mathias's magical hybrid practice amp project (The Echidna)

[mathias]

In: the GRS 8" full range speakers, Kustom 10" speaker, and misc tiny parts from Parts-Express.

The full-range 8" sound decent as left and right speakers playing music from my iphone through the class D amp. There's a lot of information online that points towards this type of speaker needing a ported+sealed speaker cabinet for hifi applications, and so I believe they're not working to their fullest potential without a box around them. That is, they're not super strong on the treble side of things, but at least they're not piercingly treble either. Bass response is hard to guess without a cabinet around them and the fact that I couldn't blast something with strong bass where I was unboxing them.

The Kustom 10" may need some time to break in ,but so far it sounds good with a guitar signal. It's not in a sealed cabinet like my Ampeg cab (Celestion Vintage 30) is, or in a partially open-back cabinet like my Weber 8" in my Epi Valve Jr, but it sounds, err, like a guitar, through the class D amp. Hard to tell if it is indeed "darker" or not than other speakers as the description stated, since I couldn't really crank it.

Have yet to actually set everything up so that I can demo them against each other.

[mathias]

Had a ton of fun rocking out with the Kustom 10", power amp, and my Joyo Ultimate Drive as a preamp. (oh, and my dept store 60's single coil guitar)

Let's just say that with the Joyo OCD-clone in front of it, the bass notes got loud enough that downstairs neighbors came and complained.. (and the Kustom speaker isn't in a cabinet yet, just sitting on top of a milk crate -- good indication that 15w SS is going to be loud enough to start.)

That said, as one might expect, when you're driving it quieter, it doesn't have much, err, cahones. I'm looking into what people have done in analog-land to emulate speaker cabinets without traversing the silly world of digital speaker cabinet emulation. So far a T-filter that rounds off the frequency response towards that of a Marshall 4x12 seems to be the most likely solution?

The Kustom speaker has got a good level of darkness and rock 'n roll in its tone. Digging it. Can't wait for the Jensen MOD 10" to get here to compare the two.

Edit: more thoughts on the Kustom: the rating for this speaker is 75 watts and its got a SPL of 99, so it's designed for a lot more power than this amp is putting out. (The power amp is barely moving it at "loud enough for bedroom" volume levels). I don't know enough about speakers to know if that should lead me towards a speaker with a lower power rating so that it is being pushed harder at lower volumes/power levels?

[AngryGoldfish]

Does negative feedback work in a solid state amp? You could try and add a depth knob to control the lowest frequencies. That's used on modern amps to mimic and better fit into different cab and volume situations.

As regards speakers, I'm not opposed to an overrated speaker. It depends on what sound you're going for. I was playing a Matamp Mini-Rock into a single Hot 100 speaker and it was great. That's 10 watts roughly into a 100 watt speaker.

[mathias]

This is just a general bit that I've edited out of the below: I'm going off of pure personal preference through experimentation. (ie, there's no real up-front design here, just experimentation and evolution.)

I will try a depth knob (but it'll have to be worked into the preamp section) as an alternative to trying the high-pass+low-pass filter as a "cab simulator". Or I could combine them, potentially, and the depth knob would let more low end "through" past the filter stage.* The class-D power amp is kind of a black box, and I'm treating it exactly like that.

I got a notification from UPS that the Jensen MOD speaker was delivered today so I'll be playing with that tonight and comparing the two. By comparison, the Jenson MOD has a much lower power rating. These things interact on so many variables that I can't say that one is going to definitely be better than the other off just the specs. We'll see!

*(I was going to shoot for simplicity over a ton of controls on this amp, but it's already shaping up to need quite a bit of tone shaping in the preamp.)

[mathias]

Also, as evidenced by renaming the initial post, I've settled on a name for this amp for awhile, but haven't mentioned it. I'm calling it the Echidna, which is basically a crazy mixed up creature that nature should have never allowed to exist. It has spines! It doesn't have teeth, but instead has a beak! It's a mammal but it lays eggs! (It's a Monotreme.) It has electrosensors in its beak! Its babies are called puggles and its genus is called Zaglossus, which sounds awesome!


http://en.wikipedia.org/wiki/Echidna

And so, since this crazy hybrid tube+SS amp is a crazy mixed up thing that also shouldn't exist, it shall be named Echidna.

[AngryGoldfish]

Fucking. Awesome. Name.

[mathias]

AngryGoldfish, what's more important to you: a non-speaker-cab-emulated line out to drive a bigger external cabinet, or an adjusted headphone out?

[AngryGoldfish]

The first one. I just don't feel headphones are designed to be used for guitars. It doesn't sound right, IMO.

[mathias]

Gotcha. That actually was what I was thinking, but I'm looking at what to use the spare channel on the stereo amp for, and it an external speaker-out that hasn't gone through any filtering for "cab simulation" seems to make the most sense.

[mathias]

I did some research today and think I've hit upon a few circuits that will get blended up to produce the preamp. Threw a bunch of pedals into BST in the hopes that I can grab the components soon and start tinkering.

So far my plan is to continue with a single 12AX7 in the preamp, but I'll be going forward with running it on proper AC voltage. I'm shelving the idea of using sub-miniature tubes due to the ubiquity and durability of 12AX7's, but it'd be cool to build a smaller version of the circuit with a 6021 triode sub-miniature tube in the future.

References for the interested:

http://www.dogstar.dantimax.dk/tubestuf/mctube.htm
http://www.dogstar.dantimax.dk/tubestuf/mctube2.pdf
http://workisforsuckers.org/prj/mini_mctube - (6021 version of the McTube)
http://www.runoffgroove.com/condor.html
http://www.hexeguitar.com/diy-cabsims_e

[goroth]

I love speakers that are massively overrated, powerwise, because I dislike speaker distortion. I wonder if you would get an answer from Eminence (or whoever, but they have good customer service in my experience) regarding whether the frequency response is significantly different with an underpowered speaker - ie, if you'd get more/less bass from a lower/higher rated speaker, or if the frequency response is relatively independent of how hard the speakers are being driven. Hmmm...

I wonder if a ported cab would help get the sort of "thump" you get with a stack? This might help.
http://www.hometheatershack.com/forums/ ... alculator/

[mathias]

I see you picked up on my other thread. That's what I'm wondering; in particular, pairing the higher-wattage Kustom with a ported cabinet and driving it as hard as the amp can push it.

I'm also considering pairing the Jensen MOD 10" (lower wattage rating, more bright and bell-like tone, less bass and darkness) with the 2x15watt power amp and building that into a practice amp, then getting a more powerful class-D board to pair with the Kustom 10", to build a slightly more powerful amp with, with a ported cabinet design. There's a 2x50watt class-D board at Parts-Express that I think I can still power off of a voltage regulator in the power supply scheme I'm thinking of using.

Thoughts?

[mathias]

Part of what I have to factor in is that making it more powerful or having more "thump" is just going to contribute to the complaining-neighbors factor, since I'll essentially be making it more powerful/louder in certain frequencies. This is, after all, supposed to be a practice amp that sounds better than the majority of little amps out there.

I'm not sure there's ways to 'emulate' the feeling of a stack being pushed, but I might be able to use the high-pass/low-pass filter approach to at least approximate what it does to the frequencies.

[AngryGoldfish]

You can 'emulate' the frequencies and dynamics of a full stack being pushed, but you can't emulate the feeling and impression. A full stack cranked feels awesome because you can...feel it. There is an interaction that no small amp, no matter how good, can replicate. You need the volume, simple as. You can replicate the dynamics and a certain amount of the bass, but the thump will not be there because the volume isn't.

I advice you to not try and emulate a cranked amp at home, but just build an excellent sounding analog transistor amp. Focusing on mirroring a loud amp is just going to do your head in. The best amps, IMO, are the ones that just sound great. You could try and go the Swart route and build a great sounding small amp, or you could go the Verellen route and make a great sounding 300 watt amp. Either way, just make something good. Keep your head. Or in your case, Rudi's head with the door of Kukundu.

[new05002]

Does negative feedback work in a solid state amp? You could try and add a depth knob to control the lowest frequencies. That's used on modern amps to mimic and better fit into different cab and volume situations.

As regards speakers, I'm not opposed to an overrated speaker. It depends on what sound you're going for. I was playing a Matamp Mini-Rock into a single Hot 100 speaker and it was great. That's 10 watts roughly into a 100 watt speaker.

negative feedback is an electrical concept, works everywhere