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Blackheart BH15H

BH15 Head and Combo

 

No Longer In Production.

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

These Amps are Class A (A/B), Push Pull, Cathode Bias, Using 2x 12AX7 Valves as the Preamp and Phase Inverter -and- 2x 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 Stock 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 ‘OPR’ and ‘OPR-1+2’ Allows the Amp to be used in any environment, From your Bedroom to the Stage.

Stay away from the Combo Amp (BH15-112) as they all have an Inherent Resonance Problem causing a Nasty Chassis Vibration when a 'G' Note is played. A Ton of work is required to cure this problem and it's just not worth it.

 

Modifications

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

1. 'OPR' - Output Power Reduction. 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 - 'OPR' really works.

2. 'OPR-1+2 - - -This Dual Function Switch allows two Distinctly Different Sounds when the Main 'OPR' Control is in Use - 'OPR-1'....Maintains the High Harmonic Content in the Final Sound - 'OPR-2'....Is Much Softer and Cleaner Sounding. Most 'RAT' Amps are Fitted with ‘OPR-1+2’ as Standard.

3. 'TRI' Rectifiers - This Option uses a Three Position Switch and a 'GZ34' Valve Rectifier, It Integrates Seamlessly into the BH15H Circuit and offers 3 different types of Rectification. Position 1= Standard Silicon Diodes - Position 2= V1, 'GZ34' Valve Running at Half Power, This gives Maximum 'SAG' - Position 3=V2, 'GZ34' Valve running at Full Power, Offers Reduced 'SAG' but maintains the Classic Vintage Valve Rectifier 'Feel'.

4. 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 two Modes. (1) Normal Mode - This is Stock 'Slightly Hot' Gain. (2) High Gain - Sets the Preamp up for Maximum Gain and Turns the Amp into a Beast.

5. 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', 'Orange Drop' and 'Silver Mica' Tone Capacitors, then '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.

6. Tone Bypass and Variable Boost Footswitch - A Switch on the Front Panel of the Amp enables the 'Tone Bypass'. This Gives the Amp 'Monster' Gain and Works in Conjunction with Footswitch. When the Footswitch is connected to the Rear Panel of the Amp, the Tone Bypass Switch is Disabled. The Footswitch has a Built-In Variable Gain Control. You can set just how much Gain you want with the 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 Mids to Cut Through Nicely.

7. Line Out and Headphone Sockets.

8. 2 x Speaker Outputs and Impedance Select - The Output Transformer offers individual Speaker Outputs of 4, 8 and 16 Ohms. 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.

9. 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.

'Harmony Central'

 

Short 'OPR' Sound Clip