Finally written it up ORST Preamp

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LD50
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Finally written it up ORST Preamp

Post by LD50 » Sun Aug 19, 2018 3:30 pm

Image

I hope it is ok to post the schematic of an amp first built nearly 50 years ago, not sure where we are on intellectual property after this elapsed time.
Please check it over, I am pretty sure it is correct. A friend, Ned Babb has a similar era amp that he has had drawn up by hand, although very similar, his has had some work done but it has 0.022uF couplers in the first stage and a 100pF cap over the volume pot. His internal trim pot was relocated to the rear panel.
Thank you to my son who has been distracted from designing Class D power amps to draw this from my blueprinting notes of the ex-Beat Club ORST you see Messrs Fraser and Kossoff playing in those old Youtube clips. Any errors will be mine, not his! Since the WA clips last year I tweaked the Drive switch which liberated some of the gain. Of course these knobs are very interactive and dialling in is tricky but ultimately very rewarding (my ears are ringing as I type after an hour of playing the clone)
The odd feedback arrangement you see around the Drive and Boost area had me puzzled and the partial bypass on V2a cathode too.
Next is to finish the 2000 blueprint, this is very similar except minus the Echo circuit although quite similar.
Last edited by LD50 on Sat Oct 27, 2018 6:02 pm, edited 1 time in total.

bclaire
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Re: Finally written it up ORST Preamp

Post by bclaire » Sun Aug 19, 2018 4:20 pm

Cool. Nice job!

Gladmarr
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Re: Finally written it up ORST Preamp

Post by Gladmarr » Sun Aug 19, 2018 4:33 pm

Wow! Awesome! 8)

tlbh
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Re: Finally written it up ORST Preamp

Post by tlbh » Sat Sep 22, 2018 2:46 pm

As a bass player, I love my OR120 (1973) blasting thru a 2x15" bassman cab onstage, but with major studios closing their doors these days, my rig is either too big or too much for Jane/John Doe's apartment/basement Pro Tools studios.

A bunch of these of kids have started trying out Matamp and Orange inspired "platform" pedals:
e.g.-Iskrem Micro Cat-o'dyne & Kurio T120...to play thru their laptops and headphones.
I noticed these pedals use AC/AC (120/240-12) wall-wart power supplies.

I don't need a pedal to switch my tone On or Off.
However,
..this post made me wonder if 48v phantom power (from a console or mic-pre/PC Interface) is enough to drive V1 and use J3 as the output for a bass DI?
Just curious.
..and
-Thanks for posting that LD50

Gladmarr
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Re: Finally written it up ORST Preamp

Post by Gladmarr » Tue Sep 25, 2018 9:13 pm

The problem would probably be how much current that phantom power supply can .....supply. The filament on that tube will likely draw more current than the actual plates.

fiveightandten
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Re: Finally written it up ORST Preamp

Post by fiveightandten » Wed Sep 26, 2018 2:31 am

tlbh wrote:
Sat Sep 22, 2018 2:46 pm
As a bass player, I love my OR120 (1973) blasting thru a 2x15" bassman cab onstage, but with major studios closing their doors these days, my rig is either too big or too much for Jane/John Doe's apartment/basement Pro Tools studios.

A bunch of these of kids have started trying out Matamp and Orange inspired "platform" pedals:
e.g.-Iskrem Micro Cat-o'dyne & Kurio T120...to play thru their laptops and headphones.
I noticed these pedals use AC/AC (120/240-12) wall-wart power supplies.

I don't need a pedal to switch my tone On or Off.
However,
..this post made me wonder if 48v phantom power (from a console or mic-pre/PC Interface) is enough to drive V1 and use J3 as the output for a bass DI?
Just curious.
..and
-Thanks for posting that LD50
Have you thought about using the amp with a load and cab IR?

-Nick
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tlbh
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Re: Finally written it up ORST Preamp

Post by tlbh » Fri Nov 02, 2018 11:30 pm

Got back to this late 'cause I didn't tick the
Notify me when a reply is posted
Thanks Gladmarr.
Not being the most "technically savvy" is why I inquired.
Most console mic-pre and PC interface descriptions just state "...with 48V phantom power".
After finally reading your reply, I inquired about the supply for the Cat-o'dyne (which uses 2x 12AX7s)
and it's rated at 1 amp.
Don't know of any mic elements that would need that much juice.

As for your suggestion Nick, I have thought about that.
The hitch is no one around here have any to try out, let alone compare.
Suppose I could build one, yet again still no where around here to get components, so would "have to order online", or dumpster dive.

As I said, an ole "..wonder if" moment.

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