Hi guys, I need a little help from the gurus!
I'm using a MiniDsp for its DiracLive function and running it into an Emotiva amp. However, Dirac Live exacts a 20 db penalty (something about not running into digital clipping) so that the MiniDsp is running nearly flat out but my music doesn't have near the dynamics it did - just sounds flat. Jumping around the MiniDsp restores proper dynamics and volume levels.
I'd like to build a simple opamp preamp to put between the MiniDsp and the amp. I'm thinking a dead simple fixed gain preamp based on a OPA2134 with a gain of 10 or so - what do you guys think and can you sketch one out for me? Thanks in advance for your help.
I'm using a MiniDsp for its DiracLive function and running it into an Emotiva amp. However, Dirac Live exacts a 20 db penalty (something about not running into digital clipping) so that the MiniDsp is running nearly flat out but my music doesn't have near the dynamics it did - just sounds flat. Jumping around the MiniDsp restores proper dynamics and volume levels.
I'd like to build a simple opamp preamp to put between the MiniDsp and the amp. I'm thinking a dead simple fixed gain preamp based on a OPA2134 with a gain of 10 or so - what do you guys think and can you sketch one out for me? Thanks in advance for your help.
Your best approach is to structure your audio system for no gain between your source components and power amp. Arrange sensible sensitivity to line level standards with your power amp, and have no adverse loading on your source components whilst attenuating for audio enjoyment.
The dynamics you refer to won't be available unless your source component has no adverse loading , so deal with that first.
The dynamics you refer to won't be available unless your source component has no adverse loading , so deal with that first.
Thanks for your suggestion Chris but there is no adverse loading. I use a Node2i and run its digital output into the MiniDsp. The MiniDsp with its volume control is acting as my system preamp but doesn't appear to have the gain to deal with the DiracLive imposed attenuation.
Doing some more thinking and exploration, I don't think I need a gain of 10 circuit but perhaps a gain of 5. I need to get some measurements but I would think the MiniDsp ( without Dirac ) would be outputting 1 - 2v into the amp at max volume so I just need to get back to that I believe.
Doing some more thinking and exploration, I don't think I need a gain of 10 circuit but perhaps a gain of 5. I need to get some measurements but I would think the MiniDsp ( without Dirac ) would be outputting 1 - 2v into the amp at max volume so I just need to get back to that I believe.
Try to ascertain the circuit in terms of a L pad , and step outside of having imposed values of resistance in the name of attenuation, that are presently require you to insert gain. At all times arrange your attenuation by not having to insert gain, rather deal with the series and shunt element values.
I find this purist approach to system design avoids the issue of having a component that emits inadequate voltage out. You have an attenuating DSP. I had a keyboard that put out maybe 0.75 volts, with a pair of power amps that required 1.6 vac for full wattage. I bought an Ampeg mono PA mixer, that is so legendary at age 60 it has been stolen.
Here are a couple of single supply circuits that might fill your needs for a 2gain or 4 gain boost.
The panasonic, I'd eliminate the 2n3055 output transistors and maybe cut spreader diode D2 leaving D1 plus a series pot. You don't need amps of current out, only 50 ma. You want idle bias current in Q3 Q4 to be about 10 ma. You can lower the output capacitor to 220 uf and cut the power supply to a single 12 v. For Q3 Q4 I'd use BD139/140 or MJE15028/15029. Put little heat sinks on them.
The chemelec, obviously use the microphone input option lower left. I'd use MPSA06 MPSA56 transistors, they are very quiet. If you can't get those, 2n5401 2n5551.
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You are obsessed with signal purity! Line level has changed over the years. Now most power amps will produce full wattage at <1 vac. Many newer ones will produce full watts at 0.7 vac. Other on diyaudio have also complained about low volume out of DSP's.
Standard line level in 1961 was 1.6 vac. OP has a objectionable volume difference between his unnamed source and the amp. I have had this problem also. I can't use the line level output of my CD players on the older amps, I have to use the earphone jack turned down. It always doesn't trash signal to noise ratio to boost signal by 2x. If I had any improvement to add to circuits post 5 I would put 100 pf ceramic cap to ground after the input cap of them. RCA cables can pick up AM CB & police band radio in my location, and RCA cables can't be bought less than 3' long.
My RIAA disco mixer has 3 db octave low bass cut control which audibly cuts up to 200 hz; no balance control, no bass or treble controls. I've trashed a woofer by walking around the floor with a LP on the turntable causing subsonics that blew Xmax. I've found I can insert a $50 Peavey PV8 mixer between the disco mixer & the power amp, with those functions, without noise increase. The disco mixer is set to flat, the PV8 has 30 hz 12 db/octave cut available. Maybe inserting another mixer noise goes from 110 db to 100 db? Who cares? LP s/n is 55 db at best. I don't listen with an oscilloscope or a spectral analyzer. If noise is below the pilot light on the gas stove, so what? The PV8 won't do RIAA deemphasis, has no room inside to be modified, and competent RIAA preamps these days are running $400 up. PV8 uses 4565 op amps, which has 1.2 uv noise.
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