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A Very Compact Hybrid Amp - Page 78

post #1156 of 2203
5/7/09 at 10:21am
How much resistance would you suggest? Would wirewound be sufficient for this?

You're suggesting upping C1H and C2H to 180uF, right? What about C3H that Alex asked about?

I'm not sure how to impliment the battery test you suggest first (I'm still very much a noob). This would require something fairily heavy duty to put out the amps required, or am I missing something?
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post #1157 of 2203
5/7/09 at 11:17am
Again I write too much in a post But wanted to get the basis/details of the heater supply out there.

My quick thoughts (look at PCB traces/images + switcher spec doc LM2595.pdf):
  • A battery test for heater would be nice to be sure we're barking up the right tree. Thinking one would lift LM2595 pin #2 / Vin (see LM2595.pdf) & lift output leg of L1H (one closest to C10P). One could tape together 4 D cells to make 6V+ & connect neg to heater ground (tube socket pin 5 ?) & pos to heater + (tube socket pin 4 ?). See if noise is gone.
  • If confirmed noise is from switcher, only C1H in ripple filter could go to 180uF. C3H & C2H are already above mins reported by SS tool. Raising them would be a future test. And I'd try resistor bit (next) 1st.
  • After battery test confirmed switcher is noise-maker, I'd try to reduce voltage into switcher by 10V or so. So I'd reconnect L1H & start w/20-40ohm 3W resistor of any type between lifted LM2595 pin #2 & its pad. Targeting something <= 24V as input to switcher under load.

Edit: added some detail
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post #1158 of 2203
5/7/09 at 11:30am
Thanks for the clarifications.
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post #1159 of 2203
5/7/09 at 1:23pm
Quote:
Originally Posted by adamus View Post
holland, i can btu not tonight, I was given the scope a few days ago, and dont have the right probes.

here is a pic of thre scope looking at lower frequencies.
any idea on how to interpret this? not being an EE, anyone explain the two traces (off one channel).

timebase is 2ms per division. looks like some ground noise on there?
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post #1160 of 2203
5/7/09 at 4:35pm
Quote:
Originally Posted by smeggy View Post
I have a quick question for all you CTH geniuses.

I have a spare switched pot from an AMB mini3 and was wondering if I could use that as the main power switch as well as pot. It seems a more elegant solution to using a separate switch for power.
smeggy, i have a spare one of these. I think it's the exact pot as the one your using in your CTH, it's the RK097 -- No ill effects then? I might do the same if so.

Also, are the pins numbers the same as the one from the BOM (except for the extra 2 pins at the back for on/off operation)?
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post #1161 of 2203
5/7/09 at 4:37pm
I don't think those switches can handle much current or voltage , need to check the data sheet ..dB
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post #1162 of 2203
5/7/09 at 4:40pm
I thinks it's wired the same but can't remember for sure.. memory like a sieve

I didn't end up using the power function on the switch after all but it should work fine if The wire is routed away from the components.
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post #1163 of 2203
5/7/09 at 4:42pm
Quote:
Originally Posted by dBel84 View Post
I don't think those switches can handle much current or voltage , need to check the data sheet ..dB
I think someone (MisterX?) said their volt/current capacity should work fine. It's a few pages back where I asked the question I think.
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post #1164 of 2203
5/7/09 at 4:48pm
Quote:
Originally Posted by smeggy View Post
I think someone (MisterX?) said their volt/current capacity should work fine. It's a few pages back where I asked the question I think.
Based on Specifications switches it sounds a bit much to me for the little bugger - 3A 16V DC... Think we're looking at like 24VAC 1A in a CTH.
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post #1165 of 2203
5/7/09 at 5:03pm
yikes... I thought smeggy ran an AC line for the vol/pwr switch to the front (accross the board) and hoping no noise/hum introduced ...*but* he's not even using the switch!

Anyway, i only wanted to know if i can save an extra hole in the back. thanks.
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post #1166 of 2203
5/7/09 at 5:07pm
That was my original plan, but I went with a seperate switch anyway
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post #1167 of 2203
5/7/09 at 5:17pm
Ok so reviewing this diagram, if I end up using the rk97 pot, what do you folks recommend is the best way to route the ac wire? (i.e. stay as far away from which components, run from top, bottom, L/R sides?)
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post #1168 of 2203
5/7/09 at 5:22pm
Quote:
Originally Posted by zkool448 View Post
Ok so reviewing this diagram, if I end up using the rk97 pot, what do you folks recommend is the best way to route the ac wire? (i.e. stay as far away from which components, run from top, bottom, L/R sides?)
Run it from the rightmost bottom side to the left most bottom side.
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post #1169 of 2203
5/7/09 at 5:34pm
cool thanks
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post #1170 of 2203
5/7/09 at 10:52pm
Quote:
Originally Posted by tacitapproval View Post
How much resistance would you suggest?
I'm not sure how to impliment the battery test you suggest first (I'm still very much a noob). This would require something fairily heavy duty to put out the amps required, or am I missing something?
TA - I know the hum is bugging you with IEMs - and I'm certainly NOT impugning your skills - but given the amount of effort you've gone to to get this amp working...

I may be able to test CF's battery suggestion this weekend. Althugh CF already did this test during the perfboard proto. The most straightforward way to test would seem to be cutting the traces to pins 4&5 and applying the battery there... I'd rather jumper traces than lift Vreg pins - it's really tight back there.

My question is - why didn't I notice this noise before? I think this hum is due to the power of suggestion
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