Increasing the gain on KT88 XL

[LincolnG]

Hello, just finished building a lovely KT88 XL with a few special mods. With standard line inputs, like CD, PS4 this sounds great. However, when using streaming, like Disney+, the volume is very quiet and the dial has to be turned up pretty much all the way. Does anyone here have any experience with changing the gain, and how would it best be done, without impacting the quality overly or making the amp unstable. EG, reducing the feedback, input resistor. Love to hear your opinions!!

[Dave999]

Ok so CD and PS4 i will assume have a standard line out . i.e somewhere about 2 volt peak to peak signal.

if the Amp is quiet when a device that processes a stream is plugged into one of its line inputs, my first port of call would be to check that the output of the device is a line level output.

is this output controlled by a volume control, Physical knob/slider or in software on the streaming device?

if volume control has an impact i'd set volume on the streaming device somewhere in the 80-90% range and try again. this will be too loud if you plug headphones into it instead. but should provide a reasonable input signal to your amp...

although it depends what the output was designed for i guess. most will be ok, but you might have one designed for specific headphones with an odd impedance

i don't know the amp in question but if its a power amp with multiple line level inputs to make it semi integrated the input sockets connect to a switch, potentially followed by a volume control. then on to the power amp i.e there is only 1 input to the power amp. so changing it for 1 source would change it for all available on the back regardless of Input switch position, unless you divert 1 set of line level input sockets off to a separate pre amp and then back into the input switching circuit

would be easier in this case not to change the power amp at all and use a pre amp between the streamer and the power amp.

keep in mind as well. your stream or digital files may have been created with reduced volume.

if you are using a PC to process the stream the analogue outputs can be at low volume even with the volume turned up fully at the speaker/Volume icon in the system tray. There are a range of settings which limit its volume range in the Mixer settings and properties, including the choices you make on speaker size and/or headphone.

sorry don't know anything about Macs but similar limiters used to be implemented in ipods.

suggest the rest of your set-up is key here rather than changing the amp, it is or will be a standard amp with standard inputs.... designed to work with most things. It strikes me that the device doing the streaming is the oddity in this situation.

what were the special mods?
and you will have to explain to me what disney+ is i thought it was a TV channel. My HUMAX TV box drives my sony receiver best at full volume on the Humax box, and sensible listening volume on the sony amp output HDMI or analogue...


Dave

[Richard]

Yes, sensitivity is 440mV for full output. I've owned this amp and didn't find it any different to any other line sensitive power amps - fine for use with CD and phono line amps etc - giving full output and just needing an attenuator to control level.

So, fine for CD as you found. CD is quoted as 2V but that is not at full recording level, 30% iirc (though newer CD recordings sound louder and I think they are using more of the headroom these days).

That means your other sources are less than CD output level so they need either their volume turning up or a pre-amp. I'm guessing they are simply turned down.

Think of this; some CD players have a volume control but that is actually an attenuator and their full vol setting is the same as fixed level CD players. Similar applies to my Squeezebox touch - it has remote digital volume but that doesn't go higher than line-level and if you don't use the remote then you set it at full output and control it on the amplifier vol control.

So, unlike power amps these sources may need setting to full vol by default for control by an external amp if not using their inbuilt vol control.

[Greg.]

Just a thought. As you say this is a new build. Have you checked your streaming source through the same input RCA’s that work ok with your CDP/PS4? If it works ok this way, you could have a fault such as a dry joints on your other signal input paths.

[bob orbell]

I also agree with all that has been replied to your post, a power amplifier with around .5 volt input for max power output is very common, as yours is, it is your other contraptions that need addressing. Bob