Members Shamdog Posted September 6, 2011 Members Share Posted September 6, 2011 This thread is dedicated to those of us who play the Handsome Devil - either the head or combo. I know that the Jet City guys have a wealth of info on how to mod the 20 watter, and would like to start the same thing here for the HD. I'll start off with the first question: How can I tighten up the bass a bit? Link to comment Share on other sites More sharing options...
Members m-theory Posted September 6, 2011 Members Share Posted September 6, 2011 I don't have this amp, but this type of issue is common to these types of amps in general, from what I've heard myself, and can be remedied similarly. In no particular order, necessarily, except for #1 and #2: 1. Need schematic 2. Proper bias 3. Increase capacitance in power supply filtering 4. Possible cap value changes on preamp tubes...need schematic to verify 5. If no choke is present, add one 6. Output transformer upgrade 7. Tone and filter cap upgrades Also, speaker and cabinet selection is very important. Open back cabinets are going to be less "tight" in lows than closed cabinets. Link to comment Share on other sites More sharing options...
Members Zozobra Posted September 6, 2011 Members Share Posted September 6, 2011 Originally Posted by Shamdog This thread is dedicated to those of us who play the Handsome Devil - either the head or combo. I know that the Jet City guys have a wealth of info on how to mod the 20 watter, and would like to start the same thing here for the HD.I'll start off with the first question:How can I tighten up the bass a bit? A schematic is going to help lots but the quickest way to tighten up the bass is reduce the size of a coupling cap somewhere. 22n throughout is a fairly common topology and perhaps a bit much for some people. Try swapping one (say the one between the 2nd and 3rd stage, assuming its a 3 stage + cf > tone stack) for a 4n7. If that isnt enough swap the first one for a 10n. Other tricks would be to reduce the cathode bypass cap on the first stage assuming it has one (dont see why it wouldnt) and its large. Finally you can reduce the coupling caps to the power tubes. Link to comment Share on other sites More sharing options...
Members Zozobra Posted September 6, 2011 Members Share Posted September 6, 2011 Okay, it appears to be a 2 stage > tone stack >PI topology so what I posted will need some adjustment... Link to comment Share on other sites More sharing options...
Members Shamdog Posted September 6, 2011 Author Members Share Posted September 6, 2011 Gotta run now, but the combo is a modified/semi-closed back. Closed, with a good sized vent grill for the tubes. I'm running an Eminence Texas Heat speaker.I was kinda hoping someone who had modded this amp would chime in, too Link to comment Share on other sites More sharing options...
Members m-theory Posted September 6, 2011 Members Share Posted September 6, 2011 I was kinda hoping someone who had modded this amp would chime in, too A loose bottom end has pretty standard fixes that aren't amp-specific. I gave you 7 things to try that will absolutely, positively have a profound impact on the problem you described. Give some or all of them a try. If it were mine, I'd do them all, but if you want to minimize expense and effort with decent return, start with output tube bias, a choke, and additional capacitance in the power supply. Running neck and neck with those recommendations would be to reduce the values of the preamp tube bypass caps, starting with V1, since that one serves as the gatekeeper for low end signal from that point on. The single most dramatic improvement you can make is to upgrade the output transformer. You don't necessarily HAVE to do this in order to have a working amp, but I can assure you that you won't regret it, if you do. I guarantee you'd be astounded at the vast improvement. Not only will it significantly tighten your low end, but it will expand the frequency response in general, and dramatically improve the overall tone, feel, and responsiveness of the entire amp. Link to comment Share on other sites More sharing options...
Members Zozobra Posted September 6, 2011 Members Share Posted September 6, 2011 Unless the OT is total dog {censored} there is no point swapping it unless fails. Changing the coupling and bypass caps will probably do what he wants here and it will cost a few dollars to try. Link to comment Share on other sites More sharing options...
Members m-theory Posted September 7, 2011 Members Share Posted September 7, 2011 Unless the OT is total dog {censored} there is no point swapping it unless fails. Actually, the output transformers in these cheaply-built, mass-produced, Chinese amps are generally quite crappy. Upgrading the heart and soul of these types of amps is far from "pointless." It's the single most significant improvement that can be made to them, and can really turn a rather mundane, uninspiring amp into something pretty special. Link to comment Share on other sites More sharing options...
Members Zozobra Posted September 7, 2011 Members Share Posted September 7, 2011 I have no experience of the amp. A friend had one of the 100W blackhearts and the trannys in that seems okay and the amp sounded decent enough, although this might not be true of this amp. You'll have to excuse my scepticism of transformer replacements as upgrades. What would you be swapping them with? I'd still start with the circuit every time though. Link to comment Share on other sites More sharing options...
Members m-theory Posted September 7, 2011 Members Share Posted September 7, 2011 I've upgraded the iron in many of these cheap amps, and have been astounded at the improvement in every case. My most recent was a jet city JCA20, which actually doesn't have horrible iron to begin with. The difference was just incredible. I went with an Allen OT22 (Heyboer-built) for that one, but an OT20 or a 125A Hammond would work as well, as would any other transformer made for similar amps. I used an MPS in a Blues Jr. with equally impressive results. I've historically started with circuit tinkering as well, but I really have come to doubt that logic, given how dramatically an output transformer upgrade improves the entire amp. In my JCA20, I actually ended up reversing some of the circuit changes I'd made before the OT swap, because the new OT simply made several other changes unnecessary. The circuit design on that amp is actually pretty good, for the most part. The component quality leaves something to be desired, and that's the norm for all of these cheap amps. Try this for yourself sometime. Buy one of these cheap amps used, and before you do anything else, upgrade the OT, replace the tubes, and set the bias. You'll become a believer. Link to comment Share on other sites More sharing options...
Members Shamdog Posted September 7, 2011 Author Members Share Posted September 7, 2011 Guys - Here's a link to the Schematic:http://rowbinet.files.wordpress.com/...4275616315.jpg Link to comment Share on other sites More sharing options...
Members m-theory Posted September 7, 2011 Members Share Posted September 7, 2011 * Fresh output tubes with proper bias * Try reducing C4 to 4.7uf, and see what that does. Play around with different values there. * Adding a choke might be beneficial * Try a different speaker and a closed back cabinet. Those things should get you audible changes, and will help determine what, if anything additional may be desired. Again, I'm a HUGE fan of output transformer upgrades! Nothing will tighten up the low end on these types of amps like that! Link to comment Share on other sites More sharing options...
Members Zozobra Posted September 7, 2011 Members Share Posted September 7, 2011 I'd reduce C2 to say 10n or 4n7. That will cut a lot of bass from the rest of the preamp.C1 and C4 could be reduced. Say V1 to 680n for a marshally flavour and C4 to 1U although C4/V1B isnt going to cause any blocking distortion as its going into a tone stack.C11 and C12 could be reduced too.The big offender (now I've scrolled across the screen ) would be the huge bypass caps on the power valves! 22uF here would deflub the poweramp a fair chunk. Link to comment Share on other sites More sharing options...
Members Zozobra Posted September 7, 2011 Members Share Posted September 7, 2011 Interestingly each gain stage has its own filter cap which is overkill and somewhat surprising for a cheap amp. Link to comment Share on other sites More sharing options...
Members Shamdog Posted September 8, 2011 Author Members Share Posted September 8, 2011 Originally Posted by Zozobra Interestingly each gain stage has its own filter cap which is overkill and somewhat surprising for a cheap amp. Yea, it's built like a tank. Like night and day to the Jet City JCA2112RC. Link to comment Share on other sites More sharing options...
Members Shamdog Posted September 8, 2011 Author Members Share Posted September 8, 2011 m-theory - Any recommendations for the tranny? Link to comment Share on other sites More sharing options...
Members rock_mumbles Posted September 9, 2011 Members Share Posted September 9, 2011 The first preamp stage is center biased and partially bypassed with R3 @ 1.5k and C1 @ 1uf so that stage should have the lows controlled well enough so that messing with C2 shouldn't do much until C2 gets really small 0.001uf or so ... the second stage is also center biased R6 is a 1.5K cathode resistor but it's fully bypassed with C4 @ 22uf cathode cap so that stage may need tweaking (smaller C4) ... Zozobra nay be onto something regarding the 100uf cathode bypass caps C14 and C15 on the EL84's ... kind of a 'rule' is 22uf to 50uf or 1000uf to 2200uf. With intermediate range values 100uf to 500uf the output can get real muddy/loose. With a small value EL84 cathode bypass cap you can bias the tubes up to almost 100% dissipation, with the really large bypass caps you have to bias like it's a fixed bias amp and use about 70% or so. Recently I did a quick and dirty build documentation of a pcb amp called the Superlite II by guitaramplifierpcbs.com, here's the schematic: http://rh-tech.org/public/Superlite_...hematic_v4.pdf I didn't use the power supply on the schematic (too brown - low voltage) but it has a very similar topography to the BH15. At moderate volumes it has decent cleans (especially with the guitar volume backed off some), cranked it has a decent amount of preamp gain and tons of power tube overdrive. The previous version was too dark, it had a 1.5k first stage cathode resistor, the new version has a 2.7k, the cold stage has a brighter bit edgier sound that's tighter. Link to comment Share on other sites More sharing options...
Members m-theory Posted September 10, 2011 Members Share Posted September 10, 2011 Any recommendations for the tranny? Any of the usual culprits that are suited to any 2xEL84 amp, such as the Marshall 18 watt. There are many, many different options. Hammond, Heyboer, Mercury Magnetics, Musical Power Supplies, Edcore, as well as a number of branded products, usually built by Heyboer, such as Allen Amps, Weber, Trinity, GDS, etc. Any of them would be dramatically better than stock in any of these cheap Chinese amps. Link to comment Share on other sites More sharing options...
Members Shamdog Posted December 22, 2011 Author Members Share Posted December 22, 2011 m- The Jet City forum guys are using a Hammond 156 for the 20watt combo. Think that would work here? I don't know a lot about this and don't want to just pick one out of thin air. Thanks. Link to comment Share on other sites More sharing options...
Members Shamdog Posted January 2, 2012 Author Members Share Posted January 2, 2012 Hello? Link to comment Share on other sites More sharing options...
Members m-theory Posted January 9, 2012 Members Share Posted January 9, 2012 I thought you were asking about an output transformer? The hammond 156 is a choke. If you're referring to a choke, a hammond 125c3a would probably work well in that amp. For output transformers, any that would suit a marshall 18 watt amp will work. Check magnetics components, allenamps, weber, trinity, gds, mercury magnetics, hammond, heyboer, musical power supplies, among others. Link to comment Share on other sites More sharing options...
Members Shamdog Posted April 11, 2012 Author Members Share Posted April 11, 2012 Here's a question on OT's. I looked at the Allen TO20 and it says it has an 8 ohm tap. Does that mean I can't run my 16 ohm speaker with it? I'm so confused! Link to comment Share on other sites More sharing options...
Members Shamdog Posted April 19, 2012 Author Members Share Posted April 19, 2012 bump??? Link to comment Share on other sites More sharing options...
Members tech21man Posted April 19, 2012 Members Share Posted April 19, 2012 Originally Posted by m-theory Actually, the output transformers in these cheaply-built, mass-produced, Chinese amps are generally quite crappy. Upgrading the heart and soul of these types of amps is far from "pointless." It's the single most significant improvement that can be made to them, and can really turn a rather mundane, uninspiring amp into something pretty special. Bullshit. Of course it will make "a" difference and only if you push the amp consistently on really high levels.Even aiken says a larger OT is not always what the design needs. Still not an "expensive" thing to do, not really and upgrade either unless as zozobra said, its dog shit. And how can you clarify that?Oh and kind of necro bump... Link to comment Share on other sites More sharing options...
Members Shamdog Posted April 21, 2012 Author Members Share Posted April 21, 2012 Uhhh...I like bumps. Link to comment Share on other sites More sharing options...
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