IRF640 substitute
Have a bunch of IRF640's as well as tube of 240's. Have you tried the640's??
IRF640s work just like the IRFP240s. The die might run a little hotter but the distortion curve matches Nelson's almost exactly. They won't fit the PCB's but I built all my ACAs on proto board reinforced with Keystone eyelets.
irf640 and the ACCA camper
Good news! Heat is not a problem as my heatsinks are more than adequate. The mosfets will be mounted separetly with short pigtail leads. That will allow me to switch to another 5w circuit also under construction.
Good news! Heat is not a problem as my heatsinks are more than adequate. The mosfets will be mounted separetly with short pigtail leads. That will allow me to switch to another 5w circuit also under construction.
I'm planning to build an ACA in a big aluminum chassis.
Is it better to have one dual transformer in a chassis or two separate transformer in one chassis?
is there any advantage or purpose of using the laptop adapter instead of transformer?
Is it better to have one dual transformer in a chassis or two separate transformer in one chassis?
is there any advantage or purpose of using the laptop adapter instead of transformer?
Pass DIY Addict
Joined 2000
Paid Member
I haven't directly compared a laptop PS to the more "traditional" transformer and caps, but the laptop PS is very clean: DEAD quiet and has virtually NO ripple at all. Plus, it is already built and allows for a smaller chassis.
Amp Camp Kit, Chassis, or Amp wanted
I would like to buy an Amp Camp kit, Chassis or completed Amps. Anyone got something for sale as the Store has not much for sale.
I would like to buy an Amp Camp kit, Chassis or completed Amps. Anyone got something for sale as the Store has not much for sale.
So we several observations plus and minus, we have Pappa's words (Get over it – it works fine) and we have the testing that showed "the output noise with the switching supply comes in around 100 uV." I wish we could settle this debate once and for all as it seems to be the number one mod for ACAs.
For me I think buying some more acoustic panels for my room would be a better improvement than changing out the laptop PS's, but I would love to see the above comparison just to put this one to bed.
Love my ACA's by the way.
Confirm what Eric says... very quiet in my rig, no urge to replace the laptop bricks with a power supply.
Great source for heat sinks if one wants to build rather than buy. Looks like toobhed may have used one of their products.
Presence control
How can I implement presence control? - shunt high frequencies from feedback to ground so at the output high frequencies will be amplified.
I have tried implementation as in the schematics, but it works exactly opposite way - cutting high frequencies instead boosting them.
How can I implement presence control? - shunt high frequencies from feedback to ground so at the output high frequencies will be amplified.
I have tried implementation as in the schematics, but it works exactly opposite way - cutting high frequencies instead boosting them.
Attachments
I used this chassis... worked well.
Enclosure RE2109H 211x90x257 - Boards | Kits | Components | Modules | Tools
If you must have a presence control, try the schematic attached below. You will probably need to increase the presence cap to 220nF or 470nF. Be aware that the input has no protection and driving the power amp too hard can damage the JFET and/or the lower MOSFET. For more fun, just disconnect the 68K and run with no feedback. Change the electrolytics on the input, you can use much smaller film caps. They will recover faster when the amp is overdriven.
Attachments
Last edited:
BS170
Has anybody tried putting in BS170 for Q4? Seems it might work.
Don't know if there is an advantage of putting this in instead of 2SK170, but BS170 is widely available for a few cents and it sounds more mellow (from memory from earlier experiments).
Sometimes more hiss with BS170 in my experience.
Has anybody tried putting in BS170 for Q4? Seems it might work.
Don't know if there is an advantage of putting this in instead of 2SK170, but BS170 is widely available for a few cents and it sounds more mellow (from memory from earlier experiments).
Sometimes more hiss with BS170 in my experience.
works allright bs170
For the sake of knowledge, I have put in BS170 for Q4. The pot has to be adjusted just the normal way. At the gate of Q4 now appears around +6,7 Volts (to get around 4 - 4.5 Volt at the gate of Q1).
The sound is okay to me, can't tell the difference with the 2SK170 yet (around the same quality I guess, not too bad for this cheapie component). Pinning and orientation is the same as 2SK170. so it's easy to swap.
For the sake of knowledge, I have put in BS170 for Q4. The pot has to be adjusted just the normal way. At the gate of Q4 now appears around +6,7 Volts (to get around 4 - 4.5 Volt at the gate of Q1).
The sound is okay to me, can't tell the difference with the 2SK170 yet (around the same quality I guess, not too bad for this cheapie component). Pinning and orientation is the same as 2SK170. so it's easy to swap.