The Brute: A 3-channel Audio Amplifier For Leslie Speaker Emulation

This post describes the design and construction of a 3-channel, 30 watts per channel, audio amplifier. Although my amp incorporates two antique HY60 power modules, construction details are given for construction using the modern TDA2050A, capable of yielding 32 watts. The amplifier is intended to be used as a Leslie Speaker Emulation driver unit, delivering power into a 3-phase speaker system, the construction of which which will form a companion post, together with a PIC microcontroller control system, also described in a separate post.
Original article posted on joebrown.org.uk around 2010


Companion posts are as follows:

  • The Brute: A 3-channel Audio Amplifier For Leslie Speaker Emulation. (this post)
  • Treslie: 3-Phase Leslie Speaker System.
  • LEMS: Leslie Emulation Control System using PIC Microcontroller (18F26K20) on Pequeno board, (Arduino-alike) and 3 DACs.

Updated 29th January 2014.
You may also be interested in this: MIDIGEN – A (belated) LEMS postscript

Why The Brute?

The introduction of the power transistor some forty-odd years ago heralded the demise of valve(tube) amplifiers – at least for everyday amplification. Unlike it’s thermionic cousin however, the transistor proved to be almost totally intolerant of heat, suffering from thermal runaway which if not checked resulted in early demise. Great ugly heatsinks started appearing on the back of amplifiers – the only manifestation of activity in what was otherwise (and still is) a boring, banal box, with little to distinguish one manufacturer’s efforts from another.

Around the same time, Gateshead Town Council cleared away large areas of pre-war (yes, 1st World War) housing, and built in it’s place great ugly blocks of flats, some of which, in an effort to hide their dullness and banality, were ‘rusticised’ by arranging to have bruised concrete ridges running vertically up the walls – not a little unlike the heatsinks on the amplifiers.

A little while ago (when this article was first posted), I received a gift of two HY60 power-amp units from a good friend, and decided to incorporate these into my Leslie speaker emulation system. I could have followed common practise and hidden the black fins on the rear of a cabinet, but decided to make a feature of these. Together with the use of a two-tiered structure, built using heavy slabs of Beech and Brass panels, I have tried to create a (back-handed) tribute to the Brutalist architecture of the age in which the HY60s were conceived.

That the result is somewhat ugly, there is no doubt, but it is also functional, the vertical construction resulting in a strong chimney effect which results in a natural flow of air both around the power transformer and up through the amplifier heatsink fins. The latter do get warm at full power, but show no signs of suffering as a result, and no fans were deemed necessary.

Since I needed 3 amplifier units in total, I purchased a similar-sized heatsink and built the 3rd amplifier using a modern integrated power amplifier – the TDA2050A.

The Shape

The shape of the amplifier apes that of the loudspeaker system, which is a ‘squashed’ hexagon thus:

The dimensions are reduced so that the power transformer and reservoir capacitors are accomodated, and the small sides of the irregular hexagon are roughly equal to the width of the heatsinks. (2.4 inches/62mm) This results in the long sides being just a little under 6 inches/150mm in length. The central dividing lines in the above drawing should be ignored, as these are not used in the amplifier unit.

Photographs of construction and the completed unit.
Unlike previous posts, I’ve confined most of the photos taken during construction to a separate post: Construction Photos
If you are considering building something similar, a glance through these should clarify my remarks regarding ventilation above.

The HY60
If you are the proud possessor of a number of HY60 (or equivalent) units, then by all means use these. I incorporated two of these into my design, using the recommended PSU of +24v, -24v, and followed the circuit schematic given in the HY60 datasheet, which I’ve linked below: HY30P.HY60.HY6060

The TDA2050
A link to the TDA2050 datasheet is here:
TDA2050

My schematic varies little from that in the datasheet:

Exports from the Eagle project of the component and foil sides of the PCB will be provided later, when time permits, together with the Eagle project files.

The power supply is simple – but large! I used a 225watt Toroidal transformer and two sets of 3 X 6800uF electrolytics. No PCB was used and the schematic is given below:

Construction

I roughed out the irregular hexagon Beech slabs using a power jigsaw, then finished the outside profiles using a high-speed router. The transformer pan cut-out was done with the power jigsaw, as was the hexagonal cut-out on the amplifier support slab. (middle-tier)

The Brass panels on the PSU are held in place in saw-cuts in the base slab done with a small circular saw (1.25 inch diameter) fitted in a small power drill. These panels fit into somewhat wider slots in the base of the middle-tier, which were cut using a small router bit fitted in the chuck of my smallest milling machine. The ventilation slots for the power amps were cut in the middle-tier, with a slightly larger router on the same machine. Using the X-Y table on the milling machine gives precise control over the cuts, resulting in a more accurate and neater cut than that obtained using a hand-held router.

Careful examination of the photos of the amplifier will reveal that the heatsink on the HY60 near-clone I built using the TDA2050A is slightly shorter than that on the original HY60s. I placed this unit at the rear of the amplifier, and the gap provides adequate space for a free-flow of air up the inside of the amplifier. No slots were cut in the bottom-side of the top slab, this is lined up and held firmly in place with three large woodscrews driven through the middle-tier upwards. The PSU is fastened to the middle-tier slab in a similar manner.

Safety should be paramount where mains voltages are concerned, and each Brass panel is connected with stoutish insulated wire to the brass panel on the PSU to which the Earth from the mains supply is connected. This was then connected via a 100 ohm resistor to the 0v line of the PSU. A similar wire connected to the transformer pan base is also connected to Earth.

For the 0v line on the PSU I used a small-diameter brass bar, which allows connections from the amplifier at any point in 360 degs. The +ve and -ve connections were done using reasonably heavy (10 amp) insulated wire. Look carefully at my photos of the PSU and you will see that a change of mind resulted in me cross-connecting colours on the capacitors, so that I ended up with a RED -ve wire and a BLUE +ve wire – don’t do this at home!

To have fitted two 20,000uF capacitors would have resulted in a larger case, so I substituted these for two sets of 3 X 6800uF, and sited these by drilling receptacles in the base slab using a Forstner bit. The bridge rectifier is fastened to one of the small Brass panels using a little silicone grease to aid cooling. Note that I made the transformer pan cut-out slightly larger than the Tx itself, to allow for the free flow of air around the periphery, via holes drilled in the pan base. The transformer (which I bought from RS components) came without a fitting kit (I had assumed this was included). I improvised bottom and top gaskets cut from a cheap silcone heat mat, and the top fixing plate from 22 gauge Aluminium.

Finally, the unit sits on three feet approximately 12mm high, to allow for the free passage of air up through the ventilation holes in the base plate of the transformer pan. I made these from ABS, but similar feet are available commercially. These sit in receptacles drilled in the bottom of the base slab and were glued using a latex-based adhesive.

Overrated PSU?

Yes, it is, but deliberately so. I wanted the facility to extend/expand the unit either to more channels and/or greater power, hence the over-specced transformer used.

Suppliers:
[ The following information was true back in 2010 ]

I purchased the transformer from: RS Components here: http://uk.rs-online.com/web/. The stock number being 6719038 (Toroidal transformer, 225VA 2X18V).
A similar unit is available from ESR here: http://www.esr.co.uk/. Stock number 328-018 (Toroidal Transformer 225VA 0 – 18, 0 – 18 (22518))
ESR can also supply the TDA2050s, as well as the PCB laminate etc., and all other electronic components.
The heatsink I used was also from RS. and the stock number for this is: 1898066 (Heatsink SK100 37.5 SA)

Annotated Gateshead Walk

A walk in Gateshead in 2012.
The views are in the order of my route on the annotated map. Start is at bottom of the map.
Click on link to view photo, use Back Button <- to return here.


Start
View from outside Civic Centre across what was High West St., to top of Nelson St.
Ditto, but looking South.
Ditto, but showing corner of Regent’s Court Flats.
View down the (now cul-de-sacced) Nelson St.

From top of Nelson St.
View across void that used to be Odeon Cinema, to Gateshead High St.
Similar, but showing corner of Regent’s Court Flats.
Moved down Nelson St a little. Amazing how big Odeon used to be.
Bottom of Nelson St – can’t remember what this pub used to be called.
Attempt to ‘beautify’ derelict Odeon site, shows how long this land has been empty.
View up to end of what used to be Sunderland Road.
Yes, do recognize this pub. Looking South to ‘top’ of High St.
View ‘along’ now blocked-off Sunderland Rd.
View north from same position.

View of would have been front of Odeon.
View north from same position. Construction crane at ‘Trinity Square’ clearly seen.
Mum & Dad’s old watering hole – still seems popular.
Regent’s Court flats again!
Back of RH side of High St., going north – this pub still same name. I remember there were underground toilets in the middle of street here. The ‘Ladies’ toilets had a missing frosted-glass brick in the roof, and myself and other ‘little devils’ from ‘All Saints’ school, used to peep down at some unfortunate woman’s bum, as she sat on the toilet. Various unprintable epithets from the poor victim would result as a consequence of our laughing and ‘comments’.
If you want a pee now, find a bush, as there is no replacement apparent on the High St.
Alas! Block containing Law’s Herbal Store is no more.
Curley’s is another pub that still clings onto life.
View of bottom of Jackson St, with Metropole still surviving.
This is now main thoroughfare east-west through Gateshead. Boilermakers club at top on right is gone though. (I saw Bobby Thompson – ‘the litte waster’ there – cracking!)

View west up Jackson St.
Apparently, the old Holy Trinity church is actually called St Edmunds??
Oldest section clearly visible here.
Doggarts – your old mate Patricia Donnelly’s place of work a long time ago..
View across to M & M – I had Fish, Chips and Mushy peas here this morning.(sit down in cramped cafe) Fish was beautiful.
View west up Jackson St.
The demise of the Co-op is complete. None of these historic buildings are now occupied by the Co-op.
Ditto.
Ditto.
View east down Jackson St.

New construction of Trinity Square can clearly be seen here.
Corner of St.Joseph’s Church.
View of Church and High West St.
Church and Metro Interchange.
Metro Interchange
Ditto and looking south down towards Newcastle.
Ditto.
Across the road now, and looking at new construction on site of ‘Get Carter’ film.
Straight down West St., good view of Tyne Bridge.
Is this going to be another ‘White Eliphant’ I wonder?

It’s certainly big enough.
Wow!
Who left that there?
See how new building abuts 60’s Coo-op building.
Ditto
One of the large cranes on the site.

This man is determined to get into all my pics. Old Post Office and Lloyds buildings still there.
Panoramic view of bottom of West St.
Now slighly west.

More west. Bit of Last block of Barn’s Close flats clearly visible.
Last Block.
Back view of old Town Hall. (and cop station)
View back along showing old Rent Office.
View south of new construction
View SW of new construction.
Another view south.
Ditto.
Back view of Tesco’s on site at junction of Ellison St., and High St
View east to High St., from all that is accessible of Ellison St.

View west along Ellison St from same position as above.

God, it’s so dreary. I was almost pleased the batteries in my camera gave up at this point.

Printable version of annotated map.
Annotated Map.

An interesting article on the state of affairs during my early life in Gateshead.
20th Century Gateshead

A short film of activities, together with Jimmy Nail singing ‘Big River’. Watch on YouTube Big River

Wendy

I never discovered why we couldn’t keep ‘our’ dog. I remember missing her very much.
The events portrayed here are true, and though the account is quite short, there is at least one scene, that though it portrays ‘typical’ behaviour of some children at the time, some folks may be upset by it. Looking back on it myself, I still find it somewhat obscene, as I did when I first witnessed it.

Wendy

Why don’t we do it in the road?

Why don’t we d-do it in the road? Mmm
Why don’t we do it in the road? Ah
Why don’t we do it in the road? Mmm
Why don’t we do it in the road? Mmm
No one will be watching us
Why don’t we do it in the road?

Apparently, Paul McCartney was inspired to write this song after witnessing two monkeys having sex in the middle of the road in India. He described it as a liberating sight.
I’m not so sure about this one.
Grateful thanks to Phil Taylor for the photo.

The Stories

A Girl’s Best Friend A sewing machine? Well let’s see..
Brainstorming  Everyone should have a Guardian Angel..
Broken  Who is broken? Is it me, or her? Or all of us?
Bus Ride To Balham  Who are you?
Closed Circle Ride with me.
I do not count the time  Everlasting Love.
Kate Another Waif.
My Beeping Heart Linked across space and time.
Penny For Rita  Brotherly Love?
Predator Retribution can be so sweet,,
Pride  You know what happens..
Rosie and Friend   A beautiful dog, a lovely lady.
Sister Mildred  A haunting personal experience.
The Carlson Imperative – Book 1
That Girl  Innocence & honesty.
Wild Thing  Indeed she was.

Broken

This short story contains explicit sexual references that some readers may find challenging and/or offensive. You have been warned.

Letters, Read Just One Last Time
© 2010 J.W.Brown

Letter #3: Broken

There are many things I would have done differently, given the chance, because I’m just the same as everyone else. And if I was given the chance of changing only one thing, it would be that I wouldn’t have accepted her dismissal of me so readily. That acceptance, that terrible acquiescence in her decision, has stalked me for the rest of my life.

Why? Because I know now that she loved me, desperately, but had two reasons, the least of which she would not, as she saw it, be the reason for the breakdown of my marriage, and secondly, but most importantly, the terrible belief that I could not, would not, be able to live with a person having a deformity. Trouble is, I was so hurt at the time, that I blindly accepted as the truth her lie that she didn’t love me.

There is part of me that says if I hadn’t waited as long before contacting her again, there would have been a real chance for us. As it was, I sought consolation for my terrible sense of loss in a succession of affairs, which ended, as you know, with you.

You have many weaknesses, but I believe in my heart that you might have fared better with someone other than me. Someone who refused to accept the terrible truth that he’d let the real love of his life walk away. I can only say that I’m sorry, with all my heart, that you haven’t found happiness, either with me, nor subsequently with anyone else.

I first saw Emily sat on one of the long bench seats, more or less alone, as everyone else was up dancing in the crowded pub. She smiled up at me when we were introduced, and as I took in her pretty face, framed in her long, dark, silky hair, and the warm, welcoming brown eyes, a bomb exploded deep within me, and shivers of Déjà vu ran up my spine as I recognised a girl, and a lover, I had only dreamed about.

She had taken my offered hand, and held it gently as our mutual friend introduced us, and when he’d finished, she had just as gently pulled me a little closer. “Sit with me Joe, and tell me more about yourself.”
Charlie left for the bar, to buy us a drink, and I sat down on her right, her hand still holding mine, which she rested on her knee.

Up close, I could smell her delicate body scent, and the second shock wave of emotion rose, and I shivered.
“Are you cold Joe?” she asked softly, her lovely eyes intent on me.
“No..”
She waited, hearing me pause. I don’t know what came over me, I only knew I didn’t want to lie.
“It’s you.”
“Me?” she asked quietly, but her hand tightened it’s grip on mine.
I blurted it out. “I feel we have met before, been lovers before. The feeling of being next to you is exquisite.”
She smiled. A wide sensuous smile, and the light seemed to dance in her eyes.
“I’m sorry..” I started to apologise, but she let go of my hand and placed her index finger to my lips.
“Don’t apologize Joe. That is one of the loveliest things that has ever been said to me.”
She moved her finger from my lips and placed her hand on the side of my face. She leant forward and I knew what she intended. I leant forward and our lips met.

Her tongue brushed mine as we moistened each other’s lips. Her fingers tightened on the side of my neck and I felt her shudder. She ran her tongue deep into my mouth, exploring, searching, as we kissed slowly. Another shiver ran up my spine, and she half-giggled.

“Christ! You two don’t waste any time, do you?”
We broke apart and her giggle turned into a laugh. She grasped my hand again and held it firmly pressed against her thigh.

Charlie put down the drinks and stared at us, looking puzzled.
“Am I being wound up here?” he asked. “Do you already know each other?”
I turned to her and we both smiled.
“In a way, yes, we do know each other, very well indeed.” she said.
He shook his head, and looked down at us, then picked up one of the pints.
“Well, it looks like you both have unfinished business, so I’ll leave you to it.”
He nodded at me. “Maybe you’ll explain later?”
I laughed. “Maybe.”
He left.

A warmth had come over me I had never felt before. I was totally at ease with her, and we talked, broken now and again with the gentle meeting of our lips, in kisses that became progressively more passionate.

I wanted to hold her. A slow number was being played. “Would you like to dance?”
A shadow crossed her face. I nearly missed it. She gripped my hand.
“There’s something I need to tell you.”
“Oh? Tell me on the dance floor. I want to hold you.”
Her hand went to my cheek. “Sweet, sweet Joe. Your lovely honesty. But I must tell you before we get up.”
I had a foreboding, but dismissed it immediately. Whatever she had to tell me, it made no difference, I loved her.
I leaned forward and kissed her. She took my hand again. She looked intently at me.
“I have a spinal condition called Scoliosis – curvature of the spine.”
I looked into her lovely sad eyes. “Will it stop you dancing?” I asked softly.
I felt her relax. The tension left her face and she smiled.
“No. But it can be seen, and people may stare at you.”
“Then I shall stare back at them.”
She leaned forward and we kissed again, then she took my hand and led me up to dance. Other than she leaned a little to one side, she looked lovely. I took her in my arms and we smooched in time to the music.

My neck felt wet. I looked down at her face and saw she was crying.
“Hey! Why the tears?”
“Fear.” she snuffled. “I’m sorry. Touch me, and let’s get it over with now, then you can go. I’ll understand.”
I was shocked. I stopped moving and stepped back to look at her. I took her head in my hands and kissed her tears, salty on my lips.

“I’m going nowhere, other than with you. Now I will touch you, just to show you that it makes no difference to how I feel about you. Then I’d like to see where you live, and make love with you.”

I took her into my arms again, and as we moved in time to the music, I gently ran my right hand down the length of her spine, from neck to coccyx.
She looked up at me, her eyes still afraid. I moved my hand to where I could feel the top of her lovely bum and gently pressed and massaged slightly down between her cheeks through her thin dress..
Her face went into my chest. “Oooh!” She tightened her arms around my neck. “More, please, more.” she whispered.

I extended my ring finger as I touched her and I felt her clenching her buttocks. With each slow movement of my hand she shuddered and moaned softly. Then she looked up at me. “Christ Joe. Let’s go, otherwise I’ll be coming in front of everyone.”

Our drinks left half-finished, we got our coats and headed for the car park. Her hand went to the inside of my thigh as I started the engine, and she gave me the first directions.

Inside the house, she threw her keys on the hall table and led me upstairs. She turned and embraced me. “I’m a little shy. Hold me as you undress me.”
Then we were in between the sheets, her lovely thighs apart as she guided me inside her. We both shivered.

I moved slowly and deeply. Her breathing became interposed with gasps of pleasure, and I could feel her fingernails in my back. Her head began to rock from side to side and she shouted. “Oh! Please, more, more.”
I slid my hand under her bum and lifted her pelvis.
She gasped “Yes. Like that.” and thrust herself up to me. Her mouth found mine again and we kissed, her tongue long and deep into the top of my throat. There was a pause, and she arched her back upwards, a long low scream escaping from her throat. I thrust ever harder as she came, wave after wave. “You. You.” she yelled looking into my face, and I let go. I buried my face in her neck as I screamed, and thrust violently into her as I started to ejaculate. “Oh God!” she shouted. “Go on, go on.”

My orgasm ended after a furious violent flurry of movement, and I lay, just above her and kissed her brow.
We lay, getting our breath back, then she started to laugh, then cried.
I lay by her, propped up by my elbow, and stroked her sweet face and neck, until the tears stopped.
“Sorry.” she said. “I can’t help myself. That was the most beautiful thing that has ever happened to me.”
She reached up and kissed me gently, then her head back on the pillow, she said softly. “I want you to look. Look now.”
I nodded. She wanted assurance from me.

She rolled over. I could make out the slight, but distinct ‘S’ curve. Other than that her back was beautiful, her bum absolutely lovely.
I put my hand on the small of her back and pressing gently, massaged up and down, reaching a little further each time, deep between her cheeks.
She turned her face toward me. “Oh Joe. That is lovely. Please don’t stop.”
I smiled, and kissed her neck, then leant back and watched her face as I massaged her.

She was breathing deeply again, her tongue licking her lips, and her eyes occasionally opening to look at me. She moved her bum so that my finger ran over her anus and she gasped. “Yes. Touch me there. Please.”
I ran my finger gently over her, and she writhed with pleasure, her breathing becoming shortened and forced. Finally, her face in the pillow, she screamed and beat the bed either side of her head with her fists.

She lifted her head and shouted. “Come inside me. I want you inside again.”
I moved over and entered her soft, hot vagina, and she thrust herself up and into me, her delicious bum wrapped around me and caressing my stomach. We moved together as she orgasmed, over and over. Only when I felt her tiring did I come, then smothered her neck and shoulders in kisses.

Finally I lay by her side, bathed in sweat.

She turned over and put her head on my chest. She spoke, her voice low and gentle. “I’m in love with you. How is that possible? We only met just over two hours ago.”
“I could ask you the same question. I don’t know. I just know that you make me feel wonderful.”
She moved her head and kissed my right nipple. “Me too.” she murmured.
Ab few blissful weeks followed. Then her announcement out of the blue, just before we said goodbye after making love again.
Yes, we had discussed my failed marriage already. When I had protested as much, she had told me her love for me had died. She was convincing, no sign of doubt, just a kind assurance that she would never forget me, but it was over. Fool that I was, I accepted her lie.

At times, when I think of her, it seemed as though it was just a dream, a dream within a dream, and the reality was that we had never met. Whether it happened or not, the profound sense of loss has never left me, and despite trying, I still grieve, ruined, and useless to anyone else.

Letter #3: Broken is a work of fiction. Any resemblance between characters in the story, and real persons, either living or dead, is purely coincidental.