TMI Amplifiers

TMI Cylcotron.

Completed 9/10/2007. Poweramp based on AX84 2W PP, Preamp based on AX84 Lead I preamp. I'd like to extend a huge thank you to the people at AX84 and to Mike Schuette, without whom I would not have been able to construct these amps.

Features:

• 3 X 12AX7 preamp w/ separate 'SLO' cold bias stage and DC drive stage
• 12AT7 phase inverter
• 6SN7 power tube for surprisingly loud 2W Push-Pull Operation
• 6CA4 rectifier tube
• Full tone stack (B/M/T) and presence control
• Dual gain controls
• Master volume

A complete Build Log is available here. Schematics will be posted soon.

Preliminary Sound Clips:

1. Overdriven Rhythm Guitar I - based on the Alice in Chains song 'Dam that River'
2. Overdriven Rhythm Guitar II - work in progress riff by Tiny Man Inside
3. Overdriven Rhythm Guitar III - based on the Jimi Hendrix song 'Manic Depression', different EQ and mic placement than clips I and II.
4. Lead Sound I - Bridge Pickup/Les Paul - G1/G2 = 10, B = 9, M = 2, T = 8, P = 9, Vol = 2
5. Lead Sound II - Neck Pickup/Les Paul - G1/G2 = 10, B = 8, M = 7, T = 5, P = 4, Vol = 2
6. Clean Sound I - Bluesy Picking - Neck Pickup/Les Paul - G1 = 2, G2= 4, B = 9, M = 7, T = 6, P = 5, Vol = 4
7. Clean Sound II - Sweep arpeggios - same settings as above

Production Notes:

Rhythm guitar tracks were recorded with the amp running through a Marshall 1936 cabinet with G12T-75 Celestion speakers. The amp was set as follows: Gain 1/Gain 2 = 10, Bass = 9, Mid = 2, Treble = 8, Presence = 9, Volume = 2. A Sennheiser e609 mic was placed on the grill of a Marshall 1936 cabinet, positioned so the mic was approximately 3 inches to the left of the cone (9 o'clock). A JoeMeek JM37 mic was placed approximately 2 feet behind the Sennheiser mic and aligned with the center of the cone. Both mics were fed into a Mackie Onyx 400F audio interface and the audio was recorded using Tracktion 3 software. The resulting two tracks of audio were panned hard left and hard right in the sound clips.

Comments:

Initial sound quality of the high gain sounds was adequate but not excellent. In direct comparisons with my modified Hi Octane, the Atom Smasher Mk II failed to produce the same quality of overdrive and crunch. However, the Atom Smasher Mk II does have a more responsive tone stack. In an attempt to increase the overdrive potential, the 3rd and 4th gain stages were coupled via Carl Berger's DC direct drive technique. This resulted in a much smoother, richer, and more pleasing overdriven sound. At this point, the Atom Smasher Mk II provides superior sound in comparison to my modified Hi Octane.

Clean tones are can be accessed by turning the gain knobs below ~5. The DC drive yields a beautifully lush sound with the gains turned down. The sweet spot seems to be with the first gain set about 2 and the second gain set slightly higher than that. This imparts a very subtle overdrive that sweetens the sound considerably. Clean tones are very satisfactory overall and sound much, much better than my Hi Octane.

Unfortunately, the sound quality of the preliminary high gain clips (I and II) does not fully and accurately represent the sound of amplifier. The general gain structure is mostly accurate, but high frequency 'fizziness' reproduced in the sound clips and low frequency mud seems to be much greater than in real life applications. Continuing to tweak the recording technique is therefore a necessity to more completely capture the sound of the amp. Recording at higher volumes (and consequently inducing poweramp breakup) may be essential to improve the quality. My previous amp (modified Hi Octane) sounds appreciably better when recorded at higher volumes.

An improvement in the sound of the high gain rhythm guitars was made in clip III, which captures the amp at a higher volume, predominantly using a JoeMeek JM37 mic, set about 2 feet from the cone. Better clarity and definition is attained in this clip, getting closer to what the amp sounds like in real life.