Bypassing A Preamp With Volume Pot In Amp

I see preamps as a convenient tool to control the volume of multiple sources. It only adds another link in the chain. It also adds to the cost of your system because you will need other pairs of interconnects and a power cable.

I was thinking about completely bypassing a preamp by adding a volume pot or a resistor based stepped attenuator into the amp, greatly reducing the signal path from the source to the amp.

The only detriment I can think of, is switching the interconnects from each source which is as troublesome as switching out a disk from the CD player.

Please chime in with your opinions and especially your experiences with this "issue".

The volume control I have in mind is the Khozmo stepped attenuator using 2 Vishay TX2575 resistors in a hybrid tubed/ss amp.
If you have the control installed in the amp this works quite well. Switching the interconnects will get old after a while though.
C_avila1: Great idea, if your source has equal or higher output voltage than the input sensitivity of your amp great, you are almost there.

If your source has a nice low ouput impedance say below 100ohms, this will happily drive down to 1kohm (1:10 ratio).

EG: The combined load of say a 10kohm passive and a 47kohm input impedance (industrie standard of most amps)amp is still 8.2kohm, the 100ohm source will happily drive this (1:82 ratio), then this will be the most transparent/dynamic sound you will get.

Cheers George
Sounds like a DIY passive preamp. Why not get a selector switch and a few more RCA's and avoid the plugging and unplugging of the interconnects?

You'll find a lot of so called intergrated amps these days are exactly just that, a power amp with a passive and input switching, many of these are coming from EU and Asia and some are "Hi-End" tube mostly but now some solid state as well.
Cheers George
@Ptmconsulting, @Atmasphere: RE: DIY passive preamp - That's pretty much what I am aiming for but having it built into the amp with only one pair of single ended inputs. I just can't use another interconnect if its not as good as the pair of Hidiamond D9 interconnects that I already have. It would really hurt my wallet to purchase another pair.

@Georgelofi: Someone recommended to use a 50kohm attenuator. Would that possibly work better than the 10kohm passive that you mentioned in your example?

You haven't mentioned the input impedance of your poweramp.

I say 10K as a general even when direct connected, as most amps are 47kohms (industry standard) input impedance.

If you have say a Rogue tube poweramp which are 1mohm input impedance then yes a 50kohm pot will be more than fine.

Just remember it's easier to manufacture a 10kohm stereo log pot so that both channels track each other within a db or so than it is to manufacture a 50kohm stereo log pot to track that well.

Cheers George
Must be some special pot.
Just ask George which is better. What you are considering doing OR just buying a Lightspeed attenuator and another pair of less expensive rca's to bridge the connection. I understand where you are coming from wanting to keep the rca's of the same quality within the chain, but I'd bet the lightspeed with some mediocore interconnects will sound better than what you are trying to do. I could be wrong...

Ask George what he thinks. By the way, I have no relation to George other than being one of many, many happy customers. His lightspeed thread is one of thelongest here, with glowing reviews!
Lse, it's not a pot (potentiometer).

It's just like a direct connection between source and power-amp with none of the contacts or preamps active components in the signal path, like a pots very lightweight wiper contact or switched resistor pots contacts in the signal path.
It's just a single fixed soldered resistor, that just happens to be able to change it's resistance value by being light sensitive.

It's the most transparent, uncoloured, dynamic way of getting the signal of the source to the power-amp, without any active tube or solid state components or contacts in the signal path.

You can read all about in these two threads.

Cheers George
«Georgelofi» LSA acts as a conventional resistance, with respect to the set of impedances?
Changing interconects not scare me, but adjust the volume behind the amp, yes. Unless you have great discipline when it comes to listening volume.
I've installed a Goldpoint stepped attenuator in my amp and soldered my interconnects directly to it. My CD player and phono pre have no trouble driving the amp.
Correct Jetrexpro, nearly all sources these days have output voltages higher than what the maximum input voltage is needed to drive amps into full output.

So there is no need for preamps with gain.
And if you have a source with low output impedance (<200ohms) as well, which most are anyway. All you need is a passive volume control, does'nt matter if it's inside the poweramp or outside connected by a meter of quality low capacitance (which most are) interconnect.

Cheers George
@Jetrexpro: Can you please tell us about your experience and opinion with having the Goldpoint stepped attenuator in your amp. Did you use a preamp before the Goldpoint? What are the benefits and detriments of the Goldpoint attenuator?
I did it! I just finished installing the Khozmo stepped attenuator. It's easy to hear the difference immediately. The sound stage has tremendously improved in depth, layering, background noise, focus, and dimension. There's no doubt that this is an upgrade. Considering the cost and effort for installation, the stepped attenuator proves to be major bang for the buck. The Khozmo is using Kimber TCSS wire and a Z-Foil TX2575 resistor per L/R channels @ 50Kohm. I also changed the cheap female RCA plugs for Cardas GRFA so I am unable to accurately measure how much each component helped to improve the sound.

I did notice that the attenuator is turned to 12 o'clock with merely average listening level. Does that mean that 10Kohm resistors would allow for more head room with volume?
No. That is just how the gain structure worked out. Reducing the value of the control will make it harder for some sources to drive the amp.
06-03-14: C_avila1
I did notice that the attenuator is turned to 12 o'clock with merely average listening level. Does that mean that 10Kohm resistors would allow for more head room with volume?

Head room will remain the same, position will be different, lower. This could psychologically make you think it's got more headroom.

Remember Nelson Pass's quote:
Nelson Pass:
"Quote We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.End Quote"

You may like the 10kohm better it will have better impedance coupling with amps that are down to around 33kohm input impedance, higher than that is no problem.
But your source should be of the industry recognized low output impedance say below 1kohm, usually this means solid state, and only a selected few tube ones.
As there are many weedy tube output sources that are high output impedance, some I've seen that are a ridiculous high 3kohm sometimes 5kohm output impedance and should never be put for sale on the market, these will prefer to see 50kohm pot or even higher.

And if you find you need to use a source switch box, select ones with rotary type selector switch. These tend to have better contacts than push type, you can also put your passive in there as well, this way you can change amps when you need, just use interconnects that are less than <100pf (picofarad) per foot, which most all quality ones are.

Cheers George
I would like to add that this upgrade also removed an "electronic glare" that was plaguing my system. This upgrade made a huge difference as much as my Hidiamond D9 ICs and bypassing the amp's PS electrolytics with .22uf V-Cap CuTF caps.

One point of concern: The attenuator is placed on the side panel, towards the rear of the amp, about 3 inches from the heat sinks. I noticed that the volume pot and knob does adsorb heat. I highly doubt that the sound quality will be affected do to the low temperature coefficient of the resistors (TX2575 TC is at 1ppm). I'm concerned for the attenuator's ability to stand the test of time with continuous heating and cooling.
Yesterday, I replaced the Kimber TCSS wire that connect the female GRFA RCA jacks in the amp to the Khozmo attenuator. The results: major improvement in tonality. The Kimber TCSS wires use teflon insulation that obviously colors the signal. This is my second test with teflon insulated wires. Both tests resulted in unfavorable opinions of teflon insulated wires within the signal and incoming A/C power. If I ever need another leap in tonal transparency, I'll switch the remaining Kimber teflon wires that connect the Khozmo to the amp. For now, I am content with the current tonality.

Revisit to my previous post: Currently, there are no issues regarding absorbed heat into the attenuator.
Teflon is a pretty good dielectric. There may be more to this than meets the eye as to why you heard a difference/improvement.
I forgot to mention the wire I used to replace the Kimber TCSS is the Neotech solid core, UP-OCC, 20 AWG wire with PVC jacket.
When you switched wires, there was more involved than just the dielectric. I agree that the Neotech copper wire sounds very good, better than TCSS, but this relates to the metal as well as dielectric. Incidentally, the Neotech copper wire is also available with Teflon.

Recently I have been using Neotech silver 20 g. with Teflon insulation. The silver sounds even better than the copper Neotech.
I recently posted regarding sonic dielectric differences including Teflon Neotech copper wire which I believe, also, colors the music. See post from 03-30-14.

You are correct about there being "more involved than just the dielectric". The TCSS wire is stranded and the Neotech is solid core. However, the 2 experiences I've had with teflon wire resulted in very similar or identical coloration.

I'm interested in the silver wire now. I might buy a couple of feet and replaced the remaining TCSS wire.
Where did you get the silk tubing? I would like to try the silk in place of Teflon or PVC.

Duelund wires use either one or two layers of silk soaked in some sort of oil. The Duelund conductor is a solid silver ribbon. I use the Duelund for both signal wiring and ground connections in my linestage and some of my power amps, and it sounds very good.
The silk tubing was purchased from Parts Connexion. Their parts numbers are: SLKTUBE-72530 (small gauge) and SLKTUBE-72531 (slightly larger guage)

You can also purchase bare copper and/or silver wire to use with the silk tubing. Let us know what you have concluded if you decide to experiment.
Thanks. I just ordered some more Neotech silver with Teflon insulation and some silk tubing. I have a spot for testing this on my outboard speaker crossover, and I will be able to swap several different wires back and forth for comparison. The samples will include Neotech silver with both Teflon and silk insulation. I will post some findings in the next few weeks. All the wires have to go through breakin on a jig I rigged up that lets me run signal through the new wire 24/7 on a dummy load in another system.

If the silk ends up sounding better, I will order more to replace the Teflon insulation on the Neotech silver wires I use for internal wiring in my speakers.
C_avila1, using your logic, a boom box is the best audio component.

Please explain your post, Tbg. Are you in favor of active pre amps? Are you in favor of teflon dialectric?

@Salectric - Thanks for letting us know about your upcoming trials. Let us know what you hear or not hear.
C_avila1, sorry I didn't mean to be insulting. What you were suggesting was to minimize interconnects and volume controls. Especially volume controls in my opinion are generally horrible. And while wiring within a metal box is much more immune to RFI and EMI.

So a boom box with all wiring within would be the optimum result of your logic. I don't even like stereo amps much less integrated amps for various reasons.
Tbg - I don't think you read the whole thread. Please read my post and Georgelofi's post from 06-03-14.

My idea with having a passive stepped attenuator in the amp is to eliminate the costs of the pre amp and interconnects while shortening the signal path and ultimately improving sound quality.

Guess what? I tested the idea and it works...for me

If Conrad Johnson makes a boom box, I would love to hear it.
C_avila1, you were right I had not read the entire thread. However, there was a time long ago that I tried passive preamps and even just pots mounted outboard. I decided that as pure as they sounded, they always had poor dynamics and bass.

But there is something about having all interconnects within the rfi and emi shielding chassis except that they would be exposed to the magnetic fields of the other wires. I once heard three preamps that were identical except for the wiring placement within them. They each sounded quite different.

I certainly would not want to discourage anyone from experimenting. Once I hardwired everything in my system from the wall outlet to the speakers. I sounded great but scared me in a lightening storm. I was a pain also as the circuit breaker was my on/off switch.