[roymail]

That was the intended use for the gain controls, to be able to adjust the gain of the amp relative to the gain of the preamp.  This was easier than having to modify the board with fixed resistors for 26dB gain or 32dB gain or whatever, particularly if it needed to be changed again for use with a different active preamp, passive preamp or buffer.
Steve

I agree with Steve.  While the included pots may attenuate the volume, I don't believe that was their intended purpose, nor do I believe that will provide the best quality sound.  Using a high quality preamp or buffered attenuator like the Pass B1 would be my preference.

However, it won't cost much to try, and you don't have to modify anything to do it.  Who knows, you may like it.

[kingnubian]

Ok, firstly please excuse my newbieness (New word).

I was thinking about how to add a volume control apart from messing with the gain. How about this setup?

Rca Inputs-->volume pot-->amp input

Is this feasible??

[roymail]

If I'm understanding your idea correctly, that would make your volume control a passive attenuator.  Nothing wrong with that as long as you use a quality VC like a Gold Point/Elma stepped attenuator.  However, if you want to save some $$$, there is one sold on ebay for $15 that some really like.  Also, the PEC pots are surprisingly good.

Given the SDS input impedance of 47K, I'd recommend you keep the attenuator's value at 10K, 20K, 25K.  50K would not be a good match.

Are you using a 2 volt source like a cd player?  The SDS amp should provide plenty of clean output.

[srb]

Ok, firstly please excuse my newbieness (New word).

Excused, but as much as we would all like to coin a new word, newbieness is already a part of AudioCircle verbiage (if not yet added to the Urban Dictionary)!
 
nathanm - 6/26/2006
"I can fully appreciate Rob's opera newbieness."
http://www.audiocircle.com/index.php?topic=25121.msg223162#msg223162
 
MichaelHiFi - 3/24/2008
"Excuse my newbieness in this forum."
http://www.audiocircle.com/index.php?topic=52620.msg470355#msg470355
 
capace - 4/1/2009
"Sorry for my newbieness!"
http://www.audiocircle.com/index.php?topic=66676.msg613831#msg613831
 
As well as around the Internet
 
 
Steve
 

[kingnubian]

Excused, but as much as we would all like to coin a new word, newbieness is already a part of AudioCircle verbiage (if not yet added to the Urban Dictionary)!
 
nathanm - 6/26/2006
"I can fully appreciate Rob's opera newbieness."
http://www.audiocircle.com/index.php?topic=25121.msg223162#msg223162
 
MichaelHiFi - 3/24/2008
"Excuse my newbieness in this forum."
http://www.audiocircle.com/index.php?topic=52620.msg470355#msg470355
 
capace - 4/1/2009
"Sorry for my newbieness!"
http://www.audiocircle.com/index.php?topic=66676.msg613831#msg613831
 
As well as around the Internet
 
 
Steve

Oops, my bad.......Didn't know........

[kingnubian]

If I'm understanding your idea correctly, that would make your volume control a passive attenuator.  Nothing wrong with that as long as you use a quality VC like a Gold Point/Elma stepped attenuator.  However, if you want to save some $$$, there is one sold on ebay for $15 that some really like.  Also, the PEC pots are surprisingly good.

Given the SDS input impedance of 47K, I'd recommend you keep the attenuator's value at 10K, 20K, 25K.  50K would not be a good match.

Are you using a 2 volt source like a cd player?  The SDS amp should provide plenty of clean output.

This is very interesting news regarding getting a 10k passive VC. Please feel free to PM me details regarding the "Ebay" item & the PEC (Precision Electronics MIL 2RV7?) pots or feel free to post a followup please.

Btw, I found this item (http://cgi.ebay.ca/Valab-23-Step-Attenuator-Potentiometer-10K-Stereo-Log-/270617059671?pt=LH_DefaultDomain_0) Uses the highly regarded Vishay precision resistors. Comments??

A cd player will be the main source, initially at least. Down the road I may even ad a quality input selector, but that's getting away from myself for now. Need to stay focused.

[mjosef]

what's the difference between atenuating gain and volume of an amplifier?

In the context of the thread, its essentially the same( or the former is used to regulate the latter)...

An attenuator is effectively the opposite of an amplifier, though the two work by different methods. While an amplifier provides gain, an attenuator provides loss, or gain less than 1.

Attenuators are usually passive devices made from simple voltage divider networks. Switching between different resistances forms adjustable stepped attenuators and continuously adjustable ones using potentiometers. For higher frequencies precisely matched low VSWR resistance networks are used...http://en.wikipedia.org/wiki/Attenuator_%28electronics%29

the term can also apply to impedance matching, which is another thing altogether.

SO you can eliminate the pot(volume control), but you may need to substitute a resistor of equal value to maintain the input impedance (of the amp)...no need for two inline pots (pre & amp)...unless, you are biamping and wish to have an additional trim option per amp.
I have never heard of a pot being used to regulate the dynamics of a signal...

[hottuner]

While the included pots may attenuate the volume, I don't believe that was their intended purpose, nor do I believe that will provide the best quality sound.  Using a high quality preamp or buffered attenuator like the Pass B1 would be my preference.

I believe using the included pots, or a ganged version, will produce the best sound, as the designer will have them in circuit optimally so as to provide the function of setting the amp gain for the sweet spot of the users pre-amp gain control. That implies the amp gain control will be transparent at any likely setting. Personally I wouldn't worry about using the gain controls in the amp as the main gain on the system, as there is no risk of sonic degradation.

The real problem is you have no input switching as you would with a pre-amp. If you only are going to use one source by all means use the amp gain, but using two mono pots day in and day out would be a royal pain, you would want to use a quality ganged stereo pot as opposed to the single channel pots that come with the amp kit.

[Mmaxed]

Hey guys, newb here.  Found a link and have read much of this thread over the last few days.  Very interesting.

My question is this.  It seems that most of you are driving more "modern" type speakers with these amps.  How do you think they would do with more vintage type speakers?  Right now my mid life crisis has Bose 901 series II (please, no rock throwing) and JBL L100T's in the living room.  I've also been playing with some Ewave stuff, much discussed over at AK, and will finish a build of them later.

Thanks for all the info here so far!     

[TrungT]

Mmaxed
Welcome to AC 
I don't think you have any problem to drive the ClassD with vintage speakers.
Actually sound very nice with my Klipsch Forte'II and ADS L-810.
May give the 901, L100 a work-out 

[dvenardos]

Here is the link to the GoldPoint page on choosing the value of your attenuator:
http://www.goldpt.com/info.html

If I'm understanding your idea correctly, that would make your volume control a passive attenuator.  Nothing wrong with that as long as you use a quality VC like a Gold Point/Elma stepped attenuator.  However, if you want to save some $$$, there is one sold on ebay for $15 that some really like.  Also, the PEC pots are surprisingly good.

Given the SDS input impedance of 47K, I'd recommend you keep the attenuator's value at 10K, 20K, 25K.  50K would not be a good match.

Are you using a 2 volt source like a cd player?  The SDS amp should provide plenty of clean output.

[guest1632]

Ok, firstly please excuse my newbieness (New word).

I was thinking about how to add a volume control apart from messing with the gain. How about this setup?

Rca Inputs-->volume pot-->amp input

Is this feasible??

Hi all,

I'll make the following suggestions for whom it may concern.

Well, first off, I'd be discussing with Tom on how to do this pot thing. Personally, I'd just get the two sets of resistors and plugs. One set for the standard 26DB and the other for the higher gain 32DB and leave it alone. These fixed resistors would replace the two pots. That's my opinion. Whatever pots you install will be compromising the amps. The present pots do play a part, but I don't know if they will achieve what it is you want. I would think that is something that Tom could elaborate mor with you.

secondly, on this capacitor upgrade for the supply, I'd buy whatever values and brands of the caps you want, and send all six of them to Tom, and he can then just solder them in to the board for you. If they are the Panasonics, then Tom can take a listen to see how the stock supply sounds versus the one you are upgrading. He says he has tried bigger supplies with no results. However, results from the various mods seem to indicate otherwise. All I know is for what it matters, is the cleaner the signal being fed from the wall, the better these amps sound. That's my take on it. it would probably be smart for now, just to get the stock supply and listen for awhile, and buy another supply, with no caps on the board, and add your caps. then you can find out just what the real deal here is. Then you can sell the stock supply, and get most of your money out of it.

That's my two sense worth.

Ray Bronk

[jtsnead]

Well, first off, I'd be discussing with Tom on how to do this pot thing. Personally, I'd just get the two sets of resistors and plugs. One set for the standard 26DB and the other for the higher gain 32DB

Hi Ray,

Tom offers resistor sets and plugs for the SDS amps?

[kingnubian]

My SDS-254 is coming Friday & after all the discussion with respect to adding  a Volume control to the unit I've decided to try these two paths.

1) Add a high quality Input selector & Volume attenuator in the box. The input(s) would go to the selector switch then on to the volume control & finally on to the amp's signal input. The advantage of this approach is lower cable length (No Interconnects needed) & not having to go through an additional rca jack.

2) Build a high quality Passive preamp with the same selector & Volume attenuator. I'm also open to preamp kits like this one.
http://cgi.ebay.ca/6N3-5670-Tube-Buffer-Unit-Gain-Amplifier-DIY-Kit-/270480477544?pt=LH_DefaultDomain_0

Btw, here is the volume attenuator I'm loking at or at least something like it.
http://cgi.ebay.ca/Assembled-Dale-23-Step-Attenuator-Volume-Control-100k-/270311271326?pt=LH_DefaultDomain_0

I will naturally test all of this on a wood platform to see how feasible this setup will be.

Questions:

I was told that use of a 10k pot would be better matched to the SDS-254's input. Can anyone verify this?

Any pitfalls or issues that others can clearly see??

My music sources will be a cd player & the amp will also be hooked up to my Panasonic Vierra Plasma Television.

P.S. I need recommendations for a high quality input selector, 2-4 sources, that won't break the bank. I'm in Canada if that helps.

[wushuliu]

My SDS-254 is coming Friday & after all the discussion with respect to adding  a Volume control to the unit I've decided to try these two paths.

1) Add a high quality Input selector & Volume attenuator in the box. The input(s) would go to the selector switch then on to the volume control & finally on to the amp's signal input. The advantage of this approach is lower cable length (No Interconnects needed) & not having to go through an additional rca jack.

2) Build a high quality Passive preamp with the same selector & Volume attenuator. I'm also open to preamp kits like this one.
http://cgi.ebay.ca/6N3-5670-Tube-Buffer-Unit-Gain-Amplifier-DIY-Kit-/270480477544?pt=LH_DefaultDomain_0

Btw, here is the volume attenuator I'm loking at or at least something like it.
http://cgi.ebay.ca/Assembled-Dale-23-Step-Attenuator-Volume-Control-100k-/270311271326?pt=LH_DefaultDomain_0

I will naturally test all of this on a wood platform to see how feasible this setup will be.

Questions:

I was told that use of a 10k pot would be better matched to the SDS-254's input. Can anyone verify this?

Any pitfalls or issues that others can clearly see??

My music sources will be a cd player & the amp will also be hooked up to my Panasonic Vierra Plasma Television.

P.S. I need recommendations for a high quality input selector, 2-4 sources, that won't break the bank. I'm in Canada if that helps.

http://cgi.ebay.com/Input-Source-Selector-DIY-Kit-4-channels-/220651819871?pt=LH_DefaultDomain_0

http://cgi.ebay.com/Remote-Volume-Control-Input-Selector-DIY-KIT-MV04-/260461954935?pt=LH_DefaultDomain_0

[wushuliu]

Oops, my bad.......Didn't know........

newbian-ness?... 

[dvenardos]

The attenuator that you linked is the 100K version, here is the link to the 10K version.
http://cgi.ebay.ca/Assembled-Dale-23-Step-Attenuator-Volume-Control-10k-/270311271534?pt=LH_DefaultDomain_0#ht_2175wt_781

[kingnubian]

http://cgi.ebay.com/Input-Source-Selector-DIY-Kit-4-channels-/220651819871?pt=LH_DefaultDomain_0

http://cgi.ebay.com/Remote-Volume-Control-Input-Selector-DIY-KIT-MV04-/260461954935?pt=LH_DefaultDomain_0

That first input selector looks great!
How is the build & sound quality? Any issues with it being part of a Passive Preamp?
I've heard rumblings about relay based selectors vs rotary and being a relay based unit I just would like some insight as to where this will be with respect to sound quality. The relays used are well thought of, at least according to some Google searches I looked at.


I'll combine it with this:
http://cgi.ebay.ca/Assembled-Dale-23-Step-Attenuator-Volume-Control-10k-/270311271534?pt=LH_DefaultDomain_0#ht_2175wt_781

[nottaway]

How would the $175 kit shown here compare with say an Emotiva UPA-2?

[jtwrace]

How would the $175 kit shown here compare with say an Emotiva UPA-2?

I've never heard the Emotiva UPA-2 but I think from a dollar to  factor you'll be ahead with the Class D.