Am I delusional, or did adding an attenuator improve the sound?

[Vynuladikt]

I have a pair of Carver C1s and a pair of PL400s running front/rear duty. I was tired of manually adjusting volume and balance between the pairs so I built and added a remote controlled attenuator. The intent was I could set a max on the C1s with proper balance and then use the remote attenuator to control volume of all 4 channels equally and easily. I had some concerns about negatively affecting the sound quality, but the pots looked like good quality gear so I proceeded.
Much to my amazement at first listen the sound seemed more clear and open, as if that could even be possible in my mind. I do have a much finer control on volume due to the fact that the C1s are set at about 11:00 and I get the full 270 degree swing of the attn. pots to set the output.
Could the change in loading of the output of the C1s or the input of the 400s make a large difference, or is it the position of the pots on the C1s being in unused area (rarely saw much above 9:00 in normal use)?
Thoughts?
Has anyone else had similar experience?

 

[WOPL Sniffer]

yes, been talking about the sweet spot on these pots for years. Guess nobody paid any attention.

 

[J!m]

What? Did you say something?

 

[WOPL Sniffer]

What? Did you say something?

exactly

 

[Vynuladikt]

yes, been talking about the sweet spot on these pots for years. Guess nobody paid any attention.

It definitely is sweet if that’s what it is. Wouldn’t have believed the difference.
Can you point me to the discussion?

 

[J!m]

Isn’t that what Bob did? Apply random components until he liked the sound? Then apply a sci-fi name to the circuit?

 

[WOPL Sniffer]

It definitely is sweet if that’s what it is. Wouldn’t have believed the difference.
Can you point me to the discussion?

That's one of the reasons I made the Adjustable Gain Board for the C-1. Sorry, YOU can dig for the thread.

 

[WOPL Sniffer]

I have a pair of Carver C1s and a pair of PL400s running front/rear duty. I was tired of manually adjusting volume and balance between the pairs so I built and added a remote controlled attenuator. The intent was I could set a max on the C1s with proper balance and then use the remote attenuator to control volume of all 4 channels equally and easily. I had some concerns about negatively affecting the sound quality, but the pots looked like good quality gear so I proceeded.
Much to my amazement at first listen the sound seemed more clear and open, as if that could even be possible in my mind. I do have a much finer control on volume due to the fact that the C1s are set at about 11:00 and I get the full 270 degree swing of the attn. pots to set the output.
Could the change in loading of the output of the C1s or the input of the 400s make a large difference, or is it the position of the pots on the C1s being in unused area (rarely saw much above 9:00 in normal use)?
Thoughts?
Has anyone else had similar experience?

I think I found changing the gain a few notches down on the gain board and then setting the volume pot up at the 13 o'clock position and that got the distortion down in the .005% range.

 

[George S.]

Found a similar effect replacing the PL2000 preamp volume control with a Dale resistor stepped ladder style attenuator. Better sound quality and equal channel balance. The equal channel balance regardless of volume setting I think was the single greatest improvement.
Still not totally happy with it though. I want to correctly measure the input impedance of the preamp, and experiment with reduced values. This may or may not depend on the signal/line resistor values just before the volume control. Basically what Sniff has remarked about.
I'm going to find his post and learn more about this.
I wonder how this changes output impedance. Lots to learn and consider.

 

[WOPL Sniffer]

Here is a chunk of the thread I was referring to .

The Gain Board is kinda slick and when you pop the top off the Pre, it's right there so moving the 4 jumpers to fine tune it to your system is as quick as removing the top screws and putting them back in..

I set the gain at Normal and got .050% THD+N

I set it at a 3dB decrease in gain and got .041% THD+N

I set it at a 6dB decrease in gain and got .037% THD+N

You have to turn the volume up on the pre a little further but it's now in the sweet spot...



There were a couple threads about this here, and over on the Carver site.

 

[WOPL Sniffer]

Here is a little more..... Just shows what you can do just by PLAYING.

I'll document the building/mods of the Power Supply when the 4000t gets here. They respond very well to that mod for sure. Between the PS mod and the Fresh Top Quality Caps in the PS, it cleans it up big time. If I have the time, I'll see if I can do the "EZ-Gain" mod too. I know after experimentation with the 4000's, that the higher output levels give much better results with the THD+N numbers but the average Joe doesn't get any benefits from the lower distortion since you are not USUALLY listening to the system with the Preamp dial in the "Sweet Spot". It MAY be the output level, or just the spot on the volume control.... I'll finger it out soon.



I monkey with lowering the volume on the amp, and bringing up the preamp volume to find the sweet spot and I always try yo get my customers to try to find that Happy Spot to get the cleanest sound but it can be elusive and frustrating. The interaction between the amp and pre changes things in the Ear World.....

 

[Vynuladikt]

That's one of the reasons I made the Adjustable Gain Board for the C-1. Sorry, YOU can dig for the thread.

I have read the thread but didn’t think about an external attenuator being a large effect on the system. That’s why I was asking if anyone else has had this result. Then I considered the possibility of impedance changes or I was just delusional. Then I considered a couple other possibilities, re-connecting the interconnects cleaned the surfaces or that the pot had worn in the lower portion. In any case it seems to be an appreciable improvement.

 

[WOPL Sniffer]

Just putting this out there, In case anybody wants to get their preamp/amp back into the sweet spot on the output/volume knob. The service manuals for a few of the aforementioned preamps, put out a procedure for adjusting the gain and to make this easier, I designed a little board to assist in that and now you'll be able to take this on easily and in the event you switch gear around as I do, reverting or changing the gain is as simple as moving a couple jumpers. The factory suggested resistor are all going to be mounted to the board so going from Normal, to reducing the gain by up to 21dB is a cake walk. I even left 2 empty spots for those wanting to customize with different values of resistors. The boards will be here in about 5 days...



I have also been experimenting with the power supplies and anybody going to carver fest and is interested, the 4000t that I am going to upgrade will have this mod and if you get Kevin to pop the top on it you can take a look. First pic is of the boards for the Gain Modification, the second its of the power supply board. It works like a charm. I had it on the Test Station and I'll continue to record results. I will be making these boards available here also. Stay tuned.... The Power supply board is in my new 4000t I'm modding (second pic) The first thing I noticed was that the PS in this 4000t was not symmetrical. The +12 read 11.5 and the -12 measured -11.9. Thats almost a half of a volt and by reworking it, I was able to get it within 200mv. THD went from .2% THD to .08% so it helped with the Noise Floor... Can your ears tell it??? Don't know but it didn't hurt.... With the recap partially Done, it's now down to .07% THD.... Gettin there.

 

[Vynuladikt]

Overlap
You posted about the same time I did

 

[WOPL Sniffer]

HUH???

 

[WOPL Sniffer]

I was just showing the possibilities you can achieve with a bit of MF'ing around. It doesn't take much test equipment to experiment with it either. GO FOR IT!!!!!

 

[WOPL Sniffer]

In the case of the C-1, this is an easy mod and all reversible in 10 second with the Gain Board.

 

[WOPL Sniffer]

I was just showing the possibilities you can achieve with a bit of MF'ing around. It doesn't take much test equipment to experiment with it either. GO FOR IT!!!!!

I did my testing with 3 swizzle sticks, a snowfling and a clean ashtray.

 

[George S.]

Exactly what I need to do. Thanks Sniff!

 

[MarkWComer]

Bumping an old thread…

Considering a stepped attenuator for the volume control of a PL 4000/II. Service manual states 100k NL. Is that NL indicating non-linear or non-logarithmic?

Or from the Netherlands…