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So got my darling amp up and running and am extremely happy with it. That was last night and I didn't have an opportunity to crank it up.

Today I turned it up and found that it sounds great and very clean all the way up to about 1/2 volume, then turning it almost to 3/4 volume the distortion amount is very high. Sounds like little of tweeter more midrange distortion. It's very pronounce that I have to turn it down immediately from fear that it may damage my speakers. Even up to the point right before distortion it's still pretty loud, but not loud enough that I have to yell to speak to anyone but I can still talk.

I have hooked up my realistic mach ones, and bose 601 speakers to it. So I don't think that it's the speaker's unable to handle the watts.

Any thoughts, or is this normal?

I have a 100k dual gang volume pot connected from Radioshack.

my parts list :

Hammond 269EX Power Transformer
Edcor XSE15-8-5K Outputs
Hammond 156R Choke

tubes are : 2 x 1626
1 x 12sl7gt

rest of parts are clementine board with the standard issue of parts from Shannon.


thanks

-Charles

Hi Charles ...

I think what is happening is that the amplifier is running out of
power, and sounds bad. The speakers you are using are very
inefficient, meaning they need way more power than the little
Darling can deliver. The best speakers to use with a small amp
are those with high sensitivity, ie: 92 db or more.

A pair of bookshelf Klipsch would be great.

Check the sensitivity ratings, I think you'll find yours to be in
the low 80s ...

Glad you got it working ... as soon as I saw your new clue about
hearing music from the transformers, I knew what was wrong.
Ty picked it up before I saw it.

... tom

Thanks for the response,

It's crazy but at this moment I only have large speakers, haha I'll keep you posted when I get an opportunity to hook some smaller ones up.

Might have to borrow from someone.

Oh and I'm sorry but I think I owe you something : D

-Charles

Size is not really the indicator. As Tom said check the sensitivity, higher the better.

Well I'm in Seattle and i have a pair of speakers here that have more sensitivity.

They're klipsch synergy b-3 bookshelf speakers. I believe sensitivity is rated at 93db. And I'm stiill having the same issues. Good volume and sound about little over half. Then from there on up it gets distorted. I'm thinking this amp would be great for guitar but i really want this to be clean. Could it be my tubes having an early break up point.

A couple of things are be happening here:

As configured in the "Darling" circuit, the 12SL7 driver stage has a voltage gain of 43. The plate current is around 1.1 mA, and the voltage across the cathode resistor is 1.1 vdc. So, any input signal above 1.1 volts + or - peak will drive the stage into saturation, and distortion will result.

The 1626s have a plate current between 25 and 27 mA. Their 1K cathode resistors will have a DC voltage of 25 to 27 VDC across them, so any grid drive voltage greater than +/- 25 - 27 V peak, will drive them into saturation, and cause distortion.

Since the driver stage has a voltage gain of 43, then the maximum input signal to its grid, should be no greater than between 0.58 and 0.63 volts +/- peak, in order to limit its signal output to the 1626s' grids to 25-27 peak volts maximum, as anything greater than that will result in distortion.

So, Anything greater than 0.58 and 0.63 volts peak drive signal to the 12SL7 grids will cause the distortion to rapidly appear.

With only 3/4 watts rms maximul power output, even 93 dB speakers aren't going to rattle the windows and shake the floors Maybe with some very efficient 103 db or greater, speakers, but then those tend to be large and very expensive

Just think of it in automotive terms: The tiny "Smart Car" isn't capable of doing zero to sixty in two seconds. Maybe, in two minutes, would be more likely. A Lamborgini can do 0 to 60 in 2 seconds, and perhaps even less time.

The 750 mW Darling is like the "Smart Car", and a hefty 100WPC amp is more like the Lambo.

Every +10 dB of power efficiency is effectively a tenfold increase (or a decrease for -10 dB) in percieved SPL (sound pressure level),

With typical small bookshelf speakers, with 83 dB efficiency, they would sound like 75 mW. into 93 dB efficient speakers Pretty weak....

With 103 dB efficient speakers, then they would sound like 7.5 watts into 93 dB speakers. Or, 75 watts into 83 dB speakers.

Your signal source probably has a line level output of +/- 2 volts which would drive the amp into distortion at about "halfway up" volume control settings.

One simple fix for this would be to connect a 200-220K resistor in series between the RCA input jack center to the "hot" end of the volume control, on each channel. THis would effectively reduce the maximum input gain by 10 dB, or 0.316 of the device's output signal.

I've used this -10 dB padding approach with a couple of overly "hot" line stages, and it worked very well.

Due to the tube's Miller Capacitance, this could very slightly affect the highest octave (10K-20KHz) frequency response, but it should not be readily apparent.

HTH

/ed B in NC

I just want to make sure that my amp is running at full efficiency, and some people have said that they can turn it all the way up to ear piercing volumes. My volume isn't ear piercing. And i wanted to know if everyone else is having distortion past the halfway volume mark. My volume is like loud enough, but i don't have to raise my voice to talk to someone.

Couple other thoughts.
Clean all tube pins, light sandpaper, spray with deoxit and wiggle back wet into socket. I did this to a pre amp I had for a friend and fixed several problems he was having. Microphonics and other distortion.
Bi pass pre amp if using one and try Ipod or computer direct to amp. Be sure the source has volume control.

Well I'll try that thanks for the input, although my amp isn't very old. I just built it not too long ago so I'm not sure if deoxit will do anything. I'll still give it a shot, and when I get the chance I'll try a source with volume control and keep you guys posted.

Thanks again for the input guys, much appreciated.

I could make my 98dB sensitive speakers distort with louder music with the Darling, so you are just running out of power - no mystery here. Only with my uber efficient Klipsch can I get distortion free, rock the house volumes with 3/4W.

Shannon