300B schematic recommendations
- By Sunwontrise
- Tubes / Valves
- 112 Replies
Hi Folks,
I already have a pair of this output transformers:
Primary: 2,5k or 3,4k
18W
I would like to build a 300b stereo amplifier or two mono amplifiers for my HiFI.
For the moment I have a SE PCL 86 amplifier with 4watts, which is actually enough for my speakers, but I hope to achieve 2x8watts with the 300b's.
There are a lot of schematics:
I would like to know which one fits my output transformer best - or if there are other schematics - feel free to post them here 😉
What would also be nice: If the amp wouldn't need a preamp - I thought about an aikido preamp to drive the 300b but the schematics from tubecad require different primary impedances.
Have a nice day!
Felix
I already have a pair of this output transformers:
Primary: 2,5k or 3,4k
18W
I would like to build a 300b stereo amplifier or two mono amplifiers for my HiFI.
For the moment I have a SE PCL 86 amplifier with 4watts, which is actually enough for my speakers, but I hope to achieve 2x8watts with the 300b's.
There are a lot of schematics:
I would like to know which one fits my output transformer best - or if there are other schematics - feel free to post them here 😉
What would also be nice: If the amp wouldn't need a preamp - I thought about an aikido preamp to drive the 300b but the schematics from tubecad require different primary impedances.
Have a nice day!
Felix
Pioneer SX-1250/5590 EQ board issue
- By gbkd80
- Solid State
- 16 Replies
Having a problem with an SX-5590 that has a problem on the equalizer board. The receiver had already been serviced and recapped by a previous tech.
I couldn't duplicate the issue at first but then noticed a bulged cap (470uf, C12). When I pulled the cap it read 63uf so, I replaced it. After I replaced it I monitored the output of a 1khz sine wave on my scope, through the phono inputs (I use a little RIAA circuit in-line to match the signal before going to the input). What I noticed was at about 9:00 on the volume, the wave would get distorted and then it would trip into protection. Lowering the volume took it out of protection but I didn't like that distortion. So I pulled the board and replaced all the transistor pairs in the right channel where I saw the bulged cap, and when I tested, R44 and R45 (150r) smoked. Nothing was installed backwards, and I used the correct subs (KSA992, KSC1845) or so I presume based on research and other threads that give viable substitutes. Dim bulb does not protect the resistors from smoking. So I pulled the board again and went through rebuilding it; new caps (again), all transistors replaced including both 2SA850/628A with KSA1013, and replaced the burned resistors. Put back together, tested on the bulb, no smoke. Ran a signal through the phono stage for about 15 minutes and everything was fine but then R44 smoked again. R45 was fine. I checked D5 and it was shorted/open. Replaced it with a 1N5252B, replaced the resistor again, and the same thing happened on power up.
I've never had an EQ board smoke before. Any insights on where to look? Obviously I'd have to disconnect power to the EQ board to test the power supply otherwise it will just keep frying that resistor in the meantime.
I couldn't duplicate the issue at first but then noticed a bulged cap (470uf, C12). When I pulled the cap it read 63uf so, I replaced it. After I replaced it I monitored the output of a 1khz sine wave on my scope, through the phono inputs (I use a little RIAA circuit in-line to match the signal before going to the input). What I noticed was at about 9:00 on the volume, the wave would get distorted and then it would trip into protection. Lowering the volume took it out of protection but I didn't like that distortion. So I pulled the board and replaced all the transistor pairs in the right channel where I saw the bulged cap, and when I tested, R44 and R45 (150r) smoked. Nothing was installed backwards, and I used the correct subs (KSA992, KSC1845) or so I presume based on research and other threads that give viable substitutes. Dim bulb does not protect the resistors from smoking. So I pulled the board again and went through rebuilding it; new caps (again), all transistors replaced including both 2SA850/628A with KSA1013, and replaced the burned resistors. Put back together, tested on the bulb, no smoke. Ran a signal through the phono stage for about 15 minutes and everything was fine but then R44 smoked again. R45 was fine. I checked D5 and it was shorted/open. Replaced it with a 1N5252B, replaced the resistor again, and the same thing happened on power up.
I've never had an EQ board smoke before. Any insights on where to look? Obviously I'd have to disconnect power to the EQ board to test the power supply otherwise it will just keep frying that resistor in the meantime.
For Sale Jensen JT-11P-1BN (With passive SE to BAL adapter)
A couple of Jensen JT-11P-1BN. They are wired on sockets as SE to BAL converter. Can be used also the other way around. Price 90e
Davide
P.S: I really like that it's all milled in a block of children wood toy 🙂
Davide
P.S: I really like that it's all milled in a block of children wood toy 🙂
Krell CD-1 Player: Successful repair of Remote Control unit
- By John Tulett
- Parts
- 2 Replies
Purpose:
Figure 1: Krell CD-1 player, serial number 99209281 - photo taken August 2023.
Figure 2: Krell CD-1 remote control unit - photo taken after repairing, August 2023.
Background:
Figure 3: Remote control unit circuit board showing corroded, broken components.
Figure 4. Presumed circuitry (broken) of Krell CD-1 remote control - infra-red transmitter section only.
Damaged Capacitor:
Table 1. Comparison of actual resistors, their resistance values vs. colour codes
Figure 5. Test setup - External 4.5 VDC connected to terminals, oscilloscope connected to battery minus terminal and photodiode's anode.
Figure 6. Test of infra-red transmitter section after circuitry repaired.
Figure 7. Zero-signal reference, oscilloscope channel 2 grounded.
Figure 8. Rest condition, touch pad buttons not activated.
Figure 9. Active condition, example of a coded pulse train when touch pad button activated.
Figure 10: Repaired circuit board of remote control unit - note 62-ohm resistor colour coding Blue, Red, Black (not White).
Figure 11. Test of touchpad's control pulses.
Figure 12. Example of control pulses coming from touchpad when button activated - approx. 1.2V amplitude.
Figure 13. Measured forward bias of original transistor 2SC548B - note unstable voltage with fluctuating final digit.
- The 2SC548 being an obsolete series I replaced it with a spare 2N3904 NPN transistor I had. A check of this transistor's Base-Emitter forward bias showed a typical ~ 0.6 V and stable (Fig. 14).
Figure 14. Measured forward bias of replacement transistor 2N3904 - typical voltage value and stable.
Figure 15. Orientation of transistor at 7002 (left) vs. reversed orientation of replaced transistor at 7003 (right).
Figure 16. Original transistor 2SC548B with broken plastic case.
Final Notes:
- To share my experience repairing a Krell CD-1 player's remote control unit.
- Although this content is relevant to both the Solid State and Digital Source forums, as the primary focus of this report is the identification and replacement of broken components, I felt best to share this content on the Parts forum.
- Krell CD-1 player serial number 99209281 (Fig. 1), supplied with infra-red remote control (Fig. 2).
Figure 1: Krell CD-1 player, serial number 99209281 - photo taken August 2023.
Figure 2: Krell CD-1 remote control unit - photo taken after repairing, August 2023.
Background:
- This Krell CD-1 player I purchased new in 1992 from Loyalty Sound Ltd in Calgary, Canada. Overall, I was very pleased with the performance of this CD player throughout 10 years of worldwide assignments. Although it was in full working condition, sadly I had to put my Krell CD-1 into storage in 2001 due to shortage of living space.
- Unfortunately, during the last international move the remote control unit got packed in a different box from the CD-1 player, with the 3 AAA batteries remaining inside the remote control unit. This led to leakage of the battery's electrolyte, further leading to corrosion and damage to the remote control's internal components rendering it inoperative (Fig. 3). Note corroded battery terminals, damaged electrolytic axial capacitor, broken (missing) resistor - more to come later.
Figure 3: Remote control unit circuit board showing corroded, broken components.
- Other than the Owner's Reference manual that came with my original purchase, I have no access to Krell's circuit diagrams or service instructions, and so contacted Krell customer service to enquire what could be done. Krell's Customer Operations Manager, Timothy Rogers kindly replied that it may be possible to send the unit back to Krell for repair, however with a minimum service charge of 1hr ($125) plus international shipping costs we deemed it probably wasn't worthwhile.
- Although I had no experience with repairing a remote control unit, I decided to investigate and attempt local repair if possible.
- With no circuit diagram, no service instructions and unable to identify the values of the corroded/damaged components presented a challenging puzzle.
- After cleaning as best I could the circuit board (Fig. 3), I then attempted to recreate a circuit diagram by observing and continuity checking each of the circuit board traces. Hopefully, Figure 4 describes a reasonable recreation of the Infra-red transmitter circuitry, with the unidentifiable components labelled in Red.
Figure 4. Presumed circuitry (broken) of Krell CD-1 remote control - infra-red transmitter section only.
Damaged Capacitor:
- The only remaining legible markings were the number "10" and the letters "PHIL-". Judging from the blue jacket colour I assumed this to be a Philips electrolytic capacitor, rated 10 V.
- Testing the capacitor out of circuit measured a capacitance of 17.2 uF and an ESR of 8.3 ohms. Presuming this to be a 22 uF, 10 V rated capacitor, the measured capacitance was low and the measured ESR was high, necessitating replacement.
- This was replaced with a fresh 22 uF, 16 V rated electrolytic axial capacitor.
- Before this resistor fell apart and crumbled, I was lucky to observe three colour bands; 1st Blue, 2nd Red and 3rd Silver. This colour band combination equates to a resistance value of 0.62 ohms, which seemed suspiciously low.
- Assuming the 1st and 2nd colour bands of Blue and Red respectively were correct, but unsure what the proper resistance value should be, I inspected the third colour bands of some actual resistors (Table 1).
Table 1. Comparison of actual resistors, their resistance values vs. colour codes
- Side note, I first learned the resistor colour code when I was a teenager in high school, where the Black coloured band signified a blank or non-value.
- However, after researching this I now learned that the colour White can also be used to signify a blank or non-value, which solves the puzzle of the original installed resistor. The 3rd colour band was most likely White, not Silver - shows you can still learn something 50-years after high school!
- So that's what I used, a fresh resistor of 62 ohms having colour bands; 1st Blue, 2nd Red and 3rd Black.
- Still apprehensive whether a 62-ohm resistor was the correct value or not, and with no visible indication to the human eye whether the infra-red photodiodes were transmitting or not, I conducted a test to observe how the circuit performed. Test setup is described in Figures 5 and 6.
- 62-ohm resistor lightly tacked in place for the test.
- External 4.5 VDC supply connected to the battery terminals.
- Oscilloscope connected from the minus battery supply to anode of the two infra-red transmit diodes.
- Touch pad buttons were activated to start signal generation.
Figure 5. Test setup - External 4.5 VDC connected to terminals, oscilloscope connected to battery minus terminal and photodiode's anode.
Figure 6. Test of infra-red transmitter section after circuitry repaired.
- To establish a baseline position of the oscilloscope trace, with no DC power applied the oscilloscope channel 2 input was grounded (Fig. 7).
Figure 7. Zero-signal reference, oscilloscope channel 2 grounded.
- With the 4.5 VDC supply connected, a stable rest voltage of ~ 1.51 VDC was observed on channel 2 (Fig. 8).
Figure 8. Rest condition, touch pad buttons not activated.
- Finally, when pushing the buttons on the touch pad, different coded pulse trains could be observed. An example of one pulse train captured on the oscilloscope is displayed on channel 2 in Figure 9.
Figure 9. Active condition, example of a coded pulse train when touch pad button activated.
- Based on this test result (Fig. 9), it showed the remote-control unit to be functioning.
- After removing external DC power, the 62-ohm resistor was fixed properly to the circuit board (Fig. 10).
Figure 10: Repaired circuit board of remote control unit - note 62-ohm resistor colour coding Blue, Red, Black (not White).
- Operating the remote control with the CD-1 player, I was pleased that 17 of the touchpad's 19 pushbuttons functioned properly, the only two inoperative buttons being the "PREV" and "NEXT" buttons. These two buttons are situated closest to the corroded battery terminals and probably became contaminated from the battery's leaking electrolyte. Still, 17 out of 19 working buttons is 90% functional (far better than 0% or having to scrap the remote control).
- After operating reliably for several days, the remote control suddenly stopped working.
- Opening the unit up again found nothing untoward, all replaced components still intact.
- Tracing the signal flow from the touchpad confirmed control pulses of ~ 1.2 V amplitude were flowing to the input of the infra-red transmitter section (Figs. 11, 12).
Figure 11. Test of touchpad's control pulses.
Figure 12. Example of control pulses coming from touchpad when button activated - approx. 1.2V amplitude.
- This test showed the touchpad and its digital circuitry were functioning properly, suggesting something wrong again in the infra-red transmitter circuit.
- Suspecting the input transistor 2SC548B (#7003 in Fig. 11), a check of its Base-Emitter forward bias showed an unstable and strange voltage, > 0.9 V vs. an expected ~ 0.6 V (Fig. 13).
Figure 13. Measured forward bias of original transistor 2SC548B - note unstable voltage with fluctuating final digit.
- The 2SC548 being an obsolete series I replaced it with a spare 2N3904 NPN transistor I had. A check of this transistor's Base-Emitter forward bias showed a typical ~ 0.6 V and stable (Fig. 14).
Figure 14. Measured forward bias of replacement transistor 2N3904 - typical voltage value and stable.
- With the new 2N3904 transistor installed in the circuit board pleased to report the remote control is now operational again!
- Just a minor issue, the physical orientation of the Emitter and Collector leads is flipped between the original 2SC548B and the replacement 2N3904. The easy remedy is to install the replacement transistor 'backwards' to align the Emitter and Collector positions (Fig. 15).
Figure 15. Orientation of transistor at 7002 (left) vs. reversed orientation of replaced transistor at 7003 (right).
- What caused the original 2SC548B transistor to fail? It was only when I gently removed this failed transistor from the circuit board that I noticed its plastic case was broken (Fig. 16). One theory could be the leaked electrolyte from the batteries penetrated the transistor case causing it to weaken and eventually fail.
Figure 16. Original transistor 2SC548B with broken plastic case.
Final Notes:
- The reason for this writing is to share my experience repairing the remote-control unit of a Krell CD-1 player, it's not to bypass factory repairs, just to share what worked for me. Hopefully no more failed components.
- Finally with the circuit board installed back in its case (Fig 2.) and fresh AAA batteries installed, pleased to report the repaired remote-control unit now operates happily with my CD-1 player!
LM337: a new epidemic?
- By Zung
- Power Supplies
- 77 Replies
The power supply of my mckinnie pre-preamp died, so I bought a small 317/337 PS kit to replace it.
The negative leg didn't work, no biggy, I ordered a handful of LM337 from Aliexpress. All bad.
I ordered another small batch from eBay, Germany. All bad. It turned out they're the same items as Ali.
The prob appears to be some kind of a short between Vout and Adjust, so Vout is always ¦Vin¦ - 2V, regardless of the setting.
Out of curiosity, I ordered another batch from eBay China, but they've not arrived yet. We'll see if this is epidemic level.
Finally, I've got some NOS Motorola 337 from eBay France, and all is well.
I don't usually have problems with parts from Ali, but stay away from the 337 for now,
The negative leg didn't work, no biggy, I ordered a handful of LM337 from Aliexpress. All bad.
I ordered another small batch from eBay, Germany. All bad. It turned out they're the same items as Ali.
The prob appears to be some kind of a short between Vout and Adjust, so Vout is always ¦Vin¦ - 2V, regardless of the setting.
Out of curiosity, I ordered another batch from eBay China, but they've not arrived yet. We'll see if this is epidemic level.
Finally, I've got some NOS Motorola 337 from eBay France, and all is well.
I don't usually have problems with parts from Ali, but stay away from the 337 for now,
Jensen 4inch Speakers
I have a pair of Jensen Coax speakers wanting to replace the cone foam.. Have tried numerous places for this ring. A place in Calif, and also a place in Florida. No luck, even tried Walley mart who said they had foam rings for 4inch Jensens..What a joke from all three places.. Where can I find a place for these foam rings??
Use Z680 Pod control in the Z5500 subwoofer, wiring provided [solved]
- By luiserasmo
- Chip Amps
- 0 Replies
Hello,
I have a Z5500 subwoofer unit (PID R745), I managed to enable as subwoofer for my home theater following other guides.
Recently I got a Z680 pod control for free, but sadly is not compatible with the Z5500.
Both uses de DB15 connector (like VGA), I connected the pod to the subwoofer and the pod powers and lights but I get no sound, luckily nothing blew out.
After research a wiring diagram without success I spend a few days to investigate, I managed to turn on the subwoofer and control four channels and the subwoofer (I cant get the center channel working)
Explanation of the table
The table of the left enumerates the pins in the Z680 pod (DB15 female), the third column indicates in which pin is connected in the Z5500 unit.
GND: Ground
NC: The pin is not connected to the Z680 pod
A dash is placed where the pin is not connected to the Z5500 subwoofer
The table in the right enumerates the pins (DB15 male) in the Z5500 unit
Enable the subwoofer (PID 745)
Is important connect the pins 7 and 8 of the Z5550 to pin 13 in the same connector of the Z5500
this is enable and mute to ground. Without this the amps does nothing.
Check for your PID label outside in the bottom (is a heavy unit). Other PIDs may need another bridging or +5v supply
Weird ground in Z5500
I don't know why. But the ground in the Z5500 behaves bad with the Z680. Testing with the multi meter and the Z5500 powered off, the pin 13 is the only one connected to the general ground. But if I connect only this ground to the ground of the Z680 and the +8v. The ground sucks a lot of current. The Z680 cannot regulates the +5v of the standby and the LCD fades out. The only ground that work for my unit was the pin 11 of the Z5500. You can connect to any ground of the Z680. May be this is related to the center channel Issue.
This problem was the stop point for me in these days.
Z680 How it works
The Z680 receives +8v on the pin 10, and enter in stand-by, when the power button is pressed the LCD screen lit and the stand by pin (#7) provides +5v. May be this was the signal to power on the amps in the unit.
I suggest to test this before go for the full cabling. (pins 10 and 11)
The +18 and -18 provides the voltage to drive the audio preamp. You can connect headphones with only the +8v but the sound is weak. The +-18 volts provides the power for a proper preamp of the signal before send it to the unit.
In fact, the Z680 unit is a nice preamp as stand alone. May be you can drive a heavy headphones with this. But the +-18 is necessary.
Center Channel
In this config the center channel is not working. May be my center channel amp is blown, but I cannot get any sound from this. Or may be is related to the grounding issue. In fact i get sparks when I open the Z5500 subwoofer to fix the +18v problem.
DB15
The DB15 connector is the same used in the VGA cables, you can cut and reuse a VGA cable, but I think is better use new solder connectors, these are cheap and easy to solder.
The pins are numbered viewing the male connector by the side of the pins, the wide part on the top. Top to bottom, left to rigth: This is the standard way
Fix +18v supply of the Z5500
When i was testing, I connect the +18v supply to the +8v in the Z680 pod (Don't do that). This fixed my poor grounding issue and the LCD stays lit... for a few seconds (30s may be) and then, I get nothing in the +18v pin of the Z5500.
Checking the Z5500 PCB, the 78M18A regulator provides the power for the +18v. near of this is a 35.5 Ohms resistor (brown). This is the fuse for overdraw current in the regulator. I tested +31volts in one leg of the resistor and nothing in the other (was burned). I replaced the resistor with a 33 Ohms (0.25 watts rating) and the sub work fine.
Be careful
Open the Z5500 is risky, for you and the unit, take care, disconnect before check. The capacitors are big and have enough power to make a short circuit and damage the components.
Always power off the unit before plug or unplug your custom made cable to test it.
Be very careful with the multimeter points..
Thanks
I made this post after read many others. Thanks to all who managed to provide diagrams and tips.
Sorry for any typo or grammar mistake, I'm mexican, and english is not my native language.
Any suggestion or question is welcome.
I have a Z5500 subwoofer unit (PID R745), I managed to enable as subwoofer for my home theater following other guides.
Recently I got a Z680 pod control for free, but sadly is not compatible with the Z5500.
Both uses de DB15 connector (like VGA), I connected the pod to the subwoofer and the pod powers and lights but I get no sound, luckily nothing blew out.
After research a wiring diagram without success I spend a few days to investigate, I managed to turn on the subwoofer and control four channels and the subwoofer (I cant get the center channel working)
Explanation of the table
The table of the left enumerates the pins in the Z680 pod (DB15 female), the third column indicates in which pin is connected in the Z5500 unit.
GND: Ground
NC: The pin is not connected to the Z680 pod
A dash is placed where the pin is not connected to the Z5500 subwoofer
The table in the right enumerates the pins (DB15 male) in the Z5500 unit
Enable the subwoofer (PID 745)
Is important connect the pins 7 and 8 of the Z5550 to pin 13 in the same connector of the Z5500
this is enable and mute to ground. Without this the amps does nothing.
Check for your PID label outside in the bottom (is a heavy unit). Other PIDs may need another bridging or +5v supply
Weird ground in Z5500
I don't know why. But the ground in the Z5500 behaves bad with the Z680. Testing with the multi meter and the Z5500 powered off, the pin 13 is the only one connected to the general ground. But if I connect only this ground to the ground of the Z680 and the +8v. The ground sucks a lot of current. The Z680 cannot regulates the +5v of the standby and the LCD fades out. The only ground that work for my unit was the pin 11 of the Z5500. You can connect to any ground of the Z680. May be this is related to the center channel Issue.
This problem was the stop point for me in these days.
Z680 How it works
The Z680 receives +8v on the pin 10, and enter in stand-by, when the power button is pressed the LCD screen lit and the stand by pin (#7) provides +5v. May be this was the signal to power on the amps in the unit.
I suggest to test this before go for the full cabling. (pins 10 and 11)
The +18 and -18 provides the voltage to drive the audio preamp. You can connect headphones with only the +8v but the sound is weak. The +-18 volts provides the power for a proper preamp of the signal before send it to the unit.
In fact, the Z680 unit is a nice preamp as stand alone. May be you can drive a heavy headphones with this. But the +-18 is necessary.
Center Channel
In this config the center channel is not working. May be my center channel amp is blown, but I cannot get any sound from this. Or may be is related to the grounding issue. In fact i get sparks when I open the Z5500 subwoofer to fix the +18v problem.
DB15
The DB15 connector is the same used in the VGA cables, you can cut and reuse a VGA cable, but I think is better use new solder connectors, these are cheap and easy to solder.
The pins are numbered viewing the male connector by the side of the pins, the wide part on the top. Top to bottom, left to rigth: This is the standard way
Fix +18v supply of the Z5500
When i was testing, I connect the +18v supply to the +8v in the Z680 pod (Don't do that). This fixed my poor grounding issue and the LCD stays lit... for a few seconds (30s may be) and then, I get nothing in the +18v pin of the Z5500.
Checking the Z5500 PCB, the 78M18A regulator provides the power for the +18v. near of this is a 35.5 Ohms resistor (brown). This is the fuse for overdraw current in the regulator. I tested +31volts in one leg of the resistor and nothing in the other (was burned). I replaced the resistor with a 33 Ohms (0.25 watts rating) and the sub work fine.
Be careful
Open the Z5500 is risky, for you and the unit, take care, disconnect before check. The capacitors are big and have enough power to make a short circuit and damage the components.
Always power off the unit before plug or unplug your custom made cable to test it.
Be very careful with the multimeter points..
Thanks
I made this post after read many others. Thanks to all who managed to provide diagrams and tips.
Sorry for any typo or grammar mistake, I'm mexican, and english is not my native language.
Any suggestion or question is welcome.
NAD C270 (C272) Power Amp Protection Mode - Stray Negative Voltages
- By pumptronics
- Solid State
- 34 Replies
Hi everyone,
I bought a non-working NAD C270 power amp a couple of weeks ago. I've made quite a bit of progress but there is still a problem somewhere (I believe) in the LEFT channel Power Amp Board. I’ve already repaired the oft-failed 68V power supply (see photo).
I wouldn't say I am at the end of my tether, but I am out of my depth understanding the fault on this one. I've read a number of forum entries here for fixing the NAD C272, which is very similar and I am using the C272 schematics because I can't find ay C270 ones. Clearly many people here on diyAudio understand schematics waaaay better than me and also some have first hand experience of these models. So any guidance or insight would be fantastic.
Current Symptoms
Amp stays in protection mode unless L channel Power Amp Board disconnected. Offset bias test points (TP2 and TP8) giving more than 56V on L channel compared to 25mV on R channel. Looking in more detail shows that the Power Amp Board comprises of a 68V end and a 64V (power transistor) end. These two ends are joined by only two connections; R328 (100 Ohm) and R356>R319+R322 (a L-FDBK call out on the schematic). All around R328 I am seeing high NEGATIVE volts compared to the right hand Power Amp Board (relative to ground).
I can't work out exactly which end of the board (68V or 64V) these volts are coming from. Initially I suspected Q311 as it was showing -64V at the collector compared to -0.03V on Q411 (same transistor on R Power Amp Board), so I replaced Q311 and then Q310 (positive side equivalent) and then the 4 diodes (D303. D304, D305, D306). Just about every other component (save a few slightly low capacity electrolytics) seemed to test ok in circuit.
TLDR;
I've got high NEGATIVE volts running along the signal path (e.g. at the offset bias test points) on the LEFT channel only. The amplifier runs correctly with just the right channel in circuit. I can't work out how to begin finding the shorted/failed/open component on the L Power Amp Board. I've marked some schematics with my measured voltages (with CZ719 disconnected). Can anyone read my numbers into the schematic logic and suggest where I look next to find the source of these high negative volts? Main schematic attached. Any help appreciated!
I bought a non-working NAD C270 power amp a couple of weeks ago. I've made quite a bit of progress but there is still a problem somewhere (I believe) in the LEFT channel Power Amp Board. I’ve already repaired the oft-failed 68V power supply (see photo).
I wouldn't say I am at the end of my tether, but I am out of my depth understanding the fault on this one. I've read a number of forum entries here for fixing the NAD C272, which is very similar and I am using the C272 schematics because I can't find ay C270 ones. Clearly many people here on diyAudio understand schematics waaaay better than me and also some have first hand experience of these models. So any guidance or insight would be fantastic.
Current Symptoms
Amp stays in protection mode unless L channel Power Amp Board disconnected. Offset bias test points (TP2 and TP8) giving more than 56V on L channel compared to 25mV on R channel. Looking in more detail shows that the Power Amp Board comprises of a 68V end and a 64V (power transistor) end. These two ends are joined by only two connections; R328 (100 Ohm) and R356>R319+R322 (a L-FDBK call out on the schematic). All around R328 I am seeing high NEGATIVE volts compared to the right hand Power Amp Board (relative to ground).
I can't work out exactly which end of the board (68V or 64V) these volts are coming from. Initially I suspected Q311 as it was showing -64V at the collector compared to -0.03V on Q411 (same transistor on R Power Amp Board), so I replaced Q311 and then Q310 (positive side equivalent) and then the 4 diodes (D303. D304, D305, D306). Just about every other component (save a few slightly low capacity electrolytics) seemed to test ok in circuit.
TLDR;
I've got high NEGATIVE volts running along the signal path (e.g. at the offset bias test points) on the LEFT channel only. The amplifier runs correctly with just the right channel in circuit. I can't work out how to begin finding the shorted/failed/open component on the L Power Amp Board. I've marked some schematics with my measured voltages (with CZ719 disconnected). Can anyone read my numbers into the schematic logic and suggest where I look next to find the source of these high negative volts? Main schematic attached. Any help appreciated!
Finishing a C3M-300B
- By ddroukas
- Tubes / Valves
- 51 Replies
I've been off-and-on working on a C3M-300B two-chassis amplifier for a while. Everything is completed except some of the final grounding in the signal chassis. I wanted to ask the forum for advice on these last few ground connections before drilling any new holes in an otherwise finished chassis. Here's the info:
The two chassis are connected by a 10-conductor umbilical. I have 2 free signal grounds and one dedicated chassis ground running through the umbilical. The chassis ground wire also connects the umbilical copper shield at the PSU end. The L+R channels are outlined in the schematic diagram below. How would you best connect the left and right ground busses as well as speaker grounds with the available connections?
Thanks for your input. Picture are below.
The two chassis are connected by a 10-conductor umbilical. I have 2 free signal grounds and one dedicated chassis ground running through the umbilical. The chassis ground wire also connects the umbilical copper shield at the PSU end. The L+R channels are outlined in the schematic diagram below. How would you best connect the left and right ground busses as well as speaker grounds with the available connections?
Thanks for your input. Picture are below.
Wiring a differential output with an audio transformer
- By msupkf
- Analog Line Level
- 11 Replies
Hi guys, I would like to put an audio transformer at the differential output of MAX4063 chip.
This transformer has a center tap. Then at secondary side, outputs will be connected to a 3-pin XLR cable (eg 10m long).
Is this a correct wiring?
I couldn't find anything similar with Google.
Thanks!
This transformer has a center tap. Then at secondary side, outputs will be connected to a 3-pin XLR cable (eg 10m long).
Is this a correct wiring?
I couldn't find anything similar with Google.
Thanks!
Vintage SABA oval fullrangers?
- By pardon
- Full Range
- 5 Replies
I just bought a pair of those vintage Saba Oval Greencones Alnico. They are 17cm x 11.5cm. Apart from the classified stating that these are 5 ohms and have the 1678 CU 60 reference printed on the backs, I cannot find any kind of informations about them. I browsed some very old school german website & forums, but still couldn't find anything.
The seller said these were sold as tweeters, but are actually very competent fullrangers. They're made of paper, and the magnet looks pretty big and heavy.
Does anyone have more informations about them? I think they look really cool and would deserve a really beautiful cabinet. Although I'm pretty sure they would need some assistance in the bass region, probably...
The seller said these were sold as tweeters, but are actually very competent fullrangers. They're made of paper, and the magnet looks pretty big and heavy.
Does anyone have more informations about them? I think they look really cool and would deserve a really beautiful cabinet. Although I'm pretty sure they would need some assistance in the bass region, probably...
Pair NOS RCA 2A3 USN tubes test as new
Closely matched pair of new old stock vintage USA made USN 2A3 tubes. Test as new on TV-7B/U. Will ship within the US, sorry no Paypal. Check or MO is fine. Selling off some of my lifetime collection of tubes that I will probably not have the occasion to use. Price is $235 plus shipping.
crossover circuit : 2nd or 3rd order?
- By clargh
- Analog Line Level
- 3 Replies
Hi everyone, I'm a new member, honored to be part of this community of fans.
(I'm Italian, sorry but I use google translate)
I have a technical question to ask you: I have a Berhinger equalizer and I can not understand the operation of its high-pass filter shown in the figure (the section in the blue box), or rather it is not clear to me how to identify the model that determines the order of the filter. From the bottom of my ignorance it seemed to me a 2nd order and calculating the min and max cutting frequencies you get values equal to about 10Hz and 250Hz. On the potentiometer instead 10Hz and 400Hz are indicated and in the description of the command we read: "The LOW CUT regulator establishes the lower frequency of the limit of the ULTRAGRAPH PRO. The high-pass filter (18 dB/oct) is adjustable in a range of 10 to 400 Hz. If this filter is in the 10 Hz position, let the signal pass through without affecting it in the slightest."
Can you help me understand the pattern and determine the formula to calculate the cutoff frequency? Does the 100 Ohm resistor (R176) have anything to do with it?
Thank you very much if you can clarify this point for me.
(the goal is to replace the potentiometer with a switch and resistors to have preset frequencies)
(I'm Italian, sorry but I use google translate)
I have a technical question to ask you: I have a Berhinger equalizer and I can not understand the operation of its high-pass filter shown in the figure (the section in the blue box), or rather it is not clear to me how to identify the model that determines the order of the filter. From the bottom of my ignorance it seemed to me a 2nd order and calculating the min and max cutting frequencies you get values equal to about 10Hz and 250Hz. On the potentiometer instead 10Hz and 400Hz are indicated and in the description of the command we read: "The LOW CUT regulator establishes the lower frequency of the limit of the ULTRAGRAPH PRO. The high-pass filter (18 dB/oct) is adjustable in a range of 10 to 400 Hz. If this filter is in the 10 Hz position, let the signal pass through without affecting it in the slightest."
Can you help me understand the pattern and determine the formula to calculate the cutoff frequency? Does the 100 Ohm resistor (R176) have anything to do with it?
Thank you very much if you can clarify this point for me.
(the goal is to replace the potentiometer with a switch and resistors to have preset frequencies)
"The Wire" Ultra-High Performance Headphone Amplifier - PCB's
- By opc
- Headphone Systems
- 2737 Replies
Attachments
Goldring 1012 GX Cartridge Head Shell Compatibility
- By jonpol3000
- Analogue Source
- 2 Replies
Attachments
High Efficiency Open Baffle w/ 10" Woofer
- Multi-Way
- 5 Replies
Greetings all,
I’m planning my next system to correspond with a new apartment. It’s a 700sq/feet with lofted cielings. The walls are very thin so I can’t bring my previous system with me. I’m trying not to disturb the neighbors. The follow are my thoughts on a system using parts on hand, but I'm open to suggestions about what would work best with the space
I already have two full range audio nirvana super 8s laying around so that’s where I’m starting. From there I have two choices: build an enclosures or go open baffle again. I have the room to set the speakers a yard away from the real wall with ample room to either side—near to mid field listening. Behind the listening position will be the kitchen.
I want to use 10” woofers in open baffle for the form factor and because I can’t have a lot of bass without disturbing the neighbors. I’ve invested in a nice set of headphones for bass heavy music. This system will primarily be used for jazz and some classical (opera).
I have an iNuke amp as well as the dual 50w ice power module to play through a miniDSP: although, I’m not beyond building a traditional 1st order crossover as well to keep amplification more tidy.
I’ve used the eminence 15a and Acoustic Elegance 15” infinite baffle thus far. Both are fantastic woofers. While the AE does really well with R&B I find the eminence’s reproduction of the upright bass fidilous in a way that makes me nostalgic for my days plays bass in high school.
The Audio Nirvanas are about 96db.I figure a bass shy system dedicated for jazz listening will keep me in check. I’ve only ever built mono systems so I am especially keen to hear in stereo for once. Sound stage and imaging are things I really want to explore.
For jazz I really appreciate a dry nimble bass.
I much prefer open baffle for ease and cost of construction, but please weigh in on what you think is right for my particular space. I’m enclosing a floor plan. No windows except on the right side of the drawing. Room treatments would be a next step and the floor is carpet.
What should I look for in a single or double 10” woofer setup that will reproduce the upright bass faithfully? I’m looking for dry and articulate.
My budget is $200 for woofers.
I’m going to cross over at 200hz and these are some of the woofers I’m looking at; although, other suggestions are very welcome.
Here’s some possibilities:
I’m planning my next system to correspond with a new apartment. It’s a 700sq/feet with lofted cielings. The walls are very thin so I can’t bring my previous system with me. I’m trying not to disturb the neighbors. The follow are my thoughts on a system using parts on hand, but I'm open to suggestions about what would work best with the space
I already have two full range audio nirvana super 8s laying around so that’s where I’m starting. From there I have two choices: build an enclosures or go open baffle again. I have the room to set the speakers a yard away from the real wall with ample room to either side—near to mid field listening. Behind the listening position will be the kitchen.
I want to use 10” woofers in open baffle for the form factor and because I can’t have a lot of bass without disturbing the neighbors. I’ve invested in a nice set of headphones for bass heavy music. This system will primarily be used for jazz and some classical (opera).
I have an iNuke amp as well as the dual 50w ice power module to play through a miniDSP: although, I’m not beyond building a traditional 1st order crossover as well to keep amplification more tidy.
I’ve used the eminence 15a and Acoustic Elegance 15” infinite baffle thus far. Both are fantastic woofers. While the AE does really well with R&B I find the eminence’s reproduction of the upright bass fidilous in a way that makes me nostalgic for my days plays bass in high school.
The Audio Nirvanas are about 96db.I figure a bass shy system dedicated for jazz listening will keep me in check. I’ve only ever built mono systems so I am especially keen to hear in stereo for once. Sound stage and imaging are things I really want to explore.
For jazz I really appreciate a dry nimble bass.
I much prefer open baffle for ease and cost of construction, but please weigh in on what you think is right for my particular space. I’m enclosing a floor plan. No windows except on the right side of the drawing. Room treatments would be a next step and the floor is carpet.
What should I look for in a single or double 10” woofer setup that will reproduce the upright bass faithfully? I’m looking for dry and articulate.
My budget is $200 for woofers.
I’m going to cross over at 200hz and these are some of the woofers I’m looking at; although, other suggestions are very welcome.
Here’s some possibilities:
- GRS 10SW-4 (QTS 0.93 90db)
- Visaton WS25 (QTS 1.43 but 88db)
- Acoustic Research, available on eBay, (Qts 0.715 93db)
- Goldwood GW-410D (Qts 0.61 96db)
- Faital 10FE200 (Qts 0.5 96db)
In wall speakers to in cabinets
- By TheFinisher
- Multi-Way
- 18 Replies
I have some Niles HDLCR in wall speakers that I will never use as they’re intended but I wondered would they make decent hifi speakers if I were to fit them into some cabinets? If so how would I calculate the size of box needed ?
Can anyone identify this DC motor from TTWeights Gem V2 tt?
Hi I'm wondering if anyone can identify this brushless DC motor from a TTW Gem V2 turntable? Possibly a Hurst or Maxon but there's no markings of any kind on it.
