost in the speakers helps, but not enough).

So I thought, OK, my new sound card is crap, so let's look for an USB audio interface. But then I realised that for the price of an USB audio interface (my budget is quite tight) I can get a second-hand amp. I have my eyes set on a second-hand Peavey KB15 that they sell around here. So here are my questions, answers from people who know about theremins or audio equipment in general would be very welcome:

- Do you think it is really better to invest on an amp with respect to an audio interface?
- Do you think the Peavey KB15 is a good (low-cost) choice? There are also second-hand guitar amps I could get, but I have read somewhere that keyboard amps are better than guitar amps for theremins.
- The amp has a "headphone out" jack but no "line out". Is it possible to connect the headphone out jack to a PC's line in or mic in? This is not essential but I wouldn't want to rule out the possibility of processing my sound with PC software.

Thanks in advance!
Posted: 10/29/2010 2:35:22 PM

From: Croxley Green, Hertfordshire, UK

Joined: 10/5/2005

It looks like it will work - my first amp was a 15 watt device for acoustic instruments, and the volume was OK, but I have never used this particular one. If you can take your theremin to a music shop and try it out that would be best.

I would choose one that has reverb - or buy a separate reverb unit - I find the theremin sound a little dry without any reverb.

From the block diagram in the documentation for the amp it appears that the speaker disconnects automatically when you plug headphones in, so recording from the headphone out is not an option.

You have the option of miking the amp. When I started I used the microphone from a Plantronics DSP500 USB headset that I had bought to use with Skype and got satisfactory results without needing to invest in an audio interface.

(The DSP500 is no longer available. Others in the DSPxxx range are still in production.)
Posted: 10/30/2010 6:48:46 AM

From: A Coruña, Spain

Joined: 9/26/2010

Thanks a lot for the advice. I had already decided to buy the KB-15, but unfortunately the seller just sold it to someone else, so I'm back where I was.

I am now doubting between the Peavey KB 1 and the Roland Mobile Cube. The KB 1 seems like a "traditional" device that should work well. But the Mobile Cube is tempting because it is really small and portable, and can be operated by batteries. The wattage seems very small in relation to other units, at 2x2.5W, but I have read some reviews and they are surprisingly good. I am not going to play gigs, only in my room alone or with friends/family, so perhaps it could be enough for me. But I at least want a sound that can comfortably "fill" a small room (unlike, e.g., the sound of a laptop).

Has anyone tried any of these two amps or have an idea of how they sound? I'm going to try on Monday to see if I can try any of them in physical stores at my town. I think there might be a chance in the case of the Mobile Cube since it seems to be a relatively "mainstream" unit, but anyway my town is small, so there is a large probability that they don't have any of them anywhere and I have to buy without trying any. So opinions would be greatly appreciated.
Posted: 10/30/2010 9:48:32 AM
Jeff S

From: N.E. Ohio

Joined: 2/14/2005

Both amps seem like decent choices for starting off. The built-in effects (reverb, chorus) and multiple inputs on the Roland are definitely a plus.

However, one issue to consider are the speakers. Normally, I wouldn't recommend anything less than an eight-inch speaker for a theremin amp.

The Peavey has an eight-inch speaker. It has no high-frequency horn, although that may actually be a plus (high frequencies will not be too shrill).

The Roland has two four-inch speakers. This is for maximum projection from a small speaker and low power amp (as well as stereo effects). I have an old Roland guitar amp with a similar arrangement (four 4-inch speakers). The problem with this is the sound will not have the richness and body in the mid and low frequencies that you would get from a larger speaker. This is OK for a guitar, but not so good for keyboards or a theremin. The low end of a theremin will sound quite buzzy.

A listening test is definitely in order. If you can find the Roland, you can compare it to almost any other amp with an eight-inch speaker. Since the Peavey has no horn, almost any other guitar amp will suffice for the purpose of comparing the effect of speaker size.
Posted: 11/1/2010 12:42:49 PM

From: Escondido, CA

Joined: 2/6/2008

You will definitely want more power than 2.5W to drive the bass notes. Personally, I never go smaller than 12" speakers for anything, but you can get excellent results with more speakers of smaller diameter. In either event, it will take some power to drive them well enough to not sound "muddy". If you will only be playing in small rooms, you could get by with 15W, but just barely.

It is not about the average volume level. It is more about dynamic headroom.
Posted: 11/1/2010 7:16:59 PM

From: A Coruña, Spain

Joined: 9/26/2010

I have managed to solve the supposed sound card problem that I mentioned in the original post, and I have gotten a really good laugh from doing it!

Half an hour ago I happened to read the post and I noticed that the distortion described by the poster was very similar to mine. So, since he said that putting his hand on the audio output stopped the distortion, I tried and did the same. My distortion stopped.

Therefore, by reading the other posts in the thread, I concluded that I probably have a grounding problem. In fact, both my PC and the theremin are plugged into an ungrounded outlet (in the case of the theremin the power supply itself is 2-prong, so I guess it's not relevant which socket I plug it in). To further test this theory, I decided to apply more advice from the thread: to use a wire to connect the theremin's audio output to ground. But alas, there was nothing nearby that (to my knowledge) could be considered "ground". I have a grounded outlet in the same room but it was like 3 metres away and I don't have wires that long. So then I think: "well, if touching the audio output stops distortion, it seems like I'm a good ground". So I took an audio cable, attached one end to my own hip, attached the other end to the metal ring around the theremin's audio output, and voila. The theremin sounded nice again!

Probably this is obvious for those of you that know a lot of electronics, but I felt like a mad scientist doing that :)

Anyway, I'm worried about the possible health risks of constantly acting as a living ground wire while playing, so tomorrow I'll buy an extender in order to plug my PC into the grounded outlet and see if this also solves the problem in a more comfortable way.

I wonder why this didn't happen with the old PC/soundcard, but I guess it had a different inner structure or something that hid/eliminated the problem.

In any case, even though I now have a decent chance that my theremin will sound OK through my new PC, I will still buy an amplifier. From the advice I have been given, I think I'll try to test the Mobile Cube if I can find one in my town, and if not, or in case of doubt, I'll go straight for the Peavey.

Thanks all for the advice.
Posted: 11/8/2010 1:46:55 PM

From: A Coruña, Spain

Joined: 9/26/2010


First of all, sorry for asking so many questions, but I want to make good investments and it's hard to find people who know about theremins if it's not online... I hope to be an answerer instead of an asker someday :)

OK, so I went to several shops and none have either of the two amps I was mentioning for display, although they can order it. So I totally discarded the Mobile Cube and Ï was decided to order the KB-1. But when I was going to order it, the shop owner told me that for only ten or so more euros than the KB-1 I can get a Peavey MAX 110 bass amp, and he thinks it's better value for the price.

Any thoughts about using a bass amp (that particular one) instead of a keyboard amp for a theremin?
Posted: 11/8/2010 2:03:33 PM
Jeff S

From: N.E. Ohio

Joined: 2/14/2005

Does your local retailer have ANY amps in house you can audition before deciding? If not, I'd try to contact a few local musicians and see if they would be game to let you try theirs. I'm guessing they would.

A bass amp would work, BUT since it is designed for an even lower range of frequencies, the high frequencies of your theremin may be overly muted.

Ordering any of these amps without having any idea of the results is a major risk, unless they are offering a 100% money back guarantee if not completely satisfied.

Grounding - It's always a good idea to make sure your computer/amp and theremin are plugged into the same circuit, if not the same outlet. This lessens (but does not eliminate) the chance of any grounding or interference issues.
Posted: 11/16/2010 12:50:35 PM

From: A Coruña, Spain

Joined: 9/26/2010

For the record, I was finally able to test some amps, including the Peavey KB-1. I was happy with the sound of the Peavey and didn't think the bass amps sounded better. So I bought the KB-1. Wow, what a difference. Not only I now have much more available volume and better sound, but where I notice it most is in the dynamic margin... not only I can make louder sounds than before, but also softer sounds than before, and I have more control over volume in general and a flatter response. I'll have to pay more attention to my left hand now.

So for anyone wanting advice about amps for a B3 theremin, in my opinion the Peavey KB-1 is fine (although this is a total newbie's opinion).

Thanks everyone for the advice given in this thread.
Posted: 11/16/2010 9:48:43 PM
Jeff S

From: N.E. Ohio

Joined: 2/14/2005

Wonderful! That will get you off to a great start. If you can afford it and ever upgrade your amp, it would be a good idea to hang on to this one. There will always be times when you want to travel light and don't want to drag a larger amp around.

Now, like Gordon said, you should look into a decent reverb/delay unit when you can afford it. You won't regret it.

For recording on the computer, you can always use the arrangement you had before. Are you SURE your soundcard was the problem? Are you sure you're not using a crappy set of computer speakers?

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