Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on July 31, 2014, 03:52:44 am

Title: BlackStar ISF - An interesting feature explained
Post by: kagliostro on July 31, 2014, 03:52:44 am

I've found some explanation about the BlackStar ISF (Infinite Shape Feature) and i think it can be of some interest

basically it is based on the use of a dual ganged pot

Here is the schematic
(http://3.bp.blogspot.com/-TPVVms8B0JI/T7eVRb9Fl0I/AAAAAAAABVw/YaPxTm_sIfU/s1600/blackstr_isf.gif)

Here is a video from BlackStar
https://www.youtube.com/watch?v=C7Xig5d3Mao (https://www.youtube.com/watch?v=C7Xig5d3Mao)

Here is the Patent with complete explanation
https://docs.google.com/file/d/0BwMWxzd7lEJ4WWZselRsb3R5Q0U/edit?pli=1 (https://docs.google.com/file/d/0BwMWxzd7lEJ4WWZselRsb3R5Q0U/edit?pli=1)

The patent didn't show any value on the schematic, but here there is the part one of the schematic of a BlackStar HT-5
(http://1.bp.blogspot.com/-uIF5rJL-0HI/T7eWPNY7rUI/AAAAAAAABV4/5oLHFazBGKA/s1600/HT-5_preamp_pt_1.gif)

Not all values are there but this can be of some help, I've find info giving this values as start values for a try
C1 = 470nF, C2 = 220nF, C3 = 220nF and C4 = 4.7nF, R4 = 1k -- pot near for sure is a dual 10k linear pot

Probably this values must be adapted for a tube circuit use

I hope you can find this thing interesting and enjoy spending some time in experimentation with fun

K

Title: Re: BlackStar ISF - An interesting feature explained
Post by: dajare on November 26, 2018, 06:34:22 am

Hi - I've been doing some websearching on Blackstar's ISF control, and ran across this post. I signed up to the forum explicitly to say "thank you" for this post -- really helpful!

And I'm glad it led me to this forum, as it looks like there is a lot of interesting material here.

So -- thanks!  :thumbsup:

Title: Re: BlackStar ISF - An interesting feature explained
Post by: jjasilli on November 26, 2018, 07:46:45 am

Despite the explanation, to me the audio clip sounds like the circuit simply cuts hi's as the contour control is turned clockwise.


FWIW, Ampeg had a frequency shifting circuit in the V2 / V4 Models (perhaps others also).  The stated purpose was to emulate the tone of any amp such as a Fender Twin or a Marshal.  The frequency shifting works, but to me the amp always sounds like an Ampeg, never like any other amp.  That works for me, but does not fulfill the stated purpose.