Tone compare vs Boogie please

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RichM
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Re: Tone compare vs Boogie please

Post by RichM » Wed May 27, 2015 5:55 am

Thanks - will have a look a the v5 compression issue but not noticed it in comparison to my other amps so far.

i will have a look at wiring up a switch (toggle or push-pull) with the two sets of resistors/caps you suggested. I am wondering how far to go ... will dig out a typical Mark diagram and see what the effective v1a cathode values are with the bass control on zero (which is how I run it). A guess a push-pull will be neater - otherwise need to look for spaces to put a switch - the generally pointless green led hole for the vintage channel could work - keen not to make any permanent changes.

WIll report back once I get round to it!!

R.

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Re: Tone compare vs Boogie please

Post by RichM » Wed May 27, 2015 5:19 pm

SabbadiusUSA wrote:
RichM wrote:Very interesting ... so in terms of the bypass cap, what would you recommend as the mod - a pull switch on a control pot to put another 2u2 cap in series lowering the total to 1.1u maybe? Or would you switch between a 2u2/1.8k and the 1u/1.5k together? What caps would you recommend for this job ... seems pretty easy.
Set it up however you want... Experiment. Just make sure the caps are situated in proper polarity. I would go 2.2/1.8 or 1/1.5 so to switch to stock setting. You could even go 3-way using a .68uf capacitor. I would contact "Kell" for detailed technical Q&A.
Quick question - what is the need to change the cathode resistor from 1.8 to 1.5? From what I've read this would change the amount of gain - is this intented to compensate for reduced low frequency gain created by reducing the capacitor value? For the moment, I am think about trying a couple of different caps (1uf and 0.47uf) to see whether I like the results - will then look to put in a switch to flip back to stock. Not planning on changing the resistor at the moment - so keen to understand if I'm missing something.

Rich.

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Re: Tone compare vs Boogie please

Post by SabbadiusUSA » Wed May 27, 2015 10:28 pm

RichM wrote:
SabbadiusUSA wrote:
RichM wrote:Very interesting ... so in terms of the bypass cap, what would you recommend as the mod - a pull switch on a control pot to put another 2u2 cap in series lowering the total to 1.1u maybe? Or would you switch between a 2u2/1.8k and the 1u/1.5k together? What caps would you recommend for this job ... seems pretty easy.
Set it up however you want... Experiment. Just make sure the caps are situated in proper polarity. I would go 2.2/1.8 or 1/1.5 so to switch to stock setting. You could even go 3-way using a .68uf capacitor. I would contact "Kell" for detailed technical Q&A.
Quick question - what is the need to change the cathode resistor from 1.8 to 1.5? From what I've read this would change the amount of gain - is this intented to compensate for reduced low frequency gain created by reducing the capacitor value? For the moment, I am think about trying a couple of different caps (1uf and 0.47uf) to see whether I like the results - will then look to put in a switch to flip back to stock. Not planning on changing the resistor at the moment - so keen to understand if I'm missing something.

Rich.
Leave the resistors stock. Like I said, these mods are geared to MK and RK circuits. I found that I prefer the 1.8/1uf (Soldano value) best on my RK100. It's a matter of personal preference, that's all. Other than a compression problem in one particular amp, I thought the Hellcat was perfect stock.

I would not make any changes that can't be reversed... i.e. Drilling the chassis.

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Re: Tone compare vs Boogie please

Post by RichM » Thu May 28, 2015 7:02 am

Cool - thanks. I have a vishay 470nF coming that I'll try and a 1uF mullard too so I'll pick what I prefer. The 470nF gives same bass roll off on V1a as a Mark (IIC+) circuit based on my research. I'll only install a switch if I can find a way of placing it that doesn't look too naff. The stock cap doesn't seem too excessive as there is roll off of about 2db at 82hz (low E string). Switching to 470nF increases that roll off to 4.5db. The 1uF gives about 3.8db cut.

I'm using this calculator site - pretty neat! http://www.ampbooks.com/mobile/amplifie ... alculator/

Rich.

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Re: Tone compare vs Boogie please

Post by SabbadiusUSA » Fri May 29, 2015 4:00 pm

RichM wrote:Cool - thanks. I have a vishay 470nF coming that I'll try and a 1uF mullard too so I'll pick what I prefer. The 470nF gives same bass roll off on V1a as a Mark (IIC+) circuit based on my research. I'll only install a switch if I can find a way of placing it that doesn't look too naff. The stock cap doesn't seem too excessive as there is roll off of about 2db at 82hz (low E string). Switching to 470nF increases that roll off to 4.5db. The 1uF gives about 3.8db cut.

I'm using this calculator site - pretty neat! http://www.ampbooks.com/mobile/amplifie ... alculator/

Rich.
You will be amazed at how much the 2db roll-off affects bottom-end gain so early in the preamp. Roll-off 2db further down the line (i.e. tone-stack), and the difference is barley noticeable. The most audible EQ changes can me heard by experimenting with various treble cap values in the tone-stack, up or down 50pf to 100pf. You may want to tweak the value there as well.

Cornford's (to my ears) sound like a Boogie voiced Marshall's. The MK50 has little more spice on the attack compared to the RK, due to the .0047 cap off the V1b plate, but lacks the "nads" of the RK's 100 watt power section. Have you seen the size of the RK100 power transformer? :eek:

While I'm thinking about it, you may also prefer the sound of a polypro .047 bass cap vs. polyester in the tone-stack. I'm using a .047 WIMA Black Box... To my ears, the bass response is smoother, with increased definition. Another great place to try polypro's, is off the phase inverter plates... Try replacing the 2 x .033 polyester to polypro. I would also avoid using JJ EL84's in the HC.

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Re: Tone compare vs Boogie please

Post by RichM » Fri May 29, 2015 7:30 pm

Hi there,

So I put in the 470nF cathode bypass cap on V1a and glad I didn't go halfway with the 1uF. The bass tightness is now on par with my Mesa StuPre which is what I was aiming for. However the change isn't that drastic ... and I don't feel the need to add in a switch to select the different values - I just prefer the .47uF value to the 2.2uF.

I will have a think about other tone stack changes ... for now I am happy that the amp sounds like itself although I am liking the general gain structure and EQ of the StuPre better - although I have been getting an interimittent issue with it where I get some wierd graininess ... I have changed every tube so I wonder if I have a dodgey solder joint somehwere ... hmm ... irritating as the unit sounds Godly!

Yep, I changed out the JJ EL84s for some 1970 Tungsram NOS valves which I prefer. In my trouble shooting the StuPre issue I tried swapping the JJ 6L6GC back in to the RH30 ... quite boomy and thin compared to my NOS Sylvania 6L6WGB that sound almost EL34 like ... just lovely mid range.

Richard.

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Re: Tone compare vs Boogie please

Post by SabbadiusUSA » Sat May 30, 2015 6:04 am

That's interesting... I tried dual .68 caps at V1a/b, but it was too thin sounding to my ears. The RK preamp seems to prefer dual 1uf. Design wise, the RK preamp is very close to the Boger "Fish" Brown channel.

I love my Mesa/Boogie Triaxis! A little smoother than the Quad, and I like it that way. The MIDI programability makes it my go-to device in my rack. The RK preamp has a sonic signature that I can't get out of any other preamp or complete amp, but then I guess they're all like that. It's not better or worse, just different.

I know what you mean about the JJ's... I don't care for them. Their long plate ECC83's are nice, but that's as far as I'll go with JJ's. I hear they make a nice GZ34 rectifier valve as well. My favorite EL34's, are the fat bottle Golden Dragon's. They almost have a Simu-Class tone to them. i.e. 6L6 meets EL34.

Good to hear you found a good recipe. Enjoy that amp! :thumbup:

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Re: Tone compare vs Boogie please

Post by RichM » Sat May 30, 2015 7:14 am

It clearly is thinner yes .. but rather than sacrifice preamp clarity, I think if I feel the need for more bass now, I'd prefer to get one of those Mesa 5 band EQ pedals to put in the loop. The frequency selection is excellent for guitar - suprosed there aren't more clones!

R.

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Re: Tone compare vs Boogie please

Post by RichM » Sat May 30, 2015 5:14 pm

I installed a switch in the end - I used one of the LED holes which is not really needed anyway so no permanent modifications needed. I am switching between the 2.2uF original and the 470nF cap. Being able to switch back and forth has proved the effect is quite mild - just a rolling off of deep bass and a little more tightness as a result - nothing drastic.

Can't figure out how to upload a picture to show but basically a small toggle below the vintage channel gain where the green light normally is.

R.

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Re: Tone compare vs Boogie please

Post by SabbadiusUSA » Sun May 31, 2015 4:51 pm

Sounds like you have it dialed-in exactly how you want it. I'm getting ready to put the 1uf caps back in my RK... The 2.2uf are just too extreme for my needs.

I picked up a Marshall Silver Jubilee 50 watt half stack yesterday that belonged to Tabitha's Secret guitarist Jay Stanley. It had an intermittent issue with popping when the amp was touched. What I found, was that Marshall neglected to solder a wire on the power switch! :wtf: The lead end was folded over the terminal, but never soldered. I'm going to do a thorough cleaning of the pots and sockets, just as soon as my Deoxit order arrives.

Update: I installed the 1uf cathode bypass capacitors this evening. I also replaced the 100n MKT tone-stack bass capacitor with a 33n Phillips MKT capacitor. No question about it... A a huge improvement in usable bass range, gain clarity and tone! I found myself having to run a 5751 valve in V2 to clean it up, same as with my old Soldano SLO. I prefer using varied brand 12AX7 valves, so the 1uf cap mod just makes sense.

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