HarpNinja
1348 posts
Apr 19, 2011
9:27 AM
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Got my modded VHT back yesterday...did the mods 5f6h suggested in a previous post. Essentially, I lowered the voice of the amp and tried to match the eq to what I use on my HG50.
It made a huge difference. In fact, the guys at the store (guitar players) absolutely loved the final result too. The amp has plenty of cut like the HG50, but has a more harp friendly bottom heavy tone. It is also less prone to feedback. The volume stayed the same, which is great for a small amp.
I will post clips soon. Granted, it sounds like a 6w amp still - meaning it won't sound as big as my HG50, but I am fairly certain that if I miked both amps and you only heard them out of a PA system, you'd be hard pressed to know which is the 6w amp.
$30 and worth every penny if for the feedback prevention alone. It sound much less boxy and has a much more pleasing midrange too!
R3 100K at 1W
R4 100K at 1W
R5 leave stock
R9 leave at 100K
R10/R12 - take an ohmmeter and measure the resistance from the middle tab of the treble pot of the HG50 (set as you play it) to the RH tab for R10, and then middle tab to LH tab for R12.....R10=223k, R12=23k
R13 measure middle tab of HG50 bass pot to LH tab of bass pot for value....R13=36.2k
R15 measure middle tab of HG50 middle pot to LH tab of middle pot for value....R15=7k
R22 don't pull the boost switch.
C8, C13 yes, 25uf...maybe try removing C13 altogether?
C11 remove
Remove C13 then add a 33K resistor from the hot side of R17 to orange speaker tap wire (16ohms, or 22K if using an 8ohm output). If the amp howls on turn on, reverse blue & red leads going to main B+ and power tube pin 3.
Eminence Ramrod Speaker
Sovtek 12ax7 - same as in the HG50
Sovtek 5881 - same as in HG50
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Mike
Quicksilver Custom Harmonicas
Last Edited by on Apr 22, 2011 6:14 PM
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Kingley
1494 posts
Apr 19, 2011
9:56 AM
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I look forward to hearing the clips. I'm off to try a VHT in a local music shop this weekend. I have a sneaking feeling it might end up coming home with me too!
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HarpNinja
1349 posts
Apr 19, 2011
10:31 AM
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The tech and other guy working kept telling me the guy who came up with the mods is a genius! I agree. Thanks again, Mark!
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Mike
Quicksilver Custom Harmonicas
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5F6H
637 posts
Apr 19, 2011
1:27 PM
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You're welcome Mike, glad to see it worked out for you.
Are you using the 6V6 or the 5881? I notice the VHT only has a 2W resistor at pin 8 of the power tube, if using the 5881/6L6 I'd probably want to up that to 5W rating (same value in ohms) at some point in the future.
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jimr
9 posts
Apr 19, 2011
3:30 PM
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Mike-
Congrads on the success of your mods! Can you list the specific changes made on your amp using the published schematic?
Jim R
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HarpNinja
1353 posts
Apr 20, 2011
6:17 AM
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I don't think it can be understated how much more I like the amp now. I haven't even checked into switching tubes beyond the JJ 6V6 and Tung Sol RI 12ax7.
I have an mp3 from this morning but noticed my work computer won't take an SD card!
R3 100K at 1W
R4 100K at 1W
R5 leave stock
R9 leave at 100K
R10/R12 - take an ohmmeter and measure the resistance from the middle tab of the treble pot of the HG50 (set as you play it) to the RH tab for R10, and then middle tab to LH tab for R12.....R10=223k, R12=23k
R13 measure middle tab of HG50 bass pot to LH tab of bass pot for value....R13=36.2k
R15 measure middle tab of HG50 middle pot to LH tab of middle pot for value....R15=7k
R22 don't pull the boost switch.
C8, C13 yes, 25uf...maybe try removing C13 altogether?
C11 remove
Remove C13 then add a 33K resistor from the hot side of R17 to orange speaker tap wire (16ohms, or 22K if using an 8ohm output). If the amp howls on turn on, reverse blue & red leads going to main B+ and power tube pin 3.
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Mike
Quicksilver Custom Harmonicas
Last Edited by on Apr 22, 2011 6:11 PM
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jimr
10 posts
Apr 20, 2011
6:38 AM
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Thanks, Mike. Can you tell us what values for R10, R12, R13, and R 15 you established after measuring resistances from your HG50?
Jim R
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HarpNinja
1354 posts
Apr 20, 2011
6:41 AM
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I have no idea, but I will talk to the tech in the next day or two. I know my HG50 settings, but that is as far as my understanding goes.
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Mike
Quicksilver Custom Harmonicas
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Matzen
171 posts
Apr 20, 2011
8:36 AM
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@5F6H: I was thinking about giving your mods a go. Below are the mods you suggested on the other thread. I was wondering what you would suggest for the values of R10, R12, R13, and R14 (I do not own a Harp Gear... and from what I can tell, HarpNinja's values might work well for him, but not for someone looking for more of a classic chicago tone)? I guess I'd be looking to lower the voice of the amp, but not match HarpNinja's EQ. Hope this makes sense! I was also wondering if there was a specific reason for using a Sovtek tube? Thanks!:
-R5 leave stock
-R9 leave at 100K
-R10/R12 - take an ohmmeter and measure the resistance from the middle tab of the treble pot of the HG50 (set as you play it) to the RH tab for R10, and then middle tab to LH tab for R12.
-R13 measure middle tab of HG50 bass pot to LH tab of bass pot for value.
-R15 measure middle tab of HG50 middle pot to LH tab of middle pot for value.
-R22 don't pull the boost switch.
-C8, C13 yes, 25uf...maybe try removing C13 altogether?
-C11 remove
-C15 try 220uf, or try removing altogether?
-Sovtek 5881WXT for the power tube.
-Make R3 & R4 100K at 1W.
-Remove C13 then add a 33K resistor from the hot side of R17 to orange speaker tap wire (16ohms, or 22K if using an 8ohm output). If the amp howls on turn on, reverse blue & red leads going to main B+ and power tube pin 3.
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HarpNinja
1355 posts
Apr 20, 2011
9:03 AM
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The Sovtek is the same as what is in the HG50. I tend to prefer a "scooped" tone in that I run the mids lower than the bass and treble. Although I can't list the specific values, I know that the amp is quite dark with the tone knob down and when turning it up, it adds a lot of cut.
In other words, my set up is VERY harp friendly, but probably not using a ton of mids. But then again, I was comparing it to an amp modded for harp, which might be different from a typical guitar amp regarding the eq.
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Mike
Quicksilver Custom Harmonicas
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Matzen
172 posts
Apr 20, 2011
9:31 AM
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@HarpNinja: So, would you say your modded (modded as above) would work well for someone looking for a "Chicago" type sound? I do like a darker tone with the mids down a bit (seems to me that my VHT could stand to loose a little of the mids)? I was thinking that the sound you were after would be a little more modern judging from what I've heard you play, thus I thought your EQ settings might be different from something I would like? Did you end up using the Sovtek?
Thanks!
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HarpNinja
1356 posts
Apr 20, 2011
9:35 AM
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I have not tried different tubes, but I'd say the amp would work for a "vintage" tone. My apologies as I did record a clip but can't upload it today. I will monkey with it more at some point...maybe this week, but I have no idea.
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Mike
Quicksilver Custom Harmonicas
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5F6H
640 posts
Apr 20, 2011
11:59 AM
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Hi Matzen,
I'm not really sure what a "classic Chicago tone" is, without a specific reference? To me there are essentially 2 harp voicings: "mid heavy" & "scooped mid". Both these sounds I have seen referred to as "Chicago" at one time or another...LW often had a pretty mid scooped tone, especially after being dosed with reverb, thicker, middier when "dry". Classic Chicago to me really means push-pull amps with high bias currents & some compression...feasible, but not easy with a single ended amp like the VHT Special 6.
R10 & R12 - R10 itself just adds series resistance after the treble cap, it doesn't do a whole lot on its own, I really just suggested changing this in the interests of completeness. R12 does the lion's share of the work in the "fixed treble pot"...without a reference, it's hard to guesstimate, hence the importance of Mike actually measuring another amp....I'd try either bare wire (treble off) up to 68K (usually around 10 o'clock on a typical 250K treble pot). Listen for fidelity & detail, not so big of a value as to make the amp glassy, just enough to let the intelligibility shine through.
R13 - 150K for an "airier" tone, 270K for a "bass full up", woofier, thicker sound.
R15 - bare wire for "Mid off" & maximum mid scoop, leave stock at 6.8K, or try halfway between the 2, say 3.3K? Mid is a bit of a misnomer, it really affects the "tightness" of the tone, low values give a more compressed, softer tone, 6.8K is really middle of the road, much higher than 10K might be too metallic/brittle/quacky? I'd alter this last.
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Matzen
175 posts
Apr 20, 2011
12:43 PM
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@5F6H: Thanks for the info! I'm not all that savy with electronics. I've built some easy FX in the past so I know how to solder. Moding the VHT doesn't seem to complicated so I thought I'd give it a shot. I remember someone saying that the "tone stack" could be lowered. I assume this is what you are calling an amp voicing? I guess that I'd just like to get a little more bass out of it, and a little less mids (I think!). I'll start sourcing some parts and I'll wait to see what NinjaHarp came up with.
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HarpNinja
1361 posts
Apr 22, 2011
6:13 PM
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See edit to my values. I added what was used for the treble, middle, and bass values.
This thing is glorious. With my rig, it sounds eerily close to the HG50 in a smaller package. I will have audio and video soon. It is hard for me to have enough time to fire it up and record at home and I was too busy enjoying it to set up for a YouTube.
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Mike
Quicksilver Custom Harmonicas
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Matzen
176 posts
Apr 22, 2011
8:42 PM
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Thanks! I look forward to the audio / video samples!
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jimr
11 posts
Apr 23, 2011
9:16 AM
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Mike- Thanks for posting your optimal HG50 tone pot resistance values. It is interesting to compare them to the stock VHT tone circuit values as shown on the schem.
R10- stock 180K, yours 223K
R12- stock 27K, yours 23K
R13- stock 33K, yours 36.2K
R15- stock 6.8K, yours 7K
The differences are in the R10 R12 "treble" shaping, and these are modest. I wonder what specific changes your tech made to the amp to produce the big change in tone, as I'd expect changes based on the optimal HG50 values to be subtle. Perhaps you can coax the specifics out of him.
jimr
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Kingley
1497 posts
Apr 23, 2011
9:42 AM
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I got a VHT Special 6 today. Only had a chance for a quick blast through it today though. It's a great little amp for the money. I'm gonna leave it stock for a while and see how it fairs at a few low volume jam nights.
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