Hi all,
I'm looking for a new amplifier (maybe) but I'm trying to match everything correctly because I'm finding that the MiniDSP SHD and Mac1900 combination is not giving me the gain I want.
The setup. QOBUZ -> MiniDSP SHD through "Amp In" inputs to the Mac receiver's amplifier. With Dirac off, I'm not getting the gain I want. Speakers are Magneplanar MC-1 with 2 DWM. I have the third and fourth channels from the DSP routed to an Aiyima A07 for the time being to drive the DWMs. I plan to buy a single four channel amplifier. The Aiyima has the same problem as what I will describe. Having three separate volume controls is not a long term solution.
The Mac1900 is a roughly 1974 model that I've loved for 20 some odd years. It has been refurbished within the last two years and is pretty well on spec. Output spec is 55WRMS / channel (20-20kHz @ .1%THD). Output spec is also Output spec is 29.98V @ 8Ohms. All the Mac specs seem to be RMS but a straight calculation there would give me 112W. I know that Mac amps are famous for being underrated, but that seems severe. What am I doing wrong?
Input spec for the amp in is 2.5V @ 100kOhms impedance. Output spec is 29.98V @ 8Ohms. That suggests a gain of 21.6dB. Notably, the Magneplanar speakers are not nominally 8 Ohms. They are spec'ed at 4 Ohms. The Mac1900 manual says the power output is the same (55WRMS) at 4 or 8 Ohms. For 16 Ohms, they spec the receiver at 30W.
The SHD unbalanced output spec is 2.0V RMS. I assume that's at 0db on the volume attenuator, but the SHD software allows me to increase the output level to 12dB. Is the 2.0VRMS with everything set at 0dB?
My problem is that the volume I want (most of the time) requires me to set the SHD volume to around -10dB which is the max setting when running Dirac. I want more dynamic range.
One solution that works is to send the output of the MiniDSP SHD into the Tape In on the Mac1900. These are spec'ed for 250mV input. I can use the DSP on the SHD to reduce the output by 18dB and then I should have the right input voltage, correct? 20log(250/2000) = -18dB. Interestingly, the manual gives the spec for gain in the preamp - 20dB. And that makes sense: 20log(2.5/.25) = 20db.
This works but I still don't get the gain I need unfortunately. I haven't found the optimal setting yet for the miniDSP but -18dB isn't enough if I keep the volume set at -10dB. I'm pretty sure the Mac1900 is fairly robust, but I can saturate the tape input, I think.
Granted the big problem is the Magnepan speakers which require more power than I'm giving them. I get all the volume I need, but I have to raise the SHD to 0dB which leaves me limited headroom. I have other speakers that do not require this much work, so I know the Magnepans are inefficient. I do like them and I like the Mac1900 but something will have to give.
Question. How much gain do I need? What amplifier is well-matched to the miniDSP SHD's 2.0VRMS output? I prefer Class D and don't plan to spend more than $2000.
One potential test. Amir shows the Aiyima A07 at 29dB gain. Aiyima's spec on their website is 21.5dB. That's a significant difference. So at some level, putting the Aiyima in as the main amp to see what happens is only valid if I know that number. Where's that dang heat sink again?
Thanks, John
I'm looking for a new amplifier (maybe) but I'm trying to match everything correctly because I'm finding that the MiniDSP SHD and Mac1900 combination is not giving me the gain I want.
The setup. QOBUZ -> MiniDSP SHD through "Amp In" inputs to the Mac receiver's amplifier. With Dirac off, I'm not getting the gain I want. Speakers are Magneplanar MC-1 with 2 DWM. I have the third and fourth channels from the DSP routed to an Aiyima A07 for the time being to drive the DWMs. I plan to buy a single four channel amplifier. The Aiyima has the same problem as what I will describe. Having three separate volume controls is not a long term solution.
The Mac1900 is a roughly 1974 model that I've loved for 20 some odd years. It has been refurbished within the last two years and is pretty well on spec. Output spec is 55WRMS / channel (20-20kHz @ .1%THD). Output spec is also Output spec is 29.98V @ 8Ohms. All the Mac specs seem to be RMS but a straight calculation there would give me 112W. I know that Mac amps are famous for being underrated, but that seems severe. What am I doing wrong?
Input spec for the amp in is 2.5V @ 100kOhms impedance. Output spec is 29.98V @ 8Ohms. That suggests a gain of 21.6dB. Notably, the Magneplanar speakers are not nominally 8 Ohms. They are spec'ed at 4 Ohms. The Mac1900 manual says the power output is the same (55WRMS) at 4 or 8 Ohms. For 16 Ohms, they spec the receiver at 30W.
The SHD unbalanced output spec is 2.0V RMS. I assume that's at 0db on the volume attenuator, but the SHD software allows me to increase the output level to 12dB. Is the 2.0VRMS with everything set at 0dB?
My problem is that the volume I want (most of the time) requires me to set the SHD volume to around -10dB which is the max setting when running Dirac. I want more dynamic range.
One solution that works is to send the output of the MiniDSP SHD into the Tape In on the Mac1900. These are spec'ed for 250mV input. I can use the DSP on the SHD to reduce the output by 18dB and then I should have the right input voltage, correct? 20log(250/2000) = -18dB. Interestingly, the manual gives the spec for gain in the preamp - 20dB. And that makes sense: 20log(2.5/.25) = 20db.
This works but I still don't get the gain I need unfortunately. I haven't found the optimal setting yet for the miniDSP but -18dB isn't enough if I keep the volume set at -10dB. I'm pretty sure the Mac1900 is fairly robust, but I can saturate the tape input, I think.
Granted the big problem is the Magnepan speakers which require more power than I'm giving them. I get all the volume I need, but I have to raise the SHD to 0dB which leaves me limited headroom. I have other speakers that do not require this much work, so I know the Magnepans are inefficient. I do like them and I like the Mac1900 but something will have to give.
Question. How much gain do I need? What amplifier is well-matched to the miniDSP SHD's 2.0VRMS output? I prefer Class D and don't plan to spend more than $2000.
One potential test. Amir shows the Aiyima A07 at 29dB gain. Aiyima's spec on their website is 21.5dB. That's a significant difference. So at some level, putting the Aiyima in as the main amp to see what happens is only valid if I know that number. Where's that dang heat sink again?
Thanks, John