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Let's talk about the Ashdown Little Bastard

#121
Nuage420 said:
Yeah. I would say it's worth your time an effort to sort it out. I bought mine with nothing wrong except the mid pot being a little scratchy. Spent another 250 shipping to and from having some leds installed and I still love it.
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Since the amp sounds so good, I will probably leave it alone...but yes I am a bit frustrated because I still have no idea what a regular LB30 or CTM 30 sounds like.

IMHO it would be a lot of work to put it back in spec with the schematic. It might require cutting the circuit board to route C15 back where it belongs. But it may be possible to simply cut one of the leads off K3, and then use a jumper from that point to connect C15 back to the original junction. It would also be necessary to change a bunch of components back to the original values and swap the Bass and Middle pots. Replacing some of the components most likely would require pulling the circuit board out of the chassis. The after you get it all back together, the labels on the front panel would no longer match the controls.

I think it's pretty obvious they put some care into selecting component values that would produce a good sound with the new configuration. Many of the component values are actually embossed on the circuit card.

I spent some time playing with an online line Tone Stack calculator. There was not an option to model the exact circuit, but by fiddling with the values in the Fender TMB and Hiwatt tone stack, I think I know what it's doing fairly well. The Middle control does appear to be as effective as the models seem to predict. It appears the mid shift selector (K3) varies the amount of mid scoop that is baked into the circuit. K4 determines where the low end rolls off. The roll of in both positions seems to be at an extremely low frequency. When I am standing next to the cab, I can't hear any change when I toggle the switch. But I may hear a very small change in the sub bass when I put a bit of distance between me and the cab. Hard to say for sure because it is very subtle as best. It might be nicer if one of the options thinned out the sub bass a bit more.
 
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#122
sifrancis said:
I have owned all three; Little Bastard, LB-30, and CTM-30. All the same amp.
I can safely say this is my favourite amp ever made. Sounds fantastic and I find the EQ really intuitive to dial in to whatever my needs may be.

The CTM-30 Little Stubby is well worth a look too - same amp design for the most part, but the "feedback" control is something quite special, and for many will prove more straight forward than the shift switches it replaces.
I'd love to grab one at some point, but it's hard to justify when I have multiples of what is essentially the same amp.
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Dynacord said:
Interesting, I thought the CTM-30/"Little Stubby" were the same but I just looked it up and they are two different amps (though mine does say "CTM 30 Little Stubby" on the faceplate...) Agree, the feedback control really is special.
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What does the feedback control do?
 
#123
rodl2005 said:
What does the feedback control do?
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It's not intuitively named and not about feedback in the way it's often used. More of a 'character' control IMO. I'm guessing it involves some sort of gain staging of feeding the preamp signal back on itself, hence the name. Not really sure. Regardless, it is quite powerful and useful.

Ashdown's PR describes it as:
"However the heart of this amp is the unique Feedback control which allows the complete character of the amp to be changed and fine tuned from old school vintage valve amp tones at one end through to tighter more mid heavy modern tones at the other."

Despite that being sales-speak, it does seem pretty accurate (to me anyway).
 
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#124
Dynacord said:
It's not intuitively named and not about feedback in the way it's often used. More of a 'character' control IMO. I'm guessing it involves some sort of gain staging of feeding the preamp signal back on itself, hence the name. Not really sure. Regardless, it is quite powerful and useful.

Ashdown's PR describes it as:
"However the heart of this amp is the unique Feedback control which allows the complete character of the amp to be changed and fine tuned from old school vintage valve amp tones at one end through to tighter more mid heavy modern tones at the other."

Despite that being sales-speak, it does seem pretty accurate (to me anyway).
Click to expand...

AFAIK it actually is a feedback control. By modifying the global feedback in the output section, you can change the amp's frequency response contour, how tight or loose the amp feels, as well as how it transitions from clean to drive.

I don't have a schematic for the Little Stubby, but here is the feedback line for the original LB30.

upload_2021-12-25_3-23-15.png


As you see, the feedback goes from the 8 ohm tap on the output transformer back to the cathode of V1B, which is part of the phase inverter circuit. Presumably the Little Stubby has a similar feedback circuit with an added control.

Here is an article that explains one possibility: Variable Damping (ozvalveamps.org)
 
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#125
Wasnex said:
AFAIK it actually is a feedback control. By modifying the global feedback in the output section, you can change the amp's frequency response contour, how tight or loose the amp feels, as well as how it transitions from clean to drive.

I don't have a schematic for the Little Stubby, but here is the feedback line for the original LB30.

View attachment 4516822

As you see, the feedback goes from the 8 ohm tap on the output transformer back to the cathode of V1B, which is part of the phase inverter circuit. Presumably the Little Stubby has a similar feedback circuit with an added control.

Here is an article that explains one possibility: Variable Damping (ozvalveamps.org)
Click to expand...

Thanks. This makes more sense. I do find it a very useful addition.
 
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#127
mrm56 said:
me too.
you want it more cleanish/hifi, dial 'er back, more loose and hairy, dial 'er up a bit.
add input gain to taste and a plethora of cool tones are at hand with just a few simple controls.
stubby is one great lil amp, imo.
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Seems very useful indeed. Ashdown sure has come up with some awesome amps, although I still prefer the looks of the Little Bastard.
 
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#128
As I noted in this and subsequent posts ( Let's talk about the Ashdown Little Bastard,) the LB 30 I bought recently is a bit different than the original

Looks like the CTM 30 may come with different versions of the tone stack as well. AFAIK, the original CTM 30 was the same amp as the LB 30. Just a new look and name.

If you can find older images of the CTM 30, the tone controls are in the following order: Middle, Bass, Treble, just like the original LB 30. Here is an image from a 2018 Talkbass for sale listing:
upload_2021-12-29_14-53-31.png

Ref: SOLD - Ashdown CTM-30


But all of the recent CTM 30 images I have found using Google show the order as Bass, Middle, Treble like my LB 30 Mk2. However, the Mid Shift and Bass Shift switches are in the original locations and have not been relocated like on my LB 30 Mk2. So maybe they just relocated the rotatories on the front panel and left the circuit alone.

upload_2021-12-29_14-57-24.png
 
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#139
Joris 55 said:
That is one hell of a practice rig!
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Thank you! It does sound REALLY nice. I'm getting some hissy breakup with the notes that wasn't there when I first got it. This is true even at lower volumes when I'm not pushing it hard. Almost sounds like static in the signal but it is only there when the note is sounding and it is there across different basses. I'm wondering if I have a tube going bad. Is my description accurate of what a tube going bad can sound like?
 
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#140
GroovyBaby said:
Thank you! It does sound REALLY nice. I'm getting some hissy breakup with the notes that wasn't there when I first got it. This is true even at lower volumes when I'm not pushing it hard. Almost sounds like static in the signal but it is only there when the note is sounding and it is there across different basses. I'm wondering if I have a tube going bad. Is my description accurate of what a tube going bad can sound like?
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Try reseating the preamp tubes. If you have spares, roll a good tube through each slot (one at a time). The amp uses two 12AX7 and one 12AU7.

You can also pull the output tubes 2 at a time. Pull either the inner pair or the outer pair.

upload_2022-1-6_13-34-0.png


Pulling two tubes causes the 4 ohm output to become 8 ohms and the 8 ohm output to become 16 ohms. Not something I would do for long, but it should be fine for testing.

You can't pull output tubes on many cathode biased amps because all of the cathodes are tied to ground through a single resistor. The bias relies on the voltage drop that develops across the cathode resistor. If you pull two tubes, the bias current is cut in half and the voltage is also cut in half. The remaining two tubes try to pull enough current to get the bias back where it stabilizes.

The LB30 has separate cathode resistor on each tube, so this is not a problem. The value of each cathode resistor is about 4 times higher than in an amp with a shared cathode resistor. So although the resistor only handles current for 1 of 4 tubes, the additional resistance results in voltage necessary to stabilize the tube in the proper current range.

Could also be a scratchy pot or a loose solder joint.
 
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