For background:
I recently purchased a Rotel RB-850 amp and RC-850 preamp on e-bay. While the seller said it “tested” good I expected given its age to be less than without issue. The amp seems okay but the preamp bass tone control was inop, turning the knot was ineffective. I suspect caps in the circuit need replacing. I was using an iPad mini using Apple Music lossless as a source. I was curious as to how it sounded bypassing the preamp.
It sounded nice.
So my question is this, given that Apple provides an equalizer, as does Spotify, is there any advantage to using a preamp if the only source is going to be a tablet or phone? Is there a possible damage to downstream devices eg amp or speakers?
pros cons?
I recently purchased a Rotel RB-850 amp and RC-850 preamp on e-bay. While the seller said it “tested” good I expected given its age to be less than without issue. The amp seems okay but the preamp bass tone control was inop, turning the knot was ineffective. I suspect caps in the circuit need replacing. I was using an iPad mini using Apple Music lossless as a source. I was curious as to how it sounded bypassing the preamp.
It sounded nice.
So my question is this, given that Apple provides an equalizer, as does Spotify, is there any advantage to using a preamp if the only source is going to be a tablet or phone? Is there a possible damage to downstream devices eg amp or speakers?
pros cons?
You may want to put a "passive preamp" i.e. mechanical volume control, between the iPad and the amp. That way you can run the volume level in the 'Pad closer to max - and turn it down to reasonable listening levels using the knob. Serves two purposes;
1. You're closer to "bit perfect" running high volume on the iPad. That is, no or less math implemented on the music signal in digital form to get a volume control function. Assuming, of course, that's how it's done...
2. With a "hard" volume, you can turn it down to zero; any mistakes with the upstream signal wont make it through to damage anything downstream.
To me a preamp was originally a means to get low level signals from phono carts and tape heads up to the level that would drive an amplifier to full power. Then they added tone controls, balance, boost, cut, mono, aural compensation, tape loops to make it versatile.
Unless you're listening to vinyl, you dont need any of it IMHO. Just more noise and distortion in the signal path, again IMHO.
1. You're closer to "bit perfect" running high volume on the iPad. That is, no or less math implemented on the music signal in digital form to get a volume control function. Assuming, of course, that's how it's done...
2. With a "hard" volume, you can turn it down to zero; any mistakes with the upstream signal wont make it through to damage anything downstream.
To me a preamp was originally a means to get low level signals from phono carts and tape heads up to the level that would drive an amplifier to full power. Then they added tone controls, balance, boost, cut, mono, aural compensation, tape loops to make it versatile.
Unless you're listening to vinyl, you dont need any of it IMHO. Just more noise and distortion in the signal path, again IMHO.
I agree with running the iPad at max volume and putting a volume pot before the amp. You are “throwing bits away” when you’re not running at max volume. I use a Bluetooth receiver with my iPad and plug it into my preamp(volume control) and it works and sounds great. You can even get a cheapish BT receiver preamp combo with bass and treble controls. Some are even tube output! That way you’re wireless and can use your iPad or phone.
Which BT or Airplay receivers do people like to use?
Ideally one with Toslink optical or S/PDIF coaxial output?
Ideally one with Toslink optical or S/PDIF coaxial output?
Advantage: only needed if you need more than 1V RMS output for the power amp.
The old pre-amp of the 20th Century was mainly needed when phono (turntable) devices needed level boosting and equalisation.
virtually all devices in C21 have output between 1-2V RMS, some even more eg. 4V, so no further amplification is needed before it goes into the power amplifier.
For instance, with an Apple device of 1V RMS output (at max volume on the device), after going into a power amp with 26dB gain, the max voltage output is 20V.
http://www.sengpielaudio.com/calculator-gainloss.htm
Power dissipated into 4 ohms = V^2 / R = 20 x 20 / 4 = 100W
Is 100W enough for your speakers. Or too much for your amplifier?
The thing about losing bits if only slightly correct- Apple devices have been using 24 bit volume control for a long time, so it's not throwing out bits.
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The first thing that came to mind reading this is the reviews done by Ken Rockwell (kenrockwell.com) about the audio performance from Apple devices. It has been a few years since I followed him, so I don't know if he has updated his opinions recently, but I remember he was extremely impressed with signal quality from Apple devices.
So one point to make is that you are not "improving" the signal by introducing more components. If I were you, I would only add a preamp or DAC if you need some extra functionality.
My advice is just experiment. There's no right or wrong way. You won't hurt your equipment, and it's no fun if you feel confined by rules of how you're supposed to set up your system!
I used to play music from a macbook, using a 3.5mm cable that terminated in two XLR connectors, which connected to my active studio monitors. Then I "upgraded" to a Toslink cable + DAC, because plugging and unplugging the 3.5mm will "pop" if the speakers are powered up. (The Toslink can be connected/ disconnected without making noise. Fun fact, some Apple products had a combination 3.5mm/ toslink connector...not sure if they are still doing that, though.) Then I upgraded to an AudioEngine bluetooth receiver + toslink + Emotiva DAC. Now I am using a M1 Mac Mini as a "HTPC", so I could go back to just using the 3.5mm direct to my speakers. But the DAC is nice to have, and it doesn't hurt anything, so I'm still using it.
Yes, I’m using that in concert with a 3.5 male to rca male to get to the amp works well.
This is really no surprise. That little dongle slays some pretty serious competition for the money as far as measured response.