Douglas Self Audio Power Amplifier Design handbook Third Edition. $50
Handbook of Transducers SOLD
Vinyl Book SOLD

Hello.
For sale is a large Ulveco toroidal transformer, dual 25v, 29a, centertapped, It is heavy, so Europe only.
Guess it would suit many pass class A designs.
What should it cost ? 200 euro?.

Long story. Got this vintage class-D amp with a borked power supply. After fixing the issue it went back to the agent who requested the repair. Fully functional. Its owner then requested a recap which the experienced agent duly executed. At powerup (on DBT) it went full latch-up. Sheepishly the agent (who shall remain nameless) came back to me after finding nothing amiss.

After two months breaking my teeth on it I found that the latchup is caused by the SITs not being switched off fully at powerup. Without the output transistors and the PWM in service mode (R119/69) it works like a charm. Now the latchup causes the power supply to be overloaded. Which is weird given that it would work fine with DBT previously. With the PSU overloaded the two gate supply rails (+/-120 V) don't rise enough to cut off the SITs. Which need more than 25 V to reach that point. I also found that the PWM modulator also goes in a latchup mode due to the current source Q103/53 not starting as its power rail also rises too slowly. I did manage to get it going by removing C155 (I am working on the right channel, left is still in service mode) and using an external power supply to get the gate supplies going. At first it would start reliably when switching on the external PSU but when I started to move SITs around that went south and now it is bursting or even flatlining fully latched up. I don't believe that the SITs are bad. The rush-in current limiters are both OK and when the amp does work properly get shorted with their respective relays. Apart from the plethora of PSU rails the circuit itself is not all that complicated but the chicken/egg situation has me utterly flummoxed. What is going on here and how can I fix it? It must be something silly that I am overlooking but for the love of all that's holy I can't see it.

Scope images might illustrate. This is the gate drive of the SITs. This is a successful start with the external PSU:


And here it fails:


Once the PSU rails are established the rushin relays kick in, followed by the speaker protect relays. The slow rise is caused by the first stage of the PSU, which builds the primary regulated voltage (240 VDC). This is then fed to the second stage which provides mains isolation and all the secondary voltage rails. There are no less than eight. The PSU has not been touched, only the amp itself has been recapped.

I am considering the following measurement of DAC chip linearity and conversion accuracy (having 16-bit current output DAC in mind, like the TDA1541A):
Feed the DAC with an offset binary digital signal so that only the MSB has 1, all other bits are 0. The output current will be 2 mA. The accuracy of this current should be better than 1/2 LSB. The LSB current is 1/32768 * 2 mA = 61 nA. Half of this is about 30 nA. 30 nA related to 2 mA is 15 ppm. Is it possible to measure the output current with 15 ppm accuracy? The are precision 6.5 or 7.5 digit DMMs that could do it, I suppose.
What do you think about this idea?

I've been accumulating tube amplifier parts for many years and decided now that I'm retired I'd spend a little time and put something together. I like the lower distortion and better load dynamic load handling of push pull triode outputs so I was designing for that. I had a pair of 6000 to 4/8/16 ohm transformers that had been removed form a 30W Sansui integrated amplifier. I don't recall the model number, I bought them many years ago from a person that was parting it out. I had a number of 6BG6 sweep tubes including several that were very well matched that I was planning to use as my outputs but I could only get about 10 watts RMS from them and that wasn't quite enough for the speakers I have. My goal was 15 to 20 watts even though I realize that's not much more than 10, it is enough to listen to the speakers in my work area without them clipping.

I experimented with a couple other tubes but then decided to try the 6AR6 triode strapped. I'd read about them many years ago but had never actually designed anything with them. They are pretty readily available and are an inexpensive alternative to most other power tubes. I looked at their tube data curves and looked like I'd need on the order of 450 volts on the plate and a -75V bias to get 20 watts RMS in class AB1 with my transformers. So working backwards I needed about 150 volts peak to peak from the drive stage. I'm fortunate to have collected many power transformers over the years and I had one that was rated at 380-0-380 at 350 mA. That allowed me to use solid state rectifiers for the driver and get a 550V DC supply to regualte down to 525 and also get 450 from a tube rectifier with a CLC filter. I've had good results with the 6SL7 long tailed pair with a constant current bias and using 525 volts and large value (220K or larger) plate resisotrs. I follow that with a 6SN7 cathode follower so the bias resistors don't load the 6SL7. The 6SL7 is capable of a very linear output over a large (nearly 300V) output. One gain stage wasn't quite enough so I fed the long tailed pair with a 6SF5 triode. I could have used many different parts there but since the other tubes were octals I went with the 6SF5. It's not used that frequently but it has a mu of 100 and is much less expensive than a 12AX7 or 12AT7 and it is an octal base tube.

The inductor in the CLC filter is a 5H 300 mA choke, way larger then what I needed, but again I had it and it does have the benefit of low series resistance. I've tried both the 5V4 and 5U4 rectifiers on this amplifier, the 5V4 gives a higher DC voltage by about 15 volts under full load. At some point I'll try a 5AR4, but I only have one of those so I wanted to make sure eveything works first.

I did some breadboarding first and then when I was reasoanbly happy with the results I put this together. The driver stag ahs a voltage gain of approximately 65dB and the entire amplifier has an open loop THD under 5%. Closed loop, I can get 20 watts RMS per channel with 0.05% THD at 1 KHz and 0.15% at 20 KHz. At 5 watts out the THD is well under .05%. I got tired of setting up meters to adjsut the bias so I used inexpensive digital voltmeters across 10 ohm cathode resistors to measure and set the bias. I can adjust the level and balance for the outputs. I'm currently running them at 32 mA, I started at 40 mA but there was no advantage to that higher current.

I included a top and bottom view. The fuse was not yet connected when I took the picture.

I enjoyed building this amplifier and welcome and questions and comments. If anyone is interested I'll post the schematic.

I spotted this new quad 32 bit ADC on the TI site, less than 2USD
https://www.ti.com/product/PCM1841-Q1?jktype=homepageproduct

The performance at both full scale and -60 dB is remarkable, not that long ago something like this would have cost a fortune

Does anyone have any experience with the Dayton Audio PT Mini-6? I'm trying to build a set of desktop speakers and my treble sounds a bit "splashy" compared to similar silk dome tweeters, almost as if it's lacking in clarity. Any suggestions?

Tip for relative beginners like myself, who specifically want to understand more about commonly used op-amp concepts such as noise, common mode, offset, etc. and want to simulate (LTSpice) and experiment with them. After a long search I found a suitable little book with a good explanation: "OP-Amps Circuits Simulations and Experiments" by Sid Antoch. For the chapters on filters and the like it is useful to pick up the basic concepts of complex arithmetic (brilliantly simple explanations in the excellent dsp_book_Ch30.pdf on analog.com) and the node voltage method.(khanacademy.org). Good LTSpice classes are easy to find on the Internet. More tips are very welcome.

Hi Everyone,

It's been a very long time since I sold all of my tools. I find myself now wanting to modify a pair of speakers to accept a plate amplifier. The speakers right now have a panel with speaker terminals which is a little small and will have to be enlarged, plus if possible I'd like to inset the plate so that it's flush with the back panel.

Is there an easy way to build a router template for a rectangular shape?

Thanks!

Erik

I have this vintage Audio Tekne power amp from Japan. There’s distortion in the left channel. Swapping tubes does not change anything. The distortion remains on the left channel.

This is fine. I’ve been told it’s likely a bad resistor. Seeing as how I have to take it to a local tech, I thought it may be a good opportunity to improve what I can while I have it with a tech.
First plan is to replace those sandcast resistors with mills resistors(or any recommended resistors of high quality) of higher ohm rating to lower bias and not run these NOS GE 6550 tubes so hard at 90mA even though I’ve read the GE 6550s can handle the high bias.

The point of the question. Does the capacitor on the tube socket make a difference in sound quality? I’ve seen Kondo builds where the electrolytic looks bypassed with a small film cap. Does that mean putting a film capacitor would yield sound changes/improvements easily heard?

Hello,

I posted a thread recently regarding a sealed 2-way all Dayton build (with 1" and 8" drivers) and I got a lot of help. Thanks a lot for that! As an alternative to that project, I started working on another sealed build with RST28F-4 and dual RS125P-8. It is for my 5.1 living room setup which has an 11" sealed sub. I would like to share with you some screenshots (crossover and full space response with diffraction) and it would be great to get your feedback knowing I am a beginner. My main questions are:

1- Is my design realist?
2- Do you see any flaws in the simulation?

Thanks in advance.

Hello im Barry. I have just bought a pair of tl speakers. The crossovers I need to figure out which wires correctly go to which driver. It's s design iv never seen before. Hopefully the pictures will help

Completed kit and sounding great! Kitted with sound-dampening material to almost eliminate microphonics. Includes power supply. $220 plus shipping.

Completed kit and sounding great! Includes power supply. $250 plus shipping.

I have two 1kW SMPS for sale:

Meanwell SE-1000-48 : $80 plus shipping
China MFG XKCL-1000-36 : $50 plus shipping

You can find info online and from the pics. These are perfect for e.g. TPA3255 amps, etc. Both are fan cooled. They are boxed in the MFG shipping packages, new and unused.

I will combine shipping if you buy both. Thanks for looking!

Last week a buddy lent me a SUT to try. I use a Denon DL103. Connected it to the Pearl. A lot of hum. Then proceeded to lower the gain in the Pearl by means of altering R14 if I recall correctly, less hum but still too much noise. The SUT had some input variables that I tried without a difference.
BTW, I could tell that there was no noticeable difference by using it.
My question is, out of curiosity, is the Pearl2 not compatible with a SUT?

How well would this dual voice coil sub work in a 1 CU FT sealed box driven by an Adcom GFA 545II with one channel per voice coil?

https://www.parts-express.com/Dayto...ce-Series-HO-DVC-Subwoofer-295-463?quantity=1

An Adcom GFA 535II will drive a pair of Klipsch bookshelf speakers.

A Kicker KX2 active crossover is used for the high pass and low pass.

Used to be active here over a decade back. Starting to pull some of my old stuff out of storage and complete some projects I started a LONG time ago. Have to finish my old Leach Amp and Alpeh-X

Can anyone tell me the 3 LEDs in the front and what they are/colors each one is? I broke them off trying to remove the PCB when it got hung on that weird light chute thing.

I came across a OTL amp using a parallel string of 6AS7 or 6080 on the top and a huge inductor on the bottom. I can't find the Japanese article again. I did come across a simpler and abbreviate schematic dated 1952, see attached, but it wasn't the same circuit. Is anyone familiar with such a circuit?
I built the P. Dickie Jr & A. Macovski (June 1954) circuit but increased the output to 9 parallel per channel to handle 8 ohms speakers which I thought might be reconfigured to the SE design if I can find it.


p

The air pressure between Leadville and New York City can vary by a lot. Does it affect loudspeakers? It should but by how much?

Hi guys,
I've got a mackie thump15 powered speaker in for repairs. The issue was the sound cuts out when the speaker is turned up loud. My initial thought was dry joints and intermittent connection due to vibration.
When I got it in and after removing the amp I measured the resistance of the drivers and the woofer measures at 1.7ohm!. That didn't look right. The marking on the speaker states that its suppose to be 8 ohms. So then my thought was the speaker coil have shorted partly and the amplifier chip was detecting a fault when driven hard and was cutting out. The amplifier chip used is TDA8924TH.
But here is where things got a bit interesting. To check whether the amplifier was functioning I connected my test woofer rated at 8 ohms and it was working fine no issues (my test woofer was not attached to the enclosure). To see whether the sound cuts out, I then checked with the faulty woofer and it worked perfectly fine :S and same as before the woofer is not attached to the enclosure.
I haven't got a working mackie thump to measure the actual resistance of the coil of the woofer. The label on the speaker says 8 ohms though I know sometimes labels can be misleading. If some one can confirm the resistance of these would be greatly appreciated. Can the TDA8924TH be paired with a 2 Ohm-ish load and work?
Thanks in advance for your input.
P.S- I don't hear any coil rubbing when driven with signal or pushed and pulled by hand

This seems to be a common design issue with many HK units, including this one.
There are a few switches that tick or pop when used. Sometimes more than other times.

I get a big pop when using the tone defeat switch, but only if I just turned the unit on.
There is usually a tick when switching to AM.
There is a tick when using the treble cut switch.

Are there any tweaks I can do to prevent this? I've tried reducing some of the signal path capacitor values, HK seems to like making their cutoff frequencies crazy low.

Power amp input capacitor was changed to 4.7uF.

And in the preamp, I tried changing C6/C33 to 4.7uf (from 47). And then C13/C40 to 4.7 from 100uF. Both are highpass filters with a 100k resistor. This should give a cutoff frequency of 0.34Hz, right?

Service manual is attached, preamp is on page 17. Does anyone see any glaring issues?

Hello,

I need your knowledge about a rega Elex mk1, PCB V2.

First of all, does anyone have a service manual for this amplifier? It's crazy, on the PCB many components have the same marking!

The amplifier worked for a short time with one channel less efficient than the other. It ended up blowing the right channel output transistors.

Someone has obviously already worked on this side of the amplifier. Some transistors have been replaced as well as diodes and resistors.

Do you know if this amp accepts being powered on without the C2837 and A1186 output transistors so that I can check if something else has failed?
Before breakdown, the power transistors were powered and +-43V and the level difference problem seemed to come from the power part of the channel in question.

Thank you in advance for your help !

Edit : surprisingly, an LED of the phono part of the same channel is also HS

Hi to all
I've been trying to repair this excellent CD player for a few days now, with no success. It reads disks only occasionally. The disc is loaded normally and starts spinning "crazy", but the laser head remains stationary at the starting point (doesn't slide at all) and of course, there is no RF signal output. However, the laser head moves up and down trying to focus every time the "PLAY" is pressed, but I couldn't detect if the laser beam is active. I did a thorough cleaning of the lens of course. I then tried to check the laser beam with my smartphone camera placed over the lens and could only see a small and very weak red dot. I checked all voltages and they look OK. The voltage across the "LD" laser diode (pins 7 and 11 of pickup assy flex ribbon, see on the left side of attached picture) is close to 1.9 volts. The spindle motor is working, the same applies to the carriage motor. Do you think the laser diode is deficient? Attached is the circuit of the PEA1343 pickup.

We have a big Lundahl Transformers sale going on, 20% off list price, for larger quantities, additional discounts will apply.
For all the details and pricing, please go here, https://www.erhard-audio.com/Transformer-Sale.html

Hello Jan-Peter, Bruno,

As this subject maybe of interest to more readers, just a few questions here on the Hypex UCD180 modules.

I received 4 UCD180 modules today. Apparently I`m one of the first customers since I had serial number 0004 to 0007 🙂
I have not yet hooked them up to a power supply, so I have not done any listening tests (will have to wait until weekend or even later).

A few questions concerning the input of the module. The module has a symmetric input using a NE5532 dual opamp. It seems to be used as an instrumental amplifier like input with the UCD itself acting as the 3rd differential amp. I can not see all traces on the PCB but it seems to be connected like an instrumental amplifier with a gain of about 4.5 or so. The outputs of the two opamps go to the inputs of the UCD amp itself. This is done by two coupling capacitors that are 22uF electrolitic capacitors. Assuming that the input impedance of the UCD amp itself is something like 1.8k for the inverting input (as stated in the classd.pdf file), then that gives a high pass filter at 4Hz. That should be fine for all apllications. However, when I`m going to use this amp for a tweeter or a midrange, I sure would want to replace the electrolitic caps with a different type of cap and of course with a lower value. Are those caps really required? What happens if they are replaced with a piece of wire (0 Ohm resistor). Would that give problems when the input voltage is not purely symmetrical? I assume that when the input signal is pure symmetrical, it sould not hurt to remove the caps, would it?

Best regards

Gertjan

Of all the things I have seen about mods for this amp, the issue in this post is an important one for reliability and safety!

The design of the output tube bias boards leaves out an important component, a "fail safe" or "emergency pull down" resistor in case the wiper on the potentiometer goes open. This can easily happen if some dust or dirt ends up inside it, corrosion or it simply fails. Without this resistor, if the wiper goes open, the output tube red plates and all sorts of bad things happen. I've read several reports of this happening to this amp.

Attached are schematics showing as built, and then with a 100K "fail safe" resistor added. You can see more about this at the Valve Wizard page here: https://www.valvewizard.co.uk/bias.html

"R3 is an emergency pull-down resistor. This ensures that if the pot wiper fails to make good contact with the rack (because it is dirty or worn out, say) the grid leaks will effectively be connected directly to the raw bias supply through R3 instead, biasing the valves safely cold. "

If you do nothing else to this amp, I highly recommend adding a pair of these resistors to the two bias boards. I uploaded a video showing how to do this.

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Has anyone else had a bad soldering day? I had to walk away yesterday, because my work was crap! Today, all is going well though.

Hello,

For sale a Soekris DAC1101 portable DAC. Perfect state, working great. I use it occasionally so it has very low running hour.

I will update the thread with some photos.

Price 275€ + shipping. Can ship worldwide.

Does anyone have a pair of LME49710 they are willing to sell? I have a headphone amp that was designed for them but I need one more pair.

Located in Houston, TX.

The aluminium body of the Audio Technica AT-34e ll cartridge is corroded. What would be the best and safest way to stop corrosion and restore the black paint?

I'm wanting to find a guide on this. I was just looking for how to use a target EQ curve, but any good information is welcome.

Hi there!

I have those amps and I like them, except for the fact that Bluetooth is available for pairing when AUX input is connected. I read that they can be flashed but this is most likely not possible (easy) with those boards and I see that it's not easy to get datasheets for the BT chip.

So: Where do you think I can make a mod to add a switch? Adding photos of the board, one is a close-up.

Edit: By a switch I mean where I can cut. I see the following options:

• Find out where to cut and add wires for an external switch
• Disable BT by placing the amp in a Faraday cage
• Disable BT in the antenna connection:
  • Doesn't work for a switch because I would change the antenna design
  • Might fry something if I cut it because of RF power not going anywhere (not sure)

Suggestions welcome.




Thanks.

I ordered some BC550 and BC560 from Mouser awhile back but they never sent the BC560 and they never came back in stock after that. I'm looking for 100 or more BC560C to use with these for an upcoming repair.

Hello again, I built this amplifier some 6 years ago and after 2 years of listening evaluation I put it in my "prototype stock". Few days ago I got an idea how to improve mains frequency components S/N by changing just one track on the PCB - the signal GND track. And it has worked very well.

The amp uses modified output stage from ExtremA by Sander Sassen which was put in the loop of a good opamp. The output stage uses local NFB and has vanishingly low distortion below 0.001% itself, but quite high output impedance of 0.235 ohm. In the opamp feedback loop the distortion falls below 0.0001% and the output impedance becomes negligible.

Below is the circuit schematics, THD vs. power plots at 1kHz and 5kHz and the 1kHz spectrum. Output noise is 23uV over 20Hz-22kHz unweighted. This was measured with OPA637 at the place of IC1.

Hi!

Since I had a v1X and it sounds acceptable, reading the posts on the forum (many thanks to SVI2004A for the inspiration) I managed to find a v4x, but only defective. The "safety operation" led it flashes quickly and the relay does not click. I checked the supply voltages and and I have the corresponding values (+/-44v, +/-16v, +5v). I put an audio signal in it and I find it at the input of SVI2004A, all audio settings are functional.
Does anyone know if I could still find an SVI2004A somewhere?

Thank you in advance!

​

Hello Guys,
anybody ever tried 4S amp by Dr. Bora ?

Many projects have accumulated during too many years and are in need of some building
- progress in the housing development is to be posted here from now on..

Suitable first pic: testing how FaitalPro 4FE42 and 3FE22 work together in the Bestway.

Comparison of 3 Faitals; 4FE42, 3FE25 and 3FE22 plus a Visaton FRS8M.
I wonder if anybody has ever tried to build a fun tapped horn using these 3 inch Faitals, they are built like a tank: triple XMech compared to the otherwise very nice Visatons!

If one were shopping for chokes to use as audio frequency filters (think graphic equalizers) for what would you search and where? All I am finding is common mode chokes and power supply chokes.

I just got this message form Mouser:

Finally bit the bullet and acquired a new SPU GM E MKII for my TD-124/II/Schick/cracked_slate_plinth.. 😀 Quite thrilled with it overall, do need transformers with more gain and a lower primary impedance although those 977 are doing a lot better than I expected..

It seems like they actually knew what they were doing back in the old days.. This is certainly by far the best sounding analog set up I have ever owned, and I think would stand up well against some very pricey modern competition - not that the comparison will ever get done.. 😀

I have a ZU and a DL-103D, neither of these cartridges come close to the SPU in detail, dynamics, imaging, speed, bass quality and quantity, etc... I also have an all original loaner SPU G/T E on hand which in its own right is pretty amazing - all the more so given its age, apparently these cartridges if treated with a little respect are very long lived..

Hi everyone, do you think the Volt VM527 midrange is a correct match with the RV2501 woofer from the same manufacturer?
Is the Bliesma m74p a better match? Does the Volt's waveguide help in home listening without acoustic treatment?
Thanks!

Hi
I need some help with this amp. What is the bias setting for this amp. The schematic shows SVR302 as the bias pot, but it does not show the voltage or the bias points. Across which component or point do I take the bias voltage reading. One more issue is that, the transistors Q304, Q305, Q306 and Q307 are getting very hot when the amp is turn on. Is this normal, but the driver and power transistors are just warm. I amplifier is working fine, just what is bugging me is why just this 4 transistors are getting so hot. Is it normal and OK for them to get hot. Please assist.


Thanks

Hi there to everyone. Academically speaking, I know very little about electronics. YouTube and DIY audio websites have taught me a lot about amplifiers. I'm trying to sketch the PCB board schematic that came from China. It's been a little unclear! Using a 15 volt zener diode, the audio stage is linked. also quite unclear in the OP-Amp input section; PINs 2 and 6 should be the input. What do you guys think about how well-built this circuit was?

Thanks
opu

Quick question, NULL modem or straight RS232 for Onkyo receiver? I haven't done a lot with ended cables and I am not sure it matters anymore. Did the ports get "smart" like Ethernet or stay dumb.

Jeremy

My Focusrite interface has developed an issue with the inputs. When I plug anything into either one of the front instrument input's I get an intermittent fault where the input just stops, the activity LED stops registering and I get a weird noise from my monitors. Sometimes it does it sparingly and other times (like in the video below) its pretty much continuous.
This happens whether the device is connected via USB to my computer or not (just monitoring the input). Playback seems to be unaffected, I can still listen to things I've already recorded in my DAW whether or not the fault is present.
I've tried different power supplies and I've tried various different TRS jack leads, it still happens, its definatly not an issue with the jack leads as it does the same with microphones. I've had it for a good few years but it hasn't been used much. Pretty disappointing really. Never had an issue before this,
I'm hoping it's a known issue and someone can advise on a repair. I'm pretty good with a soldering iron so if its a cap or something, I should be easily able to swap it out.
Here is a vid showing the issue, during the recording a bass guitar is plugged in and I'm hitting a string but as you will see, its not picking anything up except for brief moments where the LED activity meter starts to flash as normal with the hitting f the string. You can also hear the weird noise coming from the speakers.

Really hope there's a fix!

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Hi Everyone..

I'm planning out a center channel with a DSP plate amp, and I ran across something I had not been paying attention to. Per Wikipedia, the lower filter will be in phase but a period behind the next driver up.

So, help me do the math here, imagining an ideal LR4 electroacoustic crossover with 2 ideal and identical drivers crossed at 300 Hz. Does this mean the woofer will be 3ms further away from the mid??

Is it possible or desirable to compensate for this? That is, delay the mid by 3 ms, so that the 1 period delay vanishes??

Am I overthinking it or is this actually a thing that most people do already? 😀

I am using REW to take some measurements

My issue is that I am getting a very weak preamp signal out to the drivers. With a 20 watt amp I can barely hear it. With a 100 watt amp on a 3 way I have to turn it up to max just to get it to 75 db

What am I doing wrong here?

This amplifier is not working anymore. Its the 110 v version. I have a schematic,I tested the power transformer and the voltages are ok. I need a schematic showing the voltages throughout the circuit. This will help in narrowing down the problem components. There is no sound at all from both channels. See update further in this discussion. There is in fact a faint sound

I decided to do something a little wild and had a few pairs of the BetsyK built up.

If you’ve been waiting, this is your chance. I’ve also got the Betsy in stock.

As the title says, if I am combining multiple MiniDSP units, will they all play nice together? For starters, do the the older devices work with the newest version of DC?

I am currently using the HTx unit, which I purchased to be an active crossover for a 4 way system. But now I'd like to expand into multi-channel, so I need a lot more channels of DSP!

I found a MiniDSP 4x10hd on ebay, and I realized that I would need 2 of the 4x10 units to get all the channels I need for a 7.1 system. The idea would be to use the HTx as an AVR replacement, and the 4x10hd units as the active crossovers. This is assuming the 4 way active main speakers, and the rest of the system are 2 way active speakers. (I'd need 18 channels.)

But how well will that work? I'm a little concerned that the 5 PEQs per channel on the 4x10hd might annoy me later. I can combine the input and output EQs, and further tweek on the HTx output EQs...but that's a lot of EQs to keep track of!

And I noticed that the MiniDSP units don't have a 12v trigger input, so it seems they are not intended to be networked together. Granted I could wire in relays to turn everything on and off with a 12v trigger, but that is becoming a little complicated.

Any thoughts or experience?

Hello all. Firstly, I hope the mods allow this where the design gurus roam

Would someone with the time and energy please help with the design of a PCB. This is for a teleporting device. An active device would be better. Maybe something with a calculator type solar panel and a numeric keypad. No batteries or connections. If there are LED's that light with movement, then would be awesome. I know its asking for a lot but if this can be etched in, "Enter passcode to activate portal", would be awesomer

The backstory is that kids from my lil daughter's primary school have come to believe that she can teleport, so of course she must let them 'accidentally' discover the device 😀

It would awesomer again if she can solder this herself as she has a strong interest in STEM and also the school electric and double bass player

Thanks and regards
Randy

The Nak is 36 years old, I am the original owner. It has an intermittent hum that can be manipulated by jiggling input rca (cd). Remote can turn volume up but not down (could be remote). I blue stuff-ed the pots, no problems with those now. I've looked inside and don't see anything terminal-yet, but it's probably time for some work. I'm in Ronkonkoma, Suffolk county, central Long Island, N.Y., is there a reputable shop nearby that I could trust do it right? I'm not a tech, just a paint by numbers tinkerer, I've built a few things, but I don't feel confident enough to tackle this, and I would hate to ruin it. It's not my favorite anymore, but I still love it, and it's still impressive for what it is, and it is the first piece of nice gear i bought (at 17!).

The review was not long, but let's give a shout out to @cowanaudio and @Tom_Danley for being featured in this month's Stereophile.

Hi,
I'm new here, but I've been reading this forum for years.
Now it's time to say good morning to everyone! 🙂
Currently, I am hoping that one of you will help me. I have a VP-7722A with a dead DSP card, it does all the measurements fine but THD1 and THD2 are missing. I measured everything on this card pulled from unit on the extension and it looks like either the CPU or the PROMs are dead, in some cases the CPU does not respond to the RST signal with no traffic on the RD or WR lines and sometimes reads data from AD and main controller at strange intervals.
The question is - does anyone have a copy of the data stored in the AM27S191DC PROM? Mine were numbered 06490 and 06501. So i can compare.
Thank you in advance, it would be nice to have it back to full life, working properly, it is such a nice unit.
Cheers
- Lukasz

Hi guys,
i'm on an hard choice.
I'm designing 4-ways loudspekers and after long search and analyses i have come to a conclusion that the two candidates for tw are:

• Scan-Speak D2904/71000
• Satori TW29DN-B

Has anyone tried both?
I am interested not only in the technical differences but mst of alla in the timbre ones.
The cost is not an issue.

Thank in advance

Hi i have a question about batteries and capacitors I understand that when a battery is followed by a big capacitor the capacitor at surge acts as a short circuit
I am thinking to use a single 12V SLA battery and a capacitor at its output How many uF can i use in order to avoid problems ?
is there a way to slow down the cap charging cycle ?
thank you very much indeed

In this thread I will post preamps, EQ, active x-overs, VU...
ML3 is Mic/Line XLR preamp with three band EQ +/-20dB
PCB size 100x40mm
Regards

Hello,

I am looking to create two CRD models from Semitec under LTSpice: E-202 and E-562

https://www.semitec-global.com/products/crd_e_series/

I haven't found a ready-made Open Source SPICE model on the internet (a company sells them but for $30-50 each model).

I found a spice model for the E-501 but it is encrypted.

By gleaning information from the internet, I made a model of the E-202 but it doesn't seem to be any good.

I'm looking for help.

I put the working files in a .zip embedded in the topic.

Thank you in advance if you can help me.

Stef.

!!!230V (two hundred thirty voltage)!!!

Asking $1450 plus shipping

Please buy accordingly. If you are handy with electronics unlike me, rewiring this to work at 120V should not be difficult. There are no parts needed for the conversion except using the appropriate rated fuse for 120V electricity. Just desolder and solder back some wires accordingly.

Or if you live in a country with 230V electricity, you can directly use it without doing anything.

Please see photos for condition and I will mark it as fair (6/10) so I don’t oversell it. It is USED, please don’t forget and I did my best to show the flaws. The front is shiny so hard to show every little thing but please you be the judge and if you have any doubts about the condition, please do NOT buy.

I can accept Stripe (similar to PayPal), this way I can accept Visa or Mastercard as a payment but like PayPal it does come with a fee. Please add 3% if you prefer to use credit card.

Local pick up is preferred. 33326 is my zipcode. Cash, Zelle or bank transfer ONLY if picked up.

Double boxed Fully insured UPS Ground Shipping is flat rate of $75 to CONUS.
If international shipping is needed, please ask for shipping cost.

No original box but rest assured it will be packed well.

Remote is NOT included. NO cables.
490162

Do I have only 1 chip "connected" at a time? Is this done by "disconnecting" the output resistors?

Thanks!

With age, I prefer more to listen to my music at a lower sound levels and this has led me to vintage speakers, simply because vintage speakers often have higher resolution / less compression at lower listening levels, … the usual problem; moderne speakers needing some oohmmp to open up.

I have read about static friction and stiction and have noticed that speakers that retain openness and liveliness at lower sound levels have a few common features; low moving mass, high sensitivity, paper/fabric surround or very, very thin rubber surround, voicecoil former made of paper or kapton/fibreglass, …

My hypothesis is that in the bass and lower midrange, below approx. 300Hz, the spider and the surround are both important for the mechanical mobility and sonic vibrancy at lower sound levels. For shorter, quicker movements upwards in the midrange – again, at lower sound levels –, a fabric spider will by nature “always” retain a low mechanical damping, while hysteresis/damping-effects in the (thick and heavy) rubber suspension becomes a bigger problem.

A three-way speaker with a midrange driver with paper/fabric surround will almost always sound great at lower sound levels, whether it's an old Seas 17TV or 10F-M with paper surround or a newer Accuton C79 with fabric surround. Tweeters, both new and old, usually have fabric/paper surround and the problem is not as noticeable here, IME.

For two-ways suitable for lower sound levels, the big challenge has been to find a midwoofer with a super thin rubber surround that retains the mobility and vibrancy upwards in the midrange, and at the same time has a sufficient linear stroke length and enough self-oscillation (high moving mass) to produce decent bass in a relatively small cabinet.

My favorite midwoofers for low level listening are the old Seas 25TV (Dynaco A25) and various Focals from the 1990s, such as the 7V412 and 8V412, these have large and very thin rubber suspension that seems to move easily (quick tapping on the cone) and the surround seems to be mechanically dead (non-elastic), almost as very thin plastic. Advent Model 3 from the early 70s has a 6” midwoofer with the same type of very thin and mechanically dead rubber suspension. I believe they all have butyl rubber since they hold up so well with age. Model 3 sounds fabulous at lower volume levels (with its papercone tweeter), much better than my Proac 1sc's.

I've been reading with interest the recent threads about dome mids on the forum, and wonder if the reason for the dome's superior nimbleness and openness and clarity in the midrange is because they all have fabric surrounds?

Anyone with thoughts and suggestions for speakers that sounds well at lower listening levels?

(sorry for the length of the post, but this is a topic that really fascinates me).

Hi folks

I’ve done a lot of reading of past threads but thought it best to simply post a thread to the good people here.

I somewhat recently inherited a few speakers from my late father, which have led me through a nice pathway of learning a little about restoring and tinkering with speakers.

A Wharfedale Teesdale (the omni-directional 3-way) which sympathetically recapped sounds really lovely even in its mono state.

Kef Celeste IVs which after a recap, and some painting of butyl on the degraded tweeter domes sound quite impressive compared to the apparently crappy Bluetooth speakers I was used to.

The final set are some Denton 2s ….with missing tweeters. By all accounts these little speakers really were not great even in their time, and i suspect 50 years might not have done them any favours. But they were almost certainly his first set so I would ideally want to restore them and keep them around, the enclosures at the very least.

The problem I have is that it’s rather difficult to find an exact set of replacement drivers on the Bay. With an assumption that they are the purple plastic ones, there is likely a need to restore these tweeters too as I have read that they had a tendency to detach themselves , it has been 50 years after all.

Alternatively I was hoping to potentially upgrade the crossover and add a new tweeter - 6ohm, suitable for the 1750Hz crossover point. But there is very little information on woofer specs, and no other builds that i could find to crib from where a tweeter’s been successfully modded into the existing system.

In any case the original crossover design seems odd in comparison to what I normally see documented or suggested.
A 2.0mH, 50uf filter on the woofer, and 0.8mH 16uf for the tweeter/midrange. It seems that without fundamentally redesigning the crossover any dropping of a replacement driver is probably not going to work well.

I had found a driver that may work, something like the Seas 27TDFC-06 which appears to be a matching impedance and suitable for crossovers down to 1500Hz. Of course it is much more complicated than this, but in theory could this work with the existing crossover whilst retaining the current woofer?

Alternatively (and i suspect this is most sensible) I could simply rebuild a 2-way using the existing cabinet. I believe the internal volume is 12-14L, with no porting - should it be possible to build a reasonably cheap but pleasant enough sounding speaker for the kitchen for an enclosure of these rough specs?


Apologies for the length of the post, hoping that there’s possibly enough to go on from that ramble.

Hello,

Here you will find CAD files for many different loudspeakers layout that you can adjust dimensions to better fit your driver's Thiele-Small parameters. Use it to design your custom solution or to replicate well-know projects developed from others.

The advantages of this tool are:

• Free and open-source software
• Embedded spreadsheet with hornresp inputdata
• Macro script to export hornresp *.txt inputdata
• Fully parametric Sketch
• 3D model

The files were created using the FreeCAD that is very easy to use and the data were defined in a ways that even people that don't have knowledge about CAD software can still use and enjoy it.

Fell free to ask for support or additional plans.

https://freeloudspeakerplan.rf.gd

I have a 2x45W amplifier with a bad 2SA539 dc adjust transistor, TO-92 package. These are extinct, so I've attached the schematic and part specifications. The first 2 active devices are the 2SA539 and they are the first on the specs list.

Best that I ask for advice about a replacement. I’ve entered the specs into the Alltransistors search below and that might give some ideas, but I'm unsure which ones to avoid.🙂

Alltransistors.com Search for 2SA539

Hi i was trying to sim the famous JC2 by Mr Curl and failed
Changing some parts i have ended with the circuit attached Now it reduces the input voltage of about half
Is there a way of reaching unity gain ?
the idea is using it as a buffer maybe with 2 x 9V batteries
Thank you very much to all

Hey guys, found your educational forum while researching for info on some 'toroidal transformers' I picked up on eBay to use in a 'home electrical testing safety project', and am hoping someone here has some insight to my quest...

Basically, I've built myself a 'Dim Lamp Isolating box' for testing vintage devices and other power supplies (without blowing them up , or myself) and I need a 240v in , 240v out toroidal (isolation) transformer to drop into the middle of it (see image of my freshly made scary looking death box below).

Problem is, none of the transformers came with wiring diagrams and there are LOTS of pretty coloured wires sticking out, and I have no clue what they all do, as I have never even seen one before now. But, I'm hoping someone here does....

Dim Lamp Isolator (aka, The Box of Death)
(has 4 switchable test lamps, LED display, fuse, added trip switch, socket, and TEST/LIVE 'bypass' switch)



The last piece of the build-puzzle is the 'Isolation transformer', so I bought 3 x different cheap eBay toroidal transformers in the hope that at least one has the requirements for what I need. (i.e. basically only need, 240v AC in and 240V AC out). But the problem is, I think these transformers are so old there are no schematics in Google to be found.

These are the toroidal transformers in question:

1. AMETHYST DESIGNS LIMITED - AD3285T TT3001 0107 (info from seller was; "300va transformer 3.5kgs and 120mm diameter, 230 v primary, 12v secondary" , but I have no clue about the wiring. I'm not understanding how the Black + Yellow wires grouped in pairs can provide 240v and 12v...? (I'm assuming Brown + Blue are for the 240v input supply?




2. ILP TRANSFORMERS - 9T029 (that's all i have...?) From online research, I "think" this model (with having a "9" prefix) could be a 625VA , but no clue on wires V outputs?
(5 x pairs of wires) - Has, 2 x pairs of Red + Blue, then 2 x Pink, then 2 x pairs of Grey + Yellow paired)




3. ILP TRANSFORMERS - 9T631 0545 s/n506. Again, from online research, I "think" this model (with having a "9" prefix) could also be a 625VA , but no clue on wires V outputs?
(4 x pairs of wires) - Orange and Brown seem to be 'sleeved together' on each pair, then Red + Blue paired, and Grey + Yellow paired)




Hoping someone with prior knowledge can assist with, 1. How to test before using any of them, and 2. Wiring colours input/output voltages, for each transformer...?

Cheers guys

Hi guys, I tested a new SE amplifier with 300b and a mu folower type driver with D3a and EL802, DC final tube filament supply, anode voltage 420v, bias current 85mA, OT impendance-5.2K/8 ohm and a servobias system for bias regulation. All transformers are built by me and soon I will start building the chassis

Bought as new old stock and as a balanced pair .
Rocket logo 1975

Having a clear out after buying quite a few different dated Voskhod tubes recently.

Bought from a seller in Ukraine.

£150 + p&p ( I’m in the UK )

Getting ready to order caps for my crossover networks. I noticed the 450v are quite a bit higher than the 250v caps. System is a Yamaha A/V with 70w/channel. Speakers are 2-4" 4 ohm Eminence wired in series for my center channel. Do I really need to think about the 450v? I just can't imagine that much of a voltage drop inside a crossover. Thanks in advance.

Hi

I own a pair of THF-51S but at the moment I’ve got the itch to build a small SET using a 45 output tube. I own a 6B4G GSG but often wonder about the sound of the 45.
Before I go ahead and invest in a pair of 45 and driver I’d like to know if anyone has ever compared a SIT (VFET) with a 45 SET.
I’m aware that the 45 can only deliver a few Watt vs the SIT.

Thanks for your time.
Eric

Hello,
I'm designing a +-15V dual rail low noise power supply, 200mA mini per rail. A first version was the classic design with tapped transfo and a pair of LM317 and LM337 regulators. But because of the price and size, I want to make it with no transfo.
I'll use a 9Vdc or 18Vdc SMPS. First idea was to use buck / boost dual (positive and negative) converters. I find some IC's like LTC3265 (perfect ICs but not enough current, and really expensive!!), LM27762, TPS6513x, LT8335... But not easy to choose the good one and the corresponding architecture.
Do you have any recommendations, sources, schematic, to help me to design it well?
Thanks a lot!

1)

MC FIFO Multi-Channel I2S/DSD FIFO Buffer + MC DUALXO Multi-Channel Clock Board - SOLD

Asking 205€ 190€ 150€ + shipping costs and any fees


2)

RPI Dac HAT - ES9028Q2M DAC HAT Raspberry Pi / I2S & SPDIF / PCM DSD - NEW, unused - SOLD

Asking 35€ 30€ 25€ + shipping costs and any fees


3)

RPI Dac HAT - IVSTD Output stage module for DAC ES9038Q2M – ES9028Q2M + empty board - NEW, unused - SOLD

Asking 25€ 20€ + shipping costs and any fees


4)

RPI Dac HAT - IV board LL1544 transformer I/V KIT V1 - NEW, unused - SOLD

Asking 10€ + shipping costs and any fees


5)

FIFO II Series (used boards, excellent condition)

- I2S FIFO II
plus
- Digital Isolator Board
plus
- DualXO II ClockBoard + TPS7A4700 regulator board - SOLD

Asking 135€ + shipping costs and any fees


6)

OPA1622 Adapter PCB Kit Lot of 5 - NEW, UNUSED - NO MORE AVAILABLE

Free for the first buyer


All boards come with all parts as included in the original kits, as shown in the attached pics (one XLR connector - offer 4) - is missing).

If the prices are off let me know or make offers.

Please contact me through PM.

I'm using an Oppo 105D with the latest official firmware and I've had a skipping problem while streaming TIDAL for a while now. Not all songs give me a problem, actually only some, but the ones that give me a problem always skip in the same places and in the same way, as if I'm listening to vinyl with known skip places. It can be from 2 to 5 glitches on a song or just one. I emphasize that these are always the same tracks. When I try stimming with the PC Tidal desktop app on the same songs, I don't have that problem.
The sound is better when I stream directly from the Oppo, so I would like to fix the problem if possible.
I tried another rooter and it still glitches, although a little differently and a few seconds later or earlier than the usual places. I didn't take the device to someone else's system to try it on someone else's network...

These are the songs that give me trouble:

Streets of Philadelphia (Single Edit) Bruce Springsteen
The Robots (2009 Remaster) Kraftwerk
Atchafalaya - Live From Dordrecht, Het Energiehuis / 2014 Snarky PuppyMetropole Orkest

Bruce Springsteen, for example, always skips at 14 sec, 26 sec .... And I have the most glitches on that song. Also, it initially starts a little fast in the first few seconds and then picks up a good speed.
I will definitely take the player to someone else for a test, that it has nothing to do with my local internet network or some interference in the distribution of the cable operator in my building.

Oppo skips/glitches Flack HD and MQA, 16/44.1 too. Only mp3 does not skip. I use licensed Bubble UPnP for navigation with Oppo 105D as renderer.

I have no idea what could be causing this problem. Even though I'm not a regular user of Qobuz, visitors played songs from it and I didn't notice any streaming problems. Is there some miscommunication between Oppo streamer and Tidal server???

Thank you very much for the answers and ideas. I hope you try these three mentioned tracks on your Oppo 105D units and report your impressions.

Hello!

I have in my possession a UR22mkii audio interface. When I bought it many, many moons ago, I did not realise that the output impedance of the headphone amp was measured at 91 ohms!!! (According to Julian Krausse's measurements, which I trust).

I recently took apart my UR22mkii in order to redo the solder joints of the headphone socket. It was becoming a bit wiggly and I decided to do up the joints with some high quality leaded solder. The headphone socket has basically no mechanical support and just kind rests on the chassis! Hilarious! This pretty much guarantees that this solder joints are going to break. When will manufacturers learn that solder is not glue?

Anyways, while I was in here I decided to trace the output section of the headphone amp. I only did it on the main front board and not where the volume and balance controls live above it. (It's connected the front board via a ribbon cable). Attached below is the output buffer present. It's a very basic inverting opamp setup with some capacitors here and there for frequency response shaping. I wasn't able to measure the small caps that were part of this system as I'd have to take them out of the the circuit and it's all SMD stuff we're dealing with here, so I couldn't be bothered.




There is a FET switching system attached to the right output channel that probably shunts the output ground when the jack is unused, probably because they saved 5 extra cents by using an unswitched headphone jack and two transistors vs. a switched headphone jack. I didn't trace it.

To me, the issue seems blatantly obvious. 90 ohms resistance in series with the output? Was the designer for this insane? I'm thinking of just jumpering one those 181R resistors. Should I pay attention to those unmeasured caps and change their values if I do this? I imagine this will mess with the frequency response quite a bit.

Thanks for any help!

If yes, thats why low q drivers sound better?

Hiya, I'm worried about the 'boom' when i turn on my Naim NAP150 amp (maybe upstream in the pre-amp etc, ) and whether it will damage my speakers. I decided to build a speaker protection board for my speakers but all of the ones i can find on ebay etc join together the two -ve sides of the speakers together and switch the +ve.
My question; looking at the NAP 150 PCB it looks like the -ve of the speakers is routed separately and i'm worried that linking them externally might be a bad idea.
Has anyone added external protection before?
Given how old the Amp is i might have opened it up and added a delayed 2PDT relay but it's still sounding amazing and is still worth money so i don't want to destroy it completely - conversely i don't want it wrecking my speakers either.

This is admittedly a silly project but I have some time to spare.

My goal is to use PVC pipes in creating a lung powered air horn as a "noise maker" for some squadron parties and ceremonies. I've seen all kinds of DIY versions with different types of diaphragms. I have some horn lenses lying around and would like to implement those into the design but I don't remember their cutoff frequency. Let's say 1400 hz.

So, to make this as efficient as possible, from the input side/mouth of the tube to the throat of the horn lens, how long should the tubing be for a roughly 1400 hz "horn"? I'm not too worried about the diameter since the horn lens is a 1" throat. I know the wavelength is roughly 10" but I don't know what kind of interaction that would have with the horn lens.

I'm also considering using an old compression driver as the diaphragm for this; just bore out a big enough hole for a mouthpiece on the backside then mount the horn lens.