Tonebender MkI More Bass

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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mcentee2
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Post by mcentee2 »

Have a Tonebender MkI that currently has standard cap values in, from input to output:

0.01uF input
25uF between Q1 and Q2
0.1uF between Q2 and Q3
0.1uF Output

Although it probably is a "true" TB MkI sound, it is a little thin for me - what is the easiest way to get more bass from it ?

Do I need to tweak all the caps larger, or will just one of them do the trick ?

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plush
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Post by plush »

mcentee2 wrote:Have a Tonebender MkI that currently has standard cap values in, from input to output:

0.01uF input
25uF between Q1 and Q2
0.1uF between Q2 and Q3
0.1uF Output

Although it probably is a "true" TB MkI sound, it is a little thin for me - what is the easiest way to get more bass from it ?

Do I need to tweak all the caps larger, or will just one of them do the trick ?
Hi!
I'd swap 100n between q2 and q3 for larger value. 100n cap together with 8.2K resistor forms HPF, with effective cutoff freq close to 200hz. If you swap it with, lets say, 470n, it will lower cutoff freq to ~40hz.

mcentee2
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Joined: 13 Oct 2014, 10:14

Post by mcentee2 »

plush wrote:
mcentee2 wrote:Have a Tonebender MkI that currently has standard cap values in, from input to output:

0.01uF input
25uF between Q1 and Q2
0.1uF between Q2 and Q3
0.1uF Output

Although it probably is a "true" TB MkI sound, it is a little thin for me - what is the easiest way to get more bass from it ?

Do I need to tweak all the caps larger, or will just one of them do the trick ?
Hi!
I'd swap 100n between q2 and q3 for larger value. 100n cap together with 8.2K resistor forms HPF, with effective cutoff freq close to 200hz. If you swap it with, lets say, 470n, it will lower cutoff freq to ~40hz.
Thanks - I was struggling with the maths of the hpf/lpf through the circuit, so this makes sense.

I also just caught a couple f references in search to the Gary Hurst TB MkI that DAM posted years ago that has this at 25uF electro, so that fits as well even though its way huger than .47uF, you can only go so low in freq so there may not be much between them aurally !!!


Cheers

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plush
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Post by plush »

mcentee2 wrote:that has this at 25uF electro
Going higher than 1-2uf already makes no sense to me. 25 uf seems more like аll original leftover brought to us by retarded boutique builders.

mcentee2
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Post by mcentee2 »

plush wrote:
mcentee2 wrote:that has this at 25uF electro
Going higher than 1-2uf already makes no sense to me. 25 uf seems more like аll original leftover brought to us by retarded boutique builders.
lol ! But I get your drift!

Just tried some caps out - anything more than the 0.1uF does add more bass progressively.

1uF seems a sweet spot, at 10uF however starting to hear creeping in a "capacitor charging delay" after heavy chords. The cap seems to be "used up" then take up to half a second or so to recharge and start passing signal again - quiet then normal hiss creeps back in.

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Post by plush »

I hope you've checked your 10uf cap polarity before placing it :)

mcentee2
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Post by mcentee2 »

plush wrote:I hope you've checked your 10uf cap polarity before placing it :)
Yep - +ve towards Q3 base :)

mcentee2
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Post by mcentee2 »

mcentee2 wrote:
plush wrote:I hope you've checked your 10uf cap polarity before placing it :)
Yep - +ve towards Q3 base :)
Hmmmmm.....that is the way it is drawn in the Hurst schematic, however I have just measured across the cap and it is definitely +6v on the Q2 collector side Vs +0.5v on the Q3 base side.

I have made sure my -ve and +be is the right way around for measuring!

So my head tells me it should go the other way around with +be towards Q3c. ?????

mcentee2
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Joined: 13 Oct 2014, 10:14

Post by mcentee2 »

mcentee2 wrote:
mcentee2 wrote:
plush wrote:I hope you've checked your 10uf cap polarity before placing it :)
Yep - +ve towards Q3 base :)
Hmmmmm.....that is the way it is drawn in the Hurst schematic, however I have just measured across the cap and it is definitely +6v on the Q2 collector side Vs +0.5v on the Q3 base side.

I have made sure my -ve and +be is the right way around for measuring!

So my head tells me it should go the other way around with +be towards Q3c. ?????
Oops, brain fart time!

It measures -6v on Q2c and -0.5v on Q3b, so the schematic is correct, phew.

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