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Matt Faunce Matt Faunce is offline
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Default Why No Gain Control on Adcom Amp?

Why is there no gain control on the Adcom GFA-535?

I've used it in between my computer (iMac) and my speakers, and controlling
the gain from the computer works, but there's always a noticeable hiss.
Wouldn't it be better to have the output of my computer much higher and
attenuate the output of the Adcom?

Similarly, I've seen many reviews of powered speakers where the reviewers
complain that there's a noticeable hiss that can't be attenuated. Why are
they designed like that?

--
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geoff geoff is offline
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Default Why No Gain Control on Adcom Amp?

On 5/06/2018 4:02 PM, Matt Faunce wrote:
Why is there no gain control on the Adcom GFA-535?

I've used it in between my computer (iMac) and my speakers, and controlling
the gain from the computer works, but there's always a noticeable hiss.
Wouldn't it be better to have the output of my computer much higher and
attenuate the output of the Adcom?


No. Sounds like the computer output has a much higher output level that
the Adcom's max input level. Set you computer output level on max and
get a passive volume control, adjusting the level down for max Adcom
output. That will be the best background hiss level you can achieve
using the computer's line output. Or get a better computer, or better
audio D-A interface.


Similarly, I've seen many reviews of powered speakers where the reviewers
complain that there's a noticeable hiss that can't be attenuated. Why are
they designed like that?


That sounds like artifacts from a crappy implementation of a Class-D
poweramp section. Or poor power supply, or both.

If a powered speaker has a hiss that can be heard more than 30cm ( a
foot ) away, it is a heap of junk. I have some cheap-and-nasty 30W
powered speakers beside by computer monitor and can't hear hiss unless I
put my ear within a few inches.

geoff
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Matt Faunce Matt Faunce is offline
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Default Why No Gain Control on Adcom Amp?

geoff wrote:
On 5/06/2018 4:02 PM, Matt Faunce wrote:
Why is there no gain control on the Adcom GFA-535?

I've used it in between my computer (iMac) and my speakers, and controlling
the gain from the computer works, but there's always a noticeable hiss.
Wouldn't it be better to have the output of my computer much higher and
attenuate the output of the Adcom?


No. Sounds like the computer output has a much higher output level that
the Adcom's max input level. Set you computer output level on max and
get a passive volume control, adjusting the level down for max Adcom
output. That will be the best background hiss level you can achieve
using the computer's line output. Or get a better computer, or better
audio D-A interface.


Similarly, I've seen many reviews of powered speakers where the reviewers
complain that there's a noticeable hiss that can't be attenuated. Why are
they designed like that?


That sounds like artifacts from a crappy implementation of a Class-D
poweramp section. Or poor power supply, or both.

If a powered speaker has a hiss that can be heard more than 30cm ( a
foot ) away, it is a heap of junk. I have some cheap-and-nasty 30W
powered speakers beside by computer monitor and can't hear hiss unless I
put my ear within a few inches.

geoff


If I remember correctly, the Adcom caused hissing even when nothing was
plugged into its input. Tomorrow I'll hook it up again and check that.

--
Matt
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John Williamson John Williamson is offline
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Default Why No Gain Control on Adcom Amp?

On 05/06/2018 05:02, Matt Faunce wrote:
Why is there no gain control on the Adcom GFA-535?

The short answer is that it saved the makers a few cents, and cut down
the number of support calls about not enough volume when the Luser
forgot to turn it up.


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geoff geoff is offline
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Default Why No Gain Control on Adcom Amp?

On 5/06/2018 8:00 PM, Matt Faunce wrote:
geoff wrote:




If I remember correctly, the Adcom caused hissing even when nothing was
plugged into its input. Tomorrow I'll hook it up again and check that.



Could be faulty then ...

geoff


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Default Why No Gain Control on Adcom Amp?

On 5/06/2018 10:04 PM, John Williamson wrote:
On 05/06/2018 05:02, Matt Faunce wrote:
Why is there no gain control on the Adcom GFA-535?

The short answer is that it saved the makers a few cents, and cut down
the number of support calls about not enough volume when the Luser
forgot to turn it up.




Or Adcom were on a puritanical 'power amp' kick.

That being said, I have at least fout power amps with no level control.
Make that 5 .

Quad 405, home-built mega-Quad 405, Hafler DH-220, NAD 2200, old Perraux
something-or-other, home-built early 75W mosfet (Maplin kit ?). OK
that's six. Probably a few more too.

Never a problem with noise or gain-staging with any of them.

geoff
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Scott Dorsey Scott Dorsey is offline
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Default Why No Gain Control on Adcom Amp?

Matt Faunce wrote:
Why is there no gain control on the Adcom GFA-535?


Because you didn't order it with that option. If you want the level control,
you want the GFA-535L.

I've used it in between my computer (iMac) and my speakers, and controlling
the gain from the computer works, but there's always a noticeable hiss.
Wouldn't it be better to have the output of my computer much higher and
attenuate the output of the Adcom?


Yes, if you are stuck with a noisy interface, you may need to do that. You
might just be able to put a fixed attenuator in front, though, rather than
bother with a full gain control.

Similarly, I've seen many reviews of powered speakers where the reviewers
complain that there's a noticeable hiss that can't be attenuated. Why are
they designed like that?


Because the designers are expecting them to be used with sources where this
isn't a problem. Consider investing in the Behringer Monitor1 passive
attenuator or something similar if you're stuck having to structure gain
this way.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Default Why No Gain Control on Adcom Amp?

In an ideal world, all final stages should have
volume con-AHEM! - attenuators.

Beause you never know what people are going
to be combining and running up-line from that
amp.
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Default Why No Gain Control on Adcom Amp?

On Tue, 5 Jun 2018 08:00:04 -0000 (UTC), Matt Faunce
wrote:

geoff wrote:
On 5/06/2018 4:02 PM, Matt Faunce wrote:
Why is there no gain control on the Adcom GFA-535?

I've used it in between my computer (iMac) and my speakers, and controlling
the gain from the computer works, but there's always a noticeable hiss.
Wouldn't it be better to have the output of my computer much higher and
attenuate the output of the Adcom?


No. Sounds like the computer output has a much higher output level that
the Adcom's max input level. Set you computer output level on max and
get a passive volume control, adjusting the level down for max Adcom
output. That will be the best background hiss level you can achieve
using the computer's line output. Or get a better computer, or better
audio D-A interface.


Similarly, I've seen many reviews of powered speakers where the reviewers
complain that there's a noticeable hiss that can't be attenuated. Why are
they designed like that?


That sounds like artifacts from a crappy implementation of a Class-D
poweramp section. Or poor power supply, or both.

If a powered speaker has a hiss that can be heard more than 30cm ( a
foot ) away, it is a heap of junk. I have some cheap-and-nasty 30W
powered speakers beside by computer monitor and can't hear hiss unless I
put my ear within a few inches.

geoff


If I remember correctly, the Adcom caused hissing even when nothing was
plugged into its input. Tomorrow I'll hook it up again and check that.


Unless you are running Klipsch Horns, the GFA-535 should be pretty
quiet with no input. They were so reliable, we used them in
professional installations where their failure rate was almost nil.


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Matt Faunce Matt Faunce is offline
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Default Why No Gain Control on Adcom Amp?

geoff wrote:
On 5/06/2018 8:00 PM, Matt Faunce wrote:
geoff wrote:




If I remember correctly, the Adcom caused hissing even when nothing was
plugged into its input. Tomorrow I'll hook it up again and check that.



Could be faulty then ...

geoff


OK. I was wrong about the hiss (or rather a sh sound) being there without
an input source. Without a source it is dead quiet. The source of the hiss
was my computer, and, I did have to have my ear within 12" of the tweeter
to notice it. I hooked my microphones-micpre-reverb
unit-recorder-Adcom-speakers, and it was much much quieter.

(That chain in my setup was as long as it was only for convenience.)

My apologies to everyone for the misinformation--especially to Adcom.

--
Matt
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Default Why No Gain Control on Adcom Amp?

geoff wrote: "
On the other hand some people know what they are doing, how, and why.

geoff "

I also know how to gain stage, keeping stuff both
out of multiple cellars and from multiple distortion
points, but I view the final attenuator as an added
safety point.
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Scott Dorsey Scott Dorsey is offline
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Default Why No Gain Control on Adcom Amp?

Matt Faunce wrote:
OK. I was wrong about the hiss (or rather a sh sound) being there without
an input source. Without a source it is dead quiet. The source of the hiss
was my computer, and, I did have to have my ear within 12" of the tweeter
to notice it. I hooked my microphones-micpre-reverb
unit-recorder-Adcom-speakers, and it was much much quieter.


Of course.
And the level control on the amplifier, if it did have one, would be on
the _input_ side before the power amp stage. This would allow you to run
your sound card hotter and not notice so much how noisy it is.

As I said earlier, a passive attenuator box like that $65 Behringer thing
will do the exact same thing, if you're stuck having to do that.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Default Why No Gain Control on Adcom Amp?

Scott Dorsey wrote: "And the level control on the amplifier, if it did have one, would be on
the _input_ side before the power amp stage."


Just a basic tech question Scott: When is the knob on
an amp an atttenuator, and when is it a volume control?
What you describe, above, sounds like a proper
attenuator, but I could be wrong. !
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On Tuesday, June 5, 2018 at 6:48:08 PM UTC-5, wrote:
Scott Dorsey wrote: "And the level control on the amplifier, if it did have one, would be on
the _input_ side before the power amp stage."


Just a basic tech question Scott: When is the knob on
an amp an atttenuator, and when is it a volume control?
What you describe, above, sounds like a proper
attenuator, but I could be wrong. !


Hey Thekma, a volume control *is* an attenuator -- a variable one.

Peace,
Paul Stamler


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Default Why No Gain Control on Adcom Amp?

wrote:


Scott Dorsey wrote: "And the level control on the amplifier,
if it did have one, would be on the _input_ side before the power amp stage."


Just a basic tech question Scott: When is the knob on
an amp an atttenuator, and when is it a volume control?
What you describe, above, sounds like a proper
attenuator, but I could be wrong. !



** It mostly a matter of common usage.

On radios, TV sets, domestic hi-fi and guitar amps the level controls are labelled "Volume".

On power amps meant for pro audio, the word "Attenuator" is more often seen.

Mic preamps ( fitted to consoles or elsewhere) are a special case and the word "gain" is more appropriate.


..... Phil

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Default Why No Gain Control on Adcom Amp?

PStamler, Phil:

I guess the question to ask is, on Uncle Joe's
1970 color Philco, is the volume located in the
input stage, or the power amp side?

Same for the volume on a stereo receiver in
the home.
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Default Why No Gain Control on Adcom Amp?

geoff wrote:



Quad 405, home-built mega-Quad 405,



** A Kiwi service tech working in Sydney ( Brain someone ) told me how popular it was to build your own Quad 405 if you lived in NZ. Good copies of the original PCBs were available and clones of metalwork & other parts too. This was in the early/mid 80s when buying a genuine example was impossible or crazy expensive.

Like to know some details of you "mega-Quad 405".



.... Phil

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Default Why No Gain Control on Adcom Amp?

On Tuesday, June 5, 2018 at 9:21:14 PM UTC-5, wrote:
PStamler, Phil:

I guess the question to ask is, on Uncle Joe's
1970 color Philco, is the volume located in the
input stage, or the power amp side?

Same for the volume on a stereo receiver in
the home.


On Uncle Joe's Philco, the volume is located between the input stage (which, to simplify, extracts the audio and video signals from the mixture coming into the antenna terminals) and the power amplifier.

On home stereo receivers there may be a line-input amplifier which receives and maybe processes the audio signal (tone controls and the like); the volume control is usually located between this input Aamplifier and the power amplifier. Other stereo receivers don't have an input amplifier; the line input feeds directly into the volume and balance controls, and the signal then goes to the power amplifier. There are variations; for example, the tone controls may come after the volume control. But in all cases the volume control is upstream from the power amplifier.

Thekma you may be confusing all this with "power soaks", which are high-powered attenuators placed between the power amplifiers of guitar amps and their speakers, allowing players to crank the amp and overload it while maintaining a safe-and-sane volume level. That's useful in recording studios, and it's sometimes used in playing smaller clubs, so the lead guitarist can get a nice dirty sound without flattening the customers against the back wall. I've never seen power soaks used outside of guitar-amp applications, though; certainly your Adcom amp doesn't use one. In the Adcom, on the models with a volume control, the signal feeds directly into the volume control, and then goes to the power amp. That's true of most professional power amps, although some (as you've noted) don't have any level control. Those are usually used either in conjunction with a preamplifier/control center, which contains its own volume control, or an electronic crossover, which also contains volume controls for the different frequency bands.

Peace,
Paul


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Default Why No Gain Control on Adcom Amp?

On 6/06/2018 1:47 PM, Phil Allison wrote:
wrote:


Scott Dorsey wrote: "And the level control on the amplifier,
if it did have one, would be on the _input_ side before the power amp stage."


Just a basic tech question Scott: When is the knob on
an amp an atttenuator, and when is it a volume control?
What you describe, above, sounds like a proper
attenuator, but I could be wrong. !



** It mostly a matter of common usage.

On radios, TV sets, domestic hi-fi and guitar amps the level controls are labelled "Volume".

On power amps meant for pro audio, the word "Attenuator" is more often seen.


More often 'Level' in my experience. I find "Attenuator' is more often
the label on a switch, often on the rear.


Mic preamps ( fitted to consoles or elsewhere) are a special case and the word "gain" is more appropriate.



'Gain' more often relates to the gain of the input stage (sometimes is a
pot in a feedback loop which makes it very prone to noise when
adjusting, or failure) and not an attenuator/level/volume control in the
usual sense.

Similar paradigm in guitar amps, where gain boosts the input signal, and
Volume attenuates the signal between the pre and power amp sections.

The output Level/Volume, which usually comes after the whole channel
strip, is a variable potentiometer, with the 'low' side shunting the
slider right down to 'ground'. This is also the usual Level arrangement
on the input to a such-equipped power amp.

geoff
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Default Why No Gain Control on Adcom Amp?

On 6/06/2018 3:47 PM, PStamler wrote:


Thekma you may be confusing all this with "power soaks", which are high-powered attenuators placed between the power amplifiers of guitar amps and their speakers, allowing players to crank the amp and overload it while maintaining a safe-and-sane volume level.


Also useful for testing amps. Just re-built mine, 2400W worth of Ohmite
4 Ohm 300W resistors !

geoff
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Default Why No Gain Control on Adcom Amp?

On 6/06/2018 2:46 PM, Phil Allison wrote:
geoff wrote:



Quad 405, home-built mega-Quad 405,



** A Kiwi service tech working in Sydney ( Brain someone ) told me how popular it was to build your own Quad 405 if you lived in NZ. Good copies of the original PCBs were available and clones of metalwork & other parts too. This was in the early/mid 80s when buying a genuine example was impossible or crazy expensive.



Started (not by me) at NZ Railways where I was a comms tech . The main
enthusiast even went to the extent of getting heatsinks cast !



Later on NZ Broadcasting techs also did something similar (not the
heatsinks though).



Like to know some details of you "mega-Quad 405".


Twin c-core transformers, larger reservoir caps, MJ15003 outputs,
TIP42(?)C drivers and 55VDC rails. Better electro's and poplyprop caps
throughout where appropriate.


geoff
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Default Why No Gain Control on Adcom Amp?

geoff wrote:

Phil Allison wrote:



Quad 405, home-built mega-Quad 405,



** A Kiwi service tech working in Sydney ( Brain someone ) told me how popular it was to build your own Quad 405 if you lived in NZ. Good copies of the original PCBs were available and clones of metalwork & other parts too. This was in the early/mid 80s when buying a genuine example was impossible or crazy expensive.



Started (not by me) at NZ Railways where I was a comms tech . The main
enthusiast even went to the extent of getting heatsinks cast !


** That is very much like what Brian was telling me.



Like to know some details of you "mega-Quad 405".


Twin c-core transformers, larger reservoir caps, MJ15003 outputs,
TIP42(?)C drivers and 55VDC rails. Better electro's and poplyprop caps
throughout where appropriate.


** So about 150W @ 8 ohms per channel ?


The Quad 405 must be the most cloned, modified and re-engineered home hi-fi amp ever. I recapped one for a friend a few years ago, new main and PCB electros, ( all the Roederstein ones had gone high ESR ) plus a few other bits that looked ratty. Fitted gold RCA inputs and binding posts for outputs.


..... Phil


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Default Why No Gain Control on Adcom Amp?

On 6/06/2018 6:34 PM, Phil Allison wrote:
geoff wrote:

Phil Allison wrote:



Quad 405, home-built mega-Quad 405,



** A Kiwi service tech working in Sydney ( Brain someone ) told me how popular it was to build your own Quad 405 if you lived in NZ. Good copies of the original PCBs were available and clones of metalwork & other parts too. This was in the early/mid 80s when buying a genuine example was impossible or crazy expensive.



Started (not by me) at NZ Railways where I was a comms tech . The main
enthusiast even went to the extent of getting heatsinks cast !


** That is very much like what Brian was telling me.



Like to know some details of you "mega-Quad 405".


Twin c-core transformers, larger reservoir caps, MJ15003 outputs,
TIP42(?)C drivers and 55VDC rails. Better electro's and poplyprop caps
throughout where appropriate.


** So about 150W @ 8 ohms per channel ?


The Quad 405 must be the most cloned, modified and re-engineered home hi-fi amp ever. I recapped one for a friend a few years ago, new main and PCB electros, ( all the Roederstein ones had gone high ESR ) plus a few other bits that looked ratty. Fitted gold RCA inputs and binding posts for outputs.


.... Phil


I wonder if the few ZTX304 and 504 I have lying around somewhere are
worth mega-bucks on Ebay ?

My mega-wquad was in a 4U rack case and bought heatsinks on the front.
All the best connectors etc too. And heavy solid rod ground wiring, and
heavy stranded pos/neg/output wiring.

Quite often the original phenolic pcbs get baked by the 560R 2(?)W
resistors.

geoff
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Default Why No Gain Control on Adcom Amp?

Theckmah burbled:
I know how to gain stage!
d'uuuh ... what's the difference between a volume control and an
attenuator?


Priceless RDF, li'l buddy!

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Thank you to all of the adult, mature HUMANS (Rivers, PStamler, geoff,
Allison, Dorsey) who replied to and informed me regarding my
question about attenuators, in a civil fashion! Much appreciated.
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Theckhhmah, Master Gain Stager, blurted:
I'm an expert gain stager.
When I plug a salvaged CD playing into a broken boom box at my next pro
sound gig, how do I set the headphone volume?


Thanks for pretending you understand gain staging, li'l buddy. This
newsgroup needs more humour!

HTH, DFR. SDKHKSN! DF.

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PStamler wrote:
On Tuesday, June 5, 2018 at 6:48:08 PM UTC-5, wrote:
Scott Dorsey wrote: "And the level control on the amplifier, if it did have one, would be on
the _input_ side before the power amp stage."


Just a basic tech question Scott: When is the knob on
an amp an atttenuator, and when is it a volume control?
What you describe, above, sounds like a proper
attenuator, but I could be wrong. !


Hey Thekma, a volume control *is* an attenuator -- a variable one.


There are two ways you can change level: you can attenuate a signal, or
you can have an amplifier with adjustable gain (putting an attenuator in
the amplifier feedback loop).

For the most part, you'll find the first approach in any place where
there's a risk of overloading anything, or when you need to be able to
turn the level down to zero (like the faders on a console). Amp controls\
are like this.

You'll find the second approach when input overload isn't as big a worry
and where you are very concerned about S/N and want to keep the noise of
the amp stage down as low as possible (like the trims on a console).
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."


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Default Why No Gain Control on Adcom Amp?

wrote:
I guess the question to ask is, on Uncle Joe's
1970 color Philco, is the volume located in the
input stage, or the power amp side?


It's an attenuator between the FM discriminator tube and the power amp tube.

Same for the volume on a stereo receiver in
the home.


It's between the line preamp stage and the power amp stage.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Theckhhhmah gibbered ...

My question concerns where to set the volume
coming out of the boombox before setting input
gain on the board. Quarter-way? Half- way up?


And then he made the ridiculous claim ...

I also know how to gain stage


QED, DF.
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Default Why No Gain Control on Adcom Amp?

Scott Dorsey wrote:

Matt Faunce wrote:
Why is there no gain control on the Adcom GFA-535?


Because you didn't order it with that option. If you want the level
control, you want the GFA-535L.


I have the GFA-535L. For me the level control wasn't convenient enough
to be worth it. The left and right channels are controlled separately.
Trying to match them every time you change the volume is a hassle. So
is using a dime or a screwdriver to turn them.

A lot of people make their own volume controls, but I don't have any
experience with that kind of thing, so I ended up getting one of these
passive attenuators:

https://www.tisburyaudio.co.uk/mini-...e-preamplifier

Lately I came across this volume control from Nelson Pass that is
buffered but has no gain. Sounds like a good idea, but I haven't had
the opportunity to try one:

http://www.firs****t.com/b1.html

https://www.passdiy.com/project/prea...-buffer-preamp

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On 8/17/2018 1:29 PM, Tatonik wrote:
I have the GFA-535L. For me the level control wasn't convenient enough
to be worth it. The left and right channels are controlled separately.


A lot of people make their own volume controls, but I don't have any
experience with that kind of thing, so I ended up getting one of these
passive attenuators:


https://www.tisburyaudio.co.uk/mini-...e-preamplifier


That's pretty classy for a "pot-in-a-box" but the fact that they use
precision resistors for the gain steps means that they might have taken
care that each step of both channels has equal attenuation. Even a good
quality dual pot can have a variable difference of as much as 1 dB of
attenuation between channels over its range.

Lately I came across this volume control from Nelson Pass that is
buffered but has no gain. Sounds like a good idea, but I haven't had
the opportunity to try one


Those Nelson Pass designs have separate level controls for the left and
right channels, something that you decided against when you bought the
amplifier without them. You really don't need the buffer unless you're
feeding it from a tube preamp with a high impedance output.

:


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