Hi I am looking for a schematic for this amp or equivalent Audison AV 5.1K. This amp has 2 494's, and I don't have no voltage on pin 12 of either of them. Maybe someone in here has had a little run in with this amp.

Hello

In the last month I've been working on a custom digital interpolation FIR filter implemented on an FPGA. This filter does pretty much the same thing as well known DF1706, SM5847, PMD100, and so on. However, its ability to reconstruct and attenuate a signal is way beyond those 🙂

The filter contains 8192 coefficients and it interpolates the data by a factor of 16 times (e.g. 44.1 kHz to 705.6 kHz and 48 kHz to 768 kHz). It has several FIFOs built in since its core is running asynchrounsly (at 225 MHz) while the MCLK is used only to clock data out of FIFO and to create LE (latch enable) signal for the DAC.
In fact, this filter does always interpolate to 705.6 kHz and 768 kHz (an integer factor of the input) and accepts data up to 768 kHz / 32 bits. In order to do that it works like a sample rate converter, so it interpolates and decimates at the same time. However, it should be noted that for 44.1 kHz and 48 kHz it does not decimate at all, but for anything higher than 44.1 kHz and 48 kHz it still interpolates data 16 times, so e.g. having 96 kHz input means that the data is interpolated up to 1536 kHz, but decimated back to 768 kHz. The same goes to 768 kHz input which is interpolated to 12.288 MHz (in a mathematical sense of course) and decimated back to 768 kHz.

It should be noted that along with huge amount of coefficients (8192) this filter incorporates multiply-accumulate units of 32x35 bits wide. It means that the input data word is fully accepted up to 32 bits (without any truncation for that matter) and coefficients are quantized on 35 bits resulting in unmatchable accuracy of the math it does to calculate the output sample 😉

In the title of this thread I did mention you can drive PCM56, PCM58, PCM63, AD1862, AD1865 and so on up to 768 kHz. How is that possible? The filter contains a self reconfiguratable oscillator which sets its frequency depending on the output length (16, 18, 20 or 24 bits). It means that the output bit clock (CLK) is running fully asynchronously from the LE (latch enable) signal which is generated by dividing the provided MCLK signal, so data is latched in almost all DACs without any extra jitter introduced by the oscillator itself. In fact, the filter contains 3 sets of FIFOs (6 FIFOs for both channels) - one in its input (I2S) before going to the core, another one on the core output and the last one for the final oscillator to clock data into the DAC. Besides all of that this technique introduces a quiet zone after the latch signal going down, so it should give DAC some time to settle down with its output before clocking in another sample 😉

Depending on the word length the following frequencies are created on the CLK output:

16 bits - 14 MHz
18 bits - 15.5 MHz
20 bits - 17 MHz
24 bits - 20 MHz

It means that certain DACs such as PCM56 and AD1865 will be running at the edge with 768 kHz stream, but they will work just fine according to my tests. The LE (latch enable) signal is always 705.6 kHz or 768 kHz depending on the input (either multiply of 44.1 kHz or 48 kHz).

0 dBFS @ 20 kHz:



-60 dBFS @ 1 kHz:



Jitter test @ 48 kHz with LSB toggled @ 250 Hz:



Filter attenuation (linear phase) - white noise @ 48 kHz:



All measurements were performed using PCM58.

The filter has I2S input with signals of MCLK, BCLK, LRCK and DATA. However, MCLK can be fed by the same source as BCLK signal (if no MCLK is available) assuming that BCLK has a rate of 32x, 64x, 96x, 128x Fs or similar since the filter has to determine its frequency to know how to divide it in order to create LE (latch enable) signal. Any exotic values of BCLK rate will not work as MCLK, so keep that in mind. The jitter and synchronization of FIFOs depends purely on the MCLK signal, so in the long term it needs to be synchronous with LRCK (in almost all cases it is, since BCLK and LRCK should be derived from a divided MCLK clock).

Following frequencies are supported as MCLK:

49.152 MHz
45.1584 MHz
36.864 MHz *
33.8688 MHz *
24.576 MHz
22.5792 MHz
18.432 MHz *
16.9344 MHz *
12.288 MHz
11.2896 MHz
9.2160 MHz *
8.4672 MHz *
6.144 MHz
5.6448 MHz
4.608 MHz *
4.2336 MHz *
3.072 MHz
2.8224 MHz
1.536 MHz
1.4112 MHz

Those with asterisk are usually used in CD-Players and it should be possible to use the filter within a CD-Player once input is attenuated using 170 Ohm or so resistor per line (in order not to damage the FPGA and its I/O pins due to 5V logic levels). The filter can be powered by an external supply (5V or higher) or by providing a direct 3.3V power supply (it is up the user).

Following outputs are provided by the filter:

CLK - clock for data
LE - latch enable signal
SD_L - serial data for the left channel (and its inversion with the line above it, so you can create a differential DAC for XLR outputs)
SD_R - serial data for the right channel (and its inversion with the line above it, so you can create a differential DAC for XLR outputs)
3.3V - main power supply
GND - ground

It should be noted that the filter does have a TDPF (triangular probability density function) dithering algorithm as well. It can be turned on or off by a jumper depending on your preferences.

The price for a fully assembled and ready to use board will be 250 EUR.

Final revision of 16x interpolation version:







ROM jumper selects which type of filter should be loaded during boot process. There are two filters available, one is linear phase and the other one is a minimum phase 🙂 Both of them have 8192 taps.

The filter can be directly powered by an external USB to I2S converter, but it draws about 300 mA of extra current, so keep that in mind. Also, it is a 4-layer PCB. Dimensions are 50 mm x 47 mm.

For more information and orders please visit:

Digital Interpolation Filter (FIR) - KuSy Audio

I am rarely available on forums nowadays, so a friend of mine will take care of your questions.

For sale is my RJM Emerald phono stage (https://phonoclone.com/diy-pho7.html) -- $300 OBO

At $300 I'll pay shipping and PP fees.

I have built another Emerald with some different components so I am selling this one.

This is a wonderful sounding preamp. This Emerald replaced a Schiit Mani 2 in my system and it wasn't even a contest. This Emerald was compared against the internal phono stages on a Rogue Sphinx II and III and was more musical and quiet. I also compared this against a Simaudio P5.3, I preferred the Emerald my friend preferred his P5.3.

I build it per the RJM BOM but with a couple of modifications:

Power supply

• 30VA R-core transformer
• LED power switch
  • DC converter for power switch
• CRC DC filter
• Neutrik PowerCon for umbilical

Signal Chassis

• Neutrik PowerCon for umbilical
• Neutrik RCA jacks
• C3 - 1.8uF Clarity Cap SA
• RJM Switch Board for cartridge loading
  • (1-4 all open) - 47 kohms or whatever the phono stage input impedance is.
    -------
    close 1 - 1k
    close 2 - 221 ohms
    close 3 - 100 ohms
    close 2 and 3 - 68 ohms
    close 4 - 22.1 ohms
    -------
    (5-6 both open) - 0 pF (+ cable)
    -------
    close 5 - 100 pF (+ cable)
    close both 5 and 6 - 200 pF (+ cable)
• Vampire one piece hard brass ground post
• Installed are OP27 opamps
  • Can be rolled with many different single channel opamps

Umbilical is approximately 12inch but it can be easily lengthened because of the screw terminals in the PowerCon connectors.

Cases are from China off Ebay.

Thanks for looking!

Some of you may know I built a ball bearing linear arm. However, this kind of linear arm excels with low compliance cartridge and requires high VTF to do the job right. My ball bearing arm does sound wonderful with Denon DL-103R(VTF=2.2, low compliance) after fine turning, especially for jazz. Bass is excellent. Denon DL-103R usually exhibits some shrillness in high frequency, but not on my linear arm.

In my opinion, ball bearing linear arm works better with high VTF and low compliance cartridge because two reasons.

1. Heavy moving mass. In most cases, there are no too many options to reduce moving mass.
2. Ball bearings have simply too high friction for high compliance cartridges.

So, the answer is to get ride of friction in order to use high compliance cartridges. Frictionless air bearing becomes the only option.

For air bearing, the most difficult part is air compressor, specially for New Way air brushing kind of arm because it requires high air pressure. The higher air pressure, the stiffer the arm is. I used a small fridge compressor to build quiet air compressor. The end result is excellent. It runs very quiet. In my listening room, the noise level is about 25 db in night. I measured the air compressor noise level. It doesn't even register on the sound pressure meter. The noise level is just same as a small refrigerator. I also add two cooling fans. These fans bring noise level up to about 30 db. It is no problem for me because I put the air compressor in the closet. I can hear nothing on my listening seat.

Please see attached my diy air compressor diagram. My compressor has two zones, high and low pressure zones.

1. Air Filter. It prevents small particles into the air line.
2. Compressor. It is small fridge compressor. In my case, it stops for 30 mins and runs about 20 mins. The compressor can be a little more powerful so the run time will be shorter. But in my case, it is ok.
3. 1st Stage In-line Filter. I put it first because it is cheap and can easily be replaced.
4. High Pressure Regulator. This is 2nd stage filter with high pressure regulator.
5. Check Valve. Check valve permits air only going one direction because the compressor can't hold high air pressure for long time. It also prevents high pressure air goes back into the compressor.
6. Pressure Switch. Once the tank reaches 80 psi, it will shut the compressor off and turn the compressor on once it comes down to 40 psi.
7. Safety Valve. It is set at 125 psi.
8. Air Tank. I bought 10 gallon, but 5 gallon should be fine. Air tank will hold high pressure air. Whenever I want to listen, it will be ready. I bought the tank from Homedepot for $34.00. They sell 5 gallon for $30.00.
9. Cooling Fans. These fans are from my old PC power supplies.
10. Temperature Control Switch. I set the temperature at 70 F.
11. 12 V DC power supply for the fans.
12. Main Power Switch.
13. On/Off Air Valve. Juts in case I need to shut off the air to feed the arm.
14. Flow Control Valve. It slows down air flow so I can have low pressure air to feed the arm.
15. Low Pressure Regulator. It regulates air pressure in low pressure zone. It controls the pressure to feed the arm. It has filter too. The filter element is 10 micron.
16. 4th Stage Filter. It has even finer filter. .3 micron.
17. 5th Stage Filter. It is auto fuel filter. Its function is to prevent anything small particles into the air line.

I like my diy air compressor so much. It is quiet and runs cool. I don't think you can buy anything commercially available air compressor better than my diy air compressor even you may spend a lot of money. The total cost of my diy air compressor is about $350.

I have Lite DAC 38 using Burr Brown PCM 1704 R2R dac chips. It sounds beautiful analog and non fatiguing sound. I want to sell it cheap for $150 + $20 shipping within US. It is good purchase if some wants to use just the case and transformers. Local pickup in Chicago area also possible. Reach out to me on (630) 446-0165‬ for local pickup.


Kit itself is available for about $400.

http://www.analogmetric.com/goods.php?id=247

By now it has been a while since OPA828 (and OPA2828) were released. Any detailed comparison done (in the context of audio) to the opamp, OPA627, that they are supposed to replace? Thanks!

Hello everybody!

Is a simple first order lowpass filter "good enough" in front of an amplifier that drives a subwoofer?
Or do I need a higher order LPF?

I am not talking about "getting the best sound" from the system, I just don't want to damage my new subwoofer.
I am also not asking about optimizing the crossover point or phase issues and stuff like that.
Just preventing damage from occuring.

Shouldn't the inductance of the subwoofer itself cause low frequencies to be "cut off"?
Or would passing an unfiltered high frequency signal into a subwoofer cause it to heat up and burn itself out?
Is a filter needed at all?

I know a bit about electronics but almost nothing about speakers and how to drive them.
To me they are just "magic inductors that turn current into air-movement" ;-)

Usually I just try stuff to see if it works but I don't want to scrap my new subwoofer.

A bit more information about my setup:
This is what I want to do:


Yes, it is a badly drawn sketch but it explains what I want to do.
Use a subwoofer "in parallel" with an existing system that will be set to only do mid and high frequency.

The subwoofer I have is a Behringer VP1800S (please no anti-Behringer rants, thanks).
It is rated for 1600W maximum and has a frequency range from 40Hz to 200Hz.
The amplifier is built for the full audio range and can output 400W stereo, I will use it in "bridged mode" to get 800W and a single "channel".

I will never actually push 800W through the subwoofer, that would probably destroy everything around the subwoofer ;-)

Of course I tried to search online about using simple first order lowpass filters in fron of subwoofers but I couldn't find any proper information about the topic.

Any answers would be appreciated.

WTB

Please reply either here or by DM with details, condition, and asking price.


Greg in Mississippi

Hello,

May you advise me on high beta, high FT, NPN/PNP TO92 or smd please .

MPSA 018 and BC560 with beta around 500 measured for real seems interresting,

Anything better for audio ?

thanks

Hello,

Just wanted to introduce myself and say that I have been obsessed with all things home and car audio for sometime now. I don't think there is a cure for my addiction but hoping to find ways to deal with it by belonging to this forum. 🙂

Dan

Hello all. A year ago, I built this amplifier with Common Ground Collector output topology very similar to that used by QSC in one of its model called USA. A friend of mine gave me two boards which he ordered to make in China and he told me they both had an error which he had not been able to find out. After I fixed them, I mounted all the parts and the circuit was supplied with +/-55V.

For the adjustments, I just turned the null trimpot to set Offset voltage to minimum (0V). For Bias, simply turn carefully the bias trimpot until obtaining 80mV in one of the emitter resistors of the driver transistors and 160mV on both emitter resistors.

The amplifiers sounds very good 😀. I uploaded some photos of the amplifiers I made.

I bought an open box Electro-Harmonix 44 Magnum with this issue. I tried replacing the pot prior to figuring out it was only for the first 15-20 seconds after power on. The new Alpha Taiwan Pot behaves the same as the original. The pedal works fine, even when the pot is noisy. The time constant of this problem has to be in the range of 3-4 seconds and with a 10K audio taper pot, I can't think of any failure mode to induce this problem... Maybe all of them do this???

Internally the "44" watt power amp is a TI TPA3106d1 (low passive parts count class D, H-bridge output, AC coupled input). There is a quad opamp that is likely doing EQ to get it to sound guitar-amp-like. There are three large diodes, probably to protect it from reversing the 24 volt DC external supply. I suspect the opamp virtual ground is created passively with resistors and a capacitor.

E-H does not offer technical support and because I've opened it up it is no longer under warranty. They have some sort of standard repair system that requires you ship the pedal to them and is very reasonably priced at $35.

Should I ignore the problem, or send it to E-H for repair?

Thanks!
Jon
-------------------------
Here are some pictures:

I'm a college student studying electronic engineering, and I'm interested in building DACs and power supplies.

Hello, Although born and bred in Manchester, been living in the Netherlands for around 20 years now. I have been tinkering with electronics as a hobby in the world of microcontrollers, sensors and actuators. M two sons are musicians and we have listened to lots of music over the years with my very old, and still going strong, Arcam Alpha mk 2 on some equally old Castle bookshelf speakers. Kids at conservatory now and fled the nest. Then the questions from them, which sound system should I buy? how does an audio amp work, what's Class D, A, AB etc. So time to start a new hobby. The Pass Amp Camp Amp caught my attention, bought the kit built it and we're off. Hope to learn lots from you all. See you in the forums. Steve.

New member, curious to see what others are up to and follow along with some of the interesting repair work being done! long history in car audio, 2 channel audio and home theater but little in the way of DIY after car audio....

What software (preferably open source / free) do all of you use to design your PSU ?

15 years ago, I used PSUD for an Aikido preamp. I just re-downloaded that. But it is rather limited, and not suitable for more complex PSU designs that use transistor regulators.

I would like to redesign the PSU for my phono pre (EAR834p clone), using a tube rectifier (5AR4) and tube regulators (0D3s), hammond 15H choke, etc to get a stable 285V DC.

I would model the current layout. Vs my new layout.

Is LTSpice that best option? I think I last used that software back in maybe 2002?

Here is a pair (x2) of Proco (ITX) XLR Inline Line-level Input Isolation Transformers

• Eliminates hum and buzz caused by ground loop
• Plug and play easy to use – no power required
• High Quality Neutrik XLR Connectors for Balances Lines

Genuine & original part, Made in USA

Measures 95mm long

Happy to combine shipping

Price, only USD 59 for the pair

Thanks for looking and please check out the many other vintage audio items and components I have listed for sale!

Cheers, Ralph

Hello all,

Here is a Jensen Isomax CI-2RR Stereo Isolation Transformer in excellent condition

Eliminates hum and buzz caused by ground loops
• Extended frequency response from 10 Hz to 40 kHz
• Less than 2° phase deviation at 20 Hz
• Plug and play easy to use – no power required

RCA Gold Plated Connectors for Unbalances Lines

Genuine & original part, Made in USA

Measures 110mm x 66mm x 37mm high

Price Only USD 149

Happy to combine shipping

Thanks for looking and please check out the many other vintage audio items and components I have listed for sale!

Cheers, Ralph

Hello all,

Here is a pair (x2) of Proco XLR Male to TS (1/4" Phono Plug) Inline Line-level Input Isolation Transformers

• Suitable for Line-level use matching Balanced to Unbalanced equipment
• Eliminates hum and buzz caused by ground loops
• Plug and play easy to use – no power required
• High Quality Neutrik Connectors for Balances to Unbalanced Lines

Genuine & original part, Made in USA

Measures 120mm long

Price, only USD 59

Happy to combine shipping

Thanks for looking. Cheers, Ralph

Hello all,

Here is a pair (x2) of Sescom TR-122, TRS (1/4" Phono Plug) to XLR Female Inline Line-level Input Isolation Transformers in excellent condition

• Suitable for Line-level use matching Unbalanced to Balanced equipment
• Unbalanced 60k ohm High Impedance 60k to Balanced 150 ohms Low Impedance
• Eliminates hum and buzz caused by ground loops
• Plug and play easy to use – no power required

Genuine & original part, Made in USA

Measures approx 500mm long including cable

Price, only USD59

Happy to combine shipping

Thanks for looking. Cheers, Ralph

Hello all,

Here is a Metrosound Discmaster Vinyl Record Cleaning Device in original box

Complete with all parts except the cleaning fluid

Genuine & original part, Made in UK

Price USD35

Happy to combine shipping

Thanks for looking. Cheers, Ralph

Hello all,

I have a Dixson Inc Channel Balance Meter from a Quad Eight Mixing Console

Genuine & original part dates from early 1979, Made in USA

Meter measures 90mm x 71mm x 55mm deep

Complete with bezel (97.5mm x 57.5mm) & mounting hardware

Requires a 94mm x 54mm panel cutout for the bezel

Supplied without lamps

Perfect for vintage gear restoration

I'm thinking USD 30 plus postage or open to offers

Cheers, Ralph

https://audiofile.net.au/

Hi all,

I've recently bought a second-hand Roksan Kandy KA-1 MkIII amp. The amp looks like new, both from the outside and inside. It also worked absolutely fine for a few days.

However, it started suffering from two issues when I turn it on (standby) from cold:

The main issue is that sometimes (more often than not), when I turn on the amplifier, there is static in the left channel. Static gets a lot quieter after a minute or so, but the left channel remains quieter for ~5 minutes. After the amp warms up, it sounds fine - there is no static and sound balance is correct.

Turning the volume knob has no effect on the static level, turning it almost all the way up does "interrupt" the static momentarily, but it doesn't help.

If the amp is turned off (standby) and back on within a few minutes, there are no issues with static.

The second issue also relates to cold/warm amp start - if the amp is turned on from cold, there is a slight pop from the speakers when speaker relays engage. The pop is barely audible if the amp is turned on while it's still warm. I've seen DC offset begin too high mentioned in Roksan's FAQ.

The final issue is not related to cold start, and I'm not even sure it's an issue: even when the volume knob is turned all the way down, you can still hear the music (very faintly)

I've contacted both the seller and Roksan and I'm waiting for their replies, but I'd like to know if this is an easy fix, since I'd love to keep the amp. I know how to use a soldering iron and a multimeter, but I could use some guidance 🙂

Thank you!

Hi all,

I bought a cheap Sony FB920R amp from eBay as it was listed as not working so I thought I'd have a go at fixing it. I am very much an amateur at these sort of repairs but I am fine with the basics and no stranger to soldering and whatnot.

Once I got the amp I saw a couple of burnt resistors near one of the channel's MOSFETs and the amp stayed in protection mode when powered up. I immediately suspected the MOSFETs and confirmed with a multimeter that both of them were a dead short. I removed them all and replaced them with some close modern equivalents (IRFP340/IRFP9240), replaced the dead resistors, and also upped the rating of a couple of resistors in the bias circuit to allow for the higher voltage requirements of the new transistors, which then allowed me to set the bias for both channels at exactly 10mv, as per the service manual.

The amp now works and plays beautifully. Happy days.

However, here is my question. The DC offset on the left channel is about 15mv which is fine, but on the right channel (the one which was dead originally) it sits at around 69mv. This is the channel which had the failure.

Is this high enough to be cause for concern? I've read conflicting reports; some say anything under 100mv is no cause for concern, some say anything above 50 is not ideal. I am assuming something has perhaps been damaged or drifted out of spec during the failure of the channel. Any idea where I should start looking? I have read that the differential pairs are the most likely culprits of high offset. Can anyone point me in their direction for my amp?

The service manual can be seen here: https://www.manualslib.com/manual/1276748/Sony-Ta-Fb920r.html

Thank you in advance!

Hi all,

I've been building a 3-way speaker system for home listening. I've been tossing up between an active and passive system, and recently have been leaning toward a passive x-over design. I've been playing with a design for this in x-sim and have come up with the attached. Is anyone with more knowledge than I able to have a quick glance over this and let me know if there's anything that I should consider?

The drivers I'm using are :

SB Acoustics SB26SFCL38-8 10" Paper Cone Woofer
SB Acoustics SB15NRX2C30-8 Norex Midwoofer
Fountek NeoX1.0 Ribbon Tweeter

I've attached the frequency response which I'm fairly happy with, I don't particularly know how to read the impedence graph and what I should be looking for there, all I've done is try to keep the minimum above 4 Ohms so any pointers here would be great.

The main concern I have is the power dissipation graph which seems to indicate very high power through those resistors. Is there any way to resolve this?

last thing to mention this was constructed from FRD files found for these drivers online, I'll try to take some actual readings once I've loaded the drivers into the cabinets to get a more accurate picture but any help in the meantime would be great!

many thanks
Lawrence

Hi, i need precision current limiter for LM337 with TL431, as there is non existing negative version of TL431 is there alternative simple device that works in POS and NEG version of regulator?

I have here on simulation working LM317+TL431 as 250mA current precision limiter but for LM337 i can't get it working because it needs negative version of TL431.

Any suggestions of simple current limiter for LM3x7 voltage regulators? And yes i don't count BJT as limiter as they are not precise.

I've decided to sell some more of my collection of drivers as family life has taken over. No more speaker builds for a little while.

This was intended to be my dream home hi-fi speaker with supreme quality drivers in a slim sealed cabinet. I attach the T&S parameters for the drivers in question. What we have here is a total of 14 Accuton drivers making a wonderful WWMTMWW arrangement. A superb 3 way or an even more sophisticated 4 way speaker if you choose.

The tweeter is the delightful Accuton-C25-6-012, operating between 2500 HZ - 32 KHZ.

The midrange is delivered by a pair of Accuton-C90-6-079 in an MTM arrangement. These can cover from 250 Hz – 5000 Hz.

The heavy lifting is done by the amazing ACCUTON_WOOFER_C180-6-092; four of these covering midbass and down. They also spec very well for a transmission line if you wish.

The drivers were selected and supplied by Australian importer War Audio, who knows these drivers better than most.

All drivers are unused. Original boxes for each driver. Will take to PackNSend for overseas buyers.

The price is AUD$4000 for the set (USD 2700). Payment by EFT or Paypal plus fees

NB. For local collection I will include an extra pair of the C180-6-092 in cabinets. These can work as small subs 😉

Another set of drivers from the vaults! FAITALPRO HF10TX 1" Compression Driver.

Great response and a well designed Radial Phase Plug Design.

These have only been tested. So, like new.

AUD$200 for the pair

EFT or Paypal Plus Fees

Postage available at buyers expense (have original boxes)

https://faitalpro.com/en/products/archived_products/product_details/HF/index.php?id=502010200

Hi Folks,
my Roksan Kandy KA1 Mk III has a small issue. When the amp is not used for some days and then switched power on, the speaker relays take about 15 seconds to switch through. After listenning for a while, switching off and then immediately switching on, the relays switch through within 3 seconds as used. In short: the issue happens when the amp is cold. What can it be ?? Otherwise the amp is working/sounding good.

The itch first struck some years ago, arriving with the "gift" of some 78s. I tried to ignore it but the itch never quite went away. It recently recurred when I was given a dilapidated Thorens TD135 when helping a relative clean out his recording gear. After all, I had a wee solid state phone preamp that advertised EQ both for RIAA LPs and an alternative EQ for 78s - how could I not get the TD135 working again? After which, those grubby old 78s needed cleaning so that, finally, the stylus could drop into the groove and some music would emerge to scratch that itch. 🙂

Ugh! Less a case of "scratch that itch" than "itch that scratch" 😱 as the wee solid state preamp protested that it was overloading during the louder passages. Hmmmm ... perhaps not surprising with the stylus whizzing along the groove at that speed! On to the bench with the preamp to confirm that yes, indeed, it would readily run out of headroom, especially if the stylus smacked into debris in the groove.

By now I was REALLY itchy, so it was out with the soldering iron and Diego Nardi's "Monophono" preamp design from Sound Practices circa 1996. A dead Sansui AU2900 was gutted and its solid state debris replaced by valves and Diego's variable EQ networks. Once more unto the groove went the stylus and YES! Music! And no more overload! But PLENTY of surface noise, even from "clean" 78s.

The itch, which was worse on some days than others and would not entirely abate, flared red and raw when I read John Fox's article "Record Lubrication has a Significant Effect" at page 36 of the January 1959 edition of Audio magazine (here: https://www.worldradiohistory.com/Archive-All-Audio/Archive-Audio/50s/Audio-1959-Jan.pdf ). Silicone?!?! On a record? Why not! Well, not so much so that excess lube might contaminate the cartridge suspension, but enough to give that old shellac a sheen.

On to the platter with the lubricated disc. On the first play, the stylus collected a LOT of debris - and I thought that I had cleaned that shellac to within an inch of its life - but there were hints of musical glory. On the second play ... aaaah! Lots music with MUCH less surface noise - the difference was not small.

Gene Krupa and his band playing Bolero at the Savoy (Columbia 1941 issue), Sir John Barbirolli with Vaughan Williams' Symphony 5 (probably late 1930s). 🙂🙂 Many more to listen to.

I've played with a few TI ClassD amp chips over the past few years, starting off with TPA3221 and then TPA3255. I never could get the latter to give me the SQ I was looking for, no matter how many caps I put on its supply rails. TPA3221 though delivered the goods, at least until my eval module blew up, just it didn't have vast reserves of power. TPA3223 is rather like a TPA3221 but with a higher maximum rail voltage (42V) so should comfortably do 50W/8R. However no-one to my knowledge has done a commercial board for this though there is now a finished amp on Taobao and Aliexpress : https://www.aliexpress.com/item/1005006344550432.html. The TI eval board is prohibitively expensive so I figured I would need to design my own - wifey helped by laying out the PCB. I soldered up the first prototype this morning - no heatsink as yet as I'm breaking it in gently :




What attracted me to TPA3223 was the absence of on-chip regulators for the various power supplies - there are 3 5V rails to provide. Two of them are coming from LM317Ls and the third has a discrete reg. I have a buck reg stepping down the main rail prior to the linear regs. Idle current for the stereo amp is below 40mA from 30V which is impressively efficient compared to my TDA8932 amps which take 60mA per channel from 24V.

I have a pair of Paoli 60M’s and a Pas 3 that i got over 30 years ago from a good friend, along with other solid state AV equipment that I’ve acquired over the years, all plugged into the same 20-25 year old Acoustic Research power bar. The bar probably needs replacing and was wondering if any one has recommendations that would both protect the equipment and not adversely affect the sound quality or may even improve it.

I read through quite a few of the posts in the denoisonator thread and started thinking about a variation that produces similar results but over a wider frequency range. I came up with something that performed pretty well, but realized that the good result could due to my use of a "perfect" voltage source. It will be clear in the schematic below:


V2 is the voltage source in question. So I started thinking about replacing it with a suitably low-noise voltage reference, but it had to be inexpensive. A Vbe multiplier fits that category but has a very bad temperature coefficient. But borrowing some bits from IC design gave me a Vbe miultiplier whose temperature coefficient can be adjusted -- positive, negative, and very low over a selected temperature range. Combining that with the above circuit, here are some sims:


This shows the voltage change over temperature. The multiplier circuit (upper portion of the schematic) has been adjusted to also compensate for Q5. This involved changing the values of R2 and R4 until the output voltage and temperature compensation were close to what I wanted.

The next screenshot shows the PSRR, but ONLY w/regard to the input to the LM317. The Vbe multiplier's power supply is assumed to be very low-noise, probably generated by a second LM317. The power requirement will be low so a ~30-cent SMT style regulator will do fine there.


Finally, the noise voltage:


I haven't built this circuit, this is all theoretical. Anyways, the measurement gear I have is only capable of telling me if the thing is oscillating or not. I expect it will, and taming it will likely degrade the noise performance at higher frequencies.

I don't think this variation of a Vbe multiplier will be all that useful in terms of stabilizing the idle current in class AB output stages but it may be handy for other purposes.

Hello,

The amplifier in my Sony SA-CS9 home theater subwoofer is acting up and thought I would give a go at repairing it. Repairing audio amplifiers have always intrigued me and I thought now would be a good time to learn since I can't make it any worse. I do have a new digital scope as well as a DMM to help me with this and if I could get some guidance that would be awesome. I have been a lurker of this forum for sometime now and finally decided to create an account and see if I can get this amplifier going.

The transistors are MN2488 and MP1620. I believe this is a class A/B design amplifier because of the large power transformer? Enclosed are some pictures of the main amplifier board. The problem I'm having is no output and the power light stays red. Appearance wise I don't see anything that would suggest something is wrong. All the components look fine with no weird smells (burnt). Any guidance you can provide would be much appreciated.

Hello
I have two pairs (4 units) of Audiotechnology 10C77 25 10 KAP. They have a Re=4 ohm.

PLEASE BE AWARE THE UNITS ARE NOT SD, the title is wrong.


I bought them for a person who passed away last year. I thought I would build something with them but I really have no time at all, not need (my system already has a 10C77), so here for sale what I think it is the best 10" woofer (although any cheap).

They are in very good condition, slightly used for measurements and initial setup, but almost never played. They will be shipped their orighinal packaging + cardboard reinforcement.
They come without serial number. This is not the first time I see this and after asking, I was told that when you pick up them straight at the factory they come without serial numbers... but I really cannot assure if this is the truth or not. Maybe somebody can give us some light here.

Asking 750€ for one pair + pp fees + shipping (half retail price) and 1500€ for the 4 units shipped within EU. No problem shipping overseas, please, ask for shipping cost.

LCR ST-1 tweezers meter by Fnirsi​

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portable touchscreen oscilloscope (FNIRSI 2C53P)​

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Recently recapped my dh-220. on the left channel was able to set the bias current to 275ma and dc offset to 0V with no problems.
However, on the right channel, I cnat get more the 60ma on the bias. I check P2 and it seems fine. Resistance goes up to 1K.
So I started checking the other resistors in that network. R22 and R23 both measure to spec. R38 isn't the 28K resistor called for in the parts list, but is 17.4k. This is the same in both channels, however in the right channel, it measures at 17.1K (on the left it measured to spec).

So, I'm thinking I should replace that resistor. 300 ohms is almost 30% of the range of P2.

But, I thought I'd check in here first to see what the resident Hafler experts thought ;-)

Note all measurements where done with components in the board.

Thanks,
James

Hello, I'm in the process of building some single ended output transformers.

I did some experiments using iron from common AC transformers, but I noticed that with DC polarization in 5 minutes, they became magnetized. The "I" are slightly attracted to the "E".



But now I found some big old high current inductors with no specifications, they were used as a battery charger. I don't know anything about the quality of their iron.




And I have no idea whether it's an amorphous nucleus or iron-silicon sheets...
I tried to magnetize it using the original winding of a few turns of thick wire and applying 12V dc, I can assure you that it was a lot of amps and at least it didn't magnetize 🙂
Do you think I can have good results?

Current Dumping topology can achieve Class-A performance with zero biased output stage. It sounds like a fairy tale. Yet, it is true.
The famous Quad 405 amplifier is one of the examples. Please see the attached document if you want to learn more about Quad 405.

How it works, "Current Dumping for Dummies". https://connerlabs.org/current-dumping-for-dummies/

Conceptual Diagram.


What is crazier is that you can actually build it with an opamp. Modern opamps perform much better than than than the Class-A stage of Quad 405 back in 70s.
As the opamp is precompensated internally with a miller capacitor, you don't really need the capacitor shown in the Conceptual Diagram. The 3K3 resistor, together with the miller cap, they determine the "unit loop gain bandwidth", which is also the "Time Constant". Once the "Time Constant" from RC on the left side equals to the "Time Constant" from RL on the right side. The bridge is balanced. (https://en.wikipedia.org/wiki/Time_constant#Time_constants_in_electrical_circuits)
For an opamp, it usually specs the "Gain Bandwidth Product" in the manual. You also know the gain of your circuit. From there, you can get how much loop gain bandwidth in your circuit. You know the bandwidth, you can derive the Time Constant (relation between bandwidth and Time Constant, https://en.wikipedia.org/wiki/Time_constant#Relation_of_time_constant_to_bandwidth). By given the value of the inductor, then you can calculate the feed forward resistor value. The bridge is completed.

Here is the prototype that I come up with. It is almost identical with the conceptual diagram above.

NE5532 is a must, because of its current capability, up to 38mA. Also the max +-22v supply voltage is a plus. You can get 20W with it.
I would suggest to keep the bandwidth (Time Constant) near 3MHz. You want to minimize the current over the feedforward resistor R3, while keep everything stable. You only have 38mA budget from a single NE5532.
Use fast and high beta transistors, MJE15030/31 are good. I use 2SC5200/2SA1943 in my build.
Does it work? Yes, it sounds just same as my other amps. Sorry, I don't have spectrum analyzer at home.
It is just a proof of concept. You can parallel the OPAMP. You can use zero biased CFP to get more current.
It should be your first amp, because of the simplicity. It could be your last amp, because it performs so well why bother other complex designs. Look at this teeny tiny amp. You don’t even need heat sink.



Indices:
Final Version

Feedforward Resistor Value Calculation

Investigate The Current Required to Drive The Feedforward Resistor

Method to Calibrate The Feed Forward Resistor

Howdy Folks!
I just purchased a Rose RS-150b streamer today. I’m using this with my Pioneer Spec-1 preamp, and my McIntosh MC-7270 power amp, while my c-28 is undergoing pro restoration for now. The Rose 150b has (10) pre-out level settings ranging from 100mv to 5000mv’s. Rose audio warns you not to set the pre- level output too high, because if set too high it can damage the input of both your preamp and your power amp as well.
Is there’s anyone who’s had or has a Rose streamer, please help me out with this one.
Happy holidays to all!

Hi diyers,
I would like to ask you for help on the diagram I attach.
I thought of the input buffer like this, because I have some selected lsk170 / lsj74 pairs on the shelf.
I would like to maintain DC coupling at both input and output.
If the signal comes from a preamp already equipped with a DC cancellation circuit, could I think about eliminating the input servo? or does the circuit itself require DC protection?
I haven't put values on the LP and HP networks but it will be a cut on 600hz.
I would like to try as shown in the diagram to use a small inductance instead of the usual resistance to decouple the output, could it work well?
In general, at the macro block level, do you think it could be correct?
I thank everyone in advance for any help.

Pulled one of power 1000 out of storage to repair it. It currently has irf542 for the outputs and they are still offered at digikey. Does anyone recommend a different fet with higher current rating?

Hi to All !
i have a big lack of knowledge about amps stability.
Assuming that an amp circuit is stable how could i know the effect of changing its gain on its stability ?
How a designer checks the stability of his/her designs ?
If there is a thread already discussing the topic please feel free to redirect me to it
Thank you very much indeed
kind regards
gino

Hello, i had an idea of making my own, Phono preamp and se if i can make it sound better then my current one (heed questar) it was around 450$ when i got it. I realy dont want to buy a kit, i want to learn about it and make my own, i will do alot of stupid mistakes of that i am sure, but that might be the best way to learn.
so i looked around on preamps from my own and up to 10K preamps and thought i might be able to get some insperation in design decisions. and i found Sutherlands phono preamps and found that they got some good reviews and the design looks simple when i look at some other designs.
They use two separate mono preamps,For power they use alot RC filters going from 48V down to 10-15v (dont know right now) then use zener diodes for each ICs to get it down to what voltage they want, (i thought that zener made some noise and might be bad to have this late in the chain? ) They use they use ICs INA103KP for input then OPA134PA and then OPA627AP for output, the OPA627AP is not avalible anymore though........ any ideas on a replacement ? if i am going with this design that is. what do you all think, is this a good or a bad idea ?

Hello been on audiokarma for awhile. venturing into DIY. I tried to reply to a thread regarding a Parasound HCA 22005A stuck in standby mode. I traced the problem to a bridge rectifer. Wanted to thank the original poster and I got sent here.

I have a Mackie DL1608 digital mixer with analog preamps with a weird problem.
The problem lies within the preamp circuit.
The hiss is common to all channels at very high gain, close to max all of the sudden a hiss appears, even without anything connected to the preamp.
Could this be mitigated or eleminated?

But one of the channels has a different problem,
With a mic connected if I increase the gain to the noticeable hiss zone and grab or excite (talk) into the mic, something that will light the signal led, it produces a kind of humm effect that latches and does not go away unless I reduce the gain out of the hiss zone.
I will post the schematic for the preamp

Any ideas?
I have swapped op amps U21 and U22 on channel B-1 with other channels and also electrolytic capacitors C142 and C230 but the problem did not go away or migrate.

Thanks for any help!

Hey guys, got stuck on a project.

I have to do a 100v pa system with 10 speakers. Got plans about wiring but the plans weren't very specific on how to wire them so I ended up wiring individually 10 speakers which go to a networking rack where a mixer with amplifier should reside. The real problem is I just found out that the attenuator(volume pot) has a built in 24v priority relay which I believe should be to bypass the potentiometer(in case the rooms set the pot to 0 an emergency broadcast should bypass that, i think). The plans do not mention another wire except for the feed to the speakers. In fact in the plans, it says that main wire goes from the amplifier to the speaker, and from the speaker to the attenuator.

My experience with pa is absolutely 0. Can someone please tell me if the 24v relay should be powered from another wire?
Are there speakers which would power that relay?

In the equipment list I dont have anything related to additional equipments to power that relay. Just speakers, attenuator, a microphone console and an amplified mixer. Google isnt helping at all and frankly there isnt any specialist in a 200 mile radius from my place.
To make things worse the cables are now covered with 2 inches of concrete. I can somehow pull new wires through the attic in case I need to.

I'm sorry i dont have the plans with me, to post a photo, will come back.

Hello.

I've been doing electronics on-and-off since I was five. I'm in my fifties now. I studied it at university but dropped out. Over the years I've designed and built a few projects, like a neat linear capacitance meter idea using op-amps (sadly I no longer possess it, or the circuit diagram). I've built a couple of amplifiers too. My first one consisted of a 2N3055, a loudspeaker, a 5k pot, a capacitor and a 6V battery. Nothing else! It did sound quite nice too, but the standing current through the speaker probably wasn't a good idea... Then I made one with an LM380 chip. It worked better but sounded worse.

A few years ago I developed a chronic condition which means now I'm stuck in bed and can't really do much without getting exhausted. Recently I remembered a funny idea I was playing around with for a MOSFET power amplifier design with more than five components. I had abandoned it previously, but still had LTSpice files, so started looking at it again. I won't bang on about it here, but I'll start a thread about it in due course.

Obviously, one thing leads to another and now I have an interesting design which seems to work in the simulator. I'm certainly not an expert although I suppose I'm quite knowledgeable in some areas. Recently I picked up Doug Self's Power Amplifier Design, which is great and quite useful. But of course during the design process, many questions arise that aren't mentioned in books, and even Google doesn't want to tell me about.

This site kept popping up though, and it looks good. I was quite reluctant to join a community (I'm not really a "people" person, and I don't need to tell you about the reputation that audiophiles have, hehe) but after perusing the pages I came to the conclusion that at least not everyone here is insane, so maybe it might work out.

So I guess I'll have some questions later on, and in a while I'll share my ideas too.

Hi, I have managed to find a schematic for the Copland CSA14, which has the same main board as the CSA28, but I am trying to solve a problem with the remote control board behind the front panel of my CSA28.
Can anyone help me source this please?

Folks:

I’m no engineer and could use some help. I’m building a preamp and would like to have a simple power off indicator. The preamp will have a 5VDC supply that is on at all times and a separate 5VDC supply that is only on when the preamp is “on” (i.e., not in standby mode). I’d like to include a front panel mounted LED that is only on when the preamp is in standby mode. Can anyone suggest a circuit?

Many thanks!

Regards,
Scott

I want a dig out (coax) upgrade to the Philips cd player CD-100 and CD-104 so as Revox B-225

Actually I want to get a I2S format. The splitting for left and right channel was already perform outsite of digital to analog converter device by the first generation cd player, i. e., there are definitly two dac devices in use.

Who knows a circuit for transforming the "old bus" (SAA-7000) signals
"STR" (Strobe) "DOL" (Data Out Left) and "DOR" (Data Out Right) to the I2S signals
"WCLK" (Word Clock resp. L/R-Clock), BCK (BCLK Bit Clock) and Data ?

If I have this, I can create a one wire SPDIF bus (Sony Philips Data Interface) respective DOBM (digital out bi phase mark) about the PCF3523P

Datasheets for SAA7000, SAA7010, SAA7020 and SAA7030 are to download about
http://tube.freeweb.hu/index.html

In this case I have found also follow informations:
http://www.diyaudio.com/forums/showthread.php?postid=659436
http://www.diyaudio.com/forums/showthread.php?t=54970&page=3
http://www.diyaudio.com/forums/showthread.php?t=85641&page=2
but unfortunately I haven't success to find weblinks about a glue logic schematic for diy.

Thank you for your advices

Hello everyone: I have been an audiophile since I can remember, but I am now finally starting to measure things electrical, not just acoustical. It seemed this is a good forum to join, to talk about such things. Who knows, maybe I will soon start building some stuff, too, not just measure my purchased components. Happy Holidays!

Hi,

I've been tinkering with electronics since childhood and now I have a bit more time, I have a few Guitar Amps that I need to fix. My challenges all revolve around TDA7293 output stages and smoke.

I'm looking for a circuit diagram that covers the power stage of the Behringer VT100FXH. The board inside is a LPA1100.

Has anyone come across a circuit for that?

Any help or commentary would be greatly appreciated.

Thank yo in anticipation.

Original Pass DIY boards and JFets, fully populated and working. Slimline 2U chassis.
It was my only phono stage for several years, but I have just built Pearl 3 so it is time to let it go.

SOLD

Hi, I started tempering with simple electronics and assembled a few amps from pre-made boards in my high school years. In the last 40 years I have followed the audiophile communities, owned many components and do minor modifications to them. In the past 5 years or so, the mods are more and more serious with the help a number of Youtube channels. I have been following this forum for over 9 months now, read all the articles by Nelson Pass I can find, and have just completed a F5M in dual mono configuration. Plan to build a more amps of various power.

I have old electronic devices with use aluminum electrolytic capacitors and manufactured in the early 90s and early 2000s and my home conditions temperature of 33-36C, humidity 57-67% and energized devices at 220v AC 60hz if I energize all these devices under these conditions for 1 hour (60 minutes) what is the maximum interval and frequency to energize them again and prevent failures in the aluminum electrolytic capacitors caused by disuse?

I have CRT TVs 29" Philco and Toshiba, consoles Snes JR, Snes Fat, PS2 Slim 90000, power supply 5v and 12v, tvbox T95 Max Plus, DVD Drive Sata internal

Hi everybody!
With Brian Steele's spreadsheet published many years ago, I calculated the volumes of rear and front boxes for a bandpass subwoofer with the specs of the Dayton Audio UMII8-22 subwoofer. I found a nice option for Qbp = 1.0 (1.25 dB ripple) and S = 0.5, that requires Vf = 4.73 L (0.167 cubic feet) tuned at 61.3 Hz and Vr = 10.82 L (0.382 cubic feet). I apologize for not translate to English the texts in the spreadheet.
I also simulated the design with LTspice and got with agreement with those of the spreadsheet.
My main worry are the dimensions of the vent of the front box: 2.5 cm diameter and 6.5 cm long, that agrees with the calculation for a Helmholtz resonator. I will not try a bigger diameter for the vent because the length results too big, difficult to accommodate into the front chamber of box-
I would like to read your comments.
Kind regards.

A few weeks ago I received the two 1 kVA Avel Lindberg toroid transformers for a pair of monoblocks I'm building. I was hoping to find ready-made drawn metal cans in which they could be potted. There was one manufacturer that sourced such cans, but there was a considerable tooling charge plus a rather high per unit cost. While there were many such enclosures listed on Ebay, none were sufficiently wide. So I decided to fabricate enclosures in my shop. The vertical sections consisted of 3.25" x 7" OD x 0.125" wall thickness 6061 Al tube, while the top was fabricated from 0.125" 6061 sheet. The 7" tube presented a challenge to hold in the jaws of my lathe chuck, and I ended up having to grab the tube from the inside. I wanted the top covers to not have any tooling holes, so I bandsawed the covers approx 1/8" oversize and glued them onto a plywood base that was bolted to the lathe faceplate. That worked fine, but ungluing the finished Al cover proved a challenge, requiring a torch to soften the glue. The tube and Al disk were then glued together and put back on the lathe for a finishing pass. Three holes were drilled near the bottom of the tube section to accommodate grommets for wire egress, and then the grommets were then filled with silicone adhesive to prevent any potting material from leaking.

The inverted enclosures were placed on a level table (3 bolts on a 12x12" piece of plywood were used to make the leveling surface), The center of the transformer has a micarta insert that provides more reliable thread holding than tapping into the epoxy. For potting compound I selected Epic MPC epoxy which has a very long cure time permitting deep pour depths without the problem of a runaway exothermic reaction. I found the compound difficult to get a consistent cure even when carefully following the provided instructions. However, after a week the epoxy finally hardened. The final step was to cover the enclosure bottom with a thin self adhesive sponge rubber sheet.

The next step will be getting the PCBs back and starting to wire things up.

Or similar for a 4way xover

Does anyone know the part number for the phase switch on this amp

After this particular model. Not interested in the Renaissance, I already have one.

My beloved husband of 21 year, Carleton Howard Huff, has passed away on October 30, 2024. He was the kindest, smartest, most loving human being I ever known.He often talked about how much he enjoyed this forum, interacting with people from all over the world and learning new things. Thank you for sharing your life with me. I will always love you and cherish all of the wonderful memories we have together. This is not a goodbye. It is until I see you again.
Your loving wife as ever, Elena Huff

Hey guys

I recently started working on my M125 tube mono blocks from Tubes4hifi after I started their rebuild about 4 years ago. These were previously working but being the first amps I had ever made the wiring and soldering was a bit crude and I decided to start over. These amps are now offered without the triode/ultra linear switch and I would really like to bypass that switch as I'm rebuilding these to clean up the wiring inside.

I have tried reaching out through the Tubes4hifi website but I'm not getting any response. If anyone would be willing to help guide me on what to do I would appreciate it!

Using the Material skin.. About %70 of the artist images are incorrect. They usually start out incorrect in the normal Daphile WebUI as well. However, that seems to sort itself out after an hour or so. Not so on the material side. Nothing I've tried fixes it. Deleting cache on chrome (desktop and phone) gets it close. There is always still a few incorrect and or double still. A rescan can make it a little better, or just **** it up again sometimes. Even starting from fresh install... multiple times.. does nothing 🙁

I am using a custom dir with my preferred artist images.

Something else. Minor, but I cannot make the setting for "Database memory config" stick to Max. It always reverts back to high. Actually most of the setting in the performance settings page fail to stick. Server or complete hardware restart does nothing.

I also have a question. What is the RT version of the distro for?

Cheers 😀 😀

The attached image shows an example. Been farting around with it for 2 days now. So unbelievably annoying :'( 😡

I'm wanting to build the 3 way speakers that I will add to my system. My question is with tuning frequency(s). I have a sub already and ideally it would handle anything 100hz and lower and the woofer in the 3 way would pick up from there. So i guess my question is, do I tune the woofers enclosure for 100 hz or to where I want the mid range to pick up. I hope that makes sense. I've never built anything but sub enclosures. This is a whole new thing for me and I'll probably have more questions as the design progresses. Thanks for reading

I know just enough to be dangerous with tube gear so I apologize if these are stupid questions.

I have an Inspire KT88 Firebottle amp by Dennis Had. It is a single ended pentode amp with the screens of the output tube regulated at 260 volts. The voltage on the plate depends on which rectifier you use. This configuration allows you to use a variety of output tubes ranging from 6f6 through kt88 by using rectifiers like 5y3, 5u4, 5ar4, etc. It uses automatic bias and is not user changeable.

Naturally I have rolled a bunch of different tubes through it. Saw the El38, heard it was similar to a KT77 which is compatible with this amp, put it in an adapter and fired it up. Sounds incredible, amazing detail, bass is super deep and controlled, deep soundstage etc. A week later I read that the el38 needs half the bias voltage of an el34 and I’m bound to be killing the el38 with cathode bias set for a reasonable setting for an el34. That does explain how bright they were glowing and the amount of blue they showed…

My question is why they sound so much better than other tubes I have put in my amp. Presumably if I replace the cathode resister to a value better suited to the el38 the sound will change as well. Is there a way to figure out the secret sauce of the el38 and output transformer so it can be replicated (as closely as possible) with another tube? Thanks.

For sale is a used 1 input, 8 output unbalanced to balanced converter.

This was taken from my spare Najda unit as I will not have a use for it.

Just wire up the signal feeds, 12V and signal ground.



Chassis mounting screws included.

Seen here installed with Najda 1 analogue input, 4 analogue channel output





This shows where Najda supplies the 12v and signal ground connections



I don't see why it cannot be used with any suitable preamp or DSP unit.

Item is in the UK
Asking £90
Can post worldwide. Ask for postal prices.

Greetings from Italy!
I've decided to make a PCB based on the JAT501 project, I did a bunch of tests on a prototype PCB (mono) and the results are stunning, so I've designed a final PCB which incudes two mono stages and the power supply rectifying stage.

I think I would take the BD139 (voltage amplification) out of the PCB and and screw it to the heatsink, so it can be termal coupled with the 2SC5200 and the 2SA1943. Do you guys think it's a good idea? Instead of using a single heatsink like the ones used on the drivers stage (BD139-BD140)...

Here is the PCB:

I am passionate about everything that involves electronics, components, audio, video, I like to learn from the most experienced and turn my learning into practical repairs on various types of devices. I hope you accept me on the forum. Thank you.

Hello.


Does anyone tested Monacor MCE-4001 microphone? I'm wondering if it could be good replacement for DIY measuring microphone instead of WM-61.


Thanks!

https://www.aliexpress.com/item/1005006371486253.html?sourceType=1&spm=a2g0o.wish-manage-home.0.0

https://www.aliexpress.com/item/1005008151075975.html?sourceType=1&spm=a2g0o.wish-manage-home.0.0

https://www.aliexpress.com/item/1005008187492467.html?sourceType=1&spm=a2g0o.wish-manage-home.0.0



They look really handy.

I've managed to get this old Alps rotary slide switch apart and am wondering what the best solution to cleaning the contacts would be. Looking at how tarnished they are I'm guessing they are silver or a silver alloy?
I tried contact cleaner, which helped, but I was still seeing an inconsistent .3 to .7 ohms across the contacts which is why I took it apart.

Hello to All!!

A few months ago I started trying to give new life to old devices. This has helped me learn a lot and above all, do not be discouraged by the first difficulties

I have found this forum with interesting and necessary topics for my work. I hope to learn from you and contribute with what I can.

Syrck!

I have been wanting to build an amplifier and a set of speakers with each of my children as a graduation present, and wanted something with low parts cost, low distortion and a great reputation, so I was very excited when I read about the new(ish) F5M. I have enjoyed developing a physical layout and circuit board suited to my project during the past few months, but I am not an electrical engineer or designer - so I created this post to solicit feedback, document a test build and ask questions. Basically, I will need some help. The amp pulls together known designs onto a single circuit board and is housed in a custom chassis. The elements used are:

• F5M Amplifier Circuit
• F5M Power Supply Circuit
• Relay Input Selector (similar to Salas iSelect)
• VSPS Phonostage
• Whammy Regulated Power Supply (used for phonostage)

(many, many thanks to the designers of all of these circuits)

The details are best seen in the attached .pdf, but here are a couple screenshots:





After considering feedback and making updates, my next step will be a test build with the 300VA shielded transformer and heatsinks pictured. One of my biggest unknowns is putting the phonostage in the same chassis as the main transformer, even with a shield, I don't know if it will "hum", but the test build should answer that. After that make final updates and build with the kids 🙂

Hello all,

Hope you are doing well! I look forward to exploring this community. I am a local guitar amp tech in Greenville SC.

I have been working on amps for a few years now part time. I've learned alot and always enjoy a challenge.

I was recently contacted by a Widow out of Wahalla, SC. Her husband was a Tube amp enthusiast. I went there with not much Money in my pocket, and when I realized the quality of the collection, I informed her that I could only afford pieces of it. She then stated a price that I could not refuse. After a trip to the ATM, we started loading up the collection.

It is... incredible. I've never seen such quality engineering in my life. These pieces (amps) look as if they came off of a factory line. Every wire is so cleanly soldered, and each design appears flawless. I'm using them actively as well, and they add a really cool aesthetic to the room.

Here are some photos of these Amazing pieces:

1. This is the Green God. It's a small output EL84/6BQ5 powered Hifi amp that I use for my CRT Tv's stereo (since my old 1973 CRT Chromacolor sound board went out). It has a 12ax7 preamp.. which may have originally been a 12at7. 6ca4 rectifier I believe... though I could be wrong. The tube does not have any markings showing the type of rectifier it is.




2. Next is this Black Beauty complete with transparent underside. I have not tested this one. But it has a 2 dual triode 6eu7's and quad EL84 outputs.

3. Next is the "Alien Amp" which uses an 832A POWERAMP. I've NEVER seen this type of power amp before. Apparently each tube has two anodes, so it's kind of like have a quad. The preamp is composed of two 12at7's. Trusty old 5u4 supplying DC.

4 & 5 Next are 2 KT88 Hi-Fi amps I have. They appear to be identical. One has tubes. The other doesn't. I believe the preamp is composed of 6SN7's.. again, tube rectified, this time a 5y3.

6. The next amp is what I call "The Beast". I cannot guess the wattage... but am surprised it's not powered by a Quad considering the output transformer and power transformer size. I have NO IDEA what type of tubes this takes. I'll need to take off the bottom and find what the tube pin-out's are and compare them against known data sheets. It appears to have two inputs.


Also... what is that tiny circular screen??

You can see the amp has a rectifier, one preamp tube, and two power tubes.. probably KT88 or potentially KT120.

I also received alot of parts.... High end EDCOR transformers of all sizes... Dynaco transformer pairs... Tubes of both NOS and new name brand excellence.

I have the parts overflowing on 2 four tier shelves. I've sold a few desirable tubes that I've found.. but have kept the rest because it's such an excellent collection.



The builder's name was Michael Werner... I'm sure he was on one of these forums.. Do any of you know of this builder?? Perhaps there are threads that encompass the details of these builds??

Let me know.

Thanks for letting me introduce myself!

-Low

Hello, I am totally new to amp building and have zero electronics experience. Built the Camp Amp and enjoyed the process. Now doing the ACA Mini Max.

I got an SA-15 amplifier, which I want to restore:


The previous owner unsoldered many parts from it for his own needs, such as potentiometers, capacitors and the audio amplifier chip itself.
I managed to determine the approximate amplifier chip by the pinout on the board, it is AN7161N, and accordingly those capacitors that should be installed with it.
Now I need to determine the remaining capacitors on the board, but unfortunately I could not find any similar diagram on the Internet.

I only found a photo of a disassembled SA-25:



The PCB is exactly the same, but it does not show what potentiometers and capacitors are there.

Maybe someone has the same SA-15/SA-25 amplifiers or their diagram?

Hey there. I'm a new member working on setting up my home theater but a little lost. Found this community and was hoping I could solicit some help from the experts! I'm sure my problem is common. I'll continue to search the forum but it's hard to find solutions when you don't know the words to look for. 😆

Thanks for running the community!

Hi there,

To introduce my self in acoustic way, i'm passioned by speaker and whatever in touch with quality of listening. I work as an acoustic method technician for one of the greatest French pro speaker company. I used to built HI-FI loudspeaker and now i'm specialized in quality control and quality test.

Hoping to learn a lot and help by my knowledge.

See y'all.

I have a local unpopulated cap location near the + and - 12v supplies to NJM 2114 opamps (analogue out)

Panasonic left them unpopulated and I am thinking of adding a 0.1uf cap. I have a few in mind (not much room as I will need to lay flat under board 7.5mm clearance)

I have already fitted a 10uf tant here with good effect (increasing dynamics marginally) as the power is coming from a low noice LPS this is more about what might be worth adding in parallel

Thinking TDK 0.1uf ceramic X7R or WIMA MKP, possibly Kemet SMR

I can happily try all over time I have tried a WIMA MKS marginal too marginal to tell. I didn’t like a DME 0.082uf orange drop sounded a little lean and slightly edgier

Any recommendations or thoughts

This is about sound quality no problem to solve or any other reason than it might be better with another local bypass

I can see Panasonic did fit a ceramic on their Japan version but no details uncovered