Triode vs. Pentode

So my ST70/VTA70 arrived today and I put it through its paces. So far I'm pretty happy! I did notice something I wasn't expecting though... I listened to one song (Porcupine Tree's 'Shesmovedon') several times, in pentode and triode mode. I was expecting the bass to more or less disappear in Triode. But it didn't...in fact I'm more than half convinced that the bass was more prominent in Triode. Now, I'm talking about bass guitar here, which goes down to roughly 40 hz, and not pipe organ, but still... more comparisons are in order I think.

Anyone experience anything similar?

---VikeMan

Bob Latino wrote:VikeMan,

In pentode/ultralinear mode, your VTA ST-70 amp is flat to about 17 HZ. In triode mode it is flat to maybe 20 - 25 Hz. Most speakers don't go down to that range anyhow. As such, the bass rolloff is virtually unnoticeable when you switch to triode mode. You don't have less bass in triode but you do have less bass POWER and less bass headroom in triode.

In triode it appears (to me at least) that the mid-range comes "forward" in the soundstage just a little. Some people like the effect and maybe some don't. Triode is really nice for vocals and acoustic jazz. If you are a rock fan then you would probably prefer pentode/ultralinear mode which has more power and bass "slam".

Bob

Can you switch fro triode to pentode on the fly or do you have to shut down and restart

Can you switch from triode to pentode on the fly or do you have to shut down and restart ?

On the VTA ST-70 or ST-120 kits you can switch from triode to pentode or pentode to triode on the fly. It is not necessary to shut the amp off to make the switch.

Bob

Bob Latino wrote:

In triode it appears (to me at least) that the mid-range comes "forward" in the soundstage just a little. Some people like the effect and maybe some don't. Triode is really nice for vocals and acoustic jazz. If you are a rock fan then you would probably prefer pentode/ultralinear mode which has more power and bass "slam".

Bob

Bob, I listened to an LP yesterday of Mike McDonald former singer with Doobie Brothers, in both triode and pentode mode. Mike has a nice somewhat-soft bluesy voice; the selection had a good strong drum beat. I think the type of music on this album helped me distinguish the difference between triode and pentode in my system so I thought I would add another interpretation to your note that the "mid-range comes forward." In some peoples' minds that comment may mean something different than what you intended. When I listened to the music on this LP, I found that in triode mode the drum beat was a little less strong than in pentode mode - as if the drummer reduced the power of his whacks - allowing Mike's voice to be the prime focus. This may be what you mean by "coming forward" however in my mind the voice doesn't come forward, it just becomes more the focus than the drum beat. Ken