Carvin R600 Bass Head

I don’t normally buy amplifiers made for musicians but I couldn’t pass on this one.The Carvin Red Line Series R600 is what is called a Bass Head. She is normally mounted onto a bass cabinet for presumably bass players and guitarists. She boast two channels of 300W into 4Ω, hence the R600 in her name.

Apparently, she was not quite well regarded. There were complaints that the R600 sounded lifeless and under-powered. Let’s take a closer look at how this amplifier was designed and perhaps we can unravel what her problem was.

Carvin R600 Bass HeadFig 1 – Carvin R600 Bass Head Amplifier Schematic

As far as the circuit goes (Fig 1), there’s nothing that tells me there is a problem. She has a mirror image typology that is quite conventional. There’s an op-amp at the input that drives the first stage (Q102 – Red line). Collector load is 1K which is quite normal. From here, it drives the VAS (Q104) from which the driver (Q107) is connector to. This driver drives three pairs of power transistors (MJL21194/3) in the output stage.

Fig 2 – Inside the Carvin R600 Bass Head

Having ascertained the circuit is sound, I took a closer look at her power supply (Fig 2). I noted there are only two pieces of 10,000uF 80V filter capacitors serving 600W of power. 20,000uF in total is wholly inadequate. I would expect to see at least 40,000uF. Even then, it is still a bit short. Let’s not forget this is a bass amp. Bass frequencies draw higher power than treble. Personally, I would use 80,000uF, that is 40,000uF per channel.

When manufacturers cut corners like this, they will likely under-sized the power transformer to save cost. For a total of 600W, I would use a 800VA transformer. That will ensure the transformer can pass enough current when playing at full power. Judging from the size of the R600 transformer, I doubt it is 800VA.

Fig 3 – Carvin R600 Tube Section

Two 12AX7 Tubes in the R600

I was intrigued to find two 12AX7 vacuum tubes in the R600 (Fig 3). Apparently, users can introduce some tube sound by “blending” their Solid State signal in the mix. On closer examination, they ran their tubes at 36V anode voltage (Blue line). This is very low for the 12AX7 and it results in the tubes working out of their linear range. But then again, this is what it’s all about. Adding some tube distortion to the music.. Let’s not forget, this is not HiFi.

Summary

The Carvin R600 is a feature rich Head Amplifier. She has Pre-Shaped EQ, Main EQ, Compressor, Noise Gate, Electronic Crossover and a Graphic EQ. It is unfortunate that she was let down by the power amplifier side. But all is not lost. With some modifications, the Carvin R600 Bass Head Amp can sound excellent.