Really long story....in short

Amp came in with blown up capacitors in the class D output filtering, the ones 1uf 400v between the output terminals and ground. 10ohm 5W resistor was in bad condition too.
Replaced those.
Amp now has DC offset of approximately 20v which can NOT be fixed by the trim pot, it can fix only 1-2-3volts of difference not more. It plays, no protect, class D switching is present, but as You can imagine having 20v DC on a speaker = not good.

Seems like one of the amplifiers, in RED (it is full bridge class D) works with 20v-21v LESS than the other one in BLUE. These are the only differences I found between both amps driver IC's, pictures are attached. What I understand....when having a 150v rail, there should be aprox. 75v at each output terminal....now I do have 85v at the one and 65v at the other....not good. Connecting a load does not change the DC offset. How to fix this disbalance ?
One of the amps in this full bridge, the one in RED, with less voltage present, the low side outputs are warming up. 1 minutes of idle = 60-70degrees, high side stays normal/cool.
So i've put my effort in this RED "amp" where the heating up is happening, I do use the other one BLUE "amp" as a reference as it's not heating up.
What i've replaced so far - IRS20957s, both buffers (the 6 pin drivers), all of the 15v zeners, all of the MUR120 diodes, all the resistors near the driver/buffer, IC, zeners, all of output transistors. Parts are from reputable source. So even after changing all of this, there is NO single difference. It is exactly behaving the way it was before doing any work at it.

Any ideas ?
I will attached some of my draft measures.

Hello

After 14 years I decided to replace the supercap for my Denon AVR-1910.
It's a 1F, 5.5V Elko.
I just want to let you know what my measurements showed:

The capacitor now is loosing about 1V per day.
So, after 5.5 days it will be near to 0V if not charged.
The memory for the settings probably is lost earlier - I don't know it's critical voltage.

I hope this gives you a clue as to the ageing of these supercaps.

Best regards

Hello everyone.

I want to replace my midrange speaker. Now I have an audiotechnology 18H52 17 06 cut at 300 and 3000 hz with a slope of 48db. The cut is digital with Dephonica software.

My candidates are the Purifi, but I don't know which model to choose.
PTT4.0M08-NFC-01
PTT4.0M08-NAC-03
PTT5.25X08-NFA-01
PTT6.5M08-NAA-08
PTT6.5M08-NFA-01

The upper cut must be a minimum of 2500 since I have a Raal 70-10. The woofer is a TAD1603 and can be cut higher than 300hz if necessary.

The impedance must be 8 Ohm.

The aspect that I value most is the detail.

I'm open to other speakers in that price range.

Thank you so much.
Greetings

Hi fellow audio addicts,

I simply like good music of many different genre - preferably played on a (very) good system.
I've been bitten by the audio bug when exposed to better systems in a high-end show a long time ago - and it's been itching ever since.

I think there are levels of involvement in home / personal audio:

• There are people who do not hear the difference between systems or they just do not care. From finance perspective, they are certainly the luckiest.
• Then there are those who can hear the difference but still do not care much. Even luckier, I guess.
• And finally those who can hear the difference and are vexed by anything inferior to the best that they have heard (which is of course, subjective, But that is fine, hearing - intricately refined as it is - is still subjective).

To my demise, I was mesmerised on the first hifi show of my life and - pleased by the revelation - immediately concluded that I have to have a B&W CDM-1 or build something from Vifa drivers. Lack of time led me to the B&W CDM-1.

I saved up for it, ordered it, took it home intoxicated by the fact of possession. Adrenaline rushing, I hooked it up with - I think - an UHER receiver, a Technics CD and some shoelaces made of copper ... aaaaand ... was of course taken aback by the lack of musicality or detail. "Not in the same league" is an expression but the experience wasn't even on the same planet. So starting off with an emotional rollercoaster, my journey begun and fortunately hasn't ended till today.

Since then, I've been walking the El Camino of hifi enthusiasts, going step-by-step, stocking up a few of everything. Never (ok, rarely) regretted any of it, I've always learnt something, getting closer and closer to the goal that can never be reached.
I've achieved an acceptable compromise years ago (with an actively driven biamped electrostatic speaker and able amplification (partly DIY), good cabling and sources. It did cost money of course - may be considerable - but it has never wrecked the family budget. I'm quite keen on getting a good price-performance ratio.

I'm more into DIY experimenting nowadays, currently after good desktop speakers that I can listen to while in home office. A small Fountek FR135EX project is on the way, but more to come, if circumstances allow.

All the best to the community; may your journey be enjoyable!

Hi all,

I am trying to fix PA system. I would like to know what is the use of pot p2 in the drawing attached. I tried to replace all the output mosfets and audio IC with some small resistors. Amp started to oscillate good. But after a while outputs blows.

Hi Everyone -

My brother's Forte 4 lost the left channel after a power surge. I didn't have much for diagnostics while travelling, so I did what any responsible little brother would do... I gave it a VERY brief once over ... found a dud negative rail fuse... didn't see anything else suspect ... replaced the fuse ... and powered it up. The left channel came back up / warmed up.

I didn't have proper tools nor schematics while I was on vacation to do an in-depth review of the amp. I saw that it warmed up, and that the offset was <20mV. I sent him on his way. So, when he got it home, he hooked it up. The volume was lower on that channel, and then the replacement fuse blew after a few minutes.

So, someone with the proper tools and the schematics / service manual will need to give it a look. I had John Soderberg go through it many years ago and do all the updates etc. I can definitely send it back out to John if necessary.

However, I sent it to John before I ever became active in DIY. I'd have my brother send it to me, but I don't have schematics or a service manual. Also, if any of the parts need replacement, I may not have easy access to replacements.

Plus, it's is pride and joy (as it should be). So, I'd prefer to have someone that knows these amps go through it.

tl;dr - Does anyone know someone they'd vouch for in the Western NC area (near Asheville) or within a few hours drive that could repair the amp? If not, I'll have him send it off to John.

Note - My brother found https://ncstereoman.com/info/category/home/page/3/

Heck if any of you are willing to give it a looksee, I'd be more than grateful.

Thanks in advance.

Figured I should go ahead and start contributing since I've learned so much from this forum. I mostly work in the PA speaker world, but alot of my work overlaps with the DIY space having ran a custom built soundsystem for the last few years.

Hypno Tised AD797 boards, NOS.
$20 plus postage.

Hello!

I would love to hear your opinions on a project that I have in mind, which, however, may not make any sense at all... and feel free to tell me if that is the case 🙂

I am remodeling my sub-terrain wood workshop, and there is a hole in the floor from a previous heater installation, here is a close-up of that hole with its dimensions (ca. 1.5 x 2 meters, 0.5 meters deep):



It's all cement, just like the workshop floor itself. But since it is uneven, the plan is to cover the entire cement floor with a wood plank floor (leveled, sitting on shimmed beams).

But when I thought about something useful to do with this hole, the best idea I had was (at least so I think), to put a subwoofer in there.

I have two 18" McCauley 6174, which are left over from another project. For these I am planning to build a large subwoofer box (according to their T/S parameters).

Now my questions are:

• Does it make any sense at all?
• Would two much sound get lost, with the speakers under a wooden floor? Maybe cut slots into the wooden floor?
• Should I worry much about dust, and maybe build the box in a way that the speakers are not directly exposed, maybe a bandpass design?

- If all else fails... any better ideas for this hole? Here is a drawing of what the finished workshop shall look like, the whole is under the long workbench, where the dimensions are still drawn:



Thanks for any input!

Hi

Does anybody know what is better to choose for a High Pass Filter (Mic Preamp):

Big Capacitor value, small Resistor value?
or Small Capacitor value, big Resistoe value?
Or use as special Resistor value und adjust the Capacitor for the needed Frequency?

I don't have the Tools to check it by myself at home. Otherwise I would try and measure by myself ;-).

Best regards
Lukas

SOLD.

This is a package deal for a brand-new silicon nitride bearing ball and Woodsong Audio Torlon thrust pad for your Technics SP-10 MK I or MK II turntable.

I ordered several thrust pads from WA (the only supplier at this time, I believe), and several new balls to supply a few friends and myself for the turntables we are all servicing/rebuilding. I have one remaining set and am making it available to you at a discount. WA sells the thrust pads for $50 and the balls cost about $5-6 each.

Your price is SOLD including shipping in a padded envelope and PP fee (only within the continental US due to the hassle of Customs forms and higher shipping costs).

Selling a matched pair bought from Tube express and unused. Logo is different as it was changed in that years. One tube is 9.5/13ma the other 9.7/11.5ma
Years 1966 and 1972.
Price 190 Eur shipped in Europe.

Boxes are almost destroyed as you can see from picture.

Hello all , long time in the forum but never wrote or post something.
First of all forgive my bad English , maybe that can be the reason I haven’t interact up until now but it seems I’m in a “dead end” and I need a little help, even some guidance .

So I’m all Sansui enthusiasts and I’m running a 3way active set up with AU-X11 amplifiers and a CD-10 active crossover. All equipment is fully restored and are running smoothly.

My drivers are :
Tweeter : Scanspeak 28mm Dome D2905/97000
Midrange : Morel soft Dome EM 1308
Woofer( subwoofer as described in their website ) : Visaton 8” TIW 200 XS in 30Lt cabinet .

I want to “up” my game at the low end, god forbids I have no complain from the Visaton driver but I think I need a 10” woofer …..
The Visaton in the 30Lt cabinet is tight, full and precise even at the lower volume level , I’m looking for a driver that can perform a bit better and match the quality of the other drivers .

I can not go bigger than 50lt but my budget can be high , not because I’m a rich guy but building speakers is not hobby and most likely those speakers will follow me for the coming 10 years .

Any suggestions will be much appreciated and thank you in advance for that .
Again… sorry for my bad and poor English.

Hello everyone,

I have a David Clark (H9940) headset with the following pin configuration:
https://www.davidclarkcompany.com/files/partslists/pdf/PL19539P-95.pdf

• RT ear
• Ground
• LT ear
• Sens
• Mic Hi
• Mic Low
• Shield

I want to convert the analog output of this headset to a USB connection. From my research, I understand that I need an ADC board like the Behringer U-Control UCA222 to accomplish this.

My plan is to wire the pins from the headset to RCA plugs that can connect to the UCA222. However, I'm looking for some guidance on the specifics:

1. How should I wire the RT ear, LT ear, and ground to the RCA plugs?
2. How do I handle the microphone signals (Mic Hi, Mic Low, and Shield) in this setup?
3. Are there any additional components or considerations I should be aware of to ensure proper functionality?

Additionally, I know that the headset requires external voltage and impedance control for the microphone to function correctly. Could someone provide details on:

1. The required voltage levels for the microphone input.
2. How to implement impedance control in this configuration.

Any advice, wiring diagrams, or tips from those who have done a similar conversion would be greatly appreciated!

Thanks in advance for your help!

Hi,

I'm looking for the FETs mentioned in the title. Pairs prefered, but K246Y only are also from interest because I have some J103Y in stock (but only K246GR). Please offer me with shipping to Germany. Thanks!

Thanks to Schmitz77 for sparking my interest on the subject,

I am still fascinated by unusual tube circuit (read Shindo) I started collecting various tube configuration of EF86, EF80 circuit.

The first circuit comes from this thread posted by Schmitz77 :
https://www.diyaudio.com/community/threads/cathodyne-tube-line-pre.355172/

I went a little further and made a ltspice sketch and sim



FYI this is only the line stage, I'll concentrate on the phono stage later.


The most valuable info came from Stereophile, as Mr Dudley wrote :

- "The C3m is also capable of very high gain, but Ken Shindo puts it to a different sort of use: In the Vosne-Romanee, the Siemens tube functions as a resistance-coupled phase inverter, the output of which appears across the anode and the cathode."

- "The now-balanced signals for the left and right channels are directed to that pair of vintage output transformers, with DC blocking along the way by those large, lovely, and similarly ancient Sprague oil caps."

- "We brought up the volume just to the point of clipping and noted an output of approximately 5.5V RMS (which translates to just under 8V peak, possibly explaining the output level spec provided for the V-R on the Shindo site)"


From a theoretical standpoint, the split phase phase inverter comes from this reference (chap 10, page 217)



Anyways, I'm thinking building this project in the future and I wanted to know if anyone can give me some pointers on what to look for next,

I did a simulation on the frequency response, and I don't think it looks right,

Have fun fellow DIYers!

Oli

(I can link the EF80 and C3m Ltspice data I used for my schematic)

This topic came up on another thread about the best 1” horn drivers. https://www.diyaudio.com/community/threads/best-1-compression-drivers-compact-1-horns-2024.410465/

Then marco_gea posted “The answer is still the same... the "best" is still probably: https://www.proaudiodesign.com/products/tad-td-2002

So at $3,000 a pop I was wondering how expensive can an ECONOwave be? Aside from custom shop work or one time productions, what are we looking at for cost is no object two way horn tweeter loudspeaker?

Hi, I am from India and mostly interested in Vintage audio. I have several Sansui including 717,919 and a couple of alphas. Looking forward to learning from those in the forum.
Saurabh

What's the best USB-I2S for DSD?

So originally, they were going to keep the tower speakers shown to the left and right,……..but now they would like to eliminate them and integrate the mains into the enclosure. This is a modular built and the 70” screen is on an electronic lift that lowers into the cab when not used. For reference, the enclosure is 75” across and 34” tall. I REALLY don’t want to go back to square one with this and I’ve convinced them to add two thin line sources to the sides of the screen that will attach to the lift………but that creates a new set of challenges as I’ve only got 5.5 inches to work with on either side and 4” of depth!!!

I‘d like to scratch my own itch and do something OB/dipole…….there‘s nearly 8 ft of space behind there with a stairwell…….an OB would really make for an incredible soundstage…….but I’d need the OB to play down 60hz or so to blend with the subs. How am I gonna do that OB limited to 5 inch woofers?

FOUND RHEEM CALIFONE 1908 AMP NO INFO OR MANUAL CAN ANYONE HELP

Hi diy crew, my name is Matt and I live in Australia. I have been into music for years but only recently have gone down the path of replacing components in my tube amp. I look forward to learning some knowledge from you all.
Matt

Remember this guy?





I have never seen schematics or tech info - nothing at all. And I've been looking. If anyone reading this has info please post it here, especially schematics. Thank you.

Excellent condition Grade 0 THD+ with Thermostat board installed. $200 USD

Dear All,

Can I make a petition to make available the following front panels from the DIYAudio store or modushop not only as part of a kit ? I made several projects with the 4U chassis and those will really give a wonderful look and give the right cretid to the designer.

https://modushop.biz/site/index.php...ct&search=passdiy&syclid=cqf3er4om04s73fng5o0

Regards,

D.

Hello dear DIY Forum members!

As a new member, I would like to introduce myself. My name is Gerd and I live on the southern, outer green belt of Cologne, near the Rhine.

How I found the DIY Audio Forum – through reports/articles about Mark Audio speakers.

What have I planned? And that would almost answer the question of where a decision-making aid would not be bad:

I intend to build a reflex shelf speaker with a Mark Audio Alpair 10. 3 with the sonic orientation of a monitor speaker which displays clean 48 - 50 Hz.

Thanks for the tips!

Kind regards Gerd

For sale pair of DT-99. Came in a pair of DIY speakers I bought off eBay and seem to be pretty much as new. Both measure same DCR.
Look like new . Not boxed but I will find a suitable box for them. Probably a tweeter box from SB or similar
£25 plus postage
Thanks

New in box never used. I seem to have been sat on these for a couple years but they might as well go. I have a few RS225s which are my chosen 8" now.

Postage on application, will be at cost. Come in original boxes and packaging.

Sell the pair for the price of 1 new.
£115 plus delivery .
Thanks

A pair of these for sale. Barely used. I went with MCA15 instead as needed purely mid range. One has OE box but for some reason I've misplaced the other. Has the original plastic guard to cover the cones. If I find the box obviously shall come in that.
I managed to nick the surround of one of them. Don't ask how. It is barely visible and if used as a midrange it wouldn't even open up . I put a small amount of PVA to heal it and it is nigh on invisible. Took me ages to find it to photograph. I'm confident it is of zero concern.
£60 plus postage

Pair of these dome mids for sale. Came in a pair of DIY speakers I won on eBay and I haven't done anything with them since.
Pretty much as new
£60 plus post

Pair of tweeters for sale. Bought off a gentleman on here along with some Seas MCA15RCY.
Didn't use them in the end. They have been used and soldered previous to my ownership
Both measure 4.8r
£45 plus post.
Thanks

I removed the digital filter from my Philips based CD player in order to do the NOS mod. All is fine, but now there is no SPDIF output. So far it wasn't a problem, but now I want to try an external DAC. Any ideas?

If you have any general feedback on the store or its products please post them in this thread. Thanks!

Hello! I greet and thank in advance all the participants who contribute and enrich this community.

Mainly I have been reading everything related to streamers, Ian Canada....

little by little I am improving my system... and always looking for information about possible improvements.

Greetings

This 2200 has been quite problematic. I have done my usual upgrades (www.quirkaudio.com), and in this case I have been chasing a set of problems on the left channel.
The current state is that all electro caps have been replaced all the transistors from Q201to Q333, and Q327, Q325 and Q331 have been replaced as have a number of diodes, including D309/D311 and D301/D303, so now the unit comes out of protection, however Q305 gets very hot meaning their is excessive current draw.

Q305 is now a KSC3503D, which I have used mnay times here.

On measuring R307 there is 0.7v across this resistor, whereas on the right channel on R310 it is 0v, and across R303 there is 0.29v, whereas on R304 it is 0v. On R377 there is 0v the same as R378, so my assumption is that the problem is not on the output side. All the main outputs test fine, Q311 had a low Hfe and was replaced with a new 1302.

When I measure across R331 I have 1.5v, whereas on R332 it is 0v. The two reference points at D309 and D311 should be +1.77v and -1.77v respectively, whereas they are 2.2v and -1.5v. The base of Q211 is 8.7v and all the other voltages on the circuit are correct.

I have attached the circuit and any thoughts are appreciated- this has me quite puzzled.


Peter

In recent threads:

https://www.diyaudio.com/community/...crossover-frequency-in-the-near-field.401809/
https://www.diyaudio.com/community/...er-w-pd-21-drivers.402264/page-5#post-7433034


there is some discussion of the benefits of side-firing woofers. So I thought I would describe a recently completed build of mine which employs this method of woofer mounting. I have borrowed ideas from past commercial loudspeakers such as the AR9, NHT 3.3, various vintage Allison Acoustics models.

These are the features of my build that are unusual from a typical commercial enclosure:

1. Separate isolated sub-woofer enclosure, with reaction cancelling drivers.

2. 2” edge round-overs for diffraction effects control.

3. Low sub-woofer position for enhanced room boundary bass re-inforcement.

4. Tri-laminate layer (mdf/mdf/hardboard) 1.25” panels for increased rigidity.

The drivers chosen are:
sub-woofer 8" SB23MFCL45-8 (x2 in parallel), mid-woofer 5” SB15CRC30-8, upper-mid 4” SB12MNRX2-4, tweeter SB26STAC-C000-4.
I have a great respect for SB Acoustics drivers. They have great build quality, good performance and are affordable. My previous builds have used ScanSpeak drivers, but ScanSpeak prices have increased beyond my comfort zone for DIY, and I find the SB range comparable in performance. The SB drivers are affordable and offer a wide range of cone materials in the same driver format so that they can be compared to decide on a preference.
The 4” SB12MNRX2-4 upper-mid is the only dedicated mid-range driver in the standard SB range, with shortened voice coil and linear travel compared to their 4” mid-woofers and is suitable for a 4-way, where it can be high-passed crossed over well above the bass frequencies.
The 5” SB15CRC30-8 mid-woofer was chosen after comparing listening tests with the Norex and aluminium cone versions. The cone material is a Rohacell/carbon fibre laminate.

The upper enclosure is a compact sealed 3-way, decoupled from a sealed sub-woofer enclosure by 50mm diameter Sorbothane hemispheres. The chosen dimensions keep the tweeter-floor height at 1m, which is right for my listening position.

Hello, long-time lurker first time poster. I found this awesome forum while searching for pieces to fix a couple busted amps I picked up at a local garage sale. Well, they are busted now anyway! I'm using one as a plant stand and another as a platform to learn about solid state amps. I am enjoying the hobby so far. Currently stumped on something which I'll post about over in the solid-state forum. I'd like to get it working, since I already have a plant stand.

Best regards

I notice any time I try to design a bandpass filter wide it starts to sag in the middle. Is this just the nature of a 4th order bandpass filter? I have to go up to a 6th or 8th to avoid the sag?

See purple oval in the filter section.

I found this to be really elegant in its simplicity. I've attached the image of and the .dxo as a zipped file. He used it in a series xover on the former Epique 5.25" in a large 3way.

What I did:
Took full measurements of my 3 including this Peerless 8" woofer here.
Took near field of woofer
Took near filed of port
Took far field of woofer
Aligned near field measurments SPL to the near field SPL so that I can use the far field measurement for my crossover design (mic never moved between measurement of the other 2 drivers so this should keep the SPL and phase aligned for crossing over purposes)

What I don't get:
1. I kind of understand the giant rise from the port as expected something like that but this seems excessive
2. Why the woofer near field starts to rise up dramatically as well around 100 hz

Is is possible that the port output leaked into the woofer near field measurement? Is is literally about 5 inches below the woofer and this would explain a lot

It is also VERY possible I do not know what I am doing with REW. If so, please let me know. I am very good at following directions and I tried very hard to follow the REW directions to the letter.

One last question..... Do I need to combine both the nearfield woofer and port measurements to accurately crossover the woofer with the mid? I would think the port acts almost as its own driver so its response would need to be added to that of the woofer, yes?

Sorry a bit of a long post but need to get some knowledge from the group before I spend too much more time on this.

I have taken a set of baseline measurements of my 3 my speaker in an anechoic chamber (chamber has a null at 60hz but above 200hz there is no need for gating, very clean data). The measurements taken were -

• Microphone at the same position for all, 1m from centre of baffle at tweeter height.
• I had the acoustic timing bleep turned on but this was played through the driver being measured (now I know that you need a second speaker for this to work properly, doh !) therefore all measurements start at 20ms which seems to suggest the data has no acoustic offset built in, is this correct?
• I measured the Woofer (WO24P-4, 40L sealed stand mount monkey box), Mid (EM1308, includes a 39uF protection Cap) and Tweeter (ET448, Includes a 12uF protection Cap) at +/-90,75,60,45,30,20,10,0 degs on the horizontal axis. I did meaure the Mid and Tweeter withouth the protection Caps as well but will be running an active system with them included.
• I also measured the individual drivers and also driver pairs (woofer/mid, mid/tweeter).
• Finally, I did some nearfield measurments for the woofer both on tweeter axis and the woofer axis at 1cm, 30cm, 60cm and 1m.

Now the conundrum:

Using the pairs technique by loading the individual driver measurements and the paired data into VituixCad I can adjust the delays to make the summed individual match the pair data. This results in -

Woofer/Mid - Mid is -270uS which equates to 93mm this is not far from a geometric calculation using Pythagoras (88mm).
Mid/Tweeter - Tweeter is +20uS which equates to 6.9mm which again sounds about right for a dome mid and dome tweeter.

That said, I modeled up a crossover in VituixCad without adding the offset above, measured the combined speaker response (also with inverted mid to get nulls) and individual driver. The whole speaker model vs measured response matched very well and the step/impulse response also was pretty comparable. Which seems to suggest the data has the acoustic offset embedded in it and my method seems to be correct but something doesn't quite add up with respect to the acoustic offset.

So, the questions is what do I do with the offset data calculated with the pairs approach or have I measured the speaker incorrectly or have I lucked out on my measurements/modelling approach ? Any help will be very welcome and gratefully received, thanks in advance.

For info - if I add in the offsets as delays into VituixCad it is almost impossible to get the phases to line up between the Woofer and Mid.
As an aside after I did this comparison I slightly altered the VituixCad Model2a (2a1) by upping the Tweeter delay to 30uS and slightly changing to the High/Low pass which brought the phases into alignment right up to 15kHz, maintained the flat on axis response and maintained the deep nulls.

I can post the REW mdat files for the three drivers if anyone want to have a play.

Attached is a number of plots showing:

• Woofer/Mid Offset at Mid= -270uS
• Mid/Tweeter Offset at Tweeter = +20uS
• VituixCad Model2a (my model designation)
• VituixCad Model2a vs Measured full speaker and individual driver responses (note the null at 60hz if from the chamber)
• Step Model2a vs Measured
• Impulse Model2a vs Measured

I recently purchased a TT with this cartridge installed. I can find 0 info on it online. Anyone with info?

Sold

Hi:

I'm trying to respond to a post on Elektrotanya. Their website seems rather messed up.

A few days ago, it threw an error that I couldn't log on because I was using the wrong usernmame/email or password. I keep all my login credentials in a password program, so I know they were correct. So I reset my password. I logged on, and made my very first post.

Today, Elektrotanya is once again complaining that my user/pwd combination is incorrect. I'm using what I had saved in my password program from just a few days ago. So I go to reset my password AGAIN. This time, it doesn't send me the email to reset my password. I tried 3 times.

I looked for 15 mins. on the site to find a contact us page, but couldn't find one. I finally wound up having to use Google search to find the Contact page.

Once at the Contact page, I tried to send a message, but I kept getting the error: "The answer you entered for the Captcha was not correct". I clearly screwed up the first attempt, but my next attempts kept throwing that error, even though there were no pictures to click on. Nothing!

This of course eventually led to the error:
"CAPTCHA session reuse attack detected."

even though I wasn't attacking anything.

Does anyone have any way of contacting the site owner so maybe this could be fixed, or at least he could be informed of it? Logon seems to be quite a hot mess over there.

Really increadible poweramps with Exicon fets in the output stage

These amps can be used as stereo or ballanced monoblock.

I have 2 available

Asking 690 euro each.

I resurrected an old thread on the revox, so far the only responses have been to the original post from over 3yrs ago so I will not make that mistake again.

Anyway this fairly nice ReVox G36 MKIII 117V North American edition half track recorder fell into my lap recently and although I have worked on many of these decks and am relatively comfortable working on it, it has been a long time since the last one.

Long enough that although the selenium rectifiers and electrolytics all test good I seriously think I should without question replace them. Seems logical except that the design is so efficient that I will have to make significant changes to get voltages right. The only source of drop in replacement caps (vibroworld) seems to be gone, and no one seems to be able to tell me whether most decks still running are still using the stock supply components. Realistically at 42yrs out I would assume this is skirting disaster.. It's just that this deck is virgin and I want to do the updates with comparable parts that don't leave it looking like a hack worked on it.

This machine seems to be a low hours unit and hence should have a long remaining service life with care.

I'm also planning on some mods. Charlie King recommends removing the 5W PP amplifier which makes sense as this generates most of the heat in the electronics section due to its dissipation.

In addition the current input amplifier provides far too much gain with modern sources and basically I don't need it at all. I plan to just go right in at the recording level control. I could eliminate a further two tubes doing this if I so choose, but this would require modifying the dc filament supply. (Probably a performance enhancement actually)

I've replaced a couple of electrolytics in the replay electronics.

I have not yet run the deck, but I am told this is a high speed version. (7.5ips/15ips) I have not been able to prove or disprove this.. I have 15ips recorded tapes so that will be the acid test once I get it powered up.

Anyone have a guess as to what type of caps the motor phase shift caps are, and whether I should replace/rebuild (new caps in old cans?) On older versions these actually can present an electrical hazard due to leakage into the chassis. The 117V version runs the motors off of a dedicated winding on the power transformer and the motor circuitry is fully isolated from the mains.

I've provided a schematic of my version for the curious or helpful.

I'm really looking for insights, comments, advice and encouragement from people who are still working on these decks.

For one application (Linkwitz LX521) I need to at least temporarily use a MiniDSP NanoDigi. Are there any concerns about the DIR in the four stereo DACs used drifting apart?
I already have 2x SMSL 10th MkII (AK4493). I was thinking about getting either two more SMSL SU-1 (AK4493S) or SMSL PS200 (same stripped down case and display as SU-1, but ES9039Q2M). I was not too thrilled listening to earlier incarnations of ESS DACs (Motu M4 and Ultralite Mk5, Topping DM7), but the ES9039Q2M seems to be a different animal based e.g. on archimago's measurements. I also noted the manufacturer distortion measurements of the PS200 show no hint of an ESS hump but rather a slight increase from about - 5 dB FS, which is very similar to how AK4493 behaves.

If there are concerns, is there a way to use one DIR/DAC as the master and slave the others to it? I remember this was possible with some DIRs but I have no idea whether even a separate DIR chip is used in these.


The alternative would be building an 8 channel I2S in DAC as there are currently no attractive options on the market, but that is something for another thread.

PS: just realized the 10th mkii is one of the few modern DACs that still have a jitter issue with S/PDIF or optical in 🙁

https://www.audiosciencereview.com/...ds/smsl-sanskrit-10th-mk-ii-dac-review.12148/

The SU-1 seems to be a lot better in this regard (even if Amir only tested optical in):
https://www.audiosciencereview.com/forum/index.php?threads/smsl-su-1-stereo-dac-review.44029/

Who in the US offers these items for sale.

Good afternoon, getting ever nearer retirment and have decided to get into repaitring/restoring vintage audio gear. Found site when I was looking around for some ideas re: modifying a Pioneer PL-516 turntable I just purchased that needs some help.

G'day Guys,

Commericially built equipment will normally have a stated power consumption.
For example:


If I was to do the same on a DIY power amp I am building.
Do I:
A) state the maximum possible power output of the power transformer, in my case 300w or 420VA (according to the pioneer service manual it was salvaged from)
B) the maximum power that is likely to be drawn from the power transformer. Eg: 100w into 4ohm
C) B + a derating factor for power loss in the transformer say 0.6. Eg: 100w/ 0.6 = 166W

For Sale Partridge 977 in Ned Clayton case. 2mos new. I need more gain in my system. $315 shipped CONUS

Thanks for looking !!!

Hi everyone,
after reading for some time i signed up to join the conversation.

i am an artist from cologne, germany, and have been working with sound literally since i was a kid.

my main interested currently is to build sound system of different kinds, organizing free events with friends and such.
started building speakers again recently, fun things like the solar powered sound system bike in my avatar picture.

looking forward to exchange ideas and knowledge!

best, Julius

Hi there,
so here I am, Roland.
studied sound engineering in Graz - working in Engineering of broadcast mixing desks, Active Nosie Cancellation, Voicealarm sytems Sound Level meters a.s.o.
of course learned everything important beforehand in the basement building small mixers, active and passive speakers.....
Best
Roland

Hello, my name is Lonnie. I haven't used my electronics training in 42 yrs but would like to brush up and attempt some simple amp mods.

I joined in 2007 and this is now my first post, my unfortune one 🤐
In the early 90s in younger years I bought me a pair of Martin Logan Sequell II which after these years I still have. I replaced the foiles at about 2012 at the local Martin Logan representant, cause one of the speakers stood near to a window, which was often opened. Never do this again.
In the last years the panels moved downwards and I had to align them again. This was no problem until one of the speakers had a losen transducer connection. I could solder this without problems, it worked now for a few years.
But now I tried to fix it again, casue the panels went down again. And my soldering was not succesful for what ever reason. I cleaned the solder point and used a high quality solder.
The soldering point looses immediately, no way to get it soldered at that original point again.
Does anybody have an idea how to fix this, I now ordered a special glue with electrical conductivity, but that's not proven to work.
Appreciate every possible solution.

Though as it turns out I know some of you I am the knew guy so I apologize in advance if this has been covered before. I have searched and searched, turning over every rock and Googling every combination of words I can think of and can find nothing, no answers to what I thought to be noteworthy and reasonable questions.
It is my claim though I expect his as well that the Stasis 1 amplifier is in fact Mr. Pass’s signature piece. I would go even farther and say it is the most important amplifier of its era.
When I was still a teenager I was fortunate to have had an opportunity to hear the Stasis 1 amps feeding a pr. Of Magnaplanar MG III’s at the 1980 CES show in Vegas. I was quite familiar with the MAGGY’s already, at least I thought I was. I knew them powered by BRYSTON 4b’s and even stacked Naim 250’s but this was something else. I remember the new hit Money For Nothing just starting and immediately was mesmerized. I had no idea those speakers could sound like that, I already thought they were amazing but was about to learn what they could sound like. If ever there was a speaker to demonstrate what big class A power could do this was it. They revealed in the most obvious way a whole new dimension , an unveiling of there potential that came almost like a shock. It was as if they were thanking you for giving them what they needed. Pure class A at 200 watts, un compromised by the demands of sub 2ohm impedance with a truckload of current the amplifiers were just as happy as the speakers were. Not even the bigger Audio Research amps could pull that off. It was and is still my most memorable listening experience that I have carried to this day.
My point here is having brought to the market pure class A with enough power to wake up any speaker just had not been done! 200 watt class A, impossible, you will burn the house down as your listening room turns into a sauna! Nope. Cool and confident. Mr. Pass built what I believe to be possibly the most iconic amplifier of our generation. Gordon Holt still today runs them in his personal system along with his big Infinity’s. 44 years later they are still ready for a showdown with anything new. Built by hand with nothing short of military grade spec they have aged very well.

What the mystery is, to me at least is carved into the faceplate it says “LIMITED PRODUCTION”. Something decided in advance. I know of no other maker to limit the numbers except by how many they can sell. True to those words production stopped after a very successful 3 years of strong sales. It’s not like the SA1 was waiting in the wings as it would be another 3 years before it was introduced. Mr. Pass had made his mark and during those three dry years I think the Stasis 1 was talked about more than when you could go buy one! Of course given they shared the same topology the 800a and the 400a enjoyed great success. My theory is that Mr. Pass showed some brilliance outside of his engineering skills with a masterfully conducted marketing campaign. The three year drought left a thirsty public anxious and wondering about the rumours about a new version coming out, which it did and the SA1 was welcomed by thankful audiophiles everywhere and remained in production for as long as Mr. Pass was there to make them. Now the SA1 is not the same as the Stasis 1 at least in so far as it is 160 watts and not 200 but it is the other differences between them of which I can find no information. My theory being is the Stasis 1 was made no holds barred and Mr. Pass was all in on shining a light on the new technology but was aware he wasn’t making any money on them so understood limiting them made sense and would create an aura about them generating interest. Now the SA1 came out three years later and at a higher price becoming an instant sales hit. Threshold declined at the time to comment on any difference between them making sure the Stasis 1 version stopped getting attention. I can find nothing that compares the two anywhere, if you Google the Stasis 1 it thinks you mean SA1 and makes no difference between them.
I don’t think it has happened before so I think it’s time for Mr. Pass to come clean and give us what he knows in describing the engineering / design and sonic variables between them.
I believe he will agree with me that the Stasis 1 is his signature piece and the time has come to correct my theory or agree.
After not hearing them again since, I did after 44 years finally get a pair of Stasis 1’s, as a matter of fact two pr. From an aging Cowboy in Colorado who bought six in 1980 serial #’s 79-80-81-82
I have become obsessed with finding any competent commentary discussing the differences and look forward to your or any response sir with the faith of a child on Christmas morning.
Peter Smith

For Sale Nate Clayton 1254 Cinemag SUT - 2 mos old. Great unit but my ears prefer vintage. $435 including shipping CONUS

Thanks for looking

Hi !

I'm building a passive subwoofer for my home theatre and also for listening music (I don't know if it's the right place to post).

My amp will never be above 120 W (i think). Just in case I push the value for 150W.

My constraint are :

1 - High quality sound (highest i can)

2 - 20 - 250 Hz (closest i can)

3 - Around 100€ for the driver (max 150€)

4 - Box max dimensions (inside) : 550 x 500 x 2000 mm

(I have dayton audio speaker that Kirby Meets Audio designed on youtube, those are quite great but it lacks of bass)

----------------------

I found (soundimorts.eu) :
73€ - Dayton Audio SD270A-88 10" (Green)
149€ - Dayton Audio DCS305-4 12" (Blue)
109€ - Dayton Audio SD315A-88 12" (Red)

On winIsd, for a ported enclosure :



Budgetwise : SD270A-88 but too high above Xmax (at 120W)

So, Budgetwise 2 : SD315A-88 but too higher than Xmax (at 120W)

Last choice : DCS305-4 almost down to where I want, spl, group delay, cone excursion, rear port air velocity OK !
--> 120L box, tuned at 23Hz
--> 500x40 mm port (lenght 825.8 mm) BUT the 1st port resonance : 208Hz ; is not an octave above my desired LP filter.

And then, I'm completely lost on the crossover design, I made a 4th order, but it seems that it will cost so much...



So here are my questions :

- Any Ideas of other greater drivers ?

- Does a subwoofer need to go as high as 250Hz ?

• How to define the 1st port resonance ? (I read that this should be 1 ocatve higher than the LP filter)
• How to design better to meet all the requirements ? (1st port resonance, cone excursion, group delay, ...)

- Could you help me design a low budget crossover ? (I don't have much experience, I'm learning everything to achieve it)

My WinIsd files are also attached.

It might be too difficult to meet all these goals but I'm willing to get as close as I can !

Thank you very much for any answer !

Olamm

Looking for Audioharma cable cooker 3.5 with all adapters in excellent condition.
Please PM is you have one.
Thanks
Bob

Any simple - and more radical - suggestions ? - John Curl ?

Does anyone know if there is a problem with the Vinyl Engine website? I haven't been able to get it for a few days...

Hi tube friends. I got question. Have been playing simple kt88 se amp, great sound, having fun swapping various kt88 brands. However, i noticed one tube is slightly loose between the glass and base.
Any remedy?

I keep forgetting to ask, has anyone built an amp camp amp? I did mine a few years back, sounds amazing for 8 watts /ch. The only thing I never asked is when I turn the power on it makes a squeel sound for 2-3 seconds, then no hum , nosie etc. Anyone else notice this with their unit? Anyway of troubleshooting it?

I've identified a great little stereo amp that works well with the SG4 sinewave generator for use as the output stage and motor drive for AC synchronous or AC induction turntable motors. It is based on a pair of the venerable LM3886 chip amps and contains everything needed to boost the SG4 signal up to a level needed to drive a 6V to 115V (or 230V) transformer. The only additional items needed to make a complete motor drive system is the AC input power transformer, the output transformer, the SG4, a heat sink and a slight modification to the amplifier. A complete motor drive can be constructed for ~$100 plus case.

The amp is available on e-Bay for $15.17 including shipping:

60W LM3886TF Sound Audio Amplifier 2-Channel Digital Power AMP | eBay

The amp will need to be modified to reduce the gain for two reasons:

1. The SG4 output is 5VPP and the amp will go into clipping at ~0.75VPP input.
2. With the standard gain, the output waveform becomes quite distorted when connected to the output transformer. With reduced gain, distortion remains very low, even when driving heavy loads and even at 50Hz. If you do not modify the MK-154 gain, the output waveform will look terrible, especially at 50 or 60Hz.

Replace or parallel the two 22K resistors with 2.2K resistors as shown in the attached jpeg (MK-154 Modified.jpeg). With this gain setting, the 5VPP output of the SG4 will drive the output of the transformer to ~125VRMS with very little distortion.

The amp PCB has screw terminals for the AC input, removable connectors for the outputs and both a 3.5mm stereo jack and 3 pin header for the audio inputs.

I've created wiring diagrams for 3 different scenarios:

1. 115VAC input and output single phase.
2. 230VAC input and output single phase.
3. 115VAC input and output dual phase.

The design uses two low cost split bobbin transformers with dual primaries and dual secondaries. The AC input transformer is a Signal LP24-2000 (48W) and the output transformer is a Signal LP12-1900 (24W). Both are available from Mouser ($24 and $19 respectively).

For 115VAC input or output, the high voltage primary windings are connected in parallel. For 230VAC input or output, the high voltage primary windings are connected in series.

Warning: Working with high voltage can be dangerous. Do not attempt to wire these circuits unless you are comfortable and competent to work with high power and high voltage electronics. If wired incorrectly, damage to property and great bodily harm may result.

The wiring diagrams are labeled with the pin numbers on the transformers and are unique to these two parts. If you substitute different transformers you must be aware of the winding polarities of the coils, which are usually indicated with a "DOT". When connecting windings in parallel, the "dots" must be connected together on one side and the non-dot ends must be connected on the other. When connecting windings in series (for 230VAC input or output), the dot on the lower winding must connect to the non-dot end of the upper winding.

When working with AC line voltages, ALWAYS use fuses on both the input and output. The AC input transformer in the attached jpegs has an IEC socket with built in fuse holder for connection to the mains voltage; the fuse should be rated for 1A Slo-Blo type. The AC output should also have a 0.5A Slo-Blo fuse in line with the hot lead. Connect the earth safety ground (third/green wire) from the input connector to all chassis components (and the 3rd terminal on the AC output) to properly ground them.

The MK-154 PCB has detachable connectors on both the L & R outputs. Remove these for easier connection to the output transformer low voltage secondary windings and the transformer will then just plug in for assembly.

For single phase applications, both L & R audio inputs to the MK-154 are connected together and are driven by the 0° output of the SG4. The L & R outputs of the MK-154 are used to drive each winding of the dual low voltage secondary on the output transformer. When wired in phase, they will combine both channels into one output, doubling the current capability.

For dual phase applications, the 0° and 90° outputs of the SG4 drive the L & R audio inputs of the MK-154. Each MK-154 output (L & R) drives its own output transformer with the low voltage secondary windings on each transformer, connected in parallel.

Note that the output connectors on the PCB are mirror images of each other, so the + & - connections are not on the same side of the PCB for each connector. They will be on the same side of each connector that plugs into the PCB.

The MK-154 MUST have an adequate heat sink attached to the two LM-3886 output amps for proper operation. Failure to use a heat sink will result in almost immediate destruction of the amplifier. Use a heat sink with at least 40 square inches (250 cm²) of surface area and at least 2-3 inches deep. The LM3886 chips are in an isolated package so they do not require mica insulators between the chips and the heat sink, however, you will need to use silicone heat sink grease.

If you use the 3.5mm audio input jack to the MK-154, the tip is Right In, Ring is Left In and Sleeve is ground.

Hi, from Puerto Rico

Here is the list of Qtc and their characteristics from the textbook.

Qtc = 1 is Chevbychev
Qtc = 0.707 is Butterworth
Qtc = 0.58 is Bessel
Qtc = 0.5 is Linkwitz-Riley

Most of the textbooks explain all of above alignments clearly including the case that Qtc is greater than 1. Unfortunately, I couldn’t find the explanation of Qtc of lower than 0.5.

I’m curious what will happen if I design the passive crossover with extremely low Q—lower than 0.5. For example, Q = 0.25.

In fact, I have tried experimenting already; with the traditional second-order crossover. But, I couldn’t hear anything abnormally. So, I’d like to ask for clearer explanation of the results/effects when utilizing the extremely low Q crossovers (lower than that of L-R alignment).

Hi,

I have a bunch of ICEpower 80AM2 amplifiers. These are 2x80W or 1x160W BTL.

They don't have an integrated PSU as they work with the ICEpower 400SM power supply, that can power 8x 80AM2 amplifiers.

The 400SM power supply is expensive around USD$180 so I am looking for cheaper alternatives. AFAIK these amplifiers run on a dual +/-36volts power supply.

Do you think it might work? Do you have any recommendations on power supplies? What about some Hifime SMPS300RE?? (IDK if its better price wise). Maybe some Meanwell?

Looking forward to your suggestions!

Cheers.

​

Both excellent.

Is it possible to keep an IPS LCD LED display or will they all die? I have handheld consoles with these displays

the same question for class 2 smd ceramic capacitor

Hi ! in a very interesting article by Mr Pass describing is project called the Zen amplifier
https://www.passdiy.com/project/amplifiers/the-zen-amplifier
i was struck by this passage

Simplicity is not the only reason for the use of the single-ended topology. The characteristic of a single-ended gain stage is the most musically natural. Its asymmetry is similar to the compression / rarefaction characteristic of air, where for a given displacement slightly higher pressure is observed on a positive (compression) than on a negative (rarefaction). Air itself is observed to be a single-ended medium, where the pressure can become very high, but never go below 0. The harmonic distortion of such a medium is second harmonic, the least offensive variety.
It is occasionally misunderstood that single-ended amplifiers intentionally distort the signal with second harmonic in order to achieve a falsely euphonious character. This is not true. Low distortion is still an important goal, and it is my observation that deliberate injection of second harmonic into a musical signal does not improve the quality of sound.

Click to expand...

it seems to me that this position has solid bases. For instance a good compromise could a single ended front end followed by a push pull amp for convenience
I have also read that output pairs made of two same npns given their nature could sound more push than pull and in this way behave more like a single ended amp ?
I would try the single ended approach at least for preamp The only drawback mentioned is a good amount of 2nd order distortion ?
Interesting topic indeed What do you think ?

Crown Micro-Tech 1200 with an interesting fault. This amplifier was given to me to fix as someone in the past replaced the output transistors and drivers from another Micro-Tech. All done fine with matching sets but this had a strange problem where there was DC offset bouncing around between 1 and 4 volts on channel 2. When the amp was switched off the DC offset continued but at lower voltage around 1-2V for several minutes! Strange bouncing up and down . The owner complained about the noise it made through his speakers even when switched off. I checked out the voltage translator area and the control/gate transistors for DC protection and ODEP. All seemed fine. Then I powered up again and then switched off but this time removed the ribbon cables to output boards to isolate the offset at swittch off state. The DC offset still bounced around with the main board disconnected. I focused my attention to the main output board and visual check revealed sticky flux all over the driver areas. This flux was conductive. Cleaned thoroughly and then the amp was totally fine. Just goes to show that flux can cause all sorts of problems.

I also found if I re-routed the orange feedback wire (Im guessing this is for connection between high and low side bridge) from original position to going parallel to the case this dropped THD a fair bit and SNR went up. This wire seems to have quite an influence on distortion and snr. In the original position running along transformer side hum was detected through speaker. In new position running along case side it was silent even with headphones.

Anyway, after all that was done I checked/adjusted bias, ODEP voltages and adjust for lowest CMR.

Picture shows the board cleaned, cap mods and re rotored feedback wire.

Also does anyone know what these two small capacitor mods are for?

Hello to everyone. After many years of searching, I thought I would give it a try unscrewing the screws and opening it up to see what's inside. What I found wasn't what I expected, since there were no soldered wire ends but everything was fit together with little plugs. Doing some tests though I figured out that the Jack hole for phones could work just fine whether you put a trs or a trrs jack. That means that you can have Sound no matter if you plug in 1 ring or 2 rings. So what I finally did was to plug a phones cable without putting it all the way in, in such a way that I could get sound both on the Cube's speakers and the headphones at the same time.
Don't judge me early enough. When we do this on other systems, we usually get a monophonic signal on the plugged in cable. Here, this was NOT the case!!! I got a STEREO signal , with good quality also on the headphones. Usually, if you do this on any device, you get poor Sound, leaving many frequencies outside, just like taking a karaoke version of the music,right?
I repeat, here this WAS NOT the case. The only thing I noticed was I slight boost of the Bass on the "half unplugged" headphones, but I still had stereo sound of good quality both on Cube's speakers and the external ones.
So maybe ROLAND made this on purpose and this is The way to have a muted or non muted cube if you plug a jack in The output hole? I really don't know, but it works.

Hi DIY enthousiasts, just a brief introduction: I'm basically a musician (guitars, bass guitars, vocals) that is challenged to built something now and then, started of with guitar pickup changes, then a few microphones, now planning my first guitar amp. Already got a great deal of info from this forum, so I decided to join to share some experiences.

I am currently trying to design a stepped attenuator for a generator.
I want it to have a constant impedance, both for the input and the output, to be as simple as practical, to have the ability to go to 0dB and to use a single circuit selector.
This is how far I arrived:

Only 5 sections are drawn, the subsequent sections being very similar.
I have the feeling that it would be possible to streamline it further, but I cannot find useful info on the net.
Does someone have a brighter idea?

Ive searched around a few forums and lots of googling and I must say, information regarding this CDM 12.4 transport is rare. I have a BAT VK-D5SE that has a failed transport collecting dust for about 3 yrs now and I want to fix it. A quick call the BAT says I need about $500+shipping to repair it. So far, I bought a laser pick up, which appears to be cheap chinese quality and does not work. I remember the tech guy at BAT told me they need to replace and entire mechanism along with the laser pick up, so I thought there must be a compatible drop-in replacement I can buy instead of shelling out $500+. But so far, I have not found any info regarding a drop-in replacement. Do you guys think I really have to send it back in? Such a nice CD player and I miss it, not mention it was uber $$$ spent.

Hi ! i have a weird question
Should equivalent parts have a very similar (if not identical) LTSpice model ?
i am asking because (at least at sim) the part rh117h shows very impressive performance when used as unity gain buffer
As this part is not widely available i have tried the model of what i thought were an equivalent part, the lt317a also present in LTSpice default library
It does not work in a same circuit So my conclusion is that they are not equivalent at all
Am i correct ?
Thanks a lot and have a nice day
gino

Hello everyone!

I've been trying to use the amplifier ta8210ah and I need someone that knows or have used this before to help me. I've been connecting the chip like the datasheet circuit and I've been getting a very low output I do get a sound though but it's very low. Is my amp problematic or I've been missing something?

Can we find approximate impedances, i.e., 4, 6, 8 Ohms, of the drivers from crossover values?

If so, attached is the example of crossovers with unknown drivers’ impedances. Could anyone please help to find them?

TT (woofer) = …. Ohms
MT (midrange) = …. Ohms
HT (tweeter) = …. Ohms

In fact, I’ve tried simulations with various values of impedance on each driver, and found so many possible combinations. They made me more confused. So, please help me to get it.

As the title says, I'm just browsing online for 1970s cassette decks.
I am completely new to the area and have no personal experience with them.
Online, its a situation where you have to buy it before you try it.
Basically, the only criteria I have are: availibility, in working condition, and price.
Anyone have any tips?

Greetings to all participants of the forum. I like homemade pieces from the audio world.