Best Amplifier I Ever Built

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Pressed_Rat
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Best Amplifier I Ever Built

Post by Pressed_Rat » Sat Oct 06, 2018 7:35 am

.. so far. I know this is pretty much a Marshall-oriented forum, but I thought I'd share this DIY build with you guys, a total fluke.

I had this Hammond 125ESE OT from an old P1eX build sitting around wondering what to do with it. I had been listening to "Live at Leeds" for about a week, digging that awesome Hiwatt tone, and thought what about a Hiwatt pre into a parallel, single-ended amp, using two OTs. Maybe I could capture some of that crushing sound at a lower volume. Hmmm... So I started drafting up a schematic and came up with this:

http://s165.photobucket.com/user/JKCavi ... t=2&page=1

Sounds nothing like a Hiwatt.

I thought the tone stack was a big part of the Hiwatt sound, and maybe so, but the power amp is equally important. A parallel, single-ended, cathode biased, power amp sans negative feed back doesn't equate to a push-pull, fixed biased amp with feedback. This sounds more like a Marshall SL at around 20 watts - a very loud 20 watts. I like it better than my Marshall 50 watt clone. I am playing it though a 4x10" open backed cab w/Emi Ramrods. The mid control of the tone stack has more effect on the overall tone compared to a typical FMV tonestack.

The preamp is pretty much a straight forward Hiwatt DR103.I put in a switch to toggle between shared-cathode Late 60's preamp and a split cathode early 70's preamp, but it wasn't worth it - the shared is so much better. There is no cathode follower after the tone stack recovery stage; straight into the power amp.

Tubes are EH 12AX7s and EH 6CA7s. I have tried thsi with 5881s and 6550s. The 5881s sound a little bright, but the 6550s (Sovteks and Tung Sol RIs) sound very close to the 6CA7s. Both OTs are Hammond 125ESE and PT is a Hammond 270HX.

A friend of mine borrowed it to play a show last summer. He used it for the band's 3rd set, replacing two Soldano Astroverbs with my amp. Sounded very loud and good. Of course my friend can make anything sound good, but when they cut into "Since I've Ben Loving You".... wow, sounded very good.

For those interested, there is an error in the schematic. The signal to the tone stack comes after the 200K plate resistor on V2, not before.

Tazin
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Re: Best Amplifier I Ever Built

Post by Tazin » Sat Oct 06, 2018 11:39 am

Interesting concept...

jarrodthebobo
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Re: Best Amplifier I Ever Built

Post by jarrodthebobo » Sat Oct 06, 2018 10:20 pm

Pretty cool build! Quick question though; what is the point of having two output transformers?

I've built a parallel single ended amp similar to yours but with more of a marshall based flavor; I only used one output transformer. What's the benefit of using another?

Thanks!
"I hear you knocking but you can't come in-
I know you've been drinking Gin." -Louis Jordan

Pressed_Rat
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Posts: 18
Joined: Sun Aug 08, 2010 5:54 am
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Re: Best Amplifier I Ever Built

Post by Pressed_Rat » Mon Oct 08, 2018 5:22 am

Just more power. I wanted to use a leftover 15 Watt OT and the thought of pairing OTs came to mind. So I bought a big PT and another 15 Watt OT. Think I'm probably getting around 20 watts total.

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