Matching preamp to amp

Well guys, I hooked up the ARC today and it worked very well with the CAT.
Unfortunately after about 20 minutes there was a VERY loud cracking sound
and i think one of the tubes ARC'ed ( pun intended).( Luckily I managed to mute the output before it blew my speakers...whew!) At first, I thought it could have been a bad cap, but my tech seems to think it was a tube gone bad..:0(
Oh well, back to the drawing board...
Any ideas as to the problem?

Thanks Rrog, I haven't yet tried the CAT/ARC combo, but should be able to next
week.I will post as to the results.My current setup of CAT/Jeff Rowland model 8 works very well together, although I can set the input impedance on the model 8 to accommodate the CAT.

BTW, Marakanetz I agree that the CAT rules..:0)
After having listened to many preamps, both ss and tube, the CAT is here
to stay.

Daveyf, Read your question again then read my response. The CAT has the same output as Audio Research preamps that matches your D-70. Actually the ARC SP-8 is a matching preamp for your D-70 and has a maximum output of 60 volts, but you won't be using the 60 volts you will be attenuating your source.

Did you try the CAT and D-70? Maybe you should try it and let us know what happens.

Dave,
More would never hurt. I'm not sure about 50V but typically tube preamps do swing larger voltages than solid states.
I'm SS dude but CAT is on my most tube likes!

Rrog, I am not worried about the fact that the CAT has enough output to
drive the ARC, instead I am concerned that it has way too much output.
The ARC is rated at 0.95 volts to drive it to full power... Since the CAT has the ability to drive 50 volts, I am concerned that even the slightest turn of the
volume control on the preamp will overdrive the amp /or the amp will be at full power. BUT, looking at the other responses, I suspect that it will be ok, once the amp is up and running we shall see and if not, then i think Almarg's suggestion should work.

You shouldn't have any problems driving the D-70 with the CAT. Maximum output on your CAT is more like 50 volts which is the same as preamps from Audio Research.

CAT rules! It could work either with SS or tubes almost all brands you can ever imagine. The key trick is its low output impedance. Yet it doesn't have the best possible maximum output voltage as it could reach in certain units upto 20V.
If the pre's output impedance is too high compared to the input impedance of poweramp than the output impedance becomes a part of circuit and divides voltage(i.e. eats a portion of such) passed onto the next stage.
Example: if your output pre impedance is 1kOhm and input impedance of amp is 10kOhm than 1/10th part of passed voltage is lost 'without reaching' the input of amplifier.

Hi Al,
Thanks, that is what I think I need.
DaveyF

Hi Dave,

A preamp SHOULD have the ability to swing far more voltage at its output than the full power sensitivity of the power amp. The output voltage that the preamp WILL swing is not dependent on what it CAN swing.

Your volume control setting will be dependent on the gain of the preamp, the output voltage of the source component, the gain of the power amp, the sensitivity of the speakers, your listening distance, the dynamic range of the source material, and your preferred listening volume. The maximum output voltage swing that the preamp is spec'd for is not normally a factor in any of that.

If you are saying that the CAT is spec'd as having a MAXIMUM output voltage swing of 7 volts, that is probably near the low end of typical and is most likely not a concern. It is the gain of the preamp that might be a concern, if it is high and you are using a source component that has a high output level, such as most cdp's.

If that is the case, and you find yourself using the volume control at very low settings, you could use a Rothwell attenuator in series between the preamp and power amp.

Regards,
-- Al

Al, I think that the problem may be that the preamp has far more output
than the amp needs to reach full power. The CAT has the ability to swing 7 volts at its output whereas the ARC is at full power with just 0.95 volt. Therefore, i am concerned that I will be overdriving the amp at very little volume on the preamp.

Hi Dave,

I'm not sure exactly what the 7 volt number represents (see below), but I feel pretty certain that however it is defined those numbers should NOT match.

Otherwise you may find yourself either running out of range on the volume control, or clipping (overloading) the preamp. Basically, as long as you don't ever find yourself wanting to turn the volume control up past its maximum position, and you don't find yourself operating the volume control near the low end of its range (where adjustment resolution may become excessively coarse, and with some volume controls the balance between channels may degrade), you are fine.

That said, can you clarify what the 7 volt number represents? With a lot of preamps, that kind of number represents the output level at which the preamp will overload or start to distort heavily. I would guess, though, that the overload number for your CAT would be considerably higher than that.

Or does it represent the output level in response to some specific input level?

The 0.95 volt sensitivity of the power amp, btw, is fairly typical. To reach full power, most power amps will require somewhere between perhaps 0.5 and 2 volts or so.

Regards,
-- Al