help with Quickie output impedance

[aragorn723]

Hi,

I'm having some issues with the Quickie and matching it to the Inter-m R500 amp.  The Quickie has the PJCCS in it, and the input impedance of the amp in 10k.  Here are a few things i did so far:

Turn down the amp
Add 100k resistors to the input of the quickie (after the selector switch)

Turning down the amp helped with being able to control the volume (it's a hair-trigger volume right now, so just a slight turn will jack the volume way up).  The downside of turning down the amp was that it messed with the damping factor, and the treble wasn't very clean.  The resistors helped a little bit, but i'm looking for other options (not ready to change the amp yet). 

I have a sub with a pass thru on it, would it help the quickie loading by running an rca to the sub, then run the pass thru to the main amp?  The sub is a b&w asw 600.  Thanks,

Dave

[Paul Birkeland]

Hello Dave,

How did turning down the amp mess with the damping factor? (also, the damping factor isn't incredibly important for treble)

Adding resistors at the input of the power amp would be highly advisable in this case.  I would recommend a pair of 33K resistors installed inside the amplifier, installed in much the same way as you did in your Quickie. 

You can try the sub approach, it's possible that the output is buffered, but it's also possible that the buffering that's done to the signal isn't something to get excited about.

[aragorn723]

well the treble was very muted, in general the sound was kind of bland.  Not sure if that's damping factor?  Are there other options besides modifying the amp?  I haven't worked on a 110 volt amp before, how do you work on it safely?

Dave

[Paul Birkeland]

I haven't worked on a 110 volt amp before, how do you work on it safely?

Unplugging it is a good place to start. 

Generally there will be an obvious large bank of capacitors that you can measure to ensure that the power supply is well drained down.

Without looking at the schematic, it's tough to say why the treble is falling apart with the level control padding the input. 

You could also build a set of interconnects with the resistor in each plug that plugs into your amp.

[Grainger49]

Aragorn,

The Quickie duplicates circuitry that is inside the Inter-m amp.  The Quickie is a preamp and the Inter-m is an integrated preamp and power amp.  If the Inter-m had jacks where the pre and power amps could be separated it would be ideal. 

IMHO, padding the input of the Inter-m would be more effective than padding the input of the Quickie.  After all, the Inter-m is the piece that is adding too much gain. 

Turning down the input of the Inter-m should not affect damping, and as PB said, damping affects the bass rather than treble.  The loss of quality in the treble is puzzling. 

Running the Quickie into the sub then the Inter-m probably won't help.  You will still have a preamp feeding a preamp.

Just to keep you from chasing your tail can you check out the Quickie with a power amp?  You need to find where the problem exists, the Quickie or the Inter-m.

[aragorn723]

that's strange, since the r-500 is listed as a power amp, rather than an integrated unit.  It has XLR and 1/4" inputs, but only one set (there is no switching of multiple units like a sony receiver for instance).  I don't have any other power amps, so i'll probably wind up building the interconnects with 33k resistors on the signal path.  My buddy has a few amps, so maybe we can try the quickie with one of those to see if it works better with that.

Dave

[Grainger49]

Sorry, I had thought you has said it was integrated.  You didn't. 

I would say trying the Quickie in your friend's system will either nail the Quickie as the source of the high frequency problem or exonerate it.

Odd, home audio amps that I am familiar with have at least one pair of RCA inputs.

Added: Just looked at the specs.  It is very sensitive; the speck (taken from the manufacturer's PDF manual) is 0dB/0.775mV.  That is 0.000775V.

[Paul Joppa]

The Inter-M manual is on the web, as noted above. It has a block diagram which is adequate for this thread. The input sensitivity specification is 0 dBu

The hair trigger volume indicates too much gain in the total system (most systems have this problem, to one degree or another).

Bottom line - if the Quickie is over-driven then attenuation at its input is in order. To determine this you need to know the peak output voltage of whatever source device are connected to the Quickie.

Otherwise the attenuator built into the power amp (after the balanced-input buffer) would be the place to reduce gain. It will have no effect on the damping factor, which is a measure of the amps output impedance. It should have no effect on the sound of the amp, either. It is possible that, if you turn the amp down too far, it will reguire excessive signal from the Quickie so that the Quickie is overdriven and produces distortion. In that case you will need to experiment to find the position of both controls that gives the best sound.

My paper on Signals and Noise, off the Community page, is a more detailed resource.

[aragorn723]

Makes sense to me, i'll try doing that too (and read the paper).  Another option is to adjust the volume control on the dac (audioengine d1).  Not sure if this is the best option, but it seemed to keep the treble clean and give a decent amount of volume control on the quickie.  Is there any reason this wouldn't be optimal in terms of sound quality?  Thanks,

Dave

[aragorn723]

Thanks everyone, lowering the volume controls to halfway on the amp made a huge difference.  The treble and tone sounds a lot better!

Dave