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Blackheart BH15H

 

 

BH15 Head and Combo

It's the Same story Here as the BH5 Amplifiers - Superb Build Quality Let down by Very High Levels of 'BUZZ and HUM'....

These Amps are Class A (A/B), Push Pull, Cathode Bias, Using 2 x 12AX7 Valves as the Preamp and Phase Inverter -and- 2 x EL84 Power Output Valves. The Chassis is 1.5mm Thick Steel, Welded Box Construction. Correctly Rated Electronic Components, Excellent Quality Transformers and a Through-Plated, Double Sided PCB. The Circuit Design is Text-Book, with 'Slightly HOT' Bias Settings and a 'Presence' Control that works well. The HT Voltage is SPOT-ON. The Amps are Extremely Well Built, as good as some (so called) USA 'Boutique' Amps that I have seen. The First one of these that I got my Hands on - Well, the BUZZ was so bad, I thought the Amp was Faulty. A quick visual inspection of the PCB Shows part of the problem - One of the 'Noisy' Valve Heater tracks runs Very close and Parallel to one of the most 'Sensitive' Signal tracks - Not Good. In the Latest Production Batch of BH15 Head Amps, the PCB has been 'Revised' in an attempt to reduce some of the 'Noise'. It's a Bit better, but not Much.

There is this thing called 'Crosstalk' and if Noisy Supply Rail Tracks (on the PCB) are run Parallel to 'Signal' Tracks, you have a Problem - The Problem is -- 'BUZZ and HUM' --. Avoiding 'Crosstalk' is not some 'Top Secret' Design Criteria, Known only to Valve Amp Gurus - It is down to Basic Know-How of PCB Track Layout. As an example of what can be done, the Orange 'TT' Amp does not have Heater Tracks on the PCB, it Uses Twisted Wires, located above the PCB, which connect to all of the Valve Heaters - The Result - A 'Buzz Free' Amp.

Other than the 'Noise' Problems - The Amp, like the BH5, is a Top Quality Product.

The Amp's Output is a Healthy 15 Watts RMS and at FULL BLAST, it is LOUD.

Before I can start any Hot Rod work, I have to clean up the Buzz and Hum Issues, which is not easy. Once that is done, the Amp is Superb, and Wide Open to some Great Modifications. The Addition of ‘Power Scaling’ and ‘PS1+PS2’ to these Amps puts them in a 'Class of their Own' and allows the Amp to be used in any environment, From your Bedroom to the Stage.

The Combo Amp (BH15-112) is Fitted with an 'Eminence' Custom Blackheart Speaker. It's 12", Rated at 70 Watts, 16 Ohms and is Excellent Quality. It Works well in this Combo and Sounds Very Good. The Speaker and Cabinet are the Same Size as the BH5-112 (5 Watt Amp).

 

Modifications

Some or All of these Mods may be fitted - Depending on The Final Price.

1. Power Scaling - This is the Business and essential for an Amplifier used in the Home. I Have tried ALL of the other systems that claim to Reduce the Volume without changing the Tone - This is the ONLY one that really works. 'RAT Electronics' is Licensed by ‘London Power’ to Install this Technology and Pays a License Fee for each Installation.

2. PS1+PS2 - - 'PS1'....This is the Standard Method of 'Power Scaling' in which only the Valve Output Circuits are Scaled. The Preamp Circuits are 'Held' at Normal Supply Voltage - - 'PS2'.... This Setting Totally Changes the Dynamics of the Amplifier as Both the Preamp and Power Amp Circuits are Scaled. The Resulting Effect is Known as 'Brown Out'. The most Well known user of 'Brown Out' was 'EVH'. He used a 'Variac' to Achieve the 'Brown Sound', but the End Result is the Same as 'PS2', without the Risk of any Damage to the Valves. Most 'RAT' Amps are Fitted with ‘PS1’ and ‘PS2’ as Standard.

3. Twin Rectifiers - The Stock Mains Transformer already has the Required ‘Tap’ for a Valve Rectifier. Once the Valve Rectifier is Fitted - You can Switch Between the ‘Silicon Diodes’ -or- ‘Valve Rectifier’. The ‘SAG’ Produced by the Valve Rectifier Sounds Superb.
 
4. Fixed Grid Bias -or- Cathode Bias Switch. Grid Bias is much more Efficient and Dynamic than Cathode Bias and Lifts the RMS Output of the Amp from 15 Watts to 20 Watts. In Grid Bias Mode the Output Stage of the Amp runs Cooler and Sounds Different to the Standard Cathode Bias Setup. Power Scaling is disabled in Fixed Bias Mode.  

5. The Gain Structure of the Amp has been Changed so that you can get some Nice 'Cleans' if that is what you want -or- Turn it all the Way up for a Real 'Gain Monster'. The Gain can be Switched to one of three Modes. (1) Studio Mode - This Keeps the Amp Silent (No Background Noise). (2) Normal Mode - This is Stock 'Slightly Hot' Gain. (3) High Gain - Sets the Preamp up for Maximum Gain and Turns the Amp into a BEAST.

6. Output Transformer (OPT) - The Stock OPT is Very Good but not as Good as a ‘Hammond 1650E’. Changing the OPT will offer Better and Tighter ‘Bass’ Response along with Cleaner and Clearer ‘Mids’ and a Much better Defined ‘Top’ end. In Addition, the'1650E' OPT offers 'Ultra Linear' (UL) Coil Taps. UL is a type of 'Feedback' to the Output Valves which will keep the Amp 'Cleaner' Sounding. The UL Feature can be Switched 'In -or- Out' for a More Versatile Amp.These Transformers are Very Expensive but well worth it.

7. Because of the Hum and Buzz Problems, I have to Remove all of the Rotary Controls from the PCB. The Stock Controls (Pots) are OK Quality but just to be sure, I replace them with Bigger '24mm Alpha Parts' and 'Hand Wire' them back into the Amp Chassis. I Totally 'Re-Build' the Tone Stack - it can Completely Remove the 'Treble', 'Middle' or 'Bass' from the Signal (if required) - It Now Replicates a 'Fender Twin Reverb' in Operation.

8.Variable Boost Footswitch - The Footswitch has a Built-In Gain Control. You can set just how much Gain you want with a Rotary Control located near the Push-Button On/Off Switch. It Works Great and Gives you that extra 'Kick' when Needed. A Red LED Illuminates when 'Boost' is Selected. There is a Trade-off when using the Variable Boost. The Higher the Boost is set - the Less Effective the Tone Controls Are. In Practice this is not a Problem because at 'Full Boost' the Tone Network is 'Flat' and allows the Sound to Cut Through Nicely.

9. Line Out and Headphone Sockets.

10. 2 x Speaker Outputs and Impedance Select - The Output Transformer offers individual Speaker Outputs of 4, 8 and 16 Ohms and this Must be Correctly Matched to the Speaker/s in use. The Stock Speaker Outputs are Very Confusing and you can easily make a Mistake connecting your Speaker/s. The 'RAT' Setup is Simple and Straightforward to use - Connect a Speaker or Speakers and select the Correct Impedance - Done. Fitted to all ‘RAT’ Amps.

11. There are Several 'Other' Modifications that I do to All of my Amps that are Exclusive to me and both Enhance Performance and Help to Keep the Noise Levels Way Down.

The Background 'Noise' from the ‘BH15’ Amp is now so Low, you may not notice it is Switched on.

Short 'Power Scaling' Sound Clip