NAD: VHT Standard 18 (18W Clone)

[telemike]

Picked up this sweet little VHT Standard 18 hand wired amp off Reverb for a real good price. Based on the Marshall 18W TMB circuit. Nice plywood cabinet (no mdf).

This sucker is loud! Seems way louder than the AC15 I had recently. It uses a PPIVMV circuit. Just cracking the master open and the gain cranked and I'm hitting 105db in my bedroom. Man it sounds raw and chunky classic Marshall crunch. With it on a "clean" setting I can use my Lovepedal JTM & Jubilee which gives me Marshall tones. The downer was that it didn't have the factory speaker. Came with a generic 12 out of a VOX Valvetronix amp V412BK is stamped on the magnet. I didn't even try it, I swapped in the Celestion 70/80 from my Monoprice 15W and put the VOX in that amp since it's more VOXY. The Celestion sounds pretty good with the VHT. I also pulled all the JJ tubes from the Monoprice and put them in the VHT.

Thinking about getting Wharfedale GSH-1230 and seeing how that sounds.

[telemike]

Schematic:

https://drive.google.com/file/d/0B4sWvm ... sp=sharing

[telemike]

Just put in an Eminence GB128. Wow, what a great match for this amp.

I also am trying a 12AY7 in V1. Seems to smooth out the roughness when cranked. Gain is less but it's still a great vintage crunch. Using an overdrive pedal pushes it to a superlead tone. Going to get some 5751's and try those too.

[telemike]

Wonder what I could change to the non-TMB channel to make it less woofy. I'd like it a tad brighter with less wooly bass. The TMB channel lets me dial out the wooliness and add sparkle.

[JMPGuitars]

Wonder what I could change to the non-TMB channel to make it less woofy. I'd like it a tad brighter with less wooly bass. The TMB channel lets me dial out the wooliness and add sparkle.

What do you mean wooly? Typically the 18watters are considered bright already. I would guess that if you think both channels get too much bass and you need to dial it out, it's your speaker you're compensating for, not so much the circuit.

[rock_mumbles]

The 18watt Normal channel tone control is sometimes described as being muddy ...

Weird that they used a 100k TMB slope resistor with cathode follower ???

[Daviedawg]

The normal channel in an 18 watt can be dark sounding. I don't use it much for cleaner tones. It comes into its own at higher volume settings when the distortion takes over.
Do you think that the resistor you mentioned, Rock should be about half that value?

Dd

[rock_mumbles]

...
Do you think that the resistor you mentioned, Rock should be about half that value?

Dd

Yes! ... Normal values for the slope resistor with a cathode follower are 33k to 56k ... by using the 100k slope resistor the mid frequency dip is shifted to lower frequencies (More Fender like ... less Marshall like)
Also the TMB channel low end is cut by about 5dB so if that channel sounds "normal" with that much low end cut in the TMB channel the Normal channel is going to more bass heavy than a "standard" 18 watt TMB amp ...

[telemike]

I heard that the amp designer made the TMB channel more Bassman/JTM45 like. Someday, I may mod the circuit since it is handwired.

[JMPGuitars]

The normal channel in an 18 watt can be dark sounding. I don't use it much for cleaner tones. It comes into its own at higher volume settings when the distortion takes over.
Do you think that the resistor you mentioned, Rock should be about half that value?

Dd

Ha, I guess that makes sense. I never play mine low. I use an attenuator to get lower output, and I roll off the guitar volume or play lighter for cleaner tones. Otherwise, my amps are usually a little cranked.

[telemike]

Normal channel does sound good cranked. Especially with P90.

Wondering what mods I should do.

[telemike]

Any suggestions on what I should change on the TMB channel tone stack to be more Marshally? Probably fairly easy to change out resistors and caps.

Any other circuit mods I should consider?

[Crabman]

What do you not like about your TMB channel? This would would help to determine what to try and change.

The main differences I see between your TMB channel and the more traditional TMB schematics (see here and also at Trinity amps) are at the first stage, tone stack and also coupling caps following the Phase Inverter. You can certainly mod it to reflect these differences and see if you like it. You do have a Post Phase Inverter Master Volume on yours, so there is a fairly significant difference there.

For what it's worth most the mods I have made to my Trinity Plexi 18W have focused on reducing the values of the coupling caps throughout the circuit and also increasing the values of the grid stoppers on the EL84's. So far I am of the opinion that I have improved the quality of the overdrive by making these changes. The aim here was to minimize blocking distortion as outlined in Merlins book in chapter on the Long Tail Pair Phase Inverter.

[Daviedawg]

I was looking through my notes from years ago when I built my trem version. I made a note that the power valve cathode resistor increase from 125 to 150 ohms affected the tone as well as the "hotness" making the normal channel a bit brighter. That would affect both channels and it was a good while ago so I cannot recall how it was. But a small increase in size may give results.

Dd

[telemike]

May sound silly, but I wonder if I could convert the TMB channel to a Tremolo channel easily?

[Daviedawg]

The simple answer is yes. The holes on the chassis will suit. The iron should suit.

How much work you will need to do on the preamp wiring is something you will need to work out by drawing a revised schematic substituting the trem stage for the tmb stage. There may be other wrinkles too. so you need to have a good study of the two schematics.

Dd

[telemike]

I probably won't do any mods.

[Fastermouse]

I know it’s been 8 years but do you still have the schematic?