Pioneer SA-7500ii output transistor question
- By DOM123
- Solid State
- 4 Replies
Hi Everyone,
Picked up an old & very dirty Pioneer SA-7500ii showing signs of past mishaps. The original output transistors 2SB618A & 2SD588A are present on one channel, but on the other channel they have been replaced with SC2579 & SA1104, with a hole drilled in the heatsink to mount them. From the filth & dust build-up it must have been done a long time ago. Also one of the emitter resistors is is not original & the board is quite severely charred beneath this resistor, so probably from the time of the original failure.
Has anyone ever heard of these transistors being used as a sub for 2SB618A & 2SD588A and should they be OK ? On paper the specs look ok & to be fair the amp seems to work ok. Should I just leave them in or replace all 4 transistors with new ones ?
I know on various forums other replacements transistors are proposed, but to be honest most are not easily available at a reasonal cost. I can quite easily get 2SC3858 & 2SA1494 though. Any advice welcome.
Picked up an old & very dirty Pioneer SA-7500ii showing signs of past mishaps. The original output transistors 2SB618A & 2SD588A are present on one channel, but on the other channel they have been replaced with SC2579 & SA1104, with a hole drilled in the heatsink to mount them. From the filth & dust build-up it must have been done a long time ago. Also one of the emitter resistors is is not original & the board is quite severely charred beneath this resistor, so probably from the time of the original failure.
Has anyone ever heard of these transistors being used as a sub for 2SB618A & 2SD588A and should they be OK ? On paper the specs look ok & to be fair the amp seems to work ok. Should I just leave them in or replace all 4 transistors with new ones ?
I know on various forums other replacements transistors are proposed, but to be honest most are not easily available at a reasonal cost. I can quite easily get 2SC3858 & 2SA1494 though. Any advice welcome.
Fons CQ30 - power supply rebuild
- By kunlun121
- Analogue Source
- 2 Replies
As part of a project that involves a complete makeover of a Fons CQ30 turntable, I want to rebuild the power supply. The components are all ancient and the shape of the PCB is odd. No doubt this is due to its place in the turntable's enclosure, but i want to move it to a separate box. The elco on mine is most certainly dead.
As a noob (both to this forum and to diy audio) I wouldn't be able to do so if it weren't for the enclosed schematic I found over at Vinyl Engine. So a thank you to them.
Before I embark on making a new pcb from this schematic, I want to ask the open question: can any of the folks here with turntable expertise recommend straightforward ways for improving on the design of this power supply or the choice of components? (Without starting over with a blank piece of paper.) Anything that can improve the stability of the speed control for example. And I haven't checked but at least some of what is listed here must be obsolete.
The only choices I have made are the easy ones: a rotary selection switch for the speed selection, and new (rotary) potentiometers for the pitch adjustment. I plan to replace the motor with a NOS unit from a Philips GA312 I ran into recently, as mine requires some manual help to start spinning. Apparently these are are a drop-in replacement for the CQ30's motor (unlike the Philips GA212's motor, which are easier to find but makes the platter spin at around 150RPM without adjustments).
All advice would be much appreciated.
As a noob (both to this forum and to diy audio) I wouldn't be able to do so if it weren't for the enclosed schematic I found over at Vinyl Engine. So a thank you to them.
Before I embark on making a new pcb from this schematic, I want to ask the open question: can any of the folks here with turntable expertise recommend straightforward ways for improving on the design of this power supply or the choice of components? (Without starting over with a blank piece of paper.) Anything that can improve the stability of the speed control for example. And I haven't checked but at least some of what is listed here must be obsolete.
The only choices I have made are the easy ones: a rotary selection switch for the speed selection, and new (rotary) potentiometers for the pitch adjustment. I plan to replace the motor with a NOS unit from a Philips GA312 I ran into recently, as mine requires some manual help to start spinning. Apparently these are are a drop-in replacement for the CQ30's motor (unlike the Philips GA212's motor, which are easier to find but makes the platter spin at around 150RPM without adjustments).
All advice would be much appreciated.
Slate & acryl DD tt
- By trondkj
- Analogue Source
- 23 Replies
Slate & acryl DD tt
Hi folks, my first serious post here, hope you'll enjoy.
It began with a Dual 701 DD turntable, a nice turntable, but with an arm that is not up to the specs I wanted. The automatics were malfunctioning, so I slaughtered the tt and bought an acrylic platter from Diy Hifi Supply.
I was thinking about the plint, should I make a aluminium-ply-mdf-ply-aluminium sandwich like this:?
..or go for something different?
I went for something different, and since then I have done a lot of thinking, and a little work:
The acrylic platter on top of the slate plint illuminated by the midnight sun
Last easter i got a hole in the slate so that the EDS1000 motor would fit in.
Before that I had installed the power supply and speed selector / pitch control in a box:
The turntable with the motor and platter installed:
..and with a couple of arm boards temporarily placed on top:
I nice member of this forum saw the picture above on a Norwegian forum, and offered to make a couple of acrylic arm boards for me:
For this turntable the arm(s) have to be DIY as well, I am going for a Ladegaard tangential on the left arm board, and a 12" Schröder copy on the right arm board.
But I do not have enough patience to wait for the arms to be finished, so one of my temporar arm boards have to do as a base for my SME 3009/S2 Impr. for so long.
Not willing to make holes in the stone for the arm screen under the base, I had to do a little modification to the arm:
The left arm board is mounted to the stone with brass standoff/legs:
The right one is only standing on its legs, but they are shinyer than the other ones:
And of course there's something that simply does not fit in, and therefore has to go:
I am thinking about a motor cover made of black transparent acryl to replace this wooden thing.
The turntable plays with a Shure M75ED 2 with a Jico SAS needle to plow the grooves, and sounds really promishing.
Kind regards
Trond Kjetil
Hi folks, my first serious post here, hope you'll enjoy.
It began with a Dual 701 DD turntable, a nice turntable, but with an arm that is not up to the specs I wanted. The automatics were malfunctioning, so I slaughtered the tt and bought an acrylic platter from Diy Hifi Supply.
I was thinking about the plint, should I make a aluminium-ply-mdf-ply-aluminium sandwich like this:?
..or go for something different?
I went for something different, and since then I have done a lot of thinking, and a little work:
The acrylic platter on top of the slate plint illuminated by the midnight sun
Last easter i got a hole in the slate so that the EDS1000 motor would fit in.
Before that I had installed the power supply and speed selector / pitch control in a box:
The turntable with the motor and platter installed:
..and with a couple of arm boards temporarily placed on top:
I nice member of this forum saw the picture above on a Norwegian forum, and offered to make a couple of acrylic arm boards for me:
For this turntable the arm(s) have to be DIY as well, I am going for a Ladegaard tangential on the left arm board, and a 12" Schröder copy on the right arm board.
But I do not have enough patience to wait for the arms to be finished, so one of my temporar arm boards have to do as a base for my SME 3009/S2 Impr. for so long.
Not willing to make holes in the stone for the arm screen under the base, I had to do a little modification to the arm:
The left arm board is mounted to the stone with brass standoff/legs:
The right one is only standing on its legs, but they are shinyer than the other ones:
And of course there's something that simply does not fit in, and therefore has to go:
I am thinking about a motor cover made of black transparent acryl to replace this wooden thing.
The turntable plays with a Shure M75ED 2 with a Jico SAS needle to plow the grooves, and sounds really promishing.
Kind regards
Trond Kjetil
Retrofitting a GRS 2522 into an old Radio Shack CS-5 center channel
- By Vidgamer
- Planars & Exotics
- 5 Replies
I took an old Radio Shack CS-5, gutted the old Linaeum tweeter, and substituted the GRS 2522. (The old tweeter was not working well and I could not fix it.) I chose the CS-5 because I had existing RS LX-5 speakers, and thought it might make a good tonal match, but time does not seem to be kind to the Linaeum tweeters. The GRS 2522 looked like it might be a reasonable substitute, so I decided to give it a try.
I tested with REW (generating white noise) in a non-ideal location (speaker propped on other stuff, and near a wall and corner), and got the below result. Except for the dip at 8k, this is better than I expected. I managed to guesstimate the match with the woofer pretty well, and it's eerily flat through the important midrange.
Woofer and tweeter use 1st order crossovers, which seems like it could be problematic, but it matches up OK, based on this. I estimate the woofer crossover to be starting at about 1500Hz, and the tweeter at 4k, so there's a lot of overlap.
I need to do a more complete write-up, but thought in the meantime, someone might find this interesting and/or tell me what my 8k dip is from. I did add a series 2.2 ohm resistor to try to match levels, so it's possible that it brought the higher treble down more than lower treble, I suppose.
(Edit: fixed attachment)
I tested with REW (generating white noise) in a non-ideal location (speaker propped on other stuff, and near a wall and corner), and got the below result. Except for the dip at 8k, this is better than I expected. I managed to guesstimate the match with the woofer pretty well, and it's eerily flat through the important midrange.
Woofer and tweeter use 1st order crossovers, which seems like it could be problematic, but it matches up OK, based on this. I estimate the woofer crossover to be starting at about 1500Hz, and the tweeter at 4k, so there's a lot of overlap.
I need to do a more complete write-up, but thought in the meantime, someone might find this interesting and/or tell me what my 8k dip is from. I did add a series 2.2 ohm resistor to try to match levels, so it's possible that it brought the higher treble down more than lower treble, I suppose.
(Edit: fixed attachment)
EL34 triode mod
- By mongting
- Tubes / Valves
- 11 Replies
I got Jolida JD302B recently. The amplifier is EL34 PP with ultra linear. I would like to modify it as triode connection.
I got this schematic and
I was told to cut the connection to the pin #4 and put 100 ohm resistor between pin #3 and pin #4.
Then, I found another schematic about triode mod.
This one tells that I need to cut the connection to pin #3 which is connected to the plate of a tube. And it also shows the disconnection from the output transformer to C2.
I am confused now. Which one is right?
1) cut the connection to pin 3 and put 100 ohm resistor between 3 and 4.
2) cut the connection to pin 4 and put 100 ohm resistor between 3 and 4. additionally, cut the connection between the output transformer and C2.
I don't have much knowledge in circuit theory.
I got this schematic and
I was told to cut the connection to the pin #4 and put 100 ohm resistor between pin #3 and pin #4.
Then, I found another schematic about triode mod.
This one tells that I need to cut the connection to pin #3 which is connected to the plate of a tube. And it also shows the disconnection from the output transformer to C2.
I am confused now. Which one is right?
1) cut the connection to pin 3 and put 100 ohm resistor between 3 and 4.
2) cut the connection to pin 4 and put 100 ohm resistor between 3 and 4. additionally, cut the connection between the output transformer and C2.
I don't have much knowledge in circuit theory.
-
Locked
FS: Signal Transformers Altec, Jensen, Soweter, Onetics
I love transformer coupled audio circuits. But I have some transformers kicking around my parts box that need to find a new home.
$150 takes the lot. And I'll throw in some no name mic transformers.
$5 shipping each pair to USA and territories. PayPal or Venmo payment preferred. Outside USA please esquire, I'll check prices.
All working, just been sitting in the parts bin doing nothing for years. Put them in your projects and make them sing again!
$45 Pair: Altec/Peerless 15356 Octal base. Look old, sound great. Some solder on the pins.$35 Pair: Jensen JT-11-HFMPC Tested but never used.$40 Pair: Sowter type 3128. Short leads, pulled from a circuit board. Screw mount$45 Pair: Sowter 9809f. Original length leads.$20 Pair: Onetics microphone transformers. 1:1 has center tap (I think) Jensen shown for scale.
$5 shipping each pair to USA and territories. PayPal or Venmo payment preferred. Outside USA please esquire, I'll check prices.
All working, just been sitting in the parts bin doing nothing for years. Put them in your projects and make them sing again!
I pimped my Citation Sixteen! (or, resurrected?)
- By nattawa
- Solid State
- 5 Replies
Bought a beaten-up Harman Kardon Citation 16 as a fixer-up unit and thought I’d fix whatever went wrong and it’d be my sleeper amp, only to end up with gutting this legend out completely. Now this amp has nothing but chassis and heat-sinks that are left over from the Citation Sixteen. It has two-channel Leach amp in it, with an output stage consists of 5-pair/channel ThermalTrak devices, NJL3281/1032 of On-Semi. By the way, could this be the first Leach Amp on TermalTrak output devices in this forum? Any ways here go the pics:
ALL-BUCKLED-UP...will it be a rough ride?
LITTLE DRIVERS…Can they handle the ark?
HEAT-AND-ITS-SINK
I piggy-back bolted some extra aluminum--scrap extrusion yet not particularly cheap🙁 from ebay-- to the center channel of the original Citation 16 heat-sink where the TO3s used to be to hopefully beef-up the heat-sinking capacity.
PCBS
Got these fabricated in China , cheap and in better-than-okay quality
VAS
Voltage Amplification Stage assembled. I cut the GND copper foil to give the driver supply filter and the amplification stage supply filter separate ripple return paths after the PCB were made. The cuts show up on the component side as light marks mid way along the sides to the board edges
POWER-SUPPLY-BOARDS
These are hand-cut with a knife. The copper foils were later re-enforced with bus bars
PWR-CONNECTORS
Ring lugs over Erni Power-Tap was my choice of power connection
POWER CONNECTIONS
Each Power-Tap connector receives 2 ring lugs. For the center GND there are 7 wires, 3 of them form a triple #14 gauge going to the speaker binding post, the other4 are driver supply filter return, amplification stage supply filter return, output zobel GND lead, and the signal GND reference. For the power connections there are 3 wires per each rail, one goes to the amplification and driver stage, and #14 doubled go to the output transistor common rail. Why double/triple the wires you ask? The butt end of my ring lugs is too large for a #14 stranded, plus they all say size matters😉
BUS-BAR-BOT-COS
Current output board gets bus bars on the supply rails. I also put in pem nuts for easy attachment of the ring lugs. They were first pressed on the PCB into the plated holes, then got soldered to the copper foil.
BUS-BAR-TOP-COS
The output node gets a bus bar too
COS-BOT-WIRING
Ring lugs made doubled-up wiring easy
COS-DETAIL
Emitter resisters hooked up to the bus bar
COS-WIRING
Current output stage ready to go onto the transistor/heat-sink assembly. Oh, noticed the 2-conductor terminal block at about the lower left corner in the picture? They are temperature sensor terminals reserved for on-die temperature measurement or warning/protection. Four out of the 10 ThermalTrak diodes are hooked up in series and wired up to this terminal block.
MODULAR-AMP
This is how the thing looks
THE SHIELD
I sandwiched a third PCB of solid copper foil on GND in between the VAS and COS to cut down any possible capacitive couplings between the output stage and the input stage.
AMP-MODULE
Ready to go on the chassis and rock
AMP-OFF-CHASSIS
Powered up for the first time......with fingers crossed......
BIAS-ADJ
Started bias adjustment. I finally set the idle at 400mA to give the heat-sinks a nice warm touch. Stability has been good so far since the amp went into service a few months ago.
LEFT-CHNL-TOP
Left channel is on the chassis. The Neutrik RCA jacks look good, don’t they?
BINDING-POSTS
Are they too good?
R-CHNL-OFF-BINDPOSTS
Another view with right channel off chassis
TOP-VIEW
All put together! This is the "living room" of the chassis. The two black blocks sitting next to the RCA jacks are the speaker relays. These are automotive relays with 80A contact capacity. The transformer looks nice in the chassis to me, despite the fact it was scavenged from a broken Behringer EP2500 power amp.
spk-rly-RCA-jack
A close up view
BOT-VIEW
Let's go to the basement and take a look at all the supporting components. There are a few assemblies there, working on a secondary power supply. The secondary power supply transformer was scavenged from a broken CD player
INRUSH-LIMITING
This PCB has three relays of 12A AC contact capacity on board for the mains. One to connect through thermisters, the other two in parallel bypass the in-rush control when the rails have become stabilized. It also controls two out-board relays to cut in and out speakers. (more on this later). The coiled up twisted black/red wires in the middle (a bit unsightly) are not connected at this time. They are reserved for working with protection mechanisms to shutting down the power. The PCB in green behind the inrush board is a piece of scrap and work as a supporting base for other PCB assemblies to attach to.
DISCHARGR
It discharges all 4 power rails quickly when power is turned off. (more on this later) The black chunk in the lower right is the power switch with lighting. It came with 12V incandescent bulb in it, but I don’t like the yellowish color so I replaced the bulb with 4 white LEDs in series.
DC-DETECTION
It sends fault signals to the inrush PCB to have the speaker relay(s) cut out when DC is detected. It also lights up a warning LED indicating the channel in trouble.
IN-SVCE-TOP
Case closed.
IN-SVCE-REAR
Ain’t her rear end smokin’ hot? 😉
IN-SERVICE-Front
Hey, how do you like her in new shiny shoes? The original neon bulbs in the fixture have been replaced with LEDs that serve as DC warning. They seem to be glowing in the picture but they are in fact not. When they do they’d be much brighter than that.
My Paul-Sue-Barton’s are happy. So is the wifie. Beethoven has never sounded more Beethovenian.
TOE-OPERATED
The power switch is a push-button momentary switch so that one could easily operate with a toe and save his/her back. Here is how to:
http://www.flickr.com/photos/21102007@N04/4833640424/in/set-72157624460926929/
I’d get my dog to learn to do that for me if I had one.
About the Inrush PCB: (schematic will follow)
The big toroidal power transformer of over 1KVA and 80,000uF smoothing capacitance have made inrush current limiting a must. This circuit is based on hard-wired logic/timer devices, it controls the mains power relays and speaker relays. It works on a 12VDC secondary supply. This was laid out on a two-sided PCB that requires some basic SMT soldering skills to assemble. The circuit works with a lighted push-button switch with momentary contacts as the power switch, each push starts a 5-second time window during which the switch itself is disabled and the switch lamp flashes. When start from standby the soft-start relay will engage for as long as the time window lasts (5s), the mains power is applied through three GE CL-40 NTC thermister in series (15 ohms in total at room temperature). This will limit the inrush current and charge up the main caps in a controlled manner. The main caps should be charged up well within the 5-s time window and the rail voltage flats out. A flat-out detection circuit will engage a power-good monitor and if a power-good is positive the circuit enters power-on mode, the main relays (two in parallel) will bypass the inrush limiter and connect the primary winding of the power transform directly to the mains supply, the lamp in the power switch stops flashing to glow at a normal brightness, the speaker relays will also engage at the same moment given that there is no DC detected at the amplifiers’ output. The soft-start relay then cuts out at the end of the 5-s time window. If no power rail flat-out is detected or no power-good is detected during the 5-s time window, the main relays and the speaker relays will not engage, and the circuit returns to standby mode at the end of the time window, the lamp in the power switch then stops flashing to glow a dim light. Pushing the power switch during power-on mode will simply disengage power relays and speaker relays, and a 5-s time window follows to allow the main caps to be discharged deeply enough prior to responding next button push.
About the Discharger: (schematic will follow)
It brings main caps down to under 5V a few seconds of power off. It was built on prototyping board. The discharger is engaged whenever all the mains power relays cut out, and disengaged when any of the mains relays actuates. There are 4 jumpers on the board that allow for disabling the discharging operation. I used 4 photo couplers to isolate the control side from the audio GND, as well as audio GNDs of left and right channels. Such isolation also allows a very simple and uniform circuit implementation on all power rails using power MOFETs of one single model.
DC detecting circuit: (schematic will follow)
It works in tandem with the soft-start PCB to cut out speakers when DC presents at the amplifier output, it lights up a warning LED of the channel in trouble too. Built on prototyping board.
To be implemented: (schematic suggestion welcome)
An on-die temperature measurement/warning/protection using the roughed-in temperature sensor.
ALL-BUCKLED-UP...will it be a rough ride?
LITTLE DRIVERS…Can they handle the ark?
HEAT-AND-ITS-SINK
I piggy-back bolted some extra aluminum--scrap extrusion yet not particularly cheap🙁 from ebay-- to the center channel of the original Citation 16 heat-sink where the TO3s used to be to hopefully beef-up the heat-sinking capacity.
PCBS
Got these fabricated in China , cheap and in better-than-okay quality
VAS
Voltage Amplification Stage assembled. I cut the GND copper foil to give the driver supply filter and the amplification stage supply filter separate ripple return paths after the PCB were made. The cuts show up on the component side as light marks mid way along the sides to the board edges
POWER-SUPPLY-BOARDS
These are hand-cut with a knife. The copper foils were later re-enforced with bus bars
PWR-CONNECTORS
Ring lugs over Erni Power-Tap was my choice of power connection
POWER CONNECTIONS
Each Power-Tap connector receives 2 ring lugs. For the center GND there are 7 wires, 3 of them form a triple #14 gauge going to the speaker binding post, the other4 are driver supply filter return, amplification stage supply filter return, output zobel GND lead, and the signal GND reference. For the power connections there are 3 wires per each rail, one goes to the amplification and driver stage, and #14 doubled go to the output transistor common rail. Why double/triple the wires you ask? The butt end of my ring lugs is too large for a #14 stranded, plus they all say size matters😉
BUS-BAR-BOT-COS
Current output board gets bus bars on the supply rails. I also put in pem nuts for easy attachment of the ring lugs. They were first pressed on the PCB into the plated holes, then got soldered to the copper foil.
BUS-BAR-TOP-COS
The output node gets a bus bar too
COS-BOT-WIRING
Ring lugs made doubled-up wiring easy
COS-DETAIL
Emitter resisters hooked up to the bus bar
COS-WIRING
Current output stage ready to go onto the transistor/heat-sink assembly. Oh, noticed the 2-conductor terminal block at about the lower left corner in the picture? They are temperature sensor terminals reserved for on-die temperature measurement or warning/protection. Four out of the 10 ThermalTrak diodes are hooked up in series and wired up to this terminal block.
MODULAR-AMP
This is how the thing looks
THE SHIELD
I sandwiched a third PCB of solid copper foil on GND in between the VAS and COS to cut down any possible capacitive couplings between the output stage and the input stage.
AMP-MODULE
Ready to go on the chassis and rock
AMP-OFF-CHASSIS
Powered up for the first time......with fingers crossed......
BIAS-ADJ
Started bias adjustment. I finally set the idle at 400mA to give the heat-sinks a nice warm touch. Stability has been good so far since the amp went into service a few months ago.
LEFT-CHNL-TOP
Left channel is on the chassis. The Neutrik RCA jacks look good, don’t they?
BINDING-POSTS
Are they too good?
R-CHNL-OFF-BINDPOSTS
Another view with right channel off chassis
TOP-VIEW
All put together! This is the "living room" of the chassis. The two black blocks sitting next to the RCA jacks are the speaker relays. These are automotive relays with 80A contact capacity. The transformer looks nice in the chassis to me, despite the fact it was scavenged from a broken Behringer EP2500 power amp.
spk-rly-RCA-jack
A close up view
BOT-VIEW
Let's go to the basement and take a look at all the supporting components. There are a few assemblies there, working on a secondary power supply. The secondary power supply transformer was scavenged from a broken CD player
INRUSH-LIMITING
This PCB has three relays of 12A AC contact capacity on board for the mains. One to connect through thermisters, the other two in parallel bypass the in-rush control when the rails have become stabilized. It also controls two out-board relays to cut in and out speakers. (more on this later). The coiled up twisted black/red wires in the middle (a bit unsightly) are not connected at this time. They are reserved for working with protection mechanisms to shutting down the power. The PCB in green behind the inrush board is a piece of scrap and work as a supporting base for other PCB assemblies to attach to.
DISCHARGR
It discharges all 4 power rails quickly when power is turned off. (more on this later) The black chunk in the lower right is the power switch with lighting. It came with 12V incandescent bulb in it, but I don’t like the yellowish color so I replaced the bulb with 4 white LEDs in series.
DC-DETECTION
It sends fault signals to the inrush PCB to have the speaker relay(s) cut out when DC is detected. It also lights up a warning LED indicating the channel in trouble.
IN-SVCE-TOP
Case closed.
IN-SVCE-REAR
Ain’t her rear end smokin’ hot? 😉
IN-SERVICE-Front
Hey, how do you like her in new shiny shoes? The original neon bulbs in the fixture have been replaced with LEDs that serve as DC warning. They seem to be glowing in the picture but they are in fact not. When they do they’d be much brighter than that.
My Paul-Sue-Barton’s are happy. So is the wifie. Beethoven has never sounded more Beethovenian.
TOE-OPERATED
The power switch is a push-button momentary switch so that one could easily operate with a toe and save his/her back. Here is how to:
http://www.flickr.com/photos/21102007@N04/4833640424/in/set-72157624460926929/
I’d get my dog to learn to do that for me if I had one.
About the Inrush PCB: (schematic will follow)
The big toroidal power transformer of over 1KVA and 80,000uF smoothing capacitance have made inrush current limiting a must. This circuit is based on hard-wired logic/timer devices, it controls the mains power relays and speaker relays. It works on a 12VDC secondary supply. This was laid out on a two-sided PCB that requires some basic SMT soldering skills to assemble. The circuit works with a lighted push-button switch with momentary contacts as the power switch, each push starts a 5-second time window during which the switch itself is disabled and the switch lamp flashes. When start from standby the soft-start relay will engage for as long as the time window lasts (5s), the mains power is applied through three GE CL-40 NTC thermister in series (15 ohms in total at room temperature). This will limit the inrush current and charge up the main caps in a controlled manner. The main caps should be charged up well within the 5-s time window and the rail voltage flats out. A flat-out detection circuit will engage a power-good monitor and if a power-good is positive the circuit enters power-on mode, the main relays (two in parallel) will bypass the inrush limiter and connect the primary winding of the power transform directly to the mains supply, the lamp in the power switch stops flashing to glow at a normal brightness, the speaker relays will also engage at the same moment given that there is no DC detected at the amplifiers’ output. The soft-start relay then cuts out at the end of the 5-s time window. If no power rail flat-out is detected or no power-good is detected during the 5-s time window, the main relays and the speaker relays will not engage, and the circuit returns to standby mode at the end of the time window, the lamp in the power switch then stops flashing to glow a dim light. Pushing the power switch during power-on mode will simply disengage power relays and speaker relays, and a 5-s time window follows to allow the main caps to be discharged deeply enough prior to responding next button push.
About the Discharger: (schematic will follow)
It brings main caps down to under 5V a few seconds of power off. It was built on prototyping board. The discharger is engaged whenever all the mains power relays cut out, and disengaged when any of the mains relays actuates. There are 4 jumpers on the board that allow for disabling the discharging operation. I used 4 photo couplers to isolate the control side from the audio GND, as well as audio GNDs of left and right channels. Such isolation also allows a very simple and uniform circuit implementation on all power rails using power MOFETs of one single model.
DC detecting circuit: (schematic will follow)
It works in tandem with the soft-start PCB to cut out speakers when DC presents at the amplifier output, it lights up a warning LED of the channel in trouble too. Built on prototyping board.
To be implemented: (schematic suggestion welcome)
An on-die temperature measurement/warning/protection using the roughed-in temperature sensor.
Hand wound transformer question
Hey guys, i'm preparing to build a ribbon microphone and i've decided on winding my own transformer.
I've done the math and come up with the appropriate wire gauges and turn counts, and i will be using a smallish iron powder toroidal core, but i was wondering if anyone potentially has more knowledge when it comes to audio transformer construction. My biggest question currently has to do with the "layout" of the windings, more specifically, should the primary and secondary windings be wound into each other, or separated along the circumference of the toroid? i'll attach an iffy paint drawing to illustrate what i mean if it's unclear 🙂
(also another thing, but does the orientation of the windings in relation to each other, i.e. if one's would Clockwise and the other counter-clockwise?)
I've done the math and come up with the appropriate wire gauges and turn counts, and i will be using a smallish iron powder toroidal core, but i was wondering if anyone potentially has more knowledge when it comes to audio transformer construction. My biggest question currently has to do with the "layout" of the windings, more specifically, should the primary and secondary windings be wound into each other, or separated along the circumference of the toroid? i'll attach an iffy paint drawing to illustrate what i mean if it's unclear 🙂
(also another thing, but does the orientation of the windings in relation to each other, i.e. if one's would Clockwise and the other counter-clockwise?)
LM1875 Early Clipping
- By DylanBenton
- Chip Amps
- 11 Replies
Good Evening,
I have a LM1875 running single supply on a 24V SMPS which seems to be hitting the rails and clipping at about 17v (peak to peak) using a 400hz sine wave.
The chip is receiving 21.4v after regulation (LM317t) and while under load. How close can you get to the rails before distortion is expected?
Even with it biased at 10v, i thought it should get 20v without clipping. Is there anything i could be missing to cause this?
I would also assume that getting an output of 6v RMS on a 8ohm load would be pulling roughly 750ma, but it seems to be much lower.
Any help would be gratefully appreciated 🙂
I have a LM1875 running single supply on a 24V SMPS which seems to be hitting the rails and clipping at about 17v (peak to peak) using a 400hz sine wave.
The chip is receiving 21.4v after regulation (LM317t) and while under load. How close can you get to the rails before distortion is expected?
Even with it biased at 10v, i thought it should get 20v without clipping. Is there anything i could be missing to cause this?
I would also assume that getting an output of 6v RMS on a 8ohm load would be pulling roughly 750ma, but it seems to be much lower.
Any help would be gratefully appreciated 🙂
Pcb layout doubt
- By madhukannan
- Solid State
- 7 Replies
While making a PCB layout should we keep signal, Zobel, and decoupling caps grounds completely isolated? and run separate wires to the power supply ground T ? or is it required to have a connection between them in the PCB?
To which ground the constant current source ground can be combined?
To which ground the constant current source ground can be combined?
6П15П-ЕВ / 6P15P-EV = EL803S / SV83 NOS, NIB (lot of 100pcs)
- By OAA7
- Vendor's Bazaar
- 6 Replies
FS: 6П15П-ЕВ / 6P15P-EV = EL803S / SV83 NOS, NIB (lot of 100pcs)
Hi,
I have in stock excellent special quality electron tubes 6П15П-ЕВ / 6P15P-EV
= EL803S / EL83 / SV83
Index -EB means:
B = tubes of increased mechanical strength and reliability
E = tubes of increased durability (5000 hours or more)
Saratov factory "Reflector"
all the same date codes = Dec. 1976
minimum order = 100 pcs (one box)
price = $200 (i.e. $2 for 1piece)
shipping cost (2500 g)= $30 by airmail
Best regards!
-------------------
Olexandr
Kharkiv, UKRAINE
skype: OAA-1974
Hi,
I have in stock excellent special quality electron tubes 6П15П-ЕВ / 6P15P-EV
= EL803S / EL83 / SV83
Index -EB means:
B = tubes of increased mechanical strength and reliability
E = tubes of increased durability (5000 hours or more)
Saratov factory "Reflector"
all the same date codes = Dec. 1976
minimum order = 100 pcs (one box)
price = $200 (i.e. $2 for 1piece)
shipping cost (2500 g)= $30 by airmail
Best regards!
-------------------
Olexandr
Kharkiv, UKRAINE
skype: OAA-1974
Lowest safe loadline: what is the limit?
- By zintolo
- Tubes / Valves
- 135 Replies
I'm designing a amp to see the limits of a new feedback system, and I would like to know what is the limit you consider on the lowest side for the loadline.
Please consider that the DF has not to be considered here.
The amp is a PP based on a pair of EL34 at 450V B+.
Initial OPT was 6k6 with UL 23%, now I would like to test a 4k with UL 23% I have, but I would avoid to blow a pair of EL34.
The point is that the loadline is on the edge of 2x the max plate dissipation on some points (as highlighted on the image) and this considering a load of 8 Ohm, so it's even worst at mid frequencies where load is usually lower.
What is the limit you consider when you design an amp?
Is that loadline the lowest you'd use, not considering the DF in the equation?
Thank you in advance,
Roberto
Please consider that the DF has not to be considered here.
The amp is a PP based on a pair of EL34 at 450V B+.
Initial OPT was 6k6 with UL 23%, now I would like to test a 4k with UL 23% I have, but I would avoid to blow a pair of EL34.
The point is that the loadline is on the edge of 2x the max plate dissipation on some points (as highlighted on the image) and this considering a load of 8 Ohm, so it's even worst at mid frequencies where load is usually lower.
What is the limit you consider when you design an amp?
Is that loadline the lowest you'd use, not considering the DF in the equation?
Thank you in advance,
Roberto
Attachments
Microphone Isolation Panel instead of Rear Absorbtion Pads
- By Bradstone
- Room Acoustics & Mods
- 0 Replies
Attachments
Harmony H205/Silvertone 1342 OT
- By eetechTom
- Instruments and Amps
- 17 Replies
Starting my first classic amp restoration and have an output transformer question.The Harmony H205 amp I bought, had the OT replaced with a 16 ohm output sub. It’s a 6V6 pp circuit, rated at 12W I believe?. Haven’t gotten to the point of powering it up yet, but will obviously need a better OT. That orange cap needs to go too
This amp has the original Rola 12”, 3.2 ohm speaker. Any suggestions on a quality OT would be greatly appreciated. Want to do justice to this classic.
This amp has the original Rola 12”, 3.2 ohm speaker. Any suggestions on a quality OT would be greatly appreciated. Want to do justice to this classic.
Attachments
Guesstimating transformer power ratings
- By Kay Pirinha
- Power Supplies
- 12 Replies
Hi,
in the past two years I've harvested a bunch of power transformers from some cheesiy sounding and crappy Hammond transistor organs. Sadly, I didn't have a close look at their badges and the power consumption that might have been written there, but anyway, all these organs featured Leslie or Rotosonic units whose motors are of unknown power consumption as well.
The 1st pic shows a pair of identical trannies, Hammond part # 003-054471, coming from a Collonnade and a - smaller - Aurora Classic. Their lamination stacks measure 105 x 87 x 55 mm (4 1/8 x 3½ x 2 1/4 "):
Next one is the tranny of a notably bigger Concorde. Part # 003-046819. Lamination outline is the same, but stack height is a bit lower: 105 x 87 x 50 mm (4 1/8 x 3½ x 2 "):
Next one came form a Model 8022 organ. Part # 003-048011. Laminations measure 95 x 80 x 50 mm (3 3/4 x 3 1/8 x 2 "):
The next pair also was in the Colonnade and Aurora organs. Their primaries are 115 Vac, secondary is 14 Vac. Perhaps they might serve in a BTL pair (2 x 2) of amplifiers. Part # 003-054853, laminations are 76 x 63 x 41 mm (3 x 2 1/2 x 1 5/8 "):
The smallest one. Part # 003-046374, laminations are 66 x 56 x 26 mm (2 5/8 x 2 3/16 x 1 "):
Finally a 117 Vac power tranny that came from a Leslie 121 multi channel amplifier. It powered four almost identical amplifiers, consisting of a 12AU7 and a pair of fix biased 7189's each. This is the one I was referring to in my proper winding technique thread. I'm planning to rewind it as an OT of about 40 W power. Laminations are 114 x 95 x 33 mm (4½ x 3 3/4 x 1 1/4 "):
Which power capabilities can I expect from these transformers?
Best regards!
in the past two years I've harvested a bunch of power transformers from some cheesiy sounding and crappy Hammond transistor organs. Sadly, I didn't have a close look at their badges and the power consumption that might have been written there, but anyway, all these organs featured Leslie or Rotosonic units whose motors are of unknown power consumption as well.
The 1st pic shows a pair of identical trannies, Hammond part # 003-054471, coming from a Collonnade and a - smaller - Aurora Classic. Their lamination stacks measure 105 x 87 x 55 mm (4 1/8 x 3½ x 2 1/4 "):
Next one is the tranny of a notably bigger Concorde. Part # 003-046819. Lamination outline is the same, but stack height is a bit lower: 105 x 87 x 50 mm (4 1/8 x 3½ x 2 "):
Next one came form a Model 8022 organ. Part # 003-048011. Laminations measure 95 x 80 x 50 mm (3 3/4 x 3 1/8 x 2 "):
The next pair also was in the Colonnade and Aurora organs. Their primaries are 115 Vac, secondary is 14 Vac. Perhaps they might serve in a BTL pair (2 x 2) of amplifiers. Part # 003-054853, laminations are 76 x 63 x 41 mm (3 x 2 1/2 x 1 5/8 "):
The smallest one. Part # 003-046374, laminations are 66 x 56 x 26 mm (2 5/8 x 2 3/16 x 1 "):
Finally a 117 Vac power tranny that came from a Leslie 121 multi channel amplifier. It powered four almost identical amplifiers, consisting of a 12AU7 and a pair of fix biased 7189's each. This is the one I was referring to in my proper winding technique thread. I'm planning to rewind it as an OT of about 40 W power. Laminations are 114 x 95 x 33 mm (4½ x 3 3/4 x 1 1/4 "):
Which power capabilities can I expect from these transformers?
Best regards!
Goldentone single valve guitar amp troubleshoot
- By Yellow Cab
- Instruments and Amps
- 40 Replies
