- order case as plain and have Front Panel Express (FPE) make one for you front panel from scratch
- order case with fancy 10mm blank panel, ship panel to FPE and have them work on it (I believe FPE lets you provide base material)
- have HiFi 2000 do all the drilling/milling/labeling for you by providing them with CAD drawings

I am asking because each of these methods has its advantages and drawbacks. FPE made panels on their own stock suffer from lack on finish on any side that's not the front (i.e. unpolished and even rough sides, stripped anodizing etc.).

[Edited by aos on 12-31-2008 at 04:45 PM.]

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[Quoting aos]

- order case with fancy 10mm blank panel, ship panel to FPE and have them work on it (I believe FPE lets you provide base material)

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This is IMHO the best option. The 10mm front looks great and FPE are very reliable. You can find some examples in my gallery:

beta22: picasaweb.google.com/rille02/Beta22_Neu
HybridAmp for Stax phones: picasaweb.google.com/rille02/HybridAmp
more HybridAmps: picasaweb.google.com/rille02/HybridAmp2

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[Quoting amb]

Try installing a zobel at the output and see if it makes a difference in the "hum". Even though what a zobel does has nothing to do with classic "hum" issues, but sometimes high frequency instability could cause buzzing subharmonics that sounds like hum.

As for the vibrations, are you sure it isn't the transformer?

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By zobel, do you mean something like this?

What value of caps or resistor should I use? The values described on AMB webpage says 22Ω 2W metal oxide power resistor and 0.047µF 100V film capacitor in series, but is that suitable for headphone output? I have a 100Ω 1W power resistor, can I use that?

About the vibration, it's from the transformer. Previously I couldn't locate the source because I left it secured on the chassis. Apparently the vibration from the transformer caused the sound to come from a loose vibrating screw. Thank goodness nothing wrong with the board.

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[Quoting amb]

Yes, that's the zobel. See the "Wiring & ground" section of the β22 website for illustrations. My recommendation is 22 ohms 2W and 0.047uF 100V. 100 ohms might not be effective enough.

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Ok thanks. Before I go out to get the parts, maybe it might be helpful for you to know what I just found out.

When the pot is at the position when there is the sharp sound, I measured V across R34 and R35 and it reads 80mV for all 3 boards. Any position lower increases the reading to 110mV - 120 mV. Any position higher reads normal at around 75mV. Could it be a problem with the pot?

[Edited by kschong on 01-01-2009 at 02:56 AM.]

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[Quoting kschong]

When the pot is at the position when there is the sharp sound, I measured V across R34 and R35 and it reads 80mV for all 3 boards. Any position lower increases the reading to 110mV - 120 mV. Any position higher reads normal at around 75mV. Could it be a problem with the pot?

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[Edited by amb on 01-01-2009 at 03:39 AM.]

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[Quoting amb]

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[Quoting kschong]

When the pot is at the position when there is the sharp sound, I measured V across R34 and R35 and it reads 80mV for all 3 boards. Any position lower increases the reading to 110mV - 120 mV. Any position higher reads normal at around 75mV. Could it be a problem with the pot?

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I doubt it. The increase in voltage across those resistors actually supports my hunch that it's related to an ultrasonic instability. Do you measure the same change when no headphone is connected?

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When there is no headphone connected, no such change occured. (Reading remained stable).

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[Quoting kschong]

When there is no headphone connected, no such change occured. (Reading remained stable).

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I installed the zobel network and the problem is solved! The background is totally silent when nothing is played through, regardless of pot position.

Regarding the measurement of V across R34 and R35, when the amp is first powered up, the V reading can run as high as 100mV, but after about 10 mins or so, it drops and stablises at 70mV. Is this to be expected of the MOSFETs? Is it safe to use the amp during the "warming up" phase?

It is safe to use the amp as soon as you turn it on.

using AMB's B22/S22 front/rear panels FPE files, is there a way to easly convert it to 4" high panels, or do I need to start from scratch? I have taller heat sinks and it won't fit the 3" Par case.

Also a source for extension kits for volume control and Alps 50k Quad pots?

Thanks
Frank

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[Quoting fc911c]

using AMB's B22/S22 front/rear panels FPE files, is there a way to easly convert it to 4" high panels, or do I need to start from scratch? I have taller heat sinks and it won't fit the 3" Par case.

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[Quote]

Also a source for extension kits for volume control and Alps 50k Quad pots?

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Shaft extension parts are available from Ocean State Electronics but note that these are 1/4", not 6mm. You can also get 6mm ones from vt4c.com.

The only source that I know of for quad Alps RK27s is ebay seller "familygate" in Germany. I think he only has 10K versions, but that will work just fine.

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[Quoting amb]

The only source that I know of for quad Alps RK27s is ebay seller "familygate" in Germany. I think he only has 10K versions, but that will work just fine.

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Familygate has 50k quads as well.

Could you guys suggest some speakers that you have used with it?

thanks

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[Quoting mrmajestic2]

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[Quoting amb]

The only source that I know of for quad Alps RK27s is ebay seller "familygate" in Germany. I think he only has 10K versions, but that will work just fine.

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Familygate has 50k quads as well.

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Thanks

Currently it seems one of the boards having some problems.

The values of R34 and R35 are not same. R34 was 60mV while R35 was whooping 85mV!
Right now I reduced R35 to 55mV, while R34 is mere 20mV.

AMB, do you have any clues what's going on with this particular board?

Also, check all the MOSFETs on that channel for short circuits.

OK, I am not so sure about figuring out whether MOSFETs are shorted or not. Checking pin 1 and 3 (D and S) so see if there is any voltage across?

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[Quoting wnmnkh]

OK, I am not so sure about figuring out whether MOSFETs are shorted or not. Checking pin 1 and 3 (D and S) so see if there is any voltage across?

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With the power off, you can also check the resistance across the D and S, G and D, and G and S pins. All these should show very high resistance readings.

By the way, the pin-out of the MOSFETs is G-D-S when viewed from the front, pins pointed down.

[Edited by amb on 01-19-2009 at 09:41 PM.]

OK, since I really can't accurately measure the value of resistors, I will exchange them first, then measure again when powered on, then change MOSFETs if problem still occurs.

Is there other possible problems other than MOSFETs or resistors?