New EU import rules from July 1st 2021

Information for valued EU customers.

On 1st July 2021 the EU abolished VAT exemption for goods in small consignment of a value of up to EUR 22. More information here:

I set up the RSDsound website to supply hard to find repair parts that I’d sourced for my work at Keld Ampworks Guitar amp repair to other repairers and hobbyists across the world. I’m a one person show, and the repairs are a priority, in order to put food on the table. Because there’s just me, I can’t logistically manage to calculate and pay VAT to the EU via the IOSS alongside the other work I have. In addition, the requirement to appoint an EU based intermediary (accountant) for the process makes this financially impossible.

For this reason, if you buy a product from, then you will be expected to pay import VAT to the courier or postal service that imports the item that you buy. They will often charge an admin fee for this and it may cause delays.

Thank you for your understanding.

Do I need a crossover for my PA?

Do I need a crossover for my PA? Crossover Effects – How a crossover affects your sub.

Just a quick post – someone on Guitar/amp help tips and fixes Facebook group was asking about whether a sub woofer was required for use with vocals. My first reaction was that there was no need at all – I’ve always used sub only for kick and bass guitar, but he’d found that it helped his vocals at one gig. It’s always best to challenge your assumptions so I did a little test while I was eating my cornflakes this morning.

What’s a crossover, why does a sub need one?

Most subs can produce signals up to a few kHz. if they aren’t controlled. If you don’t use a crossover, the sub will let through all the mid frequency signals, competing with the tops and your band will sound like mush. The efficiency of the system is compromised and your tops still end up trying to produce the bass signals. You might as well sing into a bass amp. More later…

How can we test the crossover?

This is an audio track that has been filtered with a steep EQ treble cut, as you would expect in a good sub crossover. The track plays a few seconds of full range audio then a few seconds of sub-filtered audio.

Crossover simulation Technical details

Do I need a crossover for my PA?These crossovers are all 24dB/octave but three cutoff points were tested:

  • 80Hz crossover (typical for use with 15in sub)
  • 100Hz (pretty high, even for a 15in)
  • 200Hz (If you’re setting it this high, you’re doing something funny)

Tracks are Barry White’s “My first, My last, My Everything”, U2 ft Johnny Cash “Wanderer” and AX7’s cover of Pantera’s “Walk”.


Crossover Simulation Results

Here are the results of the test – you’ll need headphones with a good bass response to hear anything at all in the filtered sections.

Even Bazza’s vocals are pretty much in audible through the sub-filtered audio. You can see the graph opposite. Do I need a crossover for my PA? Graph

What valve should i use for lower gain?

What valve should i use for lower gain?

A customer recently asked “what valve should i use for lower gain?”


It’s a great little combo, nearly perfect and a great platform as I tend to use pedals to get my overdrive sounds. But to my ears the lack of a middle control on the clean channel is reducing the tonal flexibility and the treble is quite shrill and difficult to tame. Having played with the drive channel (which has T, M and B controls) with minimal drive dialled in, its starting to deliver more of the tone I am looking for. However, it’s the drive channel and designed to distort and therefore has a lower headroom, so I am thinking that I might be able to reduce the gain in the pre amp by replacing the 12AX7 with a 12AT 7or even a 12AU7 to help it clean up. Just wondering if you had any thoughts on this.

Replace a 12AX7 with a 12AU7 for the lowest gain

You’ll definitely find the 12AU7 cleans up your gain channel. The amplification factor is reduced from 92 to 17. You’ll also find that there’s a loss of volume, you’ll have to run the volume control much higher than you would normally. I’ve used this trick with Marshall plexi type amps and they end up sounding like a clean funk machine. I like the sound quite a lot!

Replace a 12AX7 with a 12AY7 for lower gain

The 12AY7 is the classic fender tweed valve. It is a very usable effect, midway between the 12AU7 and the 12AT7 in terms of gain. Taking Electro Harmonix valves as an example, the amplification factor is reduced from 92 to 40.

Replace a 12AX7 with a 12AT7 for slightly lower gain

The 12AT7 is a more subtle effect, midway between the 12AY7 and the 12AX7 in terms of gain. The amplification factor is reduced from 92 to 50. This is probably the valve to choose if you’re just looking to slightly clean up the amp

Replace a 12AX7 with a 5751 for a subtly lower gain

The 12A*7 series valves all have paralells in a 4 digit code series. The 12AX7 is also known as a 7025 and has another slightly lower gain cousin. The 5751 is almost a 12AX7 but the gain is dropped. The amplification factor is reduced from 92 to 70. This is another valve to choose if you’re just looking to slightly clean up the amp.


Hi Rowan,
Great success, although I’ve not yet managed to get the amp up to full ramming speed. Certainly at lowish levels the 12AU7 has really taken the sting out of the all valve channel, it cleans up beautifully and I think I can probably just about get enough grunt out of the channel for gigging by maxing out the volume on the output side. The clean sound now from the drive channel is very smooth with a different character to the clean channel – which is what I wanted to achieve although the eq on the amp doesn’t quite get me where I wanted. I suspect though when I get the amp up to louder levels and start driving it harder, the top end will expand and it will be near perfect. And it takes pedals beautifully.

A big thanks for all your help.