scottosan
Head-Fier
- Joined
- Sep 11, 2013
- Posts
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Took some time off for a few years. Previously used an Asus STX and/or Darkvoice 336. I also play guitar and have been building guitar amps and pedals for years, but not til recently decided to build and headphone amp, which lead me to the Objective2. I read alot of reviews, many of which contradicted one another, but understanding the context of the reviews and considering external factors into such reviews. Knowing that while you can build an amp that can support all sorts of headphone requirements, there really is no such thing as a true one size fits all design and that was my expectations when I set out the build. That being said, I would like to discuss some factor that I did not see heavily discussed.
DAC and Input gain - Like many DAC's on the market, the specs range from 1.0Vrms for alot of portables to +2Vrms for redbook spec'd units. For me this is critical in this build. The default build is 2.5x gain/6.5x gain. The instructions say not to use the high gain unless your cans need it, and while I understand the concern for damaging cans, from a sound quality standpoint, it's more important to get your source matched properly first. While you don't want clipping at the input, I notice significant sonic differences at similar volume levels.
6.5x Gain 1.08 VRMS (+2.9 dBu)
4.5x Gain 1.56 VRMS (+6.1 dBu)
3.5x Gain 2.00 VRMS (+8.2 dBu)
3.3x Gain 2.12 VRMS (+8.7 dBu)
2.5x Gain 2.80 VRMS (+11.2 dBu)
1.0x Gain 7.00 VRMS (+19.1 dBu)
Simply said, running a DAC with 1Vrms @ 2.5x sounds more anemic at the same volume levels as 6.5x. Just like using a DAC with the redbook 2.0Vrms specs, you simply cant run it higher than 3.5x without getting clipping.
My finding where that best results were found matching input levels and fingure if it can support you cans from there and not use the gain for simply more volume.
So for me I set @ 6.5x for for 1Vrms DACs and iphone and 3.3x for my 2Vrms DACs
I decided to go middle of the road for cans for several reasons. I went with some new beyerdynamic DT990 250 ohms. Not too current hungry and no hard to drive. With max of 100mW, that gave me alot of wiggle room to swap the NJM4556 outputs.
1mW = 500mV@2.0ma
5mW = 1.2V@4.4ma
10mW = 1.58V@6.3ma
25mW = 2.5V@10ma
100mW = 5.V@20ma
Based on some other forums, people were running OPA2134's with higher impedance cans, and this makes sense as with the higher impedance cans power requirements would sit right within specs. While the NJM4556 were ideal for the 1 size fits all design and have the heavy current draw, i think it's safe to say that it's not an optimal op amp for sound characteristics. Also the DC offset was just about null. I also come from the camp that I do not look at THD specs alone for as a standalone factor for musicality. Sometimes some coloration can be good for certain types of music. The reality is that not all music is mastered the same.
I ended up with LM4562 for U1 and OPA2134's for U3&U4.
Very natural and full sounding, almost like not wearing cans
DAC and Input gain - Like many DAC's on the market, the specs range from 1.0Vrms for alot of portables to +2Vrms for redbook spec'd units. For me this is critical in this build. The default build is 2.5x gain/6.5x gain. The instructions say not to use the high gain unless your cans need it, and while I understand the concern for damaging cans, from a sound quality standpoint, it's more important to get your source matched properly first. While you don't want clipping at the input, I notice significant sonic differences at similar volume levels.
6.5x Gain 1.08 VRMS (+2.9 dBu)
4.5x Gain 1.56 VRMS (+6.1 dBu)
3.5x Gain 2.00 VRMS (+8.2 dBu)
3.3x Gain 2.12 VRMS (+8.7 dBu)
2.5x Gain 2.80 VRMS (+11.2 dBu)
1.0x Gain 7.00 VRMS (+19.1 dBu)
Simply said, running a DAC with 1Vrms @ 2.5x sounds more anemic at the same volume levels as 6.5x. Just like using a DAC with the redbook 2.0Vrms specs, you simply cant run it higher than 3.5x without getting clipping.
My finding where that best results were found matching input levels and fingure if it can support you cans from there and not use the gain for simply more volume.
So for me I set @ 6.5x for for 1Vrms DACs and iphone and 3.3x for my 2Vrms DACs
I decided to go middle of the road for cans for several reasons. I went with some new beyerdynamic DT990 250 ohms. Not too current hungry and no hard to drive. With max of 100mW, that gave me alot of wiggle room to swap the NJM4556 outputs.
1mW = 500mV@2.0ma
5mW = 1.2V@4.4ma
10mW = 1.58V@6.3ma
25mW = 2.5V@10ma
100mW = 5.V@20ma
Based on some other forums, people were running OPA2134's with higher impedance cans, and this makes sense as with the higher impedance cans power requirements would sit right within specs. While the NJM4556 were ideal for the 1 size fits all design and have the heavy current draw, i think it's safe to say that it's not an optimal op amp for sound characteristics. Also the DC offset was just about null. I also come from the camp that I do not look at THD specs alone for as a standalone factor for musicality. Sometimes some coloration can be good for certain types of music. The reality is that not all music is mastered the same.
I ended up with LM4562 for U1 and OPA2134's for U3&U4.
Very natural and full sounding, almost like not wearing cans
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