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A New Years Rats Nest

Electronics designers use many different prototyping methods. These days, it's very likely that a new design will never actually be prototyped but rather simulated using programs such as SPICE.For very simple circuits like tube amplifiers, I like the rats-nest method. It isn't pretty, but it's fast and effective. It is also way more reliable with tube gear as SPICE models of tubes do not simulate all their characteristics, especially those in overload conditions. That's important because Low-pow...

Guitar Amplifier Now Available for Order

The Red Roo Guitar Amplifier is now available for advanced purchase.Like all Red Roo amplifiers, it uses only top-quality components and is easy to build by anyone with a little electronic construction experience. It's a stand-alone "lunchbox" type amplifier so you will need to use a separate guitar speaker.This is a fully featured progressive-distortion design with a Fender-type tone stack. Presence and Depth controls in the negative feedback path allow you to further tailor the sound and there...

SE5 - Noise and Distortion Sweeps

I've been playing around with the ARTA audio measurement software from https://artalabs.hr/ Although intended primarily for loudspeaker measurements, it does a very good job for tube amplifiers as well. I use this DAC https://focusrite.com/clarett-plusHere are some spectrum measurements of the SE5 amplifier (UL mode, Standard Transformer, Feedback ON, 3Watts RMS output).First pic: Noise floor with SE5 on but no Bluetooth module installed. There is a small peak at 50Hz but noise is...

More Power!

People have asked us how far can they push their SE5 amplifier, power-wise. As it turns out, quite a long way. By connecting a full-wave voltage-doubler circuit to the AC output from the power supply, it's possible to achieve much higher HT voltages. Using an HT voltage of 360V, just below the maximum DC voltage rating of the capacitors (400V), and KT88 tubes, we were able to get about 8.5 Watts RMS sine-wave output @ 5% distortion - 10 Watts when pushed.The power supply has jumpers th...

Using Bookshelf Speakers?

Here at RedRoo, we receive a lot of questions from people wondering how the SE5 amplifier will work with their small bookshelf speakers. That sounds like an easy question to generally answer YES, but, like anything in electronics, it depends on several factors:Speaker efficiency: The sensitivity or efficiency rating of the speaker is an important factor. Speakers with higher sensitivity ratings require less power to produce a given volume level.Desired volume levels: Consider the volume levels y...

RedRoo PR5 Vinyl Preamp Now Available

The RedRoo Vinyl Preamp is now available, both as a full kitset or an information pack with PC boards for people who want to roll their own.I've had it playing for the last few months and it sounds great. This is a high-quality kitset which will rival preamplifiers many times the cost. Its a great partner for the SE5 power amplifier.As far as moving coil cartridge inputs go; I'm still waiting for two Moving Coil transformers, so I haven't listened to that option yet, but hopefully soon. I t...

New RedRoo Guitar Amplifier

Here is a photo of the new RedRoo Guitar Amplifier, without its protective cover. This is a top-shelf guitar amplifier with all the controls that a musician needs to create their own unique sound. The kitset is in the final stages and will be available soon.  For most of this year it has been trialled by professional guitarists and is receiving glowing reports., (which is good because I can't play a note!). Check out the Guitar amplifier page here....

New RedRoo RIAA Vinyl Pre-Amp shown at Melbourne Hi-Fi Show

Here are first pictures of our prototype RIAA pre-amp that we were showing at the recent StereoNET Hi-Fi show in Melbourne. The preamp has either two switched moving-magnet phono inputs, or one moving-magnet and one moving-coil when fitted with Lundahl LL9226 step-up transformers. We hope to have the preamp kitset ready for purchase very soon.  We were asking attendees to choose between the black and white front panel lettering for the power-amp and pre-amp. It was about 50:50. Let us know ...

StereoNET Hi-Fi Show in Melbourne 2022

Come see the RedRoo SE5 up close, and first glimpses of our new RIAA Preamp, at the StereoNet HIFi show in Melbourne. Look for us on the Vinyl and Valves stand.3rd-5th June 2022, Pullman Convention and Events Centre, Albert Park. https://www.stereonet.com/show......

Valve Supply Update

Electro-Harmonix, the makers of Tung-Sol, Electro-Harmonix, EH Gold, Genalex Gold Lion, Mullard, Svetlana & Sovtek valves, announced that they have found a way around import restrictions and can continue to supply, for now. However, faced with mounting costs, they have also announced a general price increase on all their valves effective immediately.  We are watching this situation carefully but it is reassuring that it looks like we will be able to secure valves for the RedRoo kits, a...

Russian Valve Shortages

The supply of valves/tubes has been affected by the Ukraine conflict.  Electronic valves made at the New Sensor facility in Saratov, Russia, are under export/import embargoes. Tung-Sol, Electro-Harmonix, EH Gold, Genalex Gold Lion, Mullard, Svetlana and Sovtek brands are all affected. In a recent press release Mike Mathews, the owner of New Sensor, explained that the production of valves has been adversely affected by the Russian goods ban. “Given this export ban, we will not be receiving...

RedRoo "Lunchbox" Guitar Amp coming along nicely

Over the Christmas period I've been working on the new RedRoo 'Lunchbox' guitar amplifier. It's recently been with some professional musicians here in Sydney and their early reports about the sound are 'glowing'. The 15-18 Watt RMS circuit uses progressive distortion techniques through multiple stages of amplification and attenuation, and has all the features a professional guitarist needs in a small studio/portable head amplifier.  Photo coming soon.. ...

COVID UPGRADE - NEW KITSET NOW AVAILABLE

While I've been locked up in Sydney during COVID I decided to give this project an upgrade. It now has a new precision cut, folded, powder coated metal chassis with screen-printed fiberglass front and back panels. Not cheap but looks great. The new chassis also required a PC Board redesign.  I've also included a headphone attenuator which can match various impedance headphones (supplied for common 32 Ohm headphones but can be changed for other impedances). It's come together so well I'm now...

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Its been about three years since the initial design now, and quite a few RedRoo amps have been constructed in that time.  All the amps that I know about have been great performers and 100% trouble-free. I had the chance to do some tests and voltage measurements on some that have had daily use, and they were all still spot-on. After embarking on what was basically a hobby project, I've decided to put the entire design and construction details up on this website as a free download, and to off...

Circlotron Amplifier

For years I've been mucking around with valve amplifiers, much to the amusement of my family and friends. My first attempt was a version of what's called the Murray amplifier; a 20 watt per channel design by Australian Cyril Murray in the 1960's, which used 6CM5 television line-output valves. I used PL509 valves for a bit more power. Cyril Murray went on to build amplifiers for the Sydney Opera House and his work was very well respected.  Later I made a 60 Watt 'circlotron' design using fou...