Dave Freidman mod for Concorde

[aaronz28]

anyone know what this actually is?

Pete Thorn says it is a 1 cap mod that solves the sag issue.

i love my KF50 but it has way way too much sag for a high gain amp.

anyone?

thanks
Aaron

[Colossal]

If I were to guess, it would be that Dave lowered the value of the coupling cap on the second stage at the split load for Fast/Gradual. The cap there normally is 0.1uF and that seems like an invitation to blocking distortion when the amp is opened up. I would go way down in value and it should tighten things up significantly without a perceived loss of low end. There should be massive low end in that amp.

The power supply is a classic Plexi format with 40uF supplying the screens. I was under the impression that the Dave Friedman mod addresses flabby bass at high volume, not power supply sag. I'm fairly sure I read that in a thread from Pete Thorn who has had both his K50s modded by Dave Friedman.

[paulster]

Did anybody actually try asking Dave last time this came up? It might not be a trade secret since Jim Scumback said that Komet themselves are also offering the same mod now.

I would pop over and ask him but since I don't have a Concorde in my stable it would be bit of a moot question.

[Allynmey]

Replace the .1uF after the switch to .002uF. I also change the ceramic treble cap for Silver Mica. Thats it.

[Roe]

have anyone tried reducing the .1 on a k60? my k60 is a little bassy when running at high volumes.

[M Fowler]

What happens with Friedman mod when a fast/gradual foot switch has been installed because the ft sw board has two .1uf coupling caps so change those two caps out for .002?

Mark

[Roe]

The best solution is not to switch DC but to use two caps before the switch. I'm using 2n2 and 15nf

[Mark]

This is Pete Thorn's original comment about his Komet amps.

After listening to the amp, Dave looked it over and made some suggestions... he made 3 tweaks and BAM holy hell it sounds just AWESOME now. I can literally dime the amp in either fast or gradual mode and it is an amazing rock tone.

This could just be rubbish, but it's the original post.

ya basically I showed Dave what it was doing, and he kind of went "hmmm" and opened it up, and said within 2 minutes 'I bet it's this" and changed something out. That was it. hen he did a tweak to the neg feedback and that made things a little sweeter, and then we stopped there. That's what you hear on the clip. It's like a whole new beast now. Was always great in gradual mode up to 2 oclock, but now it's useable anywhere on the volume pot- makes it a true hi gain beast if that's what you want... I think I'll try and record a track with it over the next couple days. I'll post what I come up with.

[dbeasley]

Makes sense that he is reducing the .1uf cap. As far as NFB goes, if you look at Dave's mods for Marshalls he is fond of doing a fixed resonance control (cap with resistor in series with the NFB more or less), so could be something along those lines to tighten up the bottom end at higher gain settings.

Take a look at the Friedman BE type amps for more on this.

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[dbeasley]

Using the term "sweeter" is kinda vague, and I typically attribute that adjective to less harsh top end. But I could see it being as "less flabby lows" at higher gain settings.

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[Mark]

The resonance mod surely only makes the bass flabbier sounding by taking it out of the negative feedback network. Lowering the value of the feedback resistor would exert more control to a point. The other points to control the bass would be the cap on the input of the P. I. stage and changing the 220K bias resistors on the grids of the output valves to 100K. This may assist in reducing crossover distortion and roll some bass off.

Of course Pete Thorn could have been pulling our collective legs when he said three tweaks, rereading my quotes he said three things in one quote and two in another quote. I suspect it is the most obvious thing, the 0.1uF cap going to the third stage.

Try different caps in lieu of the 0.1uF cap. I'd start with 0.01uF and go for smaller values. The two favourite Express values are 0.002uF and 0.0047uF.

[Roe]

2nf and 3nf work well here