Amp15 output filters

[wadoka]

Hi,

As I understand it the amp15 is meant for 8-16 ohm loads. I run 6ohms speakers on my one, would I find any benefit altering the output filters for 4-6ohm? I do find the amp a little 'sharp' sometimes, I wonder if modding the filters would address this?

Oh yes, and if so...how? :D

Matt :)

[col_s]

The output inductor and filter on the truepath uses 11uH and 0.22uF second order filter. This is actually "tuned" for around 6ohms, being the midpoint between 4 and 8 ohms. If you plot the transfer function for that filter you will see that between 10kHz and and 20kHz that it is mostly flat with a 6 ohm load, has a slight rise with an 8 ohm load and has a slight drop with a 4 ohm load.

What inductor and cap is used for the output filter on on amp15?

[col_s]

looking at some of the photos in the amp15 photo thread, it looks like there are two 22uH inductors in parallel on each channel which results in 11uH and 0.22uF caps. That should be perfect for a 6 ohm load, but you have to keep in mind that quoted speaker impedance is just an average and actually varies across the frequency range, and this can influence the output filter.

All of this happens pretty high up in the frequency range, where most of us cannot really hear much. Possibly the "sharp"ness you are hearing is happening further down in frequency. Are you hearing excessive sibilance? It could be many things: it could be coming from the source, it could be related to noise/interference pickup, noise/oscillations in power supply, etc. etc.

[wadoka]

Hi,

Thanks for the help :) I think I'll put my amp4 back in to see if it goes away, at least i know its not the filters,

Matt.

[wadoka]

Well, the sharpness of my amp15 seems to be gone. I'm not sure I believe in 'running in' as I've never heard of a logical argument that supports its existence, but perhaps that's all it needed?
I've not made any changes...confusing.

[shovel]

Hello Matt,
this was the same thing with my amp 15.
At the beginning I was a bit dissapointed because it sounded rather sharp and "edgy" or overbrilliant.
With some time playing music the sharpness has gone but it´s still very detailed (in a positive way).
I´m very happy with the sound now.:D
Only thing that concerns me is the amp getting rather hot.
Is Your amp running cool?
I think I have to ask Vincent what can be the reason.
best regards
Simon

[wadoka]

Good to know you have had the same thing with the amp15 as me!

Where is the heat? What rail voltage do you run and what size heatsink do you have?
The output filter inductors run a bit warm on my one along with the doubled up resistors next to them. The fets are cool and the preregs only slightly warm, but I run at only 46v rail rather than 60v so I guess that helps a bit.
Anyway, V-bro will help if you ask, I'm sure.

Have fun,
Matt.

[V-bro]

I sure have to build my AMP15 in a casing and listen to it some more, I too found it a bit harsh...

What parts indeed get so warm Simon? It should only be the pre-regulators. Although when it's decently mounted on a heatsink this should be hardly noticeable as there's just a few mA involved...

What current is it drawing at idle? It should be around 130mA on one rail and around 100mA on the other if I remember correctly? And indeed what's the railvoltage?

------X-max. can be several meters on any driver, too bad it can be done only once...------

[shovel]

The inductors run very hot.
I only can measure the temperature with my cheap multimeter(with temp function),but the highest temp was above 175 degrees.
The chip itself went up to 50 degrees.
I´m a noob,so how can I measure the railvoltage and current?
I´m afraid I´m a bit overchallenged with these things,I don´t want to blow anything.[:I]

[V-bro]

That's outrageous! Are you sure your gate drive resistors are ok?!

A noob building an AMP15?!

Do you even have a multimeter?

------X-max. can be several meters on any driver, too bad it can be done only once...------

[wadoka]

I dont see how they can get to 175 Celsius. Do you mean Fahrenheit?
Even converting from Fahrenheit to Celsius its 80 which is almost twice as hot as on my ones, which are at 46 Celsius.

Perhaps the temp function on the multimeter is crap? To test it boil some water and put in a cup, should start near 95 Celsius dropping pretty quickly.
or
Can you touch the inductors without burning your fingers? If you can touch them and they just feel 'hot' or 'very hot' they aren't at 175 are they?

[wadoka]

And what voltage transformer are you using?

[spin_doctor]

Would it be worthwhile running in a new AMP15 just using a couple of high powered resistors on the speaker outputs?

You could leave it sitting for a few days permanently connected to a source playing away silently to itself and hook up a pair of speakers when it's "cooked through" properly...

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Just like a nice piece of meat...

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Mmmm dinner...[:p]


Doug :D

[V-bro]

Sure you can, but you'll miss out on all the fun of hearing it improve! :)

------X-max. can be several meters on any driver, too bad it can be done only once...------