DHA VT5-400 Yes indeed a custom Bass amp. Intial Review / Pics added

[Sugden]

Well after hunting for a few things and searching for a tube power amp and another couple of avenues I ended up speaking to Dave hall about being involved with a proto type bass head. I thought it would be good to make a thread following the build keep people who were interested up to date.

The general theory behind the amp is a small all-valve amp being backed up by a solid state power supply, very much like running a valve head through a PA. Taking the valve tone we all love from the small valve head and amplifying it with a solid-state power section. This appears to be a great concept to me and rids a huge amount of cost and weight involved with a full valve head at anywhere near 400watts.

So here's the spec and blurb:

2U rack head VT5-400 - 400W single solid D class power amp backing up an all valve 1-4watt bass amp

It’s packing 5 valves in total including the single 1W output stage. There will be a 2W output transformer in the valve output stage to help produce valve output distortion. There’s even a mullard in there.

At this point in time it has a passive EQ keeping the whole thing apart from the SS supply valve pure. I asked Dave to look into an active circuit but I don’t think it will be really necessary. There will be a by-pass in case I want to use a rack or pedal EQ at a later date. But at this time I’m using my ACG basses for almost all my tonal changes.

There will be a tuner mute, valve compressor and valve blender FX loop all selectable with the channel select via the front panel and footswitch.

There will be a DI and line out as well as 1W valve stage outputs plus 400W SS output into 4ohm.

There will be a master volume for the SS stage and a valve stage volume.

So there we go Im pretty excited I think it will suit my ACG basses a treat and hopfuly I will be coupling it with a pair of omni 10.5 crossfire cabs so should create a rather fantastic sounding setup.

Edited December 1, 2007 by Sugden

[wateroftyne]

Consider me subscribed...

[Buzz]

This sounds like it's going to shape up to be one hell of an amp.

[Tinman]

I'm well interested!

[Merton]

This sounds awesome. Can't wait for this to unfold!

[Alpha-Dave]

Interesting ...

[alexclaber]

Wow, sounds quite remarkable! Whose Class D module will you be using? SMPS?

Alex

[DHA]

[quote name='alexclaber' post='65492' date='Sep 25 2007, 07:20 PM']Wow, sounds quite remarkable! Whose Class D module will you be using? SMPS?

Alex[/quote]

It's a UcD400 OEM from Hypex Electronics in Holland. They also do 180W and 700W modules which will fit as well.

I had a good talk with Hypex today and they are very interested in the application and have given me a good deal.

Dave

[DHA]

[quote name='Sugden' post='65452' date='Sep 25 2007, 05:56 PM']2U rack head VT6-400 - 400W single solid D class power amp backing up an all valve 1-4watt bass amp

It’s packing 6 valves in total including the single 1W output stage. There will be a 2W output transformer in the valve output stage to help produce valve output distortion. There’s even a mullard in there.[/quote]

Sorry to correct you Sug but it's a VT5-400 now that you are not having the overdrive channel. So that's 5 valves. That's 1 (2 stages) in the compressor, 1 (2 stages) in the Fx loop, 1 (2 stages) in the pre-amp and 1 (2 stages) in the driver.

The output valve is a NOS Mullard EL90 which I would bet is older than 3/4 of the BC members. It is running in pure single ended Class A mode with Cathode bias. It will drive a speaker or the internal dummy load when the speaker is not connected. The 400W power stage picks up the signal from the dummy load which is reduced back to line level. So its the valve power stage signal after the output transformer that is sent into a very clean SS power stage.

I am having great fun building this amp, pictures soon.

Dave

[otis_spunkmeyer]

[quote name='DHA' post='65516' date='Sep 25 2007, 08:14 PM']Sorry to correct you Sug but it's a VT5-400 now that you are not having the overdrive channel. So that's 5 valves. That's 1 (2 stages) in the compressor, 1 (2 stages) in the Fx loop, 1 (2 stages) in the pre-amp and 1 (2 stages) in the driver.

The output valve is a NOS Mullard EL90 which I would bet is older than 3/4 of the BC members. It is running in pure single ended Class A mode with Cathode bias. It will drive a speaker or the internal dummy load when the speaker is not connected. The 400W power stage picks up the signal from the dummy load which is reduced back to line level. So its the valve power stage signal after the output transformer that is sent into a very clean SS power stage.

I am having great fun building this amp, pictures soon.

Dave[/quote]


This really does sound tastey!

Up until i've been quite happy with my hybrid Trace amp, but assuming this is as good as it sounds i may well fell a touch of GAS coming on.

Nice to hear you're enjoying it Dave. Thats what its all about really (well at least until you start rivaling the likes of Ampeg...)

Good luck with the rest of the build

-James

Edited September 25, 2007 by otis_spunkmeyer

[Sugden]

Ooo I knew id ruin my fun taking out that second channel. Im sure 5 will do me fine though. Shame VT6 had a lovely ring to it.

Cheers dave, glad your having fun making it always a good sign to get a labour of love Hope you'll want to let it go when your finished.

O I didnt mention its coming in the blue with red spatter finish which I really took to the first time I saw a picture of it on the VT bass rack. Do I get to have lots of flashing light dave? Im abit of a sad old man loving blue flashing lights.

[DHA]

[quote name='Sugden' post='65550' date='Sep 25 2007, 09:25 PM']Ooo I knew id ruin my fun taking out that second channel. Im sure 5 will do me fine though. Shame VT6 had a lovely ring to it.

Cheers dave, glad your having fun making it always a good sign to get a labour of love Hope you'll want to let it go when your finished.

O I didnt mention its coming in the blue with red spatter finish which I really took to the first time I saw a picture of it on the VT bass rack. Do I get to have lots of flashing light dave? Im abit of a sad old man loving blue flashing lights.[/quote]

You will have to wait and see what father chrismas brings (early) if you want flashing lights.

Dave

[Sugden]

[quote name='DHA' post='65552' date='Sep 25 2007, 09:31 PM']You will have to wait and see what father chrismas brings (early) if you want flashing lights.

Dave[/quote]

Rats I dont have a chimnly to egarly wait at the bottom of and set up a tree. I'll have to start sleeping on the roof.

[Kiwi]

[quote name='DHA' post='65552' date='Sep 25 2007, 09:31 PM']You will have to wait and see what father chrismas brings (early) if you want flashing lights.

Dave[/quote]
LMAO!

[d-basser]

GAS GAS GAS GAS GAS GAS GAS GAS GAS

if i get back to gigging i can see me blowing my overdraft on one of these

[TPJ]

Gosh, this sounds nice. Can't wait to see how this turns out

[steve-soar]

I agree the ACG does ALL the tone shaping, I have GAS!!!!

[neilb]

[quote]DHA said:

It is running in pure single ended Class A mode with Cathode bias. It will drive a speaker or the internal dummy load when the speaker is not connected. The 400W power stage picks up the signal from the dummy load which is reduced back to line level. So its the valve power stage signal after the output transformer that is sent into a very clean SS power stage.[/quote]

Abso-bloodly-lutey Dave....exactly the design I would use.

I would also attach a silicone nangeflaglet to the output of the reverse cathode muffplate so that the inverse current can draw sufficient voltage from the cocktruss array.

What do you reckon?


PS - Dave, loving the Purist VT1 mate. !!!

Edited September 26, 2007 by neilb

[redroque]

[quote name='neilb' post='66074' date='Sep 26 2007, 07:38 PM']so that the inverse current can draw sufficient voltage from the cocktruss array[/quote]

I think you would need 3 phase for this so it's probably impractical as there aren't many stages with a 3 phase supply....

[DHA]

[quote name='neilb' post='66074' date='Sep 26 2007, 07:38 PM']Abso-bloodly-lutey Dave....exactly the design I would use.

I would also attach a silicone nangeflaglet to the output of the reverse cathode muffplate so that the inverse current can draw sufficient voltage from the cocktruss array.

What do you reckon?
PS - Dave, loving the Purist VT1 mate. !!![/quote]

Want a job?

[jwbassman]

LOL - you guys...

Edited September 26, 2007 by jwbassman

[DHA]

[quote name='redroque' post='66086' date='Sep 26 2007, 07:59 PM']I think you would need 3 phase for this so it's probably impractical as there aren't many stages with a 3 phase supply.... [/quote]


No need for 3 phase as it has a built in atomic reactor to power the cocktruss bias anyway.

[Sugden]

You lot should write for star trek

[DHA]

I ran the valve stage power amp up today into a 4x12" - after a bit of mucking about it sounded great and even better when I used a VT1-Purist to overdrive it and acting like as pre-amp.

It goes into a nice warm output distortion at about 1/2watt, very rich in harmonics. The next stage is to DI the output and also reduce the 1 watt back to line level to drive the 400W power stage.

Dave

[neilb]

[quote name='DHA' post='66106' date='Sep 26 2007, 08:32 PM']I ran the valve stage power amp up today into a 4x12" - after a bit of mucking about it sounded great and even better when I used a VT1-Purist to overdrive it and acting like as pre-amp.

It goes into a nice warm output distortion at about 1/2watt, very rich in harmonics. The next stage is to DI the output and also reduce the 1 watt back to line level to drive the 400W power stage.

Dave[/quote]

He's off again!!