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A Very Compact Hybrid Amp - Page 65

post #961 of 2203
4/27/09 at 4:06pm
fired my amp up..... all checks out..... except there is no heat.

The heater voltage is climbs to 1.2v, then drops back to 1.

Everything looks ok, except L1H reads very very high resistance (1m +)

IS that my problem, or is the switcher unhappy?
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post #962 of 2203
4/27/09 at 4:15pm
. EDIT: Posted this question in it's own topic under the DIY forum.
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post #963 of 2203
4/27/09 at 4:23pm
Quote:
Originally Posted by adamus View Post
fired my amp up..... all checks out..... except there is no heat.

The heater voltage is climbs to 1.2v, then drops back to 1.

Everything looks ok, except L1H reads very very high resistance (1m +)

IS that my problem, or is the switcher unhappy?
Those coils should have VERY low resistance value... Don't know exactly, but thinking < 1 ohm (? see their datasheets?).

The switching heater is actually a pretty low-count circuit. You may see it in the lower-right of the PS schematic. We've not had a problem with it yet to my knowledge...

I'd inspect the heater components installed & their polarity carefully.
Then I'd pull the L1H (3.3uH one) & check voltage from its "input" lead to ground. It should measure about 12.6 or 6.3 VDC depending on the heater switch.
If the voltage there is not close, then you've a problem before L1H. It it is close then you've a problem after L1H (possibly a short).

Note: If you find it is only L1H or C1H are bad, the CTH should function with L1H position shorted (but will not have ripple filtering). But do not do this, or pop in a new L1H, until you assure that from L1H "output" lead to tube is not shorted to ground.
The "output" lead of L1H goes to (#4 or #5 of) tube socket & the other tube socket heater pin is ground (#4 or #5).

Edit: ALL part numbers are as components are shown in the schematic I referenced.
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post #964 of 2203
4/27/09 at 4:26pm
sorted it, the tiny little copper wire wasnt attached to the lead, a quick tack of solder and i have 12.6v.
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post #965 of 2203
4/27/09 at 4:35pm
Quote:
Originally Posted by adamus View Post
sorted it, the tiny little copper wire wasnt attached to the lead, a quick tack of solder and i have 12.6v.
Heh, the obvious thing I was thinking its high resistance was from an open somewhere on the coil. Nice that is was an easy fix. It is a bit sensitive.

So, later let us know how she sounds... AFAIR you've built & heard a few amps
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post #966 of 2203
4/27/09 at 4:47pm
awesome, adamus. BTW, do you still have your SOHA II that you built for someone? I was wondering if you could do a quick comparison. The main differences I notice, is the bass. The SOHA II just has that much more kick to it, even with similar tubes, though, I've got mine biased at 10mA tail current now.
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post #967 of 2203
4/27/09 at 4:59pm
afraid not, it went a while ago. i only have the bijou left at the moment.

just fired it up again, heaters are now working, but there is a bad 100hz hum. does connecting the SG make much difference (its just on the bench at the moment)?
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post #968 of 2203
4/27/09 at 5:04pm
Maybe, if it's related to external stimulii. If it's not, no, but it could be other things too. What if you move the wires around and/or physically relocate the amp? I don't hear hum on mine, but I do use a 100-120ohm output resistor.
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post #969 of 2203
4/27/09 at 5:08pm
I am having some hum when I touch the volume knob on mine. It goes dead silent when I don't touch the knob.

Am thinking it is something to do with my wiring (cold solder joint) rather than a ground loop problem, since it wasn't present with the previous (BOM) pot.

Any ideas?
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post #970 of 2203
4/27/09 at 5:11pm
hmm, pin 1 to sg reads 101v, something isnt right. that should be 80v?
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post #971 of 2203
4/27/09 at 5:13pm
Quote:
Originally Posted by sachu View Post
I am having some hum when I touch the volume knob on mine. It goes dead silent when I don't touch the knob.

Am thinking it is something to do with my wiring (cold solder joint) rather than a ground loop problem, since it wasn't present with the previous (BOM) pot.

Any ideas?
Ground the pot shaft. If you are using Alps blue, I unscrew 1 screw in the back, and wrap a thin wire around it and screw it back in. Run the wire to SG.

If that's not possible, you could use a large ring terminal, put it around the pot shaft on the inside and wire it to SG.

That only applies if the chassis is not grounded thoroughly (scraping off the coatings where ever the metal plates meet).
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post #972 of 2203
4/27/09 at 5:14pm
Quote:
Originally Posted by adamus View Post
hmm, pin 1 to sg reads 101v, something isnt right. that should be 80v?
It should be ~80V, correct. Most of us read around 78V, IIRC.

Check your CRD.
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post #973 of 2203
4/27/09 at 5:16pm
Quote:
Originally Posted by adamus View Post
hmm, pin 1 to sg reads 101v, something isnt right. that should be 80v?
with the tube it should read 80V, but without tube 101 sounds about right.

Quote:
Originally Posted by holland View Post
Ground the pot shaft. If you are using Alps blue, I unscrew 1 screw in the back, and wrap a thin wire around it and screw it back in. Run the wire to SG.

If that's not possible, you could use a large ring terminal, put it around the pot shaft on the inside and wire it to SG.

That only applies if the chassis is not grounded thoroughly (scraping off the coatings where ever the metal plates meet).
yes its the ALps blue..Will give it a try..I did that on the Ck2III, but I had other problems with that one which only went away after I put in a ground loop breaker.
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post #974 of 2203
4/27/09 at 5:31pm
thats with tube in, checked out all the values for the input components (left), they all check out fine, the CRD measures ok too.... maybe te opamp is toast?
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post #975 of 2203
4/27/09 at 5:40pm
What's the differential across the CRD? 101 is awfully close to having no current flowing through that triode. I'm not sure if it could be the opamp. What happens if you remove the opamp?

Edit: Do you have any voltage at the cathode for the left side?
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