Help a tube amp guy orient himself on an F5 build

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#43
adason said:
True. But you probably missed F4.
It can drive anything, and its the most transparent buffer there is in classA. It can have any sound signature from your preamp. You want low distortion crystal clear, use such preamp. You want sweet second harmonic oozing sound, use such preamp. Tube or solid state. F4 can do it all, drive it all.
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What do you think about an F4 driven by a BA-3 front end?
 
#44
Xaborus said:
Thanks guys! I really have almost no knowledge of these things, so I really appreciate and am relying on good feedback. Thanks again!

Hikari- How much capacitance do you recommend, and what VA power supply? I was thinking using a 500VA with an 8 ohm nominal load. Also, what are the best cap brands?

I recommend as much capacitance as you can afford. If you are using the DIYAUDIO store universal power supply you are limited to 8 capacitors at a certain diameter. You might want to choose 35V capacitors in case you want to update to 32V rails later. The best capacitors are SIKOREL or PEH or some of the more esoteric Japanese caps like Nichicon KG. All of these are big $$$. What you are looking for is low ESR and high ripple. Other cheaper brands such as Panasonic or CDE are also also good...in general the best capacitors are what we call "computer grade" which means they have screw mounting studs and will not fit a pcb. Nelson Pass uses CDE capacitors in Pass Labs stuff.

For a transformer it depends on a couple things. 600VA will allow you to experiment with increases bias. 500VA would also work. Antek transformers are nice for the money.

Also, what does bias do? I'm guessing its something I adjust with a trim pot? And does higher bias = higher dissapation wattage?

Class A amplifiers are kind of like driving a car with the gas pedal to the floor and using the brakes to adjust the speed of the car. They are "on" 100% all the time and waste the excess energy as heat. Bias, in simple terms, is how much you have pushed that gas pedal down. So...more bias is better. It lets you have more class A into tougher loads (like a 4 ohm speaker), it generally sounds more liquid and has more depth with more bias. You are able to change the bias of this amplifier with the trimpots. It does not change the wattage of the amplifier.

The problem is heat. More bias equals more heat. So it is only feasible to have so much bias. Bigger chassis lets you dissipate more heat.

Kosst- What does P3 do? Sorry, I dont have my kit yet. Also, what feedback resistor rating would you recommend if I wanted to upgrade down the turbo path eventually?

P3 allows you to adjust the harmonic distortion of the amplifier by playing with the "balance" between the positive and negative sides. Extremely useful. You can make the amplifier sound warmer or more "tube" like or cleaner and faster. You will need an analyzer of some sort (a PC and a sound card and some software works) to be able to adjust this reliably. Or leave it in the middle and enjoy.

I dont plan on it... but I want to over-build my amp anyway. I was thinking about Mills MRA-5 (5 watt).

You can use these. Be aware they may not fit the pcb.

Thanks for answering my resistor questions! I was just concerned because the regular resistors in the kit are the "RN55D" type I believe, which are 1/8th watt spec. I was really expecting atleast 1/4 watt spec.
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What kit is this? An eBay kit? Dale RN is 1/8 watt which will work in some places on the f5 but 1/4 would be better.
 
#47
Xaborus said:
Hikari1- No the official diyAudio Store "F5 parts kit".

F5 parts Kit – diyAudio Store
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I didn't know the store was selling a kit. It's hard to tell which model the small resistors are. If they are are indeed rn55 it is true that it is a 1/8 watt rated resistor.

Here's the thing...that's a military spec resistor. If it was not military speced it might be considered a 1/4 watt resistor.
 
#48
McQuaide said:
What do you think about an F4 driven by a BA-3 front end?
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I use the combination daily, its in my upstairs guest room. I got two preamps sitting on F4, BA3FA and JC2. Both work great. JC2 is softer sounding, BA3FA is a little sharper, crispier, but cleaner. Both are great.

Used Wayne's preamp with F4 too, but its now downstairs in main system with Goldmund amp. Great preamp too.
 
#49
BJosephs said:
Troels has an impedance curve here:

SBA-16-MTM

I would never listen fully cranked at 100W, I just to make sure that less compressed music can play loud without offensive clipping on peaks. In truth I’m sure I’m over inking things... this is a very popular DIY amp. I’m going to build a standard F5 and go from there.
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OP, I think I can help you with this. Here's the info you seek.

THX reference level explained - Acoustic Frontiers
 
#51
McQuaide said:
So if I use a BA-3 FE preamp with an F4, I have a BA-3 FE feeding another BA-3 FE? Sorry if I'm being dense!
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No, the F4 is basically the BA push pull output stage. The only difference is the f4 has a jet buffer before it (to provide more flexibility).

If you combine the BA-3 front end with the f4 you end up with the complete Ba-3 Ampfilier (BA-3 front end + BA output stage).

The F4/BA output stage is not rocket science. Been around a long time. Even in some of the Pass Labs amps.
 
#54
Since this thread seems to be meandering about now I guess I'll throw in an OT question:

Is anyone here using DC output protection in a DIY Pass amp (or any other I guess)? What types? I've been spoiled by the intrinsic protection of an output transformer.
 
#55
BJosephs said:
Since this thread seems to be meandering about now I guess I'll throw in an OT question:

Is anyone here using DC output protection in a DIY Pass amp (or any other I guess)? What types? I've been spoiled by the intrinsic protection of an output transformer.
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I haven't myself, but I know that many do and the diy store sells boards for building such a device. Some people won't use an amp without one. Pass didn't build any of the original amps with them though. Assuming you've been meticulous in your build, avoiding any kind of shorts such as sloppy soldering, badly insulated MOSFETs, and thermistors shorting to mounting bolts, and you stick to established formulas of success, these amps are very reliable. I think an F5 properly built and strict to the original specs and values would be very difficult to destroy in a 4U DIY chassis. Don't run wires through holes unprotected. Insulate the thermistors with shrink tubing. Make sure the MOSFETs are insulated from the heatsinks. Fuse the thing as conservatively as possible. I don't worry about mine, and I leave them on all weekend.
 
#56
Kosst Amojan said:
I haven't myself, but I know that many do and the diy store sells boards for building such a device. Some people won't use an amp without one. Pass didn't build any of the original amps with them though. Assuming you've been meticulous in your build, avoiding any kind of shorts such as sloppy soldering, badly insulated MOSFETs, and thermistors shorting to mounting bolts, and you stick to established formulas of success, these amps are very reliable. I think an F5 properly built and strict to the original specs and values would be very difficult to destroy in a 4U DIY chassis. Don't run wires through holes unprotected. Insulate the thermistors with shrink tubing. Make sure the MOSFETs are insulated from the heatsinks. Fuse the thing as conservatively as possible. I don't worry about mine, and I leave them on all weekend.
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This. Build 'em right and they will serve you well for many years. I know of no F5 that has ever damaged a speaker. I'm going on 9 years at this (just a newby) and so far these designs are very robust and dependable.
 
#59
BJosephs said:
Since this thread seems to be meandering about now I guess I'll throw in an OT question:

Is anyone here using DC output protection in a DIY Pass amp (or any other I guess)? What types? I've been spoiled by the intrinsic protection of an output transformer.
Click to expand...

I used the one from the DiyStore on my Aleph J because of the turn on/turn off thumps. I didn't use one on my M2 because it doesn't make any on/off noise.
 
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