Input Impedance a Problem?

[ouimetnick]

I currently have a Topping E30 DAC connected to a Schiit SYS (10k volume pot box) connected to a Hafler DH-101 preamp (using for tone controls since I’m hearing impaired and my idea of “neutral sounding” may be different than yours) and that is connected to a Hafler DH-120 amp (22k input impedance) or sometimes another amp with a 47k input impedance. The output level of the DAC is so high that the volume level of the preamp is either all the way off or too loud, hence the Schiit SYS pot box inline. Interconnect cables are very short, the longest being 3’ from the Hafler preamp to the power amp.

Having wired the preamp myself and looking over the schematic, the signal from the DAC/pot box goes directly through the DH-101’s own internal 50k volume potentiometer before it goes through the active high level gain stage. The DAC does have a remote and digital volume control (It can be put in pure DAC mode or preamp mode.) Should I just use the preamp mode instead? I bought the Schiit SYS since my other DAC (Schiit Modi 3+) is fixed line level out only. The Modi 3+ has an output impediance of 75 ohms. Since the Modi 3+ and SYS are wired in what is basiaclly series, it’s 5.075k ohms maximum (Schiit’s website says the SYS’s output impediance is 5k ohms maximum.) correct? I’m not sure what the output impedance of the Topping E30 is, but it would be xx ohms + 5k (max).

I ordered a Schiit Loki Mini+ a few days ago and my plan is to stop using the DH-101 and just use whatever DAC (Modi 3+ or E30), the SYS, and Loki Mini+. Is there a correct way to connect these 3, or does it not matter? I was thinking DAC > SYS > Loki Mini+ > power amplifier. Or do I want the DAC connected to the Loki Mini+ and then the Loki Mini+ connected to the SYS?

 

[Helicopter]

Doesn't matter the order of the Sys and Loki mini+. Most people would do what you were thinking; put the Sys after the DAC so that the source switch on the Sys gets tone control on both inputs, but since you are only using one input it will not matter.

Not sure how Sys and Loki work, so I am notnsure about output impedance of the system going into the amp.

I would put the modi back in this system so you have a cool Schiit stack.

 

[AnalogSteph]

OP, I hope you know that you're rather overcomplicating this.

Is there a correct way to connect these 3, or does it not matter? I was thinking DAC > SYS > Loki Mini+ > power amplifier. Or do I want the DAC connected to the Loki Mini+ and then the Loki Mini+ connected to the SYS?

According to the Loki Mini+ specs, it should handle 2 Vrms levels with ease while still having substantially lower noise than the power amp input at the same time (114 dB ref. 2 Vrms is 109 dB ref. 1.1 Vrms or ~4 µV, comparable to a decent preamp), so both versions ought to be be feasible.

Why weren't you using the input gain pot on the power amp to get the preamp volume pot into a better range? A very touchy volume setting can also be the result of a defective (interrupted carbon track) or miswired pot, btw. Since you said you wired the preamp yourself, I hope you did not hook the volume pot up backwards (or rather upside down, which would be even worse than using a linear pot). Should be easy enough to check with a multimeter, I imagine...

Impedance wise, the most sensible version would probably be SYS first, as I would tend to leave the power amp level all the way up and present the thing with a low source impedance, as provided by the Loki Mini+ (75 ohms). Using a 50k level pot on a power amp like this arguably isn't the smartest idea from a distortion/noise perspective...
BTW, from the schematic I would rather suspect that the DH120 way exceeds its rated SNR of >100 dB referred to 60 wpc at 1.1 Vrms input, or at least that the number would improve dramatically when A-weighted. This spec was probably limited by 120 Hz hum due to finite PSRR, but there won't be much in terms of wideband noise at all, which may be as low as around 20 µV across 20 kHz at min/max input level (estimated Amir 5 W score approx. 107 dB(A)), although an intermediate input gain setting may degrade this by over 10 dB.

 

[ouimetnick]

OP, I hope you know that you're rather overcomplicating this.

According to the Loki Mini+ specs, it should handle 2 Vrms levels with ease while still having substantially lower noise than the power amp input at the same time (114 dB ref. 2 Vrms is 109 dB ref. 1.1 Vrms or ~4 µV, comparable to a decent preamp), so both versions ought to be be feasible.

Why weren't you using the input gain pot on the power amp to get the preamp volume pot into a better range? A very touchy volume setting can also be the result of a defective (interrupted carbon track) or miswired pot, btw. Since you said you wired the preamp yourself, I hope you did not hook the volume pot up backwards (or rather upside down, which would be even worse than using a linear pot). Should be easy enough to check with a multimeter, I imagine...

Impedance wise, the most sensible version would probably be SYS first, as I would tend to leave the power amp level all the way up and present the thing with a low source impedance, as provided by the Loki Mini+ (75 ohms). Using a 50k level pot on a power amp like this arguably isn't the smartest idea from a distortion/noise perspective...
BTW, from the schematic I would rather suspect that the DH120 way exceeds its rated SNR of >100 dB referred to 60 wpc at 1.1 Vrms input, or at least that the number would improve dramatically when A-weighted. This spec was probably limited by 120 Hz hum due to finite PSRR, but there won't be much in terms of wideband noise at all, which may be as low as around 20 µV across 20 kHz at min/max input level (estimated Amir 5 W score approx. 107 dB(A)), although an intermediate input gain setting may degrade this by over 10 dB.

I wired the volume pot correctly. I have several DH-101, another with the factory PCB mounted volume and balance controls, same behavior. I also never had a sensitive volume control with other sources either. My other preamps (Hafler DH-100, and a FX Audio Tube-03) also exhibit the same thing.

The power amplifiers I'm using do not have a input pot. The DH-120 did, but those were bypassed to eliminate them from the signal path.

Hafler DH-120 Manual
Hafler XL-600 Manual

I'm not really familiar with terms like "A-weighted" or "114 dB ref. 2 Vrms is 109 dB ref. 1.1 Vrms or ~4 µV" I know what dB, Vrms, and µV are as a unit of measure, but not in the terms you are saying. I hope it's not too much to ask, but can you explain it for less tech savvy people like me?

I know there's talk about how a passive volume preamp (pot box) and long interconnects (capacitance) can create high pass filter, but I'm skeptical that I'd even be able to hear a difference especially since I wear hearing aids and boost the bass slightly (not fully clockwise, just a tad). I realize I've overthinking/overcomplicating, but I am curious to know the actual technical explanation as well.

 

[daclogic]

The order of the Sys and Loki does matter, and you are not overcomplicating this, but indeed are asking precisely the right question. The right answer is to go DAC>Sys>Loki>Hafler. The reason is that the Sys has a very high output impedance - up to 5K ohm - while the Loki is much lower, at 75 ohm. The Hafler has a moderately low input impedance, 22K ohm. The ratio of output/input impedance should be at least 1:10. If it's less than, it can and will have a negative effect on the sound (dull, lifeless, lacking treble clarity and bass). The ratio between the Sys, 5K, and Hafler, 22K, is roughly 1:4. It won't sound good. But the Sys into the other unnamed amp, 47K, should be OK. Sure, it's just under 1:10, but the Sys impedance varies, and most of the time (over most frequencies) will be well within range. Believe me, I've been there and made this error with passive amps. Getting this wrong is one reason why so many people say they heard a passive amp once and it was dull and lifeless... Hope that helps.