Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: phsyconoodler on December 14, 2019, 07:44:42 pm
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I have a 2007 Tophat super deluxe that has a couple issues.
First off the amp is extremely well built. Very neat.
Its is stock,no mods at all. A pair of celestion speakers,can use 6v6s or EL34s.
Cathode based.
The issues: it hums significantly if you turn the master up past 1oclock. Not when down.
The tone leaves a lot to be desired. It's ok at low volume clean but as you turn up the preamp vol8me its starts to sound nasty. Not horrible but has not nice distortion. It does not like preamp distortion. Its marginally better with humbuckers but not good with single coils.
It doesnt matter where the eq is,it has a nasty top end to it when driven. Nastier with pedals.
I've tried many tubes and all the voltages are ok for an amp like this. It uses a 56k slope resistor and parallels v1 with a shared cathode cap/resistor. It's somewhat like a bassman except for the paralleled preamp.
Kind of weird really cause this amp should scream beautifully with what it's got here but it just doesnt.
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Ciao Phsyconoodler
Is this or similar ?
(https://i.imgur.com/ohS8M8v.jpg)
Franco
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Some similarities & differences to K's posted schematic. Maybe something like this minus the reverb??? I attached a SCH editable version.
With respect, Tubenit
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IF the amp used to sound good but now doesn't ……………… I wouldn't mod anything. However, IF it's never sounded quite right, I'd maybe consider these type of mods. On V2a, I definitely would NOT use a 22uf on the cathode. When I've tried that (in a bassman type topology) , I found it sounded awful!
Other thing is sometimes I've had silver mica caps go bad. You might check for that and try a ceramic cap instead.
Nice to see you on the forum!
With respect, Tubenit
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It's similar. It has slightly more filtering but everything else is the same.
Its ghost noting. Thats what I'm hearing.
Funny thing is I swapped the v1 cathode csp/resistor from 1.5k to 2.7k_220 uf and it didnt sound any different at all. Swapped back.
Nasty ghost notes going on here
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Is the coupling cap after the first stage actually 500p?
It doesn't make much sense to use a parallel V1 and then cut the meat out of it with that value.
That's got nothing to do with ghost notes or hum, just a reason why it might not matter what you do to V1-k until you tack on a larger value.
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Are the output tubes matched? Maybe one has gone South? What about the filter caps? It's a 2007 amp, while not an excessive age for filter caps, they can and do deteriorate over time.
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Do you think this guy (Tophat) ever saw a Matchless Lightning schematic before? :dontknow:
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I think so
Is the first schematic I remembered when I've seen the Top Hat one
Franco
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Well I've decided to change all the filter caps. We shall see what happens after that. I might also bump that 500pf up .001 or something like that.
Probably warm it up considerably
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IF V2-3 cathode has a 22uf cathode cap, I strongly urge you to try it without that cap or a significantly lower value.
With respect, Tubenit
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That wont make it ghost more though so il will see what it does with new filter caps
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Ok I didnt change the filter caps but I did change that coupling cap the 500pf one. I didnt have a .0012 value on hand so I tried a .002. It got rid of 90% of the ghosting but was too dark so I changed the bypass cap from 22uf to .68uf. Much better!
Now I'll get the Lightning value. 0012uf cap in there and it should be good to go. I'll try it with pedals and see what's shaking.
Tested using my G&L legacy tribute
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Thanks for sharing your success!
As an FYI, the largest cathode cap I've been happy with in that V2-3 position (with that type of topology) is 2.2uf. However, I've found a 1uf paralleled with .68 for 1.68uf to be my favorite.
With respect, Tubenit
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Although a lot better it still doesnt like pedals much.
I have an Ibanez Jet Dtiver that sounds great with every amp.....except this one. It's just nasty sounding. It has a great eq on the pedal but there aren't any settings that this amp is happy with.
The preamp is just not my cup of tea. It would probably like Treble booster but not much else
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Try a switch to disconnect one of the triodes of V1 when you use pedals
Franco
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I can sure try that. I'm thinking of separating them completely
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If you separate the two triodes of V1, may be you want to try the AC30CC2 arrangement with the channel link switch
(https://i.imgur.com/EoIfqUN.jpg)
(https://i.imgur.com/qdgK25T.jpg)
Franco
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Try lifting the tone stack. It's obviously gonna make a huge gain boost and tonal difference but at least you'll hear what this pile of parts could possibly sound like.
If we're still looking at the guesswork schematic and yours has the voltage divider after the tone stack then that thing just looks like a loss monster.
That's what I don't get about this design....why parallel V1 and then squeeze it through 500p, then have a cathode follower into one huge loss factory?
I thought I remember sluckey saying this was the one amp he built that he really didn't bond with. (don't quote me and I'm not sure I'm quoting him). (edit - I'm referring to his build of a Matchless Lightning)
I think I see why.
Some amps sound different and that makes people think they sound "better".
With your experience and playing ability you're probably wondering "what am I missing?"
It's a ton of frequencies. that's all.
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why parallel V1 and then squeeze it through 500p, then have a cathode follower into one huge loss factory?
maybe they're looking for that big hair everyone sings soprano sound :icon_biggrin:
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500pF / 500K (1M + 1M pot in ||) will have about -3dB rolloff at ~~600Hz. dumb design or someone at matchless forgot how to use a calculator - IMO, 0.0047uF there would sound best.
treble network cap - 50pF is probably way too bright - try 120-250pF there.
change 56K CF Rk to 100K - 56K will compress too soon.
make bypass of first stage switchable or delete - first stage has a gain of over 80 with 2 triodes in ||, without bypass the pair have a more typical single 12AX7 triode gain (av~50). probably why your pedals sound like crap - gross distortion with too much LF gain with that 22uF Ck.
--pete