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ATC Monitor built in amps are Junk?

SCM40A is what my intended upgrade is. Currently I have passive 19s, with Quad 909 and EAR 868PL preamp.

As 868 is pretty much my dream preamp (used 864 for a long time before it) with incredible phono stage (TT is my primary source).

The only thing I can't figure out regarding compatibility of 868 and power modules in SCM40A is whether gain I'm going to have is going to be higher or smaller than now with quad 909 and SCM19. I wouldn't want more gain.

868 has output impedance of 600ohms. It has max output voltage of 5V.

909 has input sensitivity of 0.775V

Power amps in 40A have input sensitivity of 1V.

Sensitivity of both SCM19 passive and SCM40 (this rating is stated only for the passive version on ATC's site) is 85dB.

Am I right in thinking that the 868/SCM40A should have a bit lower gain than 868/909/SCM19?

Has anyone tried EAR 868 with active 40s and what was the resukt gain-wise?
 
popol_vuh said:
SCM40A is what my intended upgrade is. Currently I have passive 19s, with Quad 909 and EAR 868PL preamp.

As 868 is pretty much my dream preamp (used 864 for a long time before it) with incredible phono stage (TT is my primary source).

The only thing I can't figure out regarding compatibility of 868 and power modules in SCM40A is whether gain I'm going to have is going to be higher or smaller than now with quad 909 and SCM19. I wouldn't want more gain.

868 has output impedance of 600ohms. It has max output voltage of 5V.

909 has input sensitivity of 0.775V

Power amps in 40A have input sensitivity of 1V.

Sensitivity of both SCM19 passive and SCM40 (this rating is stated only for the passive version on ATC's site) is 85dB.

Am I right in thinking that the 868/SCM40A should have a bit lower gain than 868/909/SCM19?

Has anyone tried EAR 868 with active 40s and what was the resukt gain-wise?
Click to expand...
This is a quick theoretical sum to compare system gains in terms of dB SPL output for 1 V input from the preamp:

Quad 909: 0.775 V sensitivity for (I assume) maximum specified output of 140 W / 8 Ohms => gain = 32.7 dB
SCM19: 85 dB SPL for 1 W / 8 Ohms (2.83 V) => 76 dB SPL for 1 V input (i.e. 9 dB less)
Quad 909 + SCM19: 32.7 + 76 => 109 dB SPL for 1 V input.

SCM40A: 1 V sensitivity for (I assume) maximum specified output of 112 dB SPL => 112 dB SPL for 1 V input.

There are some assumptions above about what "sensitivity" means exactly. Perhaps someone can sanity check these sums.

It looks (if I have the figures, assumptions and sums right) like the SCM40A has just over 3 dB more gain rather than less.

If so, the volume control on the EAR 868 will have to sit a little lower for the same volume level with the SCM40A. That 3 dB difference is equivalent to between quarter of an hour and half an hour lower with a normal audio potentiometer in about the 09:00 position, but I don't know what the EAR 868 has. However unless the volume control knob is very low right now it is probably not an issue.
 
Tony L said:
I have heard some tiny “full-range” single-drivers I’ve liked a lot, e.g. 47 Labs, plus bigger things like Frugal Horns, some Lowthers etc. I could imagine a pair of really nice small single driver speakers of this genre being great on a desktop either side of a computer monitor and I suspect I’d prefer that point-source presentation to a small two-way at that listening distance.

PS The thing that puts me off about these is they have passive crossover components. Much of the attraction to my mind of the single driver mindset is the life and dynamic subtlety that comes from getting rid of crossovers from the equation entirely. I’d likely prefer a point-source two-way such as an LS50 or small Tannoy if I had to have passive response shaping. To put it another way if I was designing that speaker I’d have picked a better single driver!
Click to expand...
I've an unqualified suspicion that a larger drive unit might work better in this application, one that uses some cone mechanics to reduce the radiating area as frequency rises. Or he needs to add a high pass function to the 'crossover'. Or perhaps just delete the port. Not a speaker designer...
 
Yes, I’d agree with that. I don’t see the point of going so small. Modern cone materials make for some very good 5” single drivers and really this is what I’ve had in mind when I’ve commented.
 
John Phillips said:
This is a quick theoretical sum to compare system gains in terms of dB SPL output for 1 V input from the preamp:

Quad 909: 0.775 V sensitivity for (I assume) maximum specified output of 140 W / 8 Ohms => gain = 32.7 dB
SCM19: 85 dB SPL for 1 W / 8 Ohms (2.83 V) => 76 dB SPL for 1 V input (i.e. 9 dB less)
Quad 909 + SCM19: 32.7 + 76 => 109 dB SPL for 1 V input.

SCM40A: 1 V sensitivity for (I assume) maximum specified output of 112 dB SPL => 112 dB SPL for 1 V input.

There are some assumptions above about what "sensitivity" means exactly. Perhaps someone can sanity check these sums.

It looks (if I have the figures, assumptions and sums right) like the SCM40A has just over 3 dB more gain rather than less.

If so, the volume control on the EAR 868 will have to sit a little lower for the same volume level with the SCM40A. That 3 dB difference is equivalent to between quarter of an hour and half an hour lower with a normal audio potentiometer in about the 09:00 position, but I don't know what the EAR 868 has. However unless the volume control knob is very low right now it is probably not an issue.
Click to expand...

John, thank you very much for such a detailed and quality reply.
The only thing I don't understand is why you took the sensitivity rating of SCM19 as 85 dB SPL for 1 W / 8 Ohms (which is what ATC states), but for 40A you took maximum rating of 112dB SPL (while SCM40 passive is also rated as 85 dB SPL for 1 W / 8 Ohms).

Thank you for explaining things, since this gain thing is not so straightforward to understand sine there's quite a few variables in interplay here that determine gain of the system.

Am I right in understanding that (if all other variables were the same) input sensitivity of power amp of (for example) 1V will produce lower gain than input sensitivity of 0,5V?
Also, the same as above - if all other variables were the same - does the preamp max output of (for example) 5V produce more or less gain than that of 8V?

Other than that, regarding your calculation, it seems to me that 3dB difference shouldn't produce much difference on the volume pot. At the moment, I'm listening with volume knob mostly at about 9:00 when listening to vinyl and between 9 and 10 when listening through my DAC.
 
A typical power amplifier has a voltage gain of 28, 1 volt in gives 28v out.(This is coincidentally just over 28dB of gain.) Anyway if we connect this power amp to a speaker with a sensitivity of 85dB we need to put 2.8/28 volts in to get that 85dB out of the speaker, which is conveniently 0.1v or 100mv. The ATC amp pack will produce something similar for a similar input. But we don't have sufficient specs to confirm.

All I can offer is that with an old Naim setup using a Naim power amp into small speakers gives about the same levels as going direct to ATC50ASL. So given the small speakers will be about 85dB it all fits.

I think your Quad amp may have more gain than (for example) the Naim. So when you upgrade you will need to turn the preamp up for similar levels. This is a good thing, having the volume control around the mid point for normal usage is more ergonomic than 9 o'clock. IME.
 
popol_vuh said:
John, thank you very much for such a detailed and quality reply.
The only thing I don't understand is why you took the sensitivity rating of SCM19 as 85 dB SPL for 1 W / 8 Ohms (which is what ATC states), but for 40A you took maximum rating of 112dB SPL (while SCM40 passive is also rated as 85 dB SPL for 1 W / 8 Ohms). ...
Click to expand...
The principle was to look at the Quad 909 + passive SCM19 as a complete system and work out how to compare that system with the most direct equivalent specification for the SCM40A.

I see your point about assuming the passive 40 and the passive 19 may be comparable and we could just compare the gain of the Quad 909 with the gain of the internal amplifiers in the 40A (accounting for absence of the crossover loss in a passive 40). However I think that way of comparing the two situations still needs the gain of the internal amplifier of the SCM40A and the loss of the SCM40 passive crossover, which I think we just don't know.

AFAICS we only have a "sensitivity" figure for the SCM40A of 1 V. So it's a matter of interpreting what that "sensitivity" means. Conventionally "sensitivity" is for some rated output - often the maximum output. This maximum output for the SCM40A is specified by ATC as 112 dB SPL.

However the accuracy of this interpretation is not completely clear to me so that's why I was uncertain about the interpretation in my post. I would welcome anyone criticizing or confirming my interpretation.

It looks like @Paul R comes to a different conclusion to mine but I don't understand his last sentence at least: if an amplifier has a higher gain you need to turn the volume knob down to get the same volume. I will take a more careful look to see what it is I misunderstand.

It may be the only way for you to be sure of the proposed combination is to take your preamp and a known source to a dealer demonstration of the SCM40A.
 
popol_vuh said:
compatibility of 868 and power modules in SCM40A

Has anyone tried EAR 868 with active 40s and what was the resukt gain-wise?
Click to expand...

I'd be surprised if there was a mis match in gain with this combination. Fwiw, we recently used a CEN.GRAND Audio DSDAC 1.0 Advanced/Deluxe XLR Outputs > (XLR In) Qualiton Audio C200 (XLR Out) > SCM40A and everything was spot on.

https://audiohungary.com/product/c200--preamplifier/21
 
John Phillips said:
It looks like @Paul R comes to a different conclusion to mine but I don't understand his last sentence at least: if an amplifier has a higher gain you need to turn the volume knob down to get the same volume. I will take a more careful look to see what it is I misunderstand.
Click to expand...
The extant Quad has more gain that that implied for the active ATCs by my experience. So after upgrade volume will need turning up and this is a good thing.

But happy to be incorrect, and regardless I think it is really unlikely to be an issue.
 
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