Preamp Section Of the DHA Valve Hybrid Amp

[The Funk]

Hi Dave

I've been a user of your VT2 Dual Bass for almost a year now. Great pedal and couldn't be happier with it. I'm now trying to convince my guitarist to ditch his distortion pedal for a DHA one.

What would be awesome would be a pedal containing two preamp valves in a similar configuration to the VT2 Dual with a power amp valve on a dummy load, as in the VT5 Valve Hybrid head.

Do you think this would be possible and could you give an indication of potential size and cost?

Thanks
Syed

[DHA]

[quote name='The Funk' post='96006' date='Nov 29 2007, 10:25 AM']Hi Dave

I've been a user of your VT2 Dual Bass for almost a year now. Great pedal and couldn't be happier with it. I'm now trying to convince my guitarist to ditch his distortion pedal for a DHA one.

What would be awesome would be a pedal containing two preamp valves in a similar configuration to the VT2 Dual with a power amp valve on a dummy load, as in the VT5 Valve Hybrid head.

Do you think this would be possible and could you give an indication of potential size and cost?

Thanks
Syed[/quote]

A VT5-Bass is really this already, just has the compressor and FX loop as well but no SS power amp. I am making one of those at the moment for a BC member.

It would be a big pedal with 2 large transformers and not really useable. A better solution might be a 2U or a small head. The problem is output valves need output transformers and high voltage supplies which means another large transformer. Some have used pre-amp valves generating sub-watt levels into a load but this is not the same as having an output transformer and dummy load.

As it happens I am just about to relaunch my Class A single ended valve amps.

regards

Dave

[The Funk]

Thanks for the info Dave. What I was looking for was a preamp/effect to go into the guitar input of a valve head. Therefore a small head on a dummy load with a line output (or instrument level output) would be great.

In fact, there would probably be two uses for such a head:
1. As a effect to send the preamp/power amp overdrive tone to a clean, higher-powered guitar amp;
2. To drive a talkbox with an overdriven tone at low volume.

What kind of price would one of these come in at? If you'd rather tell me privately, then please PM me.

Thanks

[Alien]

[quote name='DHA' post='96153' date='Nov 29 2007, 02:37 PM']The problem is output valves need output transformers and high voltage supplies which means another large transformer. Some have used pre-amp valves generating sub-watt levels into a load but this is not the same as having an output transformer and dummy load.[/quote]

Does the output transformer make a difference? I thought that a good transformer worked fairly evenly across all frequencies. Wouldn't it be possible to leave it out and simply use a higher resistance in the dummy load (obviously with the same power rating), since the transformer is used to match the high output impedance of the valve to the low impedance of the speaker. It's just matching the dummy load to the valve impedance.

Andy

[DHA]

[quote name='Alien' post='97021' date='Nov 30 2007, 10:38 PM']Does the output transformer make a difference? I thought that a good transformer worked fairly evenly across all frequencies. Wouldn't it be possible to leave it out and simply use a higher resistance in the dummy load (obviously with the same power rating), since the transformer is used to match the high output impedance of the valve to the low impedance of the speaker. It's just matching the dummy load to the valve impedance.

Andy[/quote]

Hi Andy,

Yes, the output transformer does add a lot of colour to the tone. The transformer as you say does match the speaker impedance to the plate load resitance but it also generates a back emf as the current flow changes this softens the sound which is part of the output valve distortion.

I don't use a resistor as a dummy load, I use a 3.5" speaker. So my dummy load is not really a dummy!

The load the speaker gives at different frequencies varys in impedence unlike a resistor. A speaker has inductance and capacitance as well as resistance and the inductance and capacitance of the speaker affect the phase angle of the voltage and current flowing.

So, a resistor could be used as a load instead of transformer as you suggust and I know that there are designs out there that do that but IMHO it's no where near as good so not something I am interested in doing.

I would go as far as to say that an output valve without an output transformer will sound the same as a pre-amp valve with pre-amp overdrive distortion but no output valve softclipping distortion.

Dave

[The Funk]

[quote name='DHA' post='97209' date='Dec 1 2007, 01:15 PM']I would go as far as to say that an output valve without an output transformer will sound the same as a pre-amp valve with pre-amp overdrive distortion but no output valve softclipping distortion.[/quote]

Very informative. Thanks for the info!