I've lost my bass....

I disagree that changing amps will not affect the quantity of bass and there are several reasons why i believe this. The two reasons listed below basically sum up all the various reasons that may fall into multiple different categories though.

1) Various amps are of different circuitry from one another

2) Various amps don't respond the same to various loads / impedances

As such, not only can the solidity, impact, control, definition, etc... of the bass be altered when changing amps, so can the quantity. While i don't think that this is your main problem ( probably room acoustics ), i did want to point out that it is quite possible that changing amps could provide you with a very different sonic presentation over the entire frequency range. Sean
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adding active sub may be even more pricewise beneficial than changing amp.

A few things to try.

1. Push the speakers either 1/5 or 1/3 out into the room and try moving them around until you hear the bass get stronger. You might want a friend to help you with this. Even better, I would reference the AP setup guide on www.immediasound.com or the cardas setup guide on www.cardas.com. If you follow these carefully, often times you might find a big increase in performance. I've found with the AP's that placement can have a large impact on bass.

2. Try closing any doors. If the speaker has a smaller space to pressurize it will evidence more bass.

3. Try moving the speakers closer and further apart while listening for more bass. Following the setup guides will probably get you fairly close but moving/listening will get you to the place where the speaker is truly working with the room. Just small amounds of 1-3 inches should do it.

4. Clean your interconnects and contacts using contact cleaner. This tends to improve bass. Also try to use the shortest interconnect cables possible and perhaps experiment with cables. I like Nordost Red Dawn on up and Cardas Golden Reference cables with the virgo's. For less expensive I have had good results using Harmonic Tech Truthlink ic's (or red dawn) and Acoustic Zen Satori speaker cables. The Zen speaker cables are a great way to go.

5. Your amp is a on the small side with the Virgo's. I used to run an MV-50 with my old Virgo II's and I recall that it was not exactly a bass monster but still a wonderful sound. I remember swapping in a 185 watt per channel McCormack amp caused the speakers personality to change dramatically - they had much stronger bass. Almost seemed like a different speaker. It was going from 45wpc to 375 so this should not have been a surprise. If the above did not help I would try first using a borrowed/extra amplifier to see if this indeed will solve your problem. Your preamp is also known for slightly recessed bass. I'm not surprised by what you are reporting. Make sure the amp is biased and perhaps try swapping in some Svetlana EL-34's. Those are Mullard copies and exhibit some nice strong bass.

Disclaimer: I do sell Cardas and Audio Physic.

Your amplifier ABSOLUTELY affects your bass resolution and response.
Ever notice that powered Sub-Woofers are usually built with amplifiers that put out anywhere from 400 to 1,500 watts? It is because it takes a lot of power to resolve the lower octaves and control a bass speaker. Low powered tube amps are notorious for producing weak and/or flabby bass. Tube fans typically sacrifice the lower octaves in order to get the reputed liquid midrange and highs. Somehow, the smaller room was configured in such a way as to maximize the bass. This is a puzzle because the lower octaves usually need a bigger room to fully develop.
But, every room is so different and the variables are many. If you want to stick with your gear, the answer is going to be found in speaker placement and room treatment. Might be worth your while to hire an
acoustic consultant to come over for an hour or two and help you tune
your systems to your new rooms, to help you get maximum bass response from your tube gear, bring your system back into balance. Or, you can add a Sub-Woofer. But, I would try the consultant first. He/she
can also help you decide if a Sub-Woofer is warranted and can help you
integrate it into your system. Just a suggestion.

I agree with Sean, the amp can definitely impact bass response. I had a McCormack DNA2 in my system for awhile, and the bass was subterrainian, far better than with any other amp I have owned. However, I couldn't live with the way it sounded in the mids/highs. If you are happy with the overall sound from your current amp, I would listen to those who recommended getting a sub. Get one that is fast and musical, not an HT muscle sub, and one that integrates well with your Virgos, then cut it off as low as possible to achieve the extra bass you are looking for. Doesn't AP make a highly regarded musical sub?