Ashdown amps can sound awesome, but I have found their tone controls to be a bit quirky. After spending some time with a CTM300 I thought I would write this in an effort to help others get the most out of their amps.
The following is IMHO and based on my experience with my particular amp…YMMV. For reference, I used a pair of home-built EV TL405s speakers loaded with EVM18Bs and a Series 1 Yamaha TRB6P bass.
The CTM300 is the most heavily voiced/least transparent, quality amp I have ever played. Vintage, thick, punchy, tight, growly, snarly, and grindy are words I would use to describe its basic tone. Very much in the SVT tonal universe but the CTM lacks extended highs so it is hard to find a glassy or hifi tone. Similar low-mid push to an SVT, but the top end tends to be more snarly (upper mid drive) than grindy (high drive). Tightest lows of any tube amp I have played and can be a bit dryer and more articulate than an SVT. The CTM can produce solid and full bass, but not super deep bass. Volume wise the CTM seems slightly louder and less compressed than the blue line and skunkworks SVTs I have compared it to.
This video provides a good representation of the CTM300’s basic tone:
Initially I had a hard time getting a good sound out of the CTM. Eventually, I found the secret is keeping the tone controls below 11 o’clock. The EQ bands interact significantly with each other and for higher settings do not function in a very intuitive manner. On most amps, a good starting point is all tone controls at noon, I would suggest starting with the CTM’s tone controls at 9 o’clock. There is a lot of tonal variation available between 7 and 10 o’clock.
Buttons:
Mellow Increases gain and low mids and gently rolls of the highs. Change is similar to engaging the shift button, but pre EQ.
Deep Scoops out mids.
Shift Raises the upper knee of the bass control well into the mid-bass range.
Bright Greatly emphasizes high mids. Pretty much unusable except when the mellow button is engaged. Might be useful with a darker voiced fridge.
EQ Controls:
Bass Effects mostly low bass with shift button disengaged. Extends well into mid bass when shift button is engaged. Effective range of this control is fairly limited and boost maxes out around 10 o’clock. For driven tones, some subtle shaping of the distortion occurs as the control is increased past 10 o’clock.
Middle Fairly wide band and seems to extend above the response of the treble control. Lots of range on this control and it completely swamps out the bass control and, to some degree, the treble control if pushed above about 10 o’clock.
Treble Fairly wide band, boosting primarily mids to high mids. Increasing control above 11 o’clock adds little additional high end emphasis but increasingly rolls off the lows making the overall tone mid focused. Truest highs are obtained with the treble off and the bass and middle at about 9 o’clock.
Because the tone controls are so interactive, it is often necessary to adjust two controls instead of one to achieve the desired tonal balance.
Favorite Settings (all buttons out)
(Bass/Middle/Treble)
9/9/0 Classic tube tone with the most extended lows and highs; as well as, the most even response.
9/8/11 As the treble control is turned up the amp becomes snarly and mid focused. A slight decrease of the middle control can be used to offset some of the additional mid drive from the treble control.
Overdrive: Tonally one of the best bass overdrive sounds I have heard: dark and even across the tonal spectrum. With the mellow button engaged, the fundamental pops out clearly even with the gain maxed. Unfortunately the distortion is not very touch sensitive with the installed tubes. Rolling tubes in V1 and V2 might help with the touch a bit, but in my experience 12DW7/7247/ECC832 tube types do not have as much drive and tonal variation as 12AX7/7025/ECC83 tube types.
Technical Issues:
The amp came to me (previously new) with a 6.5V meter bulb. I went through a couple of those quickly before I measured and found the voltage applied to the lamp is 8V. I couldn’t find any 8V lamps domestically, so I spec’d out two 14V lamps: #1487 lamp 2.8W, 14V, 3,000 hrs and #258 lamp 3.78W, 14V, 500 hrs. #258 looks better but I opted for the longer life #1487 which is a bit dim (looks extremely vintage). I also found a couple of viable 12V lamps but they were only rated for 250 hrs. For those in the UK, Ashdown recommends an 8V BARTHELME 00640850.
Bias—Originally the output tubes could not be biased above 20% and the amp was not making much power. I replaced the 47K bias ranging resistor with a 33K, 3W resistor and was able to bias a set of significantly mismatched KT88s to spec. Ashdown recommends biasing the output tubes to 28ma and says this is achieved when the CTM’s bias meter indicates 12 o’clock.
Output Tube Orientation
6............................1
5............................2
4............................3
.......Front of Amp
Low drive and early distortion—On a couple of occasions the preamp started loosing drive and distorting at low levels. Reseating V1 and V2 cleared the problem. The amp has JJ ECC832s in these positions, and from what I understand, JJs have smaller pins than most other tubes, which can lead to problems. Last time I had the amp open to reseat the JJs, I rolled in a GE and Raytheon 7247. Both had extended highs over the JJs and definitely had bigger pins.
Bottom Line: If you want a snarling, belching beast, this may be the amp for you.
The following is IMHO and based on my experience with my particular amp…YMMV. For reference, I used a pair of home-built EV TL405s speakers loaded with EVM18Bs and a Series 1 Yamaha TRB6P bass.
The CTM300 is the most heavily voiced/least transparent, quality amp I have ever played. Vintage, thick, punchy, tight, growly, snarly, and grindy are words I would use to describe its basic tone. Very much in the SVT tonal universe but the CTM lacks extended highs so it is hard to find a glassy or hifi tone. Similar low-mid push to an SVT, but the top end tends to be more snarly (upper mid drive) than grindy (high drive). Tightest lows of any tube amp I have played and can be a bit dryer and more articulate than an SVT. The CTM can produce solid and full bass, but not super deep bass. Volume wise the CTM seems slightly louder and less compressed than the blue line and skunkworks SVTs I have compared it to.
This video provides a good representation of the CTM300’s basic tone:
Initially I had a hard time getting a good sound out of the CTM. Eventually, I found the secret is keeping the tone controls below 11 o’clock. The EQ bands interact significantly with each other and for higher settings do not function in a very intuitive manner. On most amps, a good starting point is all tone controls at noon, I would suggest starting with the CTM’s tone controls at 9 o’clock. There is a lot of tonal variation available between 7 and 10 o’clock.
Buttons:
Mellow Increases gain and low mids and gently rolls of the highs. Change is similar to engaging the shift button, but pre EQ.
Deep Scoops out mids.
Shift Raises the upper knee of the bass control well into the mid-bass range.
Bright Greatly emphasizes high mids. Pretty much unusable except when the mellow button is engaged. Might be useful with a darker voiced fridge.
EQ Controls:
Bass Effects mostly low bass with shift button disengaged. Extends well into mid bass when shift button is engaged. Effective range of this control is fairly limited and boost maxes out around 10 o’clock. For driven tones, some subtle shaping of the distortion occurs as the control is increased past 10 o’clock.
Middle Fairly wide band and seems to extend above the response of the treble control. Lots of range on this control and it completely swamps out the bass control and, to some degree, the treble control if pushed above about 10 o’clock.
Treble Fairly wide band, boosting primarily mids to high mids. Increasing control above 11 o’clock adds little additional high end emphasis but increasingly rolls off the lows making the overall tone mid focused. Truest highs are obtained with the treble off and the bass and middle at about 9 o’clock.
Because the tone controls are so interactive, it is often necessary to adjust two controls instead of one to achieve the desired tonal balance.
Favorite Settings (all buttons out)
(Bass/Middle/Treble)
9/9/0 Classic tube tone with the most extended lows and highs; as well as, the most even response.
9/8/11 As the treble control is turned up the amp becomes snarly and mid focused. A slight decrease of the middle control can be used to offset some of the additional mid drive from the treble control.
Overdrive: Tonally one of the best bass overdrive sounds I have heard: dark and even across the tonal spectrum. With the mellow button engaged, the fundamental pops out clearly even with the gain maxed. Unfortunately the distortion is not very touch sensitive with the installed tubes. Rolling tubes in V1 and V2 might help with the touch a bit, but in my experience 12DW7/7247/ECC832 tube types do not have as much drive and tonal variation as 12AX7/7025/ECC83 tube types.
Technical Issues:
The amp came to me (previously new) with a 6.5V meter bulb. I went through a couple of those quickly before I measured and found the voltage applied to the lamp is 8V. I couldn’t find any 8V lamps domestically, so I spec’d out two 14V lamps: #1487 lamp 2.8W, 14V, 3,000 hrs and #258 lamp 3.78W, 14V, 500 hrs. #258 looks better but I opted for the longer life #1487 which is a bit dim (looks extremely vintage). I also found a couple of viable 12V lamps but they were only rated for 250 hrs. For those in the UK, Ashdown recommends an 8V BARTHELME 00640850.
Bias—Originally the output tubes could not be biased above 20% and the amp was not making much power. I replaced the 47K bias ranging resistor with a 33K, 3W resistor and was able to bias a set of significantly mismatched KT88s to spec. Ashdown recommends biasing the output tubes to 28ma and says this is achieved when the CTM’s bias meter indicates 12 o’clock.
Output Tube Orientation
6............................1
5............................2
4............................3
.......Front of Amp
Low drive and early distortion—On a couple of occasions the preamp started loosing drive and distorting at low levels. Reseating V1 and V2 cleared the problem. The amp has JJ ECC832s in these positions, and from what I understand, JJs have smaller pins than most other tubes, which can lead to problems. Last time I had the amp open to reseat the JJs, I rolled in a GE and Raytheon 7247. Both had extended highs over the JJs and definitely had bigger pins.
Bottom Line: If you want a snarling, belching beast, this may be the amp for you.
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