Best Trace Head

[thodrik]

1 hour ago, TheGreek said:

Careful now...you'll have to move stealthfully through my neighbourhood with statements like that..😉😉

I did say ‘for home practice and recording’. When I tried to use my old SMX for home practice it sent tremors through the whole tenement I was living in at the time!

[Stub Mandrel]

On 13/05/2020 at 19:26, shine182 said:

That's my fear, that a trace purchase will just be too clean

People forget to to turn up the gain until the overload light comes on regularly during normal playing, then take it back one click.

Makes a big difference to the sound.

[Deedee]

1 hour ago, Stub Mandrel said:

People forget to to turn up the gain until the overload light comes on regularly during normal playing, then take it back one click.

Makes a big difference to the sound.

Very true. I’ve had people coming up to me between sets horrified when they see the position of the gain knob, but that’s how it should be set.

[Stub Mandrel]

14 hours ago, Deedee said:

Very true. I’ve had people coming up to me between sets horrified when they see the position of the gain knob, but that’s how it should be set.

The circuits is laid out so the frequency response changes with how the gain knob is set, which is different from most designs.

[nilebodgers]

6 hours ago, Stub Mandrel said:

The circuits is laid out so the frequency response changes with how the gain knob is set, which is different from most designs.

Hmmm - I've got the schematics for both series 6 and SMX and there is nothing in there designed to do that. Do you have a reference explaining why+how?

[Stub Mandrel]

3 hours ago, nilebodgers said:

Hmmm - I've got the schematics for both series 6 and SMX and there is nothing in there designed to do that. Do you have a reference explaining why+how?

This is the GP11 preamp.

VR1 is 500K, R4 is 220K. C1 is 1.5uF, C2 is 0.47uF. R5 is 1M. C3 is 1000pF

As gain is increased the resistive element of the input impedance drops considerably. Without modelling it I would expect this to mean the low-frequency gain will drop more than high frequency as the gain is increased.

I don't know if this is the case, but the GP11 certainly has the reputation of changing the character of the sound as the gain is changed.

It's certainly unusual to vary the gain in this way.

[nilebodgers]

15 hours ago, Stub Mandrel said:

This is the GP11 preamp.

VR1 is 500K, R4 is 220K. C1 is 1.5uF, C2 is 0.47uF. R5 is 1M. C3 is 1000pF

As gain is increased the resistive element of the input impedance drops considerably. Without modelling it I would expect this to mean the low-frequency gain will drop more than high frequency as the gain is increased.

I don't know if this is the case, but the GP11 certainly has the reputation of changing the character of the sound as the gain is changed.

It's certainly unusual to vary the gain in this way.

That is the same as Series 6, SMX is completely different with a FET buffer and a valve in parallel.

I modelled up the input circuit in LTSpice and at 100% gain the passive input sees approx 13k input impedence, at 90% it is 50k, at 80% is 74k and at lower gains it rises to 120k-ish. The frequency response of the input stage doesn't change significantly and it is -3db down at 13Hz and over 100kHz at the other end.

I'd expect the sound with a passive bass (with no switched-on or buffered pedals in line) to change very markedly with gain as the pickups see a different impedence input. It's not frequency-dependent though, so not like a passive tone control.

With my engineers hat on I'd never design an input that behaved like that, but the Trace amps were massively successful, so what do I know!

 

[Stub Mandrel]

10 minutes ago, nilebodgers said:

With my engineers hat on I'd never design an input that behaved like that, but the Trace amps were massively successful, so what do I know!

I'm only a hobbyist at electronics, but I've certainly never seen an input stage like that elsewhere.

My spice skills are minimal (limited to some very basic online modelling)...

[uk_lefty]

The best Trace Head is the one you haven't managed to try yet. 

They're all awesome in their own way, I love em but am being sensible and not buying one for just when I fancy it. 

[Japhet]

GP 12SMX was my favorite, and unlike many, I actually like the pre shape options too. As said previously, setting the preamp to just before it clips is good advice. Wish I still had mine in many ways. One thing they were prone to was a dodgy internal earth that could take out the whole amp. I'd advise getting that checked and improved if you find one.