Amp Camp Amp - ACA

[6L6]

Naah... If your interfaces are smooth and have some kind of thermal compound, you are as good as you can get. The temp is fine.

[bcmbob]

[Congo5]

First Thanks to all involved with this project..
This sounds really nice...
Its difficult to find projects with enough documentation.
The guides and pictures really help.

I used a Hammond Manufacturing 1455ZT2201 case..
and from LoudThud's recommendation, left off R1 and R3 to cut the current in half,
lower heat and power requirements. As its for headphones. I did use sockets so the
resistors can be added later..

I need to add cooling vents as it is a sealed case, and Plan to put a 80W CPU cooler on top.

internal case temp is 101F as of now...

[Congo5]

I found it needed a bit of heatsink.

[jongneng]

Has anyone ever seen ACA turbo version with parellel output mosfet?
irfp240 x 4 per channel. More than 10 watt/channel

[Loudthud]

Originally Posted by jongneng

Has anyone ever seen ACA turbo version with parellel output mosfet?
irfp240 x 4 per channel. More than 10 watt/channel

It's very hard to drive more than one IRFP240 with a single JFET (Q4). The rise in distortion at high frequencies gets bad pretty fast, you start to see visible distortion at 1KHz, especially as you try to swing near the rail. I've had some success driving a bigger Q1 with a PNP bipolar emitter follower, but you rapidly get away from the simplicity of the ACA. A more complex circuit creates more complex distortion. 10 Watts is doable with a single IRFP240, a 30V power supply and a big heat sink(s). Another option is to use more but smaller Q1s just to spread the heat. I'm liking the sound of IRF520s with the feedback disconnected in the stock circuit.

Note that changes to Q1 or the resistors R1-R4 changes the open loop gain. To maintain the distortion character of the amp, changes to the amount of feedback are needed.

I recommend you look at the PLH article: http://www.passdiy.com/pdf/PLH_amplifier.pdf

[jongneng]

Originally Posted by Loudthud

It's very hard to drive more than one IRFP240 with a single JFET (Q4). The rise in distortion at high frequencies gets bad pretty fast, you start to see visible distortion at 1KHz, especially as you try to swing near the rail. I've had some success driving a bigger Q1 with a PNP bipolar emitter follower, but you rapidly get away from the simplicity of the ACA. A more complex circuit creates more complex distortion. 10 Watts is doable with a single IRFP240, a 30V power supply and a big heat sink(s). Another option is to use more but smaller Q1s just to spread the heat. I'm liking the sound of IRF520s with the feedback disconnected in the stock circuit.

Note that changes to Q1 or the resistors R1-R4 changes the open loop gain. To maintain the distortion character of the amp, changes to the amount of feedback are needed.

I recommend you look at the PLH article: http://www.passdiy.com/pdf/PLH_amplifier.pdf

Thanks Loudthud. But they do and they say "excellent sound"
BuRaPha Camp turbo

[DHT2009]

Originally Posted by jongneng

Thanks Loudthud. But they do and they say "excellent sound"
BuRaPha Camp turbo

You have to do it or not.

[jcastellano]

Hi,
I have some questions and I hope someone of you can answer them...

I have built the ACA and I have found the sound a little "laid back". The type of sound that seems to come from the back of the speakers. I have tried with two different speakers, one Rega RS1 and one Monitor Audio Silver RX1. The sound was better with the Monitor Audio speakers (89dB) but the sound was similar to the Regas, as I said before, laid back. This sound is there from the very beginning, with no burning or run in.

For simplicity I am using only one SMPS block for both channels, could this be the reason for this sound?

Do I have to run it for several hours before making up any judgement over the sound of it?

Also I found a little fuzzy to set the 10.00V bias. The pot did not allowed for an easy set, any kind of movement of the pot and the values went from one side to the other like a pendulous. I did my best to set the bias at 10.03 more or less each channel but it was really difficult.

Did I make an error?

Best Regards,

Jorge

[nicoch58]

laid back is positive for my taste