Signal Chain Help

[fafnir]

Hi there,

I'm an ASR newbie who could really use a hand with optimizing the signal chain/levels for my passive loudspeaker set up. The parts I'm working with are:

SMSL m200 DAC
Khadas Tone Board
Alva Solo Phono Preamp
vintage tape deck
flat screen with optical/coax/RCA out
Rolls ss412 attenuator/source selector (all RCA)
JDS Atom amp
Behringer A800
Elac DBR62

Here are a few of the specs:

SMSL M200
RCA out: 2Vrms
XLR: 4.1Vrms

Alva Solo
Output: 300mV
Output Sensitivity: 3.35mV
Overload Margin: >30dB

JDS Atom Amp
Input Impedance: 10k
Output Impedance: .1 ohm
Max Output @ 600Ω: 125mW (8.68 VRMS)
Max Output @ 150Ω: 502 mW (8.66 VRMS)
Max Output @ 32Ω: 1 Watt (5.66 VRMS)

Behringer A800
Input Impedance
- XLR/TRS(Bal): 20K
- RCA/TRS (Un-Bal): 10K
Voltage Gain @ Max
- Bal: 30 dB
- RCA: 41dB
Sensitivity
- XLR: +4dBu
- RCA: -10dBV

Elac DBR62
Sensitivity: 86db @ 2.83v/1m
Max power: 120 Watts
Impedance: 6 ohm

The main questions I'm struggling to answer are:

- Would it be advisable to plug the 4 sources (DAC/TV/phono/tape) into the Rolls selector at full volume and then attenuate with the selector?
- Will the attenuator change the frequency response and/or impedance?
- Should I keep the Behringer gain at maximum?
- Can I plug the DAC directly into the A800 via a balanced connection (is has a preamp function) and still use the RCA input for the source selector?
- Should I sell the Atom/KTB/Rolls and put it towards a better preamp like the "Schiit Freya S"?
- Should I sell everything except the speakers and put it towards a nice integrated amp?

Currently, I have the JDS Atom plugged into the A800 (gain at noon) and I swap out the components as I need to use them. I'll probably keep doing this until I can figure out the best way to connect everything together that is both safe for the equipment and pleasant for the listener.

Any advice would be greatly appreciated!

 

[Daverz]

The input impedance of the JDS amp and the Behringer (10 kOhm) may not be ideal for a passive selector. The attenuator will have variable output impedance and thus potentially change the frequency response if the connected load impedance is too low, but probably only at the frequency extremes (20 Hz and 20 kHz). The rule of thumb is 10-1 for input impedance to output impedance (i.e. you don't want the output impedance of the Rolls to fall much below 1 kOhm). In practice, the effect on the frequency response may not be audible. It would be nice if Rolls specified a minimum input impedance compatible with its output.

I think it's safe to assume that the Atom can handle typical single-ended DAC and CD output levels. It also looks like it will handle the output of the phono pre just fine. I think the best practice would be to leave the Rolls at max volume, then set the volume of the Behringer so that your preferred listening volume is not too low in the Atom's volume range.

 

[AudioStudies]

I had a similar situation with a passive selector, though not a Rolls. I opted to have a Technician bypass the attenuator, thereby making it a selector only. This arrangement worked well for me, and you could consider it, if you are equipped to control volume by other means.

 

[Bob-23]

bypass the attenuator

If the voume is fully up, the attenuator is bypassed.
So Daverz' recommendation is sufficient:

leave the Rolls at max volume

 

[AudioStudies]

If the voume is fully up, the attenuator is bypassed.
So Daverz' recommendation is sufficient:

I think you mean that it is not applying any attenuation when the volume knob is fully up and you are correct in that regard. I just thought it would be better to have one less thing in the signal path = why I had it bypassed (removed from the circuit).