DIY talk

I believe this is inherent to all designs not just his. On some of his DIY models you can adjust performance for H2 or H3 to suit your preference. Look up "P3" on the F5 amp for example. P3 is a potentiometer with which you can dial in your preferred distortion profile.

 

"The purpose of the gain trimmer (so called P3) is to allow you to adjust the relative closed loop gain of the top and the bottom halves of the F5 circuit.
In doing so, it allows you, with your particular combination of JFETs and MOSFETs, to balance the gain such as to maximise even harmonic distortion cancellation.
In particular, if you do not have matched devices between the two (stereo) channels, it allows you to compensate the difference to an extent."

I think that's a little different vs what happens in a single ended circuit using a SIT? Again, I could be wrong.

 

Is this the same as what's going on in the ACA mini with the jumper?

 

From the first watt f5 turbo manual:
One thing that many will appreciate is the addition of P3, which due to inattention on my part was not public until recently. It allows the adjustment of the distortion character between complete nulling of the second harmonic distortion to an arbitrary ratio of second to third harmonic. It definitely alters the sound, and reaffirms that things going on below 0.1% are audible. In any case, you can adjust it to taste.

So it does let you tweak h2/h3 ratio.

There was also a little board, I think it was going around here for a while to evaluate, that Pass designed to add h2 at line level. Don't remember the name.

 

https://www.superbestaudiofriends.o...on-pass-diy-h2-injector-for-loaner-tour.8660/

 

Pancakes I think ACA mini is using something else to compensate for N channel having more gain, if you want lower H2 measurement. Either way it's a personal choice I guess.

 

I was looking up transformer based volume controls and I came across this Electra-print project

https://audioxpress.com/article/you-can-diy-passive-preamp-transformer-implemented

This is not an AVC or TVC. It really just looks like a regular pot with an input transformer. What are the benefits for this?

 

Interesting. Using the transformer just for voltage gain, so if you don't need the gain there is no reason to add it.
I recently bought a cinemag tx to add gain for an class a amp I'm building, a sissysit.

 

I was just thinking about speaker protection and was wondering if a balanced amp is as much of a concern

Say the positive rail fails and you only have the negative rail. Wouldn’t both contacts have the same voltage which would mean 0 VDC?

 

I have thought of this situation as being potentially dire.

1. If there is DC on the output, no concellation occurs any longer.
2. The failure event 'may' have some knock on effect and destabilize the working rail.

If however there is no DC on either output (which should be the case) then you simply have a single rail but no grounding on the output.

Alex developed a balanced headphone sensor, it can probably be adapted for speaker use. On DIYA, I have seen folk use whatever single ended output they choose and double up to protect both pos and neg signals (this becomes expensive as the good ones run around $70 a piece = small price to pay relative to expensive speakers)

Be curious as to other thoughts on this too.

 

I bought one of these from xrkaudio
Its not an easy assembly, lots of tiny parts. Putting it together for my next amp, a Sissysit to drive HE6SE's.

He also sells assembled speaker versions of it, but I think this will be fine for my application.
The amp output has to go through a mosfet. Supposed to be transparent, just going to install and see how it goes.

Randy

 

Wacky idea time:

So the USB-C standard allows high power delivery which is primarily to quick charge devices like laptops and smartphones, up to 20V and 5amps.

That means 100w delivered through USB-C. Would it be possible to do a USB powered desktop amp?

 

It would only ask for a nice beefy battery bank. Then it has a hope to sound good, too.
20 cells of Li-ion would do for 70 W to 8 ohms amp.
Say 250 Wh capacity (4 Ah 21700 cells), decent class AB amp would give 2 hours play time at full blast (averaging 50 W rms, probably less) while portable. Cool, huh?
That is close to the limit with the USB-C and Clas AB. Going full switcher, a bit more can be expected.

 

Don't see why not. But in the context of DIY, it would be pretty complex. With regular USB you have 5V 1A you can tap directly without any other concerns. Whereas using the full 20V 5A requires a dedicated USB-PD interface chip to negotiate power draw and delivery. Maybe there are already DIY friendly interface boards for this?

 

I'm glad you asked. People have made modules to access USB-PD.

https://www.tindie.com/products/oxplot/fpx-easy-usbc-power-for-all-your-devices/#product-description

The main issue is these seem to be nice if you only need power but I also want access to datalines to interface with a DAC.

 

Yeah, I suspect you would need something like an Amanero updated with USB-PD capabilities.

My luddite solution would be to just accept you have to run two cables.

 

I expect laptops and other sources can limited power through usb c. Seems that a macbook can supply 10w on its usb c port. They are intended to use the usb c to be charged, not to charge other devices at high power.

And then reading USB data is complicated, even harder to make it sound good.

Randy

 

Not every USB-C has power delivery but there are PCI-E cards for desktops that can deliver 100w through USB

https://www.gigabyte.com/Motherboard/GC-TITAN-RIDGE-rev-20#kf

 

I just got a RAAL PDT-1a tube amp designed for orthos and electrodynamics and it sounds really good I'm amazed especially considering the size. But it gets incredibly hot, which according to RAAL is normal. But I've never had or seen am amp get so hot. Touching the side for more than a second would burn my hand. And the volume knob gets so hot that touching it for more than a couple seconds would burn my fingers.

I'm thinking of adding heat sinks to the sides.

But I'm wondering if it's ever a bad idea to cool an amp? Is it possible that it sounds better running this hot?

If heat sinks are a good idea, any links to some good sources? And how to attach them?

Thanks

 

Is it good to cool an amp (more than factory)? It depends. Keeping components cooler prolongs their life. However, components' performance does depend on temperature. If the designer wanted particular parts to be operating within a specific temp range then cooling them has the potential to change the sonic performance of the amp. Maybe better, maybe worse.

I would ask RAAL. It's not a budget category item so I doubt they skimped on heat sinking just to meet a price point.

It's suspicious though that the volume knob is burning your fingers. Maybe your unit has a fault?