Hybrid ODS rack preamp

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M Fowler
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Hybrid ODS rack preamp

Post by M Fowler » Thu Sep 28, 2017 8:05 pm

Actually it's a JM into OD rather than an ODS.
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romberg
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Re: Hybrid ODS rack preamp

Post by romberg » Fri Sep 29, 2017 12:19 am

Nice! I'm looking forward to see how it turns out. What are you doing to buffer/attenuate the output level? I suppose one could build in something like a D-lator into a preamp like this. Or just keep the output the same as a complete amp's fx out.

I'm toying with the idea of creating a standalone preamp that includes an overdriven phase inverter that drives something like an interstage transformer. So, I find your build very interesting.

Mike

Guy77
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Re: Hybrid ODS rack preamp

Post by Guy77 » Fri Sep 29, 2017 3:17 am

Looks really nice!
I am also interested in hearing how it turns . I really like the sound of JM style amps. Currently working on another 50 watter.
Will you use 5 preamp tubes like the John Mayer does? Or are you building it with no reverb.

Cheers
Guy

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M Fowler
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Re: Hybrid ODS rack preamp

Post by M Fowler » Fri Sep 29, 2017 10:13 am

The Master Volume will control the output signal.

No reverb since this is a preamp for studio use and I have rack mount tube reverb plus plenty of other reverb effects.

Designing while building.

dcribbs1412
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Re: Hybrid ODS rack preamp

Post by dcribbs1412 » Fri Sep 29, 2017 4:34 pm

Looks great Mark
What transformer you using?
Where is the chassis from?

D

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M Fowler
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Re: Hybrid ODS rack preamp

Post by M Fowler » Fri Sep 29, 2017 11:59 pm

Using the TR-PW-13 transformer which after going over spec's is not going to work for 2 12ax7's so may add additional filament transformer.

Chassis from Markertek.com it's a Middle Atlantic EC-1-6 inch deep econo rackmount 19" chassis 1 RU. $51.75

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M Fowler
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Re: Hybrid ODS rack preamp

Post by M Fowler » Wed Dec 06, 2017 9:24 pm

Some continued work but trying to figure out a good circuit isn't easy for this dumb shit.

OD trimmer used when no loop?
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ODS preamp.png
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Guy77
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Re: Hybrid ODS rack preamp

Post by Guy77 » Wed Dec 06, 2017 9:45 pm

Looking great, very clean! Will there be a switch installed to go from the clean channel to the Overdrive channel or is it the JM straight into the Overdrive and all one channel?

Cheers

Guy

dcribbs1412
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Re: Hybrid ODS rack preamp

Post by dcribbs1412 » Wed Dec 06, 2017 9:52 pm

Looks cool Mark
No Relays makes it a little less complicated
Maybe 100k on front panel for OD trigger?

D

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M Fowler
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Re: Hybrid ODS rack preamp

Post by M Fowler » Wed Dec 06, 2017 9:54 pm

thanks man I'm trying.

That push/pull pot is the switch for clean/OD.

Looked at an old #094 Schematic and removed the power section maybe that will tell me what to do.

Mark
#094 Schematic 1.3 rack mtg preamp.jpg
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M Fowler
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Re: Hybrid ODS rack preamp

Post by M Fowler » Sat Dec 09, 2017 2:26 pm

Slow process since I don't work on it very often and should design before I attempt to build. :roll:

Mark
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martin manning
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Re: Hybrid ODS rack preamp

Post by martin manning » Sat Dec 09, 2017 2:54 pm

Looks good Mark! What is the spec for the PT? Looks like a nice little unit.

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M Fowler
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Re: Hybrid ODS rack preamp

Post by M Fowler » Sat Dec 09, 2017 3:47 pm

Martin the PT is under rated for what I have here, two 12ax7 tubes but I'm going to try it anyway and if I have to will source another PT that will fit in the 1 space chassis.
Single Preamp Tube Project Power Transformer.pdf
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martin manning
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Re: Hybrid ODS rack preamp

Post by martin manning » Sat Dec 09, 2017 3:59 pm

The one in the PDF (Button) is Heyboer, and yes looks a too light; you need about twice that rating on both filament and HT. The one in your pic looks different- has a Mag Components-type part number??

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M Fowler
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Re: Hybrid ODS rack preamp

Post by M Fowler » Sat Dec 09, 2017 5:28 pm

Yeah I swore I had found a different correct size PT but with more amps for two tubes but the number on my PT is the same as the button PT I bought.

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