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The ugliest headphone amp on the planet? - Page 2

post #16 of 94
1/17/06 at 6:57pm
Lose the butt ugly wood cover,shoot the entire chassis with charcoal Hammerite paint (bake in a toaster oven at 200F for two hours) then toss a piece of solid walnut on for a front panel.Add a yellow LED then repost as "is this amp cool looking or what ?"
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post #17 of 94
1/17/06 at 7:17pm
Thread Starter 
Quote:
Originally Posted by rickcr42
Lose the butt ugly wood cover,shoot the entire chassis with charcoal Hammerite paint (bake in a toaster oven at 200F for two hours) then toss a piece of solid walnut on for a front panel.Add a yellow LED then repost as "is this amp cool looking or what ?"
Way ahead of you there new parts already being fitted inside, will probably whack on a nice piece of wood in place of the veneered chipboard that's already on it.... just waiting to see how it sounds first and will then decide if it's worth doing the cosmetics.
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post #18 of 94
1/17/06 at 7:35pm
Quote:
just waiting to see how it sounds first and will then decide if it's worth doing the cosmetics
looks to have a discrete output (fairly common in the eighties for such use even though headphone amps were not as a class of equipment) and DC coupled so I think maybe a good chance it sounds good but measure the DC offset to be safe.

The power section looks a tad weak (cap size) for driving a dynamic headphone below 150 ohms which may be what it was designed to drive so also check any series resistor on the output for size.You may find 100-150 ohms there and again not good for low Z cans (again though common for the time).

Finally the cosmetics-

Everyone has different taste so what I like another may find AWFUL !

However.

If you shake loose that nasty a*s wood "jacket" you may find the actual lines of the amp not too shabby.Deeper than wide works very well on a shelf along side of a Cd palyer even though looking out of place on a bench for a photo shoot.

Disregarding a replacement for the wood cover think on what actually is visible when this amp is "in system" and that is the front panel and not much else so why I suggested painting the metalwork and then adding only a front panel of hardwood.That is what the Rickster would do.

The Mikester ? I don't think even he knows
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post #19 of 94
1/17/06 at 7:54pm
Hmmm. I wonder what Larry/Headphile could do with that?
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post #20 of 94
1/17/06 at 8:12pm
Wrap it in some "gold" foil paper left from Christmas to raise the bling factor.
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post #21 of 94
1/17/06 at 8:30pm
It's log, log ..

It's big, it's heavy, it's wood..

It's log, log ..

It's better then bad, It's GOOD!

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post #22 of 94
1/17/06 at 8:32pm
Thread Starter 
Quote:
Originally Posted by rickcr42
looks to have a discrete output (fairly common in the eighties for such use even though headphone amps were not as a class of equipment) and DC coupled so I think maybe a good chance it sounds good but measure the DC offset to be safe.
The offset was actually quite high L/H 270mV R/H 84mV so unless I change something it looks like non polar 1000uF caps in series with the output are the order of the day.

Quote:
Originally Posted by rickcr42
The power section looks a tad weak (cap size) for driving a dynamic headphone below 150 ohms which may be what it was designed to drive so also check any series resistor on the output for size.You may find 100-150 ohms there and again not good for low Z cans (again though common for the time).
6,000uF total in the PSU it may be prudent to double that "but" capacitor size is an issue in this design as the shaft extension for the potentiometer runs bang through the centre of each 1000uF 10V cap so I'll either have to fit more capacitance elsewhere on the board or relocate the potentiometer / lose the shaft extension which I'm reluctant to do as it would detract from the original design too much. I really want to keep things as close to the original as possible. It's the only one of its type I have come across and, as such, is unique.. it would be a shame to totally bastardise it. Having said that I intend to replace the dual log carbon pot with either a cheap omeg pot or a half decent RK27 and will obviously be replacing the caps with low ESR 105C variants and the carbon resistors with metal film types. Other than that I'm keeping the interior as close to original as possible.

Quote:
Originally Posted by rickcr42
Finally the cosmetics-


Disregarding a replacement for the wood cover think on what actually is visible when this amp is "in system" and that is the front panel and not much else so why I suggested painting the metalwork and then adding only a front panel of hardwood.That is what the Rickster would do.
Probably something along those lines though I don't want to try and hide the length, in some ways the length is very attractive.... it'll probably end up gunmetal all over as that's the only colour I've got in spray paint.. time to get it sprayed onto something
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post #23 of 94
1/17/06 at 9:27pm
Quote:
6,000uF total in the PSU it may be prudent to double that "but" capacitor size is an issue in this design as the shaft extension for the potentiometer runs bang through the centre of each 1000uF 10V cap so I'll either have to fit more capacitance elsewhere on the board or relocate the potentiometer / lose the shaft extension which I'm reluctant to do as it would detract from the original design too much.
Ouch ! I was off big time on that one thinking the caps looked small hence low capacitance.Because this amp is multistage the power supply most likely also has individual caps for each stage but either way 6K should be enough with one "um" in there.Unless i am off on the scale of the part sizes these caps ARE small for the amount of UF so would lead me to not a very good ESR rating.The age of the amp may also tend to reinforce this.

Quote:
The offset was actually quite high L/H 270mV R/H 84mV so unless I change something it looks like non polar 1000uF caps in series with the output are the order of the day.
Bigger OUCH !

Sounds like a DC balance pot is inline for inclusion or a DC servo (set to a LOW dominant pole) if you want to avoid a blocking cap.If yes to the cap then maybe as low as the 220uf-470uF range (still no bargain ) depending on can impedance or if there is a resistor to raise amp output impedance or not

Quote:
gunmetal all over as that's the only colour I've got in spray paint.. time to get it sprayed onto something
you do realise walnut is a perfect wood tone to use with any gray shades right ?
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post #24 of 94
1/17/06 at 9:30pm
It would be funny if after you modify it then it becomes your favorite amp.
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post #25 of 94
1/18/06 at 2:04am
That's one for the headphone museum. The collector in me thinks you should preserve it as is and just build a smaller, better, clone based on the circuit with the parts you bought...
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post #26 of 94
1/18/06 at 2:13am
You should put rhinestones all around the edge. Then put a sticker in the middle that says Fit-e Cent.
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post #27 of 94
1/18/06 at 2:21am
Quote:
Originally Posted by mjg
It's log, log ..

It's big, it's heavy, it's wood..

It's log, log ..

It's better then bad, It's GOOD!
LMFAO

Man that brings back some good memories.
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post #28 of 94
1/18/06 at 2:53am
I say keep it like it is, just clean it a bit.
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post #29 of 94
1/18/06 at 3:00am
I bet it plays the banjo theme from Deliverance with impeccable tonal accuracy.

"You shrrr gaahht a purdy amp."
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post #30 of 94
1/18/06 at 5:26pm
Thread Starter 
Quote:
Originally Posted by rickcr42
Ouch ! I was off big time on that one thinking the caps looked small hence low capacitance.Because this amp is multistage the power supply most likely also has individual caps for each stage but either way 6K should be enough with one "um" in there.Unless i am off on the scale of the part sizes these caps ARE small for the amount of UF so would lead me to not a very good ESR rating.The age of the amp may also tend to reinforce this.
Yep, Rick, they are 1000uF 10V per piece and there's six of them on the board (85C General Purpose "Hitano" capacitors) I propose replacing all six of them with NIC "NRSZ" 10V 1000uF 105C low impedance varieties, they're pretty good caps (sonically) and are very competitive pricewise (about 25p each) They should inject a bit of oomph back into the amp with a bit of luck. The only other two caps on the board are 6nF ceramic decouplers coming off terminal 3 and 5 (non inverting input A & B) of the TL082 opamp (caps between terminals 3 and 5 and ground), I'll replace them with similar types or polyester if it makes any difference.



Quote:
Originally Posted by rickcr42
Sounds like a DC balance pot is inline for inclusion or a DC servo (set to a LOW dominant pole) if you want to avoid a blocking cap.If yes to the cap then maybe as low as the 220uf-470uF range (still no bargain ) depending on can impedance or if there is a resistor to raise amp output impedance or not
I've checked the impedance of the output resistors and it is 120R per channel which was pretty much industry standard then..... do you think it's worthwhile removing them and fitting zero ohm links? For simplicity (and purely down to the fact I've got a couple of dozen of them) I'll fit a 35V 1000uF non polar DC blocking cap in series with the output... in fact I can probably mount them on the spare pads where the 120R output resistor used to be, that would be pretty much ideal?


Quote:
Originally Posted by rickcr42
you do realise walnut is a perfect wood tone to use with any gray shades right ?
Was discussing all this with a friend this afternoon. He's a tree surgeon and makes some beautiful wooden sculptures (I mean so good he sells them for thousands) I kinda run it by him that I would love an amp in a yew log and he's going to see if he's got a suitable piece of tree to use.... quite a few pieces of tree hanging in his workshop so I'm sure he's got a bit that will do the job very nicely should I decide to go down that route.... He'd be doing the carving, not me.
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