300B Headphone Amp

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ed
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#91 Re: 300B Headphone Amp

Post by ed »

Nice one Ray, well shoddy.

Regarding lm317, I had a failure on my simple hpa. I just googled 'faulty lm317' and it looks like it's the norm rather than the exception. There were a few links to things such as 'how to check lm317' so it seems it may be prudent to check the little critters before fitting. I haven't looked in detail but I'm not sure if the checks would reveal ones that cause buzzing.
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#92 Re: 300B Headphone Amp

Post by Ray P »

ed wrote: Sun Apr 25, 2021 11:54 am Nice one Ray, well shoddy.

Regarding lm317, I had a failure on my simple hpa. I just googled 'faulty lm317' and it looks like it's the norm rather than the exception. There were a few links to things such as 'how to check lm317' so it seems it may be prudent to check the little critters before fitting. I haven't looked in detail but I'm not sure if the checks would reveal ones that cause buzzing.
I don't use any LM317s in this project Ed so can't comment. For the current sinks I'm using TL783s.

Not sure what was causing the buzzing but I've got a complete set of new transformers and reinstalled everything else from scratch - anyway, it has gone.
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#93 Re: 300B Headphone Amp

Post by Nick »

I just googled 'faulty lm317' and it looks like it's the norm rather than the exception
Do the links you have point to any particular fault, as when I google that I just get a bunch of links to people being people. I get much the same if I google "faulty lm338" or "faulty 2n3055"
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#94 Re: 300B Headphone Amp

Post by ed »

Nick wrote: Mon Apr 26, 2021 10:08 am
I just googled 'faulty lm317' and it looks like it's the norm rather than the exception
Do the links you have point to any particular fault, as when I google that I just get a bunch of links to people being people. I get much the same if I google "faulty lm338" or "faulty 2n3055"
In truth I didn't follow any of the links so I might be guilty of scandalizing. I was just taken aback by the number of entries.
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#95 Re: 300B Headphone Amp

Post by pre65 »

ed wrote: Mon Apr 26, 2021 10:16 am
Nick wrote: Mon Apr 26, 2021 10:08 am
I just googled 'faulty lm317' and it looks like it's the norm rather than the exception
Do the links you have point to any particular fault, as when I google that I just get a bunch of links to people being people. I get much the same if I google "faulty lm338" or "faulty 2n3055"
In truth I didn't follow any of the links so I might be guilty of scandalizing. I was just taken aback by the number of entries.
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#96 Re: 300B Headphone Amp

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I think that’s the effect of google. Most of the links were to people who were having problems or didn't follow (or read) the spec, I just wondered if you had seen any underlying problem I hadn't.
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#97 Re: 300B Headphone Amp

Post by Ray P »

I think Nick is right, if you search for 'faulty LM317' you get lots of hits on faulty LM317s but not many on non-faulty LM317s.

I'm not aware of a general issue with LM317s though I have seen something recently about different brands behaving differently - I don't recall the specifics but it was something like one brand working perfectly but another not regulating or possibly oscillating - a very narrow use case though so not really a failure trend per se. It was on DIY Audio.
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#98 Re: 300B Headphone Amp

Post by Ray P »

Just wondering if any of you guys might have a pair of 'vintage' 300Bs that I could borrow for a week or two?

Since rebuilding my transcendent Masterpiece 300B HPA, sans intergrated Soekris DAC I've been really enjoying the sounds using one of my DSD decoders as the source and with Electro Harmonix Gold 300Bs installed in the HPA. I'm just curious about whether a pair of 'good' 300Bs would be worth saving up for. I'll obviously be happy to pick up shipping/insurance costs.

Cheers
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#99 Re: 300B Headphone Amp

Post by Ray P »

No offers of a loan forthcoming so i treated myself to a pair of used Psvane 300B-T valves, these are the ones with the black glass;

Image

I've been listening to them in my Masterpiece HPA - a definite step up from the Electro Harmonix 300B Golds - more space around instruments/performers with a sharper focus to the presentation, more solid bass too.

Result!
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#100 Re: 300B Headphone Amp

Post by Ray P »

I'm really enjoying listening with my Transcendent Masterpiece 300B HPA and BeyerDynamic DT880 headphones, the PSVane 300Bs have lifted it to a new level. I can happily listen to it for hours and my only niggle is the temperature of the pair of Andrew's DHT supplies that I'm using in it - worrying about how long they'll last.

Each DHT supply has its own 30VA transformer, nominally rated at 9VAC. I'm actually seeing a bit more than 10.5VAC at the input to the DHT supplies so the regulator is seeing something like 14.8VDC so is having to burn about 10V @ 1.25A = approx 12W - so it's not surprising they're running hot.

I'm already using the tallest heatsinks that'll fit the PCBs so the obvious solution is to install some dropper resistors in the AC lines - something like 1ohm 10W types should drop the 10.5VAC to around 8VAC and if I use aluminium clad types or TO247 'power' resistors I can fix them to the chassis to dissipate their heat.

However, I also have a couple of 30VA 6VAC transformers and I'm wondering if I can use them and solve the problem 'at source' - if the regulation is anything like the 9V transformers I will expect to see something like 7VAC at the input to the DHT supplies, so perhaps close to 10VDC at the regulator - any thoughts?

Ta muchly
Last edited by Ray P on Mon Jul 26, 2021 1:52 pm, edited 1 time in total.
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#101 Re: 300B Headphone Amp

Post by Nick »

Not sure that will have enough headroom.
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#102 Re: 300B Headphone Amp

Post by Andrew »

I tend to agree, not enough headroom, but worth trying, from memory you need 3v DC, at least.

If you try the resistor, I'd be tempted just to try the resistor in the "positive" leg of the transformer, first.
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#103 Re: 300B Headphone Amp

Post by Nick »

so perhaps close to 10VDC at the regulator
To expand on that, it won't be 10v DC it will be 10v RMS DC with some fast low going charging spikes that go a half volt or so lower, its the low spikes that gets below the needed headroom and finds its way through the regulator. You can't see them on a multimeter but can on a scope.
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#104 Re: 300B Headphone Amp

Post by Ray P »

Thanks Andrew & Nick, that's helpful.

I guess iteratively experimenting with some resistors is the starting point - burn off some volts and see how if it lowers the temperature of the regulator heatsink to a tolerable level.

I had a rummage this morning and found a 25VA 7VAC toroidal transformer so it maybe worth giving that a try too.

Ray
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#105 Re: 300B Headphone Amp

Post by IslandPink »

I've had success with more than 4.5V headroom after rectification
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