[DaveC113]

My preamp has 29 db of gain, there is a switch to change the gain, but it inserts a resistor in the output signal of the preamp, which doen't sound good. It was recommended to me by the preamp designer (Anthem Pre1, I called Parts Connexion) to run it at maximum gain.

Another AC member suggested a female to male rca adapter device that goes in between the preamp inputs and the IC that attenuates the signal, but they are more money than I want to spend, about $80. The mfg and the AC member claim the results are not audible, so I wanted to incorporate attenuation in an IC that I can build, if possible.

I'm not sure if the attenuation is done with a resistor in line with the signal wire, or if there's more to it? I also don't know how much resistance to add to get a certain level of attenuation either. My speakers are 93 db, and the preamp volume control never (rarely  ) gets over 9 o'clock. I was thinking of starting with 12-16 dB of attenuation, but would like suggestions on how much attenuation, and the best way to accomplish this.

Dave

[arthurs]

I bought a 10db pair of these, the build quality is excellent, when I have used them I found no audible change in my sound other than the signal attenuated, and the seller was a real pleasure to deal with, lightening fast shipment from England.  You might shoot him a note to discuss details of what you need and want to know....no affiliation, just a customer.

http://cgi.ebay.com/GOLDENJACKS-LINE-I-P-ATTENUATORS-for-optimal-CD-sound_W0QQitemZ300162237169QQihZ020QQcategoryZ3272QQrdZ1QQssPageNameZWD2VQQcmdZViewItem

[DaveC113]

Thanks for the link, they seem reasonably priced. I would like to know "whats in the box" or plug in this case. I have a feeling its just a resistor in series with the signal wire? If so I could build an IC with a resistor built into it. 

Dave

[Steve Eddy]

If so I could build an IC with a resistor built into it.

But that would ultimately be no different than the "resistor in the output signal of the preamp" that you already have now but say sounds bad.

Why not get a preamp that doesn't have so much gain? I mean, 29dB is just crazy. That's a factor of 28. Most power amps out there don't have input sensitivities higher than a volt or so. Divide that by 28 and you're talking only 36mV. What sources out there have 36mV output levels?

Looking at it the other way, the 2 volts out from a CD player multiplied by 28 is 56 volts. 56 volts into an 8 ohm load is about 200 watts. If your preamp could actually swing 56 volts, you wouldn't need a power amp. You'd just need a unity gain power buffer.

se

[Steve Eddy]

My speakers are 93 db, and the preamp volume control never (rarely  ) gets over 9 o'clock.

By the way, as long as you're able to adjust the volume where you want it, even though the knob doesn't go over 9 O'clock, what exactly is the "problem" you're trying to fix?

se

[DaveC113]

The preamp can swing 44V  aa   I kind of doubt the current capacity is there, though...

Yes, its a lot... but the preamp does sound good. I think the difference is attenuating the source signal between my DAC and the preamp, and attenuating the preamp's output signal.

I'd guess a simple voltage divider circuit would work, so I need 2 resistors per channel... So is cutting the voltage in half equivilant to a 3 dB reduction? Would I want 1/8 of the voltage for a 12 db cut? What resistor values would be good to use for this?

EDIT: the problem is that I can't play at very low volumes, and I'd like more range on the volume dial. Where its at now isn't considered ideal, and I figure it will probably sound better if the volume control isn't right at its operating limits...

Dave

[Bill Baker]

Basically what you are describing is a voltage divider and quite simple to execute for less than a dollar as well as being easily reversable if you don't like the results.

Here is a simple description of what the in-line attenuators are doing.
 
http://www.goldpt.com/mods.html

[Steve Eddy]

The preamp can swing 44V  aa   I kind of doubt the current capacity is there, though...

Right. Which is why I said you'd just need a power buffer. Something like Neson's new First Watt F4.

Yes, its a lot... but the preamp does sound good. I think the difference is attenuating the source signal between my DAC and the preamp, and attenuating the preamp's output signal.

Not much of a difference that I can see. Seems if you're going to add resistors, it'd be best to do it at the higher signal level rather than the lower.

I'd guess a simple voltage divider circuit would work, so I need 2 resistors per channel... So is cutting the voltage in half equivilant to a 3 dB reduction? Would I want 1/8 of the voltage for a 12 db cut? What resistor values would be good to use for this?

What's the input impedance of your preamp?

EDIT: the problem is that I can't play at very low volumes, and I'd like more range on the volume dial. Where its at now isn't considered ideal, and I figure it will probably sound better if the volume control isn't right at its operating limits...

Gotcha. So you do indeed have a "problem" you're wanting to solve. Just making sure as otherwise I'd suggest just leaving things as they are short of getting a different preamp.

se

[DaveC113]

What's the input impedance of your preamp?

It is 50,000 Ohms.

Also, I want to attenuate before the preamp because the 2 commercial attenuators, like the one arthurs posted, indicate use before the preamp, and arthurs is the second person to tell me that it wasn't audible when used in this position. Theres nothing keeping me from trying it before the amp too, I guess...

Bill, Thanks for the link!

Dave

[Steve Eddy]

It is 50,000 Ohms.

Ok. Any chance you can swap out the volume pots for some 10ks?

Also, I want to attenuate before the preamp because the 2 commercial attenuators, like the one arthurs posted, indicate use before the preamp, and arthurs is the second person to tell me that it wasn't audible when used in this position. Theres nothing keeping me from trying it before the amp too, I guess...

Yeah, well maybe the resistor on the output of your preamp wouldn't be audible to him either.

se

[DaveC113]

Ok. Any chance you can swap out the volume pots for some 10ks?

I'd like to get a better pot, but its out of the budget right now. It currently uses a Noble pot. I guess you don't want to increase the input impedence too much... but would using some lower value resistors be ok, say 1000 and 250 Ohms, which would reduce voltage 80%?

This might not be a permanent mod... I agree it might have exactly the same effect as the gain switch in the preamp. The circuit in the preamp isn't horrible, but maybe with some good resistors it can be better.

Dave

[Steve Eddy]

I'd like to get a better pot, but its out of the budget right now. It currently uses a Noble pot. I guess you don't want to increase the input impedence too much... but would using some lower value resistors be ok, say 1000 and 250 Ohms, which would reduce voltage 80%?

Well, what I was trying to work toward was using a lower value pot for the volume control in the preamp and then using a single series resistor connected to the pot's input. This would let you get the attenuation you want without raising the effective source impedance compared to if you were to apply the same amount of attenuation using the 50k pot.

I just think this would be a more elegant solution compared to using a two resistor voltage divider ahead of the pot.

This might not be a permanent mod... I agree it might have exactly the same effect as the gain switch in the preamp. The circuit in the preamp isn't horrible, but maybe with some good resistors it can be better.

Are you sure the gain switch in the preamp is simply putting a resistor in series with the preamp's output and is not actually adjusting the gain of the circuit itself? I mean, if it's just doing the former, it's a bit misleading to call it a "gain" switch. It's really just an attenuator.

se

[DaveC113]

I went and looked at the preamp again... there is a switch that engages a single resistor per channel between the balance control and volume pot. It looks like a 3920 Ohm resistor, .25%, 25ppm. So yes, this isn't really a gain switch.

This seems to be the solution you're thinking about...(I was wrong about it attenuating the output it seems  ) . Perhaps replaceing them with higher quality resistors would be the way to go? This would certainly be a cheap, easy solution. The difference in sound with it being in the signal path shouldn't be any worse than a voltage divider, I would think. 

Dave

[Steve Eddy]

I went and looked at the preamp again... there is a switch that engages a single resistor per channel between the balance control and volume pot. It looks like a 3920 Ohm resistor, .25%, 25ppm. So yes, this isn't really a gain switch.

Ah, ok.

This seems to be the solution you're thinking about...(I was wrong about it attenuating the output it seems  ) . Perhaps replaceing them with higher quality resistors would be the way to go? This would certainly be a cheap, easy solution. The difference in sound with it being in the signal path shouldn't be any worse than a voltage divider, I would think.

Yeah, I don't see how it could possibly be any better using an external resistor or voltage divider. Try a better resistor and see how that goes. Pretty simple and inexpensive to try.

Good luck!

se

[DaveC113]

Thanks, I appreciate your help!

Dave