secretguy
1,397 posts
Like any of you could hear the difference in volume controls
Showing how much you know…….again.
The volume control used in a preamp is more important than the topology.
Budget preamp with quality volume control
Dear Audiogoners,
I used to be a firm believer that the signal path should be as short as possible and, as such, I have been using the two-channel system without a dedicated preamp. For a long period of time, I have relied on the digital attenuator in DAC for volume control, knowing the digital attenuator would compress the dynamic range of the sound. Therefore, I switch the volume control on DAC to the fixed mode, bypass the digital attenuation and use the unity gain knob in the back of the power amp for volume control. Depending on the music recording level, however, sometimes I need to turn the unity gain control way down to get proper sound level. This is particularly painful when I use the full-balance connection because of the double voltage gain.
In short, I am looking for a budgetary preamp with quality volume control that either has relay switch stepped control or precise potentiometer for left-right channel match to curb the issue. I try to summarize important (to me) performance catgories as best I can for various good sounding preamp I know (with or without headphone amp/dac) as shown below. It is found the Schiit Magnius happens to have the highest performance ratio. However, I am pretty sure that I likely miss other good performers due to my limited knowledge and would like to solicit for your inputs. Your kind assistance is appreciated.
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- 80 posts total
@pwayland I could not find that gain stage info in the manual for my Parasound amp. The control on the back are the unity gain control whose function, as you know, is to throw away some of the preamp output to get the main volume control in the region one likes best (gain staging process). I am not sure if I could simply get rid of it but I could max it out so there won’t be any variable resistor in the signal path. Then I could use Active preamp without gain in lieu of with gain (like you said) to adjust the volume. At the mean time, I could also bypass the digital attenuator in DAC by switch the volume to the "fixed" mode to avoid sound degradation. By reading the specs, the SPL Volume 2 as you have suggested or several Schiit products such as Freya, Asgard 3, Jot 2, or Magnius on my list will serve that purpose in addition to impedance matching. These Schiit products also come with active w/ gain so is handy when needed. Thank you that really helps me to eliminate a few other choices.Btw, while reading the tech info. (as shown below) in SPL Volume 2 manual, it really explains what I have experienced with the SYS... It is actually a much better passive preamp compared to the cheap in-line attenutor I purchased for the sub. I therefore decide to retain SYS for my sub. instead.
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As many of you know, the basic relationship between the signal transfer (in terms of voltage) ratio to impedance between output (source) and input (load) is Vi / Vo = Ri / (Ri+Ro+cable impedance), where V = voltage and R = impdenace For a standard 75 ohms interconnect cable, without loss of generality, if your preamp output imp. is roughly comparable to the cable impedance, Vi / Vo = Ri / (Ri+2Ro). As a rule of thumb, it is desirable to have Ri is at least 10 times higher than Ro. The corresponding Vi / Vo = 83%. There will be 17% signal loss, acceptable (see below for the coveat) but not ideal. If Ri is 100 times Ro, the Vi / Vo ratio will be 98%, only 2% signal loss and will be deemed ideal. In @jpasko01 case, i.e., Freya -> Bryston 4B3, Ri = 100 Ro and therefore the signal loss is only 2%. The pariing should work like charm. In the case of a passive preamp SYS (Ro = 5000 ohms) into my Parasound A23 (Ri = 33k ohms) where the ratio is merely 6.6, the Vi / Vo = 33000 / (33000+5000+75) = 87%. This 13% signal loss is significant enough to cause noticeable sound degradation that I heard. This demonstrates that the ratio of 10 is just a rule of thumb, the ratio should be as high as possible like 100 to be ideal. Since I have not seen a passive preamp impedance is lower than 5k ohms, practically only the active preamp is possible to achieve an ideal impedance match. |
@jpasko01 Two things regarding the impedance matching with the Freya, if you are using unbalanced, you are fine, however output impedance is 600 ohms for balanced. More importantly, read John Atkinson’s analysis in the Stereophile review. Again, regarding balanced connections, but he suggests anything under 10Kohm input impedance may not do well with the Freya. My amp is right at 10K, and seems fine. |
- 80 posts total