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Stub Mandrel

3D Printed Replacement Knob Cap for Trace Elliot

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These little b****rs cost about $22 a pair to import from British Audio in the US.

I need a green one, so I've done a trial 3D printed one, with layers 0.05mm (0.002") high. Unfortunately it's blue, but it looks a lot smoother than the picture with such thin layers, it cold be tidied up a bit and polished.

I've ordered some green PLA and I will print another one with 0.025mm layers which is as close to injection moulding as I can get. The white dots appear to be painted on.

1482510639_traceknob1.thumb.JPG.ff1e4a39005711e0fc21868987342f45.JPG

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Posted (edited)

Here is an example of Polymorph used to fashion a fader cap on a cocktail stick. This was based on the flat type on my SMX, takes less than a minute.

321806017_PolymorphCap.jpg.b137547fdd5ab7352328affd215c4a60.jpg

https://www.amazon.co.uk/Thermoworx-Polymorph-mouldable-eco-friendly-thermoplastic/dp/B06XXQ4CZJ/ref=pd_lpo_vtph_lp_t_3?_encoding=UTF8&psc=1&refRID=YFSA6HK71XPX056X6BCG

Edited by goingdownslow
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I fitted proper knobs to my Laney, as a Trace rip-off it originally had little white 'nips'. Rather than  fill gaps I fitted proper slider caps. Check out the controls, it's 100% a Trace clone on the outside. Inside it uses op-amp based circuitry, rather than pure transistor like the GP11. Also uses remote FET switches rather than having mechanical ones in the signal path. So strangely its technically more advanced but it doesn't sound as good!

It would be a shame to spoil the TE, but I honestly think these knobs do look better:

image.thumb.png.195cdb1826918a87d841212dfb1b3a54.png

Dang, now I'm getting really BAD thoughts about bi-amping, but that would demand another 8R cab... room for a 15" perhaps?

 

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On 30 May 2019 at 21:41, Stub Mandrel said:

These little b****rs cost about $22 a pair to import from British Audio in the US.

I need a green one, so I've done a trial 3D printed one, with layers 0.05mm (0.002") high. Unfortunately it's blue, but it looks a lot smoother than the picture with such thin layers, it cold be tidied up a bit and polished.

I've ordered some green PLA and I will print another one with 0.025mm layers which is as close to injection moulding as I can get. The white dots appear to be painted on.

1482510639_traceknob1.thumb.JPG.ff1e4a39005711e0fc21868987342f45.JPG

That's quite amazingly impressive.......O.o

On 31 May 2019 at 09:51, Stub Mandrel said:

I fitted proper knobs to my Laney, as a Trace rip-off it originally had little white 'nips'. Rather than  fill gaps I fitted proper slider caps. Check out the controls, it's 100% a Trace clone on the outside. Inside it uses op-amp based circuitry, rather than pure transistor like the GP11. Also uses remote FET switches rather than having mechanical ones in the signal path. So strangely its technically more advanced but it doesn't sound as good!

It would be a shame to spoil the TE, but I honestly think these knobs do look better:

image.thumb.png.195cdb1826918a87d841212dfb1b3a54.png

Dang, now I'm getting really BAD thoughts about bi-amping, but that would demand another 8R cab... room for a 15" perhaps?

 

If you could print the slider caps for the TE in fluoro green, that would look so cool.   

And bi- amping is the way to go.....

The "little white nip" slider caps seem to be ubiquitous on Brit amps - whilst looking for spares for the TE I noticed the ones on my Ashdown MK 500 were exactly the same (pic below)

image.png

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I've got into a scrap with an amp designer on 'the other forum' who claimed my estimate that a 150W TE could put out a 400W transient.

I just did a test with my oscillscope on the output. When driven to a square wave, it was happily putting a constant 350W plus into 8 ohms.

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18 minutes ago, Shaggy said:

If you could print the slider caps for the TE in fluoro green, that would look so cool.   

I could... unfortunately I've ordered ordinary green.

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On 02/06/2019 at 04:52, Stub Mandrel said:

I've got into a scrap with an amp designer on 'the other forum' who claimed my estimate that a 150W TE could(n't) put out a 400W transient.

I just did a test with my oscillscope on the output. When driven to a square wave, it was happily putting a constant 350W plus into 8 ohms.

Sir, the scrap you got yourself into (with me) was of your own doing so let's be accurate here if you are going to claim something that's not true,.

It is categorically impossible for your 150 watt (RMS) Trace amp to deliver 400 watt (RMS) under transient conditions, there simply isn't the supply voltage present to make this happen no matter what. I also pulled my product data for that amp and it supported my statement and the math I presented. Perhaps you forgot the part where I had worked for the parent company of Trace and was familiar with the amp?

Now, you choose to change the argument or the scenario and consider power at "square wave clipping". (note that I have mentioned many times on that other forum that an amp (any amp) can deliver almost twice it's rated undistorted power when driven deep into clipping because that's an often unrecognized cause of damage of speakers due to overpowering). This is not "transient" power, or "headroom", or anything even remotely useful except to save face. 

Is is a great amp? Sure it is, no problem with that. Will it deliver 400 watts RMS even under transient conditions, no way. 

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Posted (edited)

Maybe I'm wrong.

I can't make a proper analysis because my only DSO is a cheap battery powered gadget and combined with an x10 probe it's reading well below the Hameg (which I trust).

<edit> FWIW according to the Hameg the peak to peak voltage into 8R if I pop G string really hard is 130V. That's running at a slow timebase and observing first the top, then the bottom peaks, 264W. I really can't be bothered to get another cab out of storage and see if it hits 112V into 4R for a 400W transient because you wouldn't believe me anyway...

Edited by Stub Mandrel

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13 hours ago, Stub Mandrel said:

Maybe I'm wrong.

I can't make a proper analysis because my only DSO is a cheap battery powered gadget and combined with an x10 probe it's reading well below the Hameg (which I trust).

<edit> FWIW according to the Hameg the peak to peak voltage into 8R if I pop G string really hard is 130V. That's running at a slow timebase and observing first the top, then the bottom peaks, 264W. I really can't be bothered to get another cab out of storage and see if it hits 112V into 4R for a 400W transient because you wouldn't believe me anyway...

112V peak to peak calculates to ~170 watts (RMS) not 264 watts.

 

Once you get the math correct, you will find that your argument falls apart. You simply can't get 400 watts transient (in RMS metrics) with a pair of 56 volt rails. It's not that I don't believe you, but it's simply impossible.

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Posted (edited)
18 hours ago, agedhorse said:

Once you get the math correct

Not being facetious, as I would like to get this right... where am I going wrong?

56 / 1.414 = 39.6V RMS

P=V^2 / R

39.6*39.6 = ~1600

1600 / 4 =400W

 

Alternatively

I = 39.6/4 = ~10A

P = I * V

39.6 * 10 = ~400W

Edited by Stub Mandrel
MIght as well try and spell facetious right...

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Posted (edited)

The 170 volts that I stated was for the 8 ohm example that you gave, I was simply following up on those numbers you gave.

The 4 ohm value would be 340 watts, BUT you have to subtract about 2 volts (probably a bit more than this)  for Vce(sat) from each rail (because it can't swing fully rail to rail) and because of the emitter resistors you have to subtract for that as well. 

Presumably, you have the module that has 4 bipolar output transistors (which is actually the 300 watt module, remember what I said earlier that these modules got mixed and matched with various transformers in order to ship products) because if you were really able to get 10 amps RMS which is 14 amps peak, you would have destroyed a single output transistor as soon as the output transistor got hot and the SOA derating kicked in (at right around 10 amps with these circuit voltages) So with each transistor handling 7 amps peak, and the emitter resistor being .22 ohms, the additional voltage drop of 1.5 volts applies (it would try to be 3 volts if it was a single output transistor).

Now, doing your calculations on real world numbers, your output under load conditions is based on 56V - 2V - 1.5V = 52.5V, now divide this by 1.414 and your maximum RMS voltage is 37 volts RMS, which is 342 watts, which agrees closely with my prediction above. These are transient, ideal values (in RMS terms) that will be lower in practice because we didn't account for peak IR losses in the transformer, and other smaller factors.

Now there are a couple of other possibilities, the first is that you really have a GP11-AH150 which uses MOSFET outputs and does have 2 pair per rail (one pair just didn't work out well, found that out early on for the reasons I mentioned above), which should have about the same performance as the bipolar example above (which is for the 300 watt/4 ohm rated module). 

The other possibility, and the one that I THINK is responsible for both your confusion as well as my confusion, is that this amp (with either the bipolar or MOSFET module) is rated at 150 watts RMS with a minimum load of 4 ohms in the marketing materials. In the production service docs, the test values given vary from 250 to 275 watts depending on the module and version. The 150 watts, I will agree is a very conservative number IF you consider that it's really a 250 - 275 watt/4 ohm rated amp by the designers/engineers BUT also confusing for nomenclature because they changed their module model numbers from 4 ohm power value from the bipolar series to the 8 ohm power value in the MOSFET series (and even this wasn't consistent depending on the particular documents).

As an engineer, I spent a lot of time reviewing TE documentation and designs while working for one of the companies that owned Trace in a previous incarnation. There were a lot of really cool things about the designs but there were a lot of things that did not make sense from model to model or even build to build for the same model. This sort of thing is one example, and it was at the very core of the company's personality.

 

So, in a way we are both right and wrong, for different reasons 

 

Edited by agedhorse
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21 hours ago, onehandclapping said:

I have 2 red ones and a green one  and one with no front,free,just pay postage from Australia

Thanks for the kind offer. I have been offered one from France .

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