[zoboomofo]

Hi. I've got an amp at home which I'd like to understand a bit more so I can tweak it further.(the Creek [soon-to-be Music Hall] obh-11. Here's my question:

How do you ID diodes , and mosfets when there's no writing on them to spell out their model? Thanks. If measurements need to be made to reveal their specs, then please note that I do have a multimeter.

I've only done a couple cap upgrades - substitute polypropylenes for stock film type, and sub 220 uF Cerafines for stock electrolytics. I'll sub a pair each of Cerafines, and Black Gates for the 47uF caps eventually. Panasonic FC 2200uF substitute for Samwha cap will arrive later today (along with my Art DI/O cap upgrades

).

P.S. I've kept the stock opamp in place, but may upgrade to an AD825/2xAD797 in the future. The jfet opamps i've tried (opa2132, 2xopa627) don't sound right - the treble is too lean and cold. Another wierd observation is the apparent gradual deterioration of sound whenever I try a replacement opamp. I always come back to the NE5532. You don't suppose that these alternate opamps are harmed in the circuit do you (something like that reverse bias current damage)?

P.P.S. I can provide a newbie's version of a schematic if it helps.

I know what you're thinking - why bother tinkering with this old amp when there are more exciting projects around? Well I just want to see how far I can reasonably go with this thing.


Thanks for reading, zoboo.

 

[joe_cool]

If you like the sound of the NE5532 you might want to listen to the LM6172. I prefer the sound of the AD8620 and AD825.

 

[rickcr42]

I would not sweat the actual diode ID . If you are doing a replacement just measure the voltage and current of the power supply and purchase a diode that fits the VA rating , with some headroom of course . Always a good idea to oversize parts in power supplies.

The mosfet ID is a bit more involved . You will need to pull it from the circuit and put the part in a "simulation' circut and then measure the parameters.

Probably a much easier task to as above measure the voltage to the part and the current output across an output load .This will give you a ballpark figure that you can use to replace the part .

but this is where you DON'T want to oversize the part if you can help it .The more current delivery the mosfet can produce usually means a higher gate capacitance .Bad ,very very BAD.

 

[zoboomofo]

Quote:

Originally posted by joe_cool If you like the sound of the NE5532 you might want to listen to the LM6172. I prefer the sound of the AD8620 and AD825.

Hey I DO happen to have the LM6172. I'll pop that in. I just tried the 8620, and it sounds a bit 2-dimensional and lean like the other replacements

!!??

Quote:

Originally posted by rickcr42 ...measure the voltage and current of the power supply and purchase a diode that fits the VA rating. ... ...measure the voltage to the part and the current output across an output load...

Great! Somehow I knew you'd respond. Thanks, man!

 

[Sol_Zhen]

Quote:

Originally posted by zoboomofo (the Creek [soon-to-be Music Hall] obh-11.

Music Hall is buying Creek?

 

[tangent]

You might be surprised about those diodes -- they might be labelled after all. Especially with the DO-35 style, it can look like there's no labelling, put put them under strong magnification and you can make out the lettering.

You can also tell a lot about a diode just by looking at it. If it's DO-35, it's probably 100mA or lower. If it's DO-41, it's probably got a 1A or so rating. And so on. The next trick is figuring out what kind of diode it is: is it a regular silicon diode? Or a Zener? Or a Schottky? Or, maybe it just looks like a diode but it's something else like a CRD.

What you might try is just tracing out the circuit without worrying too much about the individual parts. Then when you get the rough schematic drawn out, you can start to straighten it out and make reasoned guesses as to the function of the parts you couldn't identify.

 

[rickcr42]

Quote:

You might be surprised about those diodes -- they might be labelled after all. Especially with the DO-35 style, it can look like there's no labelling, put put them under strong magnification and you can make out the lettering.

man , the worst has got to be zeners .I needed to whip together a shunt supply today and realized my zeners were all mixed up somehow so I had to separate them into voltage groups.
Talk about getting a damn headache !

The writing is there but not only is it tiny on a tiny little glass pack but separated as well

IN
47
44

jeez !

Quote:

Great! Somehow I knew you'd respond. Thanks, man!

You are very welcome

Rickeraptor

 

[zoboomofo]

Great feedback guys. Gimme a couple hours, and I'll whip up a jpeg of the circuit. Again, mucho gracias.

Oh yeah, according to one online retailer, there will be a Music Hall obh-11 product in their catalog soon. I can't remember who the vendor is, but this development doesn't surprise me. Anyone remember the Shanling cd-s100 aka MMF cd-25? Anyway, I hope Music Hall can price this classic amp competitively.

 

[zoboomofo]

Quote:

Originally posted by tangent You might be surprised about those diodes -- they might be labelled after all. Especially with the DO-35 style, it can look like there's no labelling, put put them under strong magnification and you can make out the lettering.

Quote:

Originally posted by rickcr42 The writing is there but not only is it tiny on a tiny little glass pack but separated as well IN 47 44 jeez !

Ok, so I've taken a closer look at the diodes D1, D2, D3. Yes, there is writing on them! They are labelled 1N. ZD1 is labelled 24. No doubt about it though, it IS faintly written on the glass package.

Quote:

You can also tell a lot about a diode just by looking at it. If it's DO-35, it's probably 100mA or lower. If it's DO-41, it's probably got a 1A or so rating. And so on. The next trick is figuring out what kind of diode it is: is it a regular silicon diode? Or a Zener? Or a Schottky? Or, maybe it just looks like a diode but it's something else like a CRD.

I'll get on that. All diodes are orange with a black band, and a clear band around the barrel. D1 - 3 are roughly 1.5mm thick. ZD1 is about 2mm thick.

Quote:

What you might try is just tracing out the circuit without worrying too much about the individual parts. Then when you get the rough schematic drawn out, you can start to straighten it out and make reasoned guesses as to the function of the parts you couldn't identify.

I've attached my rough draft schematic for the obh-11. I'll add resistor, and capacitor values hopefully this evening. The grey shapes label components whose layout I'm not sure of. Please feel free to help me fine tune/correct the circuit. I'll be back.

 

[tangent]

Quote:

They are labelled 1N. ZD1 is labelled 24.

You're only looking at one row of lettering on each part. 1N is a prefix for a diode. (It means 1 'n'-doped silicon layer, implying 1 'p' as well, which is what a diode is.) There will be 3 or 4 numbers following that. ZD1 sounds like a Zener, and "24" is probably the suffix.

 

[zoboomofo]

Yes, I'll have to desolder these diodes out to get a proper look at them.

I'm sorry to have delayed any work on the creek gif, but the unit is closed up while I'm enjoying the result of my Art DI/O mods

.