Fisher SA-300b - best way to control volume?

[chapps]

Need some tubular advice......

I have need to be able to control the volume of a Fisher SA-300b tube amp. Of course, there is no volume control, so I am thinking of buying a passive volume control unit.

1, Is a passive control or an active controller better?
2. Will the passive controller attenuate the signal - will I reach 100% of the original SA-300 volume when the volume unit is full opened?
3. Any suggestions for any such commercial unit?

Many thanks for any help !

EDIT: If you have a volume controller to sell, pm me....

 

[heyraz]

The SA-300B has input sensitivity potentiometers (volume controls) at the inputs. They are "passive" volume controls.
What is the rest of your system?
Do you use a preamp?

Is a passive control or an active controller better?

A passive control is simply potentiometer without any amplification circuitry in the path. A stepped control with precision matched resistors at each step would be the most accurate.

An example of an active control would be a preamp with gain.

 

[primosounds]

Passive or Active VC depends on your situation. One of the considerations is the distance between your source and the amp. For longer distances, greater than about 6 feet (this also depends on your IC). The loss of signal through the interconnect can be an issue. So, having an Active preamp can give you better sound. Another issue is the strength of your signal from source and the input sensitivity of the SA 300. I don't have enough info from your post to know whether there will be an issue. Ideally, you want enough input signal to drive the amp to full power.

 

[FlaCharlie]

I have a Fisher SA-16 which has the same type of "level adjustment" pots on the inputs. If you're using a modern line level source they should do fine.

They are the same as having a passive VC so turning them up all the way and then adding another passive VC doesn't change anything really. Most power amps don't need gain if your input signal is strong enough. I use a CD player and iTunes from my computer with mine.

A preamp might add convenience, however, such as the ability to switch between multiple inputs and, in some cases, they might have tone controls. I found a simple switch box at a thrift store that lets me choose different sources.

 

[triode17]

If its just for the front panel, how about an ALPS "Blue Velvet" stereo pot. They track very well and all you need is to drill one hole.

 

[chapps]

The SA-300B has input sensitivity potentiometers (volume controls) at the inputs. They are "passive" volume controls.
What is the rest of your system?
Do you use a preamp?


A passive control is simply potentiometer without any amplification circuitry in the path. A stepped control with precision matched resistors at each step would be the most accurate.

An example of an active control would be a preamp with gain.

Sorry for the late response. I never got notifications and forgot I have this question up!!!

Thank you for the response.

I have a preamp with pre-outs, which I know can control the volume to the Fisher SA300B. But in some testing scenarios I am using vintage tube amps as phono preamps and the amps do not have a pre-outs. The only way is the Tape Out, in which case it gain bypasses the volume/tone circuitry. Its this last scenario I am trying to sole where there is no pre-out access.

I notice the two real small knobs right at each of the input connectors.

1. First, the "inputs" have two connectors one marked 'in' and another marked 'out' . I am using the one marked 'in' to send signal into the SA300B IS this correct?
2. So the output from the SA300B is direct to speakers. The two small pots near each connector - are these going to control the volume going to the speakers?
3. With ref to point 1, does it then matter which connector i use.

Thanks again for your comments.

 

[heyraz]

I notice the two real small knobs right at each of the input connectors.

1. First, the "inputs" have two connectors one marked 'in' and another marked 'out' . I am using the one marked 'in' to send signal into the SA300B IS this correct?

The two inputs are "Filter In" and "Filter Out".
"Filter In" has an internal capacitor network to filter ultrasonic frequencies from entering the SA300.
"Filter Out" has no such filter network.

The two small pots near each connector - are these going to control the volume going to the speakers?

They will...but they're not " output volume controls". They are "input sensitivity controls". They control how much signal enters the amp from the preamp.

does it then matter which connector i use.

According to the sales brochure, the filtered input is to protect electrostatic speakers from ultrasonic frequencies. Both inputs pass through the same input sensitivity potentiometer.
I can't hear a difference on my conventional speakers when using either input.

 

[primosounds]

Sorry for the late response. I never got notifications and forgot I have this question up!!!

Thank you for the response.

I have a preamp with pre-outs, which I know can control the volume to the Fisher SA300B. But in some testing scenarios I am using vintage tube amps as phono preamps and the amps do not have a pre-outs. The only way is the Tape Out, in which case it gain bypasses the volume/tone circuitry. Its this last scenario I am trying to sole where there is no pre-out access.

I notice the two real small knobs right at each of the input connectors.

1. First, the "inputs" have two connectors one marked 'in' and another marked 'out' . I am using the one marked 'in' to send signal into the SA300B IS this correct?
2. So the output from the SA300B is direct to speakers. The two small pots near each connector - are these going to control the volume going to the speakers?
3. With ref to point 1, does it then matter which connector i use.

Thanks again for your comments.

If you loan out your equipment, it is good to have DC protection on the input circuit to prevent a device with DC on the output hooking up to your amp and causing a large signal which can fry your speakers as well as your amp. If your amp is only at home and you are very familiar with all the ancillary equipment then having the cap input is not necessary and can cause some audible artifacts if it is of poor quality.

 

[heyraz]

If you loan out your equipment, it is good to have DC protection on the input circuit to prevent a device with DC on the output hooking up to your amp and causing a large signal which can fry your speakers as well as your amp. If your amp is only at home and you are very familiar with all the ancillary equipment then having the cap input is not necessary and can cause some audible artifacts if it is of poor quality.

Sound advice but I don't think pertinent for the SA300.
The input grid is protected by a .047uf blocking capacitor from both the filtered and unfiltered input signals.
My bad on the filtered input...it's not to protect subsonic frequencies, it's to protect electrostatic speakers from ultrasonic frequencies.

(Corrected previous post)

 

[dcgillespie]

Depending on the version you have, both of Heyraz's response's were technically correct. In the original SA-300, the input filter network attenuated both sub and super sonic frequencies -- again, with the filter's use intended for service with electrostatic speakers, which were the hot new ticket of the day. Fisher also trumpeted the stability of the SA-300 when operating into highly capacitive loads in their marketing literature, which electrostatic speakers represent. It is clear then that they were going after the potential electrostatic buyer. The sub-sonic filter was installed to prevent electrostatic speakers from receiving any significant subsonic garbage as they don't handle that kind of information well, while the supersonic filter was actually installed to protect the amplifier itself from trying to dump any significant supersonic power into electrostatic speakers, which represent a near dead short to the amplifier at such frequencies.

With the release of the 300B, the sub-sonic portion of the filter was removed, leaving only the amplifier protecting supersonic filter installed when using the Filter IN jack. Unknown what motivated this move, but likely it was a combination of improvements made to electrostatic speaker panels combined with low sales of such units that provided the motivation. Adding a Center Channel output rounded out the differences between the original SA-300, and SA-300B offerings.

Dave

 

[chapps]

The two inputs are "Filter In" and "Filter Out".
"Filter In" has an internal capacitor network to filter ultrasonic frequencies from entering the SA300.
"Filter Out" has no such filter network.


They will...but they're not " output volume controls". They are "input sensitivity controls". They control how much signal enters the amp from the preamp.


According to the sales brochure, the filtered input is to protect electrostatic speakers from ultrasonic frequencies. Both inputs pass through the same input sensitivity potentiometer.
I can't hear a difference on my conventional speakers when using either input.

If you loan out your equipment, it is good to have DC protection on the input circuit to prevent a device with DC on the output hooking up to your amp and causing a large signal which can fry your speakers as well as your amp. If your amp is only at home and you are very familiar with all the ancillary equipment then having the cap input is not necessary and can cause some audible artifacts if it is of poor quality.

Depending on the version you have, both of Heyraz's response's were technically correct. In the original SA-300, the input filter network attenuated both sub and super sonic frequencies -- again, with the filter's use intended for service with electrostatic speakers, which were the hot new ticket of the day. Fisher also trumpeted the stability of the SA-300 when operating into highly capacitive loads in their marketing literature, which electrostatic speakers represent. It is clear then that they were going after the potential electrostatic buyer. The sub-sonic filter was installed to prevent electrostatic speakers from receiving any significant subsonic garbage as they don't handle that kind of information well, while the supersonic filter was actually installed to protect the amplifier itself from trying to dump any significant supersonic power into electrostatic speakers, which represent a near dead short to the amplifier at such frequencies.

With the release of the 300B, the sub-sonic portion of the filter was removed, leaving only the amplifier protecting supersonic filter installed when using the Filter IN jack. Unknown what motivated this move, but likely it was a combination of improvements made to electrostatic speaker panels combined with low sales of such units that provided the motivation. Adding a Center Channel output rounded out the differences between the original SA-300, and SA-300B offerings.

Dave

Thank you so much for the input to you all.

The control of input sensitivity is I now realize a great feature, once one realizes what it's doing. I was wondering why my Yamaha C4 sounded so strongly more "amplified" compared to other preamps (Kenwood. Apt HOLMAN) and now it makes sense that the input on the Fisher can be adjusted to bring the other preamps "up" in amplification.. , if that's a technical phrase!

 

[chapps]

One more queston: What is the easiest way to adjust the input sensitivity? Using my ears is not very technical, right. Can I use a simple voltmeter?