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Cavalli EHHA Embedded Hybrid Headphone Amp - Page 114

post #1696 of 1816

So I need 2 approximately 21 ohm resistors rated at least 2.5watts eh?  Guess I should use 4 10 ohm power resistors?  I have the 2 boards wired up in parallel to the transformer should I put 1 10 ohm resistor per heater supply connection wire, or do 2 in series from the transformer to those wires?  Or 2 in series on only 1 side of each heater supply?  Sorry, this was actually my first diy amp and honestly I think I'm doing pretty good if my only problems are I broke 1 1$ mosfet and my filament transformer is giving me a bit too much voltage/current.

 

or is it .33a = 6.3 / R, R = 19.0909 so I = 7.1/19 == .372A and to get .33A I need an additional 2.5ohms? (.33 = 7.1/R, R= 21.51515?) guess I will find out when I get home regardless ;p.


Edited by BebopMcJiggy - 11/17/10 at 8:22am
post #1697 of 1816

Since nobody else asked:

Are you running the transformer loaded? IE were the tubes in when you measured that voltage? 

 

What load is your transformer sized for? A transformer rated for 10A@6.3v wont light up at 6.3v under a 2.4A load - It will probably be much higher.

 

A few posts ago you asked if you should get a smaller transformer. If you measured the voltages under load I would probably do that. Resistors to drop heater voltages work if your in a bind, but they mean several watts more heat floating around the chassis which is no fun. Unless you have very good reasons* for using a resistor to drop heater voltages dont do it.

 

*good reasons:

You want to do the 6/12V heater with no switch trick on tubes like 6/12SN7

The heater windings are in the same custom wound transformer as the B+ windings and they just didnt work out right.

post #1698 of 1816

Okay I will just get a smaller transformer then, it was loaded.  Thanks for the help, I was wondering about the heat a bit myself :O.  I suppose I wasted 6$ on some resistors at radio shack but oh well.


Edited by BebopMcJiggy - 11/17/10 at 9:53am
post #1699 of 1816

So it was definitely that I needed 2.5 ohms or so... I used 1 10w 1.1ohm resistor to drop the voltage to 6.4 and the 10w is definitely some serious overkill, it barely gets warm at all.


Edited by BebopMcJiggy - 11/17/10 at 9:50pm
post #1700 of 1816

Meh I think I'm just gonna leave it with the resistor, I don't even think it is dissipating 1 watt (should be 1/10th of ~2 watts per filament? so 2/10ths of ~2 watts?)  If my math is right anyhow and it's 6.4 volts through 21.090909 (21.290909? ;p) ohms (twice).

post #1701 of 1816

P=I x V

V=I x R

therefore P=R x I^2

post #1702 of 1816

Well it's rated for .33a @ 6.3v so I assume it is 19.090909 ohm resistance when loaded...  theres 21.090909 ohm resistance now @ 6.4v (1 1ohm resistor wired before the filaments which are in parallel) but I'm not clear how you separate the 1 (2...) ohms out of that and figure out the current going through it only but I think the whole 21.090909 dissipates 1.94207 watts in heat or so? or like 2.5ish watts if you use the source voltage?  Regardless I don't see how the resistor could be responsible for more than a small amount of heat :O

post #1703 of 1816

Sigh so upon arriving home today one of my boards no longer seems to work.  I now get 0v across R4 and 3v across R3, obviously something is horribly wrong.  The mosfet gets really hot on the +30v input side and well I don't know what else as I shut it off.  For the life of me I can't find a short or anything...  should I replace IC3 and all the transistors on that side or what?  Kind of really furious right now and about to smash that particular board as it was working fine before and I am a sad sad panda :(

post #1704 of 1816

Not that anyone really cares but my terrible case work :( It looks better on the outside heh... evil locking 1/4" plugs :O

 

DSC_0120.JPG

 

and the non working channel :(

 

DSC_0121.JPG

 

I replaced the mosfet  But yeah r3 and r4 are all messed up, I don't even think the old mosfet was broken :(  Will replace the transistors and try again I guess :O  not really sure what is wrong here but the voltages to q8m are ridiculously high by the end of it and it heats up really fast.

 

So the one channel that is working sounds good, except when I tried with the athM50 there was a bad hiss but I am just assuming that hp was too sensitive... sounded great with LCD2...


Edited by BebopMcJiggy - 11/20/10 at 4:20pm
post #1705 of 1816

Q : Which opamps can be substituted for OPA134 in EHHA ?

      Would the TL081 ( used in rev.A} do ?

post #1706 of 1816

Will do fine.

post #1707 of 1816

Well I fixed the other channel and I am not one for flowery language about how the amplifier tickled my ear's prostate but it sounds pretty good so far.  I have a slight hum in the right ear when I put the output (input?) to max.  Not really noticeable while things are playing and also I would never listen to things loud enough for it to be audible, I just notice when there is no input and the volume is set as high as it can go.  I think it is from the heater transformer but oh well.  It really only seems to get slightly warm above the tubes and that is it, and they're not so hot I can't touch them... the heatsinks barely heat up at all so far.  I think perhaps I went overboard perforating the lid now but it can always use more ventilation I suppose.

post #1708 of 1816
Quote:
Originally Posted by BebopMcJiggy View Post

Well I fixed the other channel and I am not one for flowery language about how the amplifier tickled my ear's prostate...


basshead.gif

post #1709 of 1816

Can anyone help me with some casing option for this amp? I want to build an end all amp for my bedroom, so really wanted to configure it for speaker use as well. I have seen some build b22's in a box type enclosure, and was wondering if such an enclose might work for the ehha as well, also no idea where I would source such a case. Really want to build this or the Rev. A, just thinking it might be a bit over my head as I've never had to do such casework, also never worked with transformers. Have a cmoy and compact tube hybrid I've built. Any help nudging me along is appreciated :).

post #1710 of 1816

If you look over the past couple of pages or so you'll find johnwmclean's excellent build that works for speaker duties. :)

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