Vht d-50h tweaks

[Dansamp1]

Hello All,
I haven't been on this forum in a long time, and I mostly hung out on the TW side.
So consider this my first post.

I have been looking to try a D style amp for a while and I was thinking about getting a
Trinity OSD kit, but I happened to find a VHT D50 used at GC so with a 45 day return option and at $680.00 plus tax I jumped on it.

First, I noticed the bright switch didn't do anything so I started to poke around in it. everything looked ok
but then I found one side of the two caps in series located at the input jack was detached . I found this post
and verified my findings.
I re-soldered the end that connects to the resistor across the input jack, and now the bright switch works.
Not sure what those caps are doing in the circuit ( maybe someone can explain)

I am not familiar with this type of amp and it seems a bit dark to me. Especially when rolling the volume down on any of my guitars,
even my McCarty , with a treble bleed cap. ( any suggestions greatly appreciated)

Again, reading this post I was thinking about changing the snubber caps on V2 from 330pf to 25pf as mentioned above.
I pulled the chassis out again and found on my D50 the caps on V2 are different .
One side is a ceramic 330pf and the other side has two 100pf caps in series.
So it seems these are not all the same ???

I am not sure changing these back to 25pf would brighten the sound though since V2 is the overdrive portion.
Am I correct in my thinking.

Last comment,
I also found a used SSS style amp and am thinking about getting that.
I read somewhere that the SSS was basically a D style preamp into an SVT . So as an experiment I took the D50 preamp out and plugged it into
my SVT II power amp in and ran that into a Boogie Thiele 1x12 with an EV and let it rip !!!
It was very loud, even though I had the master just below 9:00 , but I was able to get those clean SSS overtones jumping into clean
sustain and feedback : )

Hope this all makes sense, and I look forward to any suggestions or mods.

Thank You,
Dan,

[pompeiisneaks]

Dan,

a bright cap is just a capacitor of a specific value between the input and output of the volume pot on an amp. It lets some of the higher frequencies always bleed through and bypass the attenuation of the volume pot. Thus making it 'brighter' Someone might have wanted a darker amp and thus cut that one out. Sometimes tweaking that value up/down will make the amp sound a bit more like you'd want it to, and people often experiment with them, or add a bright switch that allows you to switch them in/out of circuit easily when say switching between a guitar with humbuckers and one with single coils etc.

As for the SSS, I've not built or played one, but the tons I've read hear, I'd say your explanation is a very broad generalization, but roughly right. First every SSS that's been reverse engineered was a bit different, second, saying 'a dumble preamp' is a bit of a misnomer too, as there are hundreds of those if not more. Every preamp he built was custom for a customer and slightly or massively different depending on the situation. You'll need to do a lot of reading here to start understanding that.

Also generally the ODS style preamp's 'clean' channel aren't close to as clean as the SSS ones are on purpose, they're designed to give strong signal into a drive channel, not be clean. they're still clean, but not as pure clean as the SSS ones are.

Again, this is only from my reading comprehension and listening to videos of them played etc, as I've only built ODS amps and no SSS.

Some of the other things you noticed could have been the same person tweaking things attempting to get the amp tone shaped into something they wanted.

As for specific mods to the amp, the best way to know would be to get a schematic, share it here and specify in more detail the exact changes on the schematic you're suggesting, otherwise it can be nearly impossible to determine the exact ideas you have in mind without the full schematic to paint a full picture.

~Phil

[Dansamp1]

Phil,
Thank you for the response.
I guess it never dawned on me that someone might have been inside the amp prior to my purchase.
Makes me feel kind of silly now.

I understand how a bright cap works across a volume pot, but the caps I was referring to are located at the input jack.
Two caps in series going to ground. I have not seen this before in an amp circuit, and was wondering what their function is.
Also how they correspond to the bright caps located on the bright switch and ultimately to the volume pot.

I believe a schematic was posted prior on this thread referencing what version "clone" this amp is.
the more I play this amp it seems I am adjusting to the sound.
the tone controls do not seem to be very effective, they are quite subtle,

If anyone else has tried this amp I would appreciate any input.

Again thanks,
Dan.

[dbharris]

I think you may be mixing up different pairs of caps? If you look at the pics posted on page 1 of this thread, the two red colored caps attached to volume pot and bright switch are in parallel, but never in circuit at the same time. The bright switch is on-off-on to select the either option or no bright cap at all. They are not connected to the input jack.

The two blue caps on the input jack are in series from input after the pull down resistor to ground. They would have an effective capacitance of 50pf (2 100pf in series) and together with a 22K grid resistor, are serving as a Low Pass Filter with a cutoff of about 14.4KHZ. I have typically seen a cap to ground arrangement like that in pedals to shunt out RF interference. Think of an old Si fuzz face that picks up a radio station when on. I'm not sure they would serve much purpose here?

-Other Dan

[Dansamp1]

ok, I get that
thanks,
I do know that with those caps at the input jack disconnected, my bright switch did not work, or at least there was no audible
difference.
once I reattached the leg of the first cap back on to the end of the resistor, I had a functioning bright switch.
My initial question was why ?
but I guess it doesn't matter either way. It now works as it should.
I will just wait and see if anyone else has experience with this type of amp.

Thanks,
Dan.

[dbharris]

Can you post a couple pictures of your amp? The input jack and volume pot/bright switch.

[Dansamp1]

my amp looks just like the photos on page one of this thread, since I re-soldered the caps at the input jack

Dan.

[Audiodog]

That amp needs to be gutted. Immediately replace all signal path metal oxides with metal films and carbon films. Put back a 390pf treble cap. Lower snubbers to 250pf. Then play. After assessing, you then can start replacing the preamp caps with Orange Drops. Is the NFB a on the 4 or 8 ohm tap? Make sure it is on the four ohm. Since this is a 6L6 amp, my guess is that it will sound better with a LNFB loop on V1. Consider that. Lastly, I would replace the 50k OD trim pot on the back with a 25k pot with a a 15k tail to ground. Use a 280k series resistor to feed it. This will give you far better control and make optimal settings around noon. My experience is that going to 100k OD pots will also be much better since it is 6L6 tubes as well. Make sure you have a .05uf out of V1, regardless of clean or OD. No way that thing can ever sound good as it sits. IMO.

[Dansamp1]

Audiodog,
Thanks for the info. That's a lot to process.
This seems like quite a lot to change. I feel like I might be better off building something from scratch. I suspect the transformers should also be upgraded ??
Maybe I should return it and save up some more money.
I guess this was too good to be true.
The only complete kits I have found so far, is from Trinity Amps, but at best that is a 33 watt amp. I would want minimum 50 watts but would prefer 100 .
I play pretty cleanly.

I borrowed a Glasswerks Zingaro for about a week, ( I think that was a 25 watt 6V6 amp) it seemed very tight and harsh but it didn't have many hours on it when I had it.
This VHT seems a bit more open, but still doesn't sound like the other higher end clones I have heard online .
It seems like it's opening up more, but maybe I am just getting use to the sound.
I don't have much experience with this type of amp.

Once again, thanks for the input.
Dan.

[dbharris]

I wouldn't get overwhelmed with the thought of swapping parts out. You could do it in phases, which may also help you hear what makes a difference (in certain directions of timbre). For instance, you could do all plate and cathode resistors first. Then the signal path, etc. If you break it into phases it will be more manageable. As for the transformers, there is likely no need to swap the PT. After you sub out all of the passive parts you could swap the OT if you still weren't where you want to be.

One last thought, did you mention the cab and speakers you are playing through other than the Thiele EV? That may be a very good match for the amp anyways. But, speakers and cab type can make a rather large difference. For instance, I did some experimenting with my Wonderland amp last weekend. I hooked it up to the speaker in my Mesa Lonestar Special Combo (a 1x12 celestion black shadow C90)...it sounded terrible. Really tinny and aggressive. All the things I don't like about the LSS. I then hooked it up to my 2x12 closed back bluesbreaker style cab with WGS Green Berets. It sounded much better, but still not as good as the Dumble style 2x12 with G12-65s.

-Dan

[ijedouglas]

While I totally agree with Audiodog on the recommended changes, I would also say, if the amp sounds good to you, that is what really matters. I have often swapped out shitty parts for more "correct" parts only to find that it did something that I didn't like.

This may also be an awesome test bed for you to change parts and see what really makes a difference. Make small, incremental changes and listen to what difference each change made. I would start with Audiodog's recommendations replacing the metal oxides and concentrate on getting your clean (V1 and PI) sounding good. BTW I would also swap out all the plate resistors... they are not in the signal chain but they have a big impact on it. Once you have the clean dialed, move on to the overdrive section.

Have fun!

[talbany]

Audiodog,
Thanks for the info. That's a lot to process.
This seems like quite a lot to change. I feel like I might be better off building something from scratch. I suspect the transformers should also be upgraded ??
Maybe I should return it and save up some more money.
I guess this was too good to be true.
The only complete kits I have found so far, is from Trinity Amps, but at best that is a 33 watt amp. I would want minimum 50 watts but would prefer 100 .
I play pretty cleanly.

I borrowed a Glasswerks Zingaro for about a week, ( I think that was a 25 watt 6V6 amp) it seemed very tight and harsh but it didn't have many hours on it when I had it.
This VHT seems a bit more open, but still doesn't sound like the other higher end clones I have heard online .
It seems like it's opening up more, but maybe I am just getting use to the sound.
I don't have much experience with this type of amp.

Once again, thanks for the input.
Dan.

Just like cooking the schematic (or design) is the recipe and the parts are the ingredients.
The ODS 2 channel (183)cascading (clean feeds the OD) design is especially sensitive to parts section' you have no way to balance or EQ the sound of the (non HRM) overdrive side other than the organic sound that the parts themselves generate. Everybody has their definition of what sounds good and what doesn't..If you do not have any frame of reference as to how certain parts sound in a given section of the amp..Listen to those that do know like audiodog. Like Ian states take it one circuit or section at a time listen for the changes.Some will be more drastic than others. it's the sum of all parts that creates the overall balance of the amp when channel switching and PAB boosting. A PCB amp is not what i would consider an ideal platform to experiment with different parts since you have only so many times you can throw in iron to them without lifting the pads?

Good luck!
Tony

[Dansamp1]

I appreciate all the input.
I was thinking about this overnight, and came up with the same conclusion.
Someone suggested adding LNFB to V1 but looking at the 183 schematic, I don't think it had it originally ??

what would this give me if I added it ?

It was suggested to change Plate and Cathode resistors , but do cathode resistors affect sound, or tone ??
should I use carbon film or carbon comp ?
regarding speakers , the only other cab I have is and old Vox Buckingham two twelve open back ( with oval cut-out) loaded with 30 watt Scumnicos
not sure that would be a good match.

regarding capacitors, should I use polyester film or polyprop.

Thanks
Dan.

PS:
well looking at the photos on page 1 of this thread it looks like V1b already has the LNFB .
I see the two 20meg resistors and capacitor

[neskor]

yes, it have LNFB
you can make a switch for that

[ijedouglas]

Plates and cathodes made a big difference for me, YMMV. I am currently playing around with different cathode caps and you'd be surprised at the difference they make

As Tony states, depending on what you want from the amp, will depend on what resistors and caps you use. Here is a good thread that may help you decide: https://ampgarage.com/forum/viewtopic.php?f=4&t=32580

I prefer Polyester 6PS caps and use them mostly throughout my amps. 183 has polypropylene SBE 715s on the PI couplers and on my 102 I use a Sprague 715 on the mid cap.

In my 183 I used NTE MFs, Roederstein MK3s, Draloric LCAs. For the 124 I used mostly carbon film (MF on cathodes) and 102 I used a mixture of NTE MF, MK3 and Carbon film.

The 183/124/102 layouts are well documented and tried and tested. You may want to start there when deciding how you want to approach this.