hi
I want to build a class a1 amplifier with 2a3, however I don't understand why half 12ax7 tube is never used as a tube stage driver.
according to my calculations to make a 2a3 work at full power you need 30 vpp on the grid that with a half of 12ax7 (with a gain of about 100) I should be able to obtain with about 300 mVpp (100 mV rms) in input
why for the driving of these tubes (2a3, 300b) we always see "strange" drivers like srpp, parallel triode, cathode follower and not a trivial amplifier stage with only one tube?

I sell a brand new pair ( never used ) of rare Lowther PM4A.
They are original packed.
I opened one package to do Fotos.

Can an F6 kit be fit into a 3U 300mm chassis with PSU?

Im designing a crc psu for my gainclone and debating on whether to use a solid ground plane or a slitted one such as seen on myref fremen edition. On that board its clearly seen that the plane is slitted to where the return currents are forced to go between the negative pin of each smoothing cap.

Whats more curious to me tho is how the plane is then split all the way to the rectifiers. The myref im talking about is a double rectifiers design and thru that slit the + and - ends of the rectifiers that form the ground are seperated and only joined inbetween the smoothing cap.

I guess what im looking at is sort of a star ground arrangement? Id like to know what the merit would be for that vs the plain solid ground pour.

Refurbing an old valve mic. I want to replace a couple of high R presumably Carbons with the quietest available. Presumably Vishay Metal Film? There is no current flowing but 1/2W would be a suitable physical size. The values are the problem. And shipping to Ireland kinda makes the UK and USA a nuisance. 60 Megohm and 100 Megohm. Help!
DD

Hi all,


I'm looking to build an open-baffle subwoofer, likely H-frame, that is small and will be placed near-field right behind the main seat at head level in an apartment. The intent of the design (OB/H-frame) is to centralize the volume to the listener while creating as little resonance in the room that could transfer to others in the complex. I do not need heavy bass, just something to augment the surround setup I have and add a bit more to the low end.


I'm a fan of the Dayton brand, and that's what I'm using for my surround setup, so I'm wondering if anyone has any suggestions on a 10" (or MAYBE 12", space is an issue behind the couch) Dayton subwoofer to use in this design. Secondarily, any suggestions on how to do the math for the size/depth of the enclosure.


I'm somewhat experienced with speaker design, but not with open-baffle at all.



Thanks!

So I found myself wanting a couple channels of amplification for some subwoofers in a medium sized room. I was intrigued by the promised performance/$ of these TPA3255 boards. I am not building from scratch or anything, just going to play with the Lego pieces that are out there. That being said, I was hoping someone could talk some sense in to me about my possible configurations.

I am looking at the boards put together by 3e-audio and power supplies from connex electronic . . . as these seem to be decently well respected. All other parts being the same, I am just comparing the two components.

The board offerings are either a BTL ($70) or 2x PBTL (2x $65).

The supplies are the SMPS600RS ($89) or 2x SMPS300RS (2x $65)

The possible configurations are as follows:

1. SMPS600RS + BTL = $159 (Base)
2. SMPS600RS + 2x PBTL = $219 (Base + $60)
3. 2x SMPS300RS + 2x PBTL = $260 (Base + $101)

Thoughts:

Assume 4 ohm speakers for now . . .

1. Plenty of supply, 4 ohm stable . . . perhaps cooling becomes an issue? Cheap.

2. Plenty of supply, 2 ohm stable, twice the onboard capacitance . . . twice the cooling as base. Not as cheap

3. Discrete power supplies, 2 ohm stable, twice the onboard capacitance, twice the cooling as base. Approaching what it would cost just to buy an off the shelf Crown XLS 1002, albeit without getting to play with Lego.

Is there any true benefit in going to the higher cost configurations?


Links:

BTL

PBTL

SMPS300RS

SMPS600RS

I had luck with single capped morel cat378 with eminence b102 run wide open.


Seeing stuff on tekton enzo and pendragon. mmttt / mtttm


Since i sit darn far now, can i get away with a mttm or mmtt ?

Less distortion, more sd for bass far away.

Joined this group about a year ago and have been lurking and learning!
Built Wayne J's Veritas about 12 years ago, still love them for my HT.
Next on the bench was a vented subwoofer with the Shiva drivers I bought when I was part of the Bass List. Turned out pretty good, but I blew it up with the EP 4000 that I drove it with. Replaced the Shiva with a Dayton UM 12, built a new 3 CF sealed box and and the Dayton 1000 plate amp and all I can say is , wow,

Then the Classix II landed i the shop last year for surrounds, amazing design Paul!


Now comes the Tarkus!
Have had them on my bench for almost a year and am getting close.
Thought I would stop by for a curb check!
Build PICs to come

Hi all,


This is a follow-up to my Open Baffle question thread, but more about speaker selection to pair with my amp.


I'm evaluating the RSS265HF-8 or RSS265HO-44 but I'm not sure which to choose between 4Ohm or 8Ohm. Here are the main specs for the speakers:

• RSS265HF-8
  • 8Ohm
  • 84.2dB Sensitivity
  • 24.9Hz Fs
  • 14.33mm Xmax
• RSS265HO-44
  • 4Ohm
  • 90.5dB Sensitivity
  • 27.6Hz Fs
  • 13.25mm Xmax

And my amp is an Adcom GFA-555 II:

• 600 watts into 8 Ω bridged from 20 - 20,000 Hz at less than 0.04% THD
• 850 watts into 4 Ω bridged from 20 - 20,000 Hz at less than 0.09% THD

What would be better in my environment? I remember from car audio days that I should stick with 4Ohm, but I'm not sure for this.


Thanks in advance.

FS: Jensen F12N Field Coil Loudspeaker and PS Hammond 6V6 Amp

Jensen F12N Field Coil and power supply $75 + shipping
DCR field coil = 672 ohms, DCR voice coil = 6.6 ohms
Early Hammond 14-1B 6V6 amplifier with built-in field supply $50 + shipping

FS: KR 6SN7GT 6V6G 12AY7 Tubes Tested

All tested on calibrated and maintained testers (539C, TV-2, TV-7). Get 'em while they last...
NOS TungSol 12AY7 pair, test at 98,90 and 110,105. $50/pair

NOS RCA 6J5GT pair. Test matching at 90 and 91 / 54. $20/pair

Six Ken Rad 6SN7GT, copper rods. 85,90/59, 87,88/59, 89,89/59, 90,88/59, 89,92/59, 96,97/59 all for $80


Raytheon 6SN7GT tall support rod. 539C test matching at 2700 6.4mA 2680 6.7mA. $15

Hi all,

It's been a while since I was on the forum!

I have a QSC RMX 2450 amplifier that I bought with Channel 1 blown on ebay as a repair challenge. I finally got around to spending some time on it the other day, with mixed results:

2x output transistors were blown on each side of CH1, as well as almost all the emitter resistors, one of the 22R B-E resistors on the negative side and the negative step driver FET as well. I replaced all the output transistors in the blown channel and the drivers for good measure, as well as the step driver FET. I was able to get the amplifier up and running and set the bias. Initial load tests looked good. I verified that the step drivers were working OK when the signal was big enough to need the higher-voltage rails. I connected a speaker and played some music, so far so good. However, a couple of gremlins remained.

The first is that there is a slight thump in the speakers when it turns on. It is very slight, really not much, but it is noticeable. I thought the mute circuit was not being activated for long enough, however the manual says that approx 1 second muting is normal and I measured it as > 1second. Blue is negative rail, Yellow is one of the -15V opamp rails:



I am not sure why it still creates a bit of a thump, so I am open to some suggestions here.


The second issue was the fan - it always runs, and it is a bit noisy. I assumed that the fan would be off until the amp warmed up enough to turn it on, but the circuit shows that it is always connected by at least 120R. I temporarily disconnected the cable from the Channel 2 PCBA to the AC PCBA and the fan ran a bit slower, so from this I know the optocoupler and the TIP31 are working OK - and the control circuitry on the Ch2 PCBA seemed to be working OK. With the amp off, the PTC on Ch1 reads 4-5 ohms higher than the one on Ch2 but other than that I could not find any anomalies with the circuit. It must just be a noisy fan, I will source a replacement.

However, while probing around - I inadvertently created a short. I use long, insulated HV probes which only have about 1mm of exposed metal on the tips when probing a live amplifier, but in their wisdom, QSC placed an uncovered via directly beneath the leg of D13 and while I was probing D13, I shorted its anode to ground with the tip of my probe. As far as I can tell from the schematic, this has the effect of collapsing the -15V opamp rail on Ch2. The effect of this was a little horrifying - the output emitter resistors on Ch1 all went up in smoke.

Now, before I pull it apart and replace the blown transistors again, I am trying to work out why this happened. I could believe that maybe some DC was fed to the driver stage when the negative opamp rail collapsed, but Ch2 seems to still be intact whereas Ch1 is now blown. Why? The opamps have separate sets of rails for each channel. The amplifier was in bridge mono mode at the time, so I am assuming that the signal was somehow coupled this way into Ch1, but again, why did Ch1 go up in smoke and Ch2 did not? I never set the current limiting on Ch1 after replacing the output transistors as I had trouble finding a 1200W 2-ohm load with which to do it, could this possibly be why? I measured the resistance across the current limiting trim pots and they are quite different between the 'good' Ch2 (540R and 570R) and the blown Ch1 (800R and 420R).

The thing is, I bought the amp with Ch1 blown, so I am just wondering if there is something else I have not considered that is leaving Ch1 vulnerable in some way. I'd welcome any advice or suggestions.

Any observations or advice would be quite welcome!

Hi all,

Currently we have an old PCBA which consists of a "KE 4-211-2" with a preamp.
As you know the "KE 4-211-2" is obsolete.

Does anyone know a replacer for this microphone which has ~same spec (freq response/operating voltage/SPL)?

Thanks.

Hi,

Found that B&W DM14 on the side of the road. This sealed 2.5 ways made from chipboard two 18 cm polypro like cone and a 2.5 cm tweeter sounds a little boxy but I find the high mid and treble to be very nice. Quite heavy box assembled September 1980.

Shouted some pics of the drivers and the internal for Diyaudio archives:

1" (2.5cm) tweeter : TW26, 8 ohms soft dome, seems hand coated and is a little bright for a fabric dome. The dome is very soft at finger push but recover its shape back.

7.3" (18.5 cm) mid-bass x 2 : DW150/14 (14 ohms?) from the half of the surround it's a 5.76" (14.5 cm) polypro cone. back of the cone has a sort of wave a little like plastic coated paper but front cone suggest it's a full plastic cone. Not sure what the dust cover is : hard coated paper ? Surrounds are butylene, very light and thin... Speeder is weak, aging or born like that ? Qm should exhibit a high number. My ears are saying it has a good high mid and mid but not so a good bass. Perhaps the load, the drift value of the caps changing the crossover characteristics ? I can't say.

Not studied the filter yet. Lytic caps are PYE brand cap (the red 560 uF & 5 uF), some MKT or Mica (the browns) and mkp (10 uF) There is a little resistors network probably to supply the red led of the loudspeaker in the low left edge as it's not an active speaker and just mono wired.

Veneering varnish reacts to the methylated spirit. Enclosure has two U pieces of dense foam to line the walls and the top/ back. Full of stuffing, synthetic wool. Enclosure is 57 cm x 25,5 cm x 28 cm (deep)

Any thoughts or documents/links about this loudspeaker and/or drivers please ?

Hi,

I have built a dual linear power supply based on the LM317/337 to provide +-12V from a toroid transformer.

If I connect to the positive rail a 10R resistor to the positive rail, the output voltage is 11.6V, if I connect a 15R resistor, the output voltage is 11.8V, for both in series, it is 12.0V (I have tuned the output voltage with those in series).

Does the LM317 really have this poor load regulation?

Further, when connecting both resistors in series (25R, i.e. 480 mA), I get an input ripple of 288mV, and an output ripple of 25mV.
Shouldn't that be much lower? The datasheet of my particular LM317 says 60-80db ripple rejection at 120Hz (I have 100Hz)

The schematic is attached.

Have I messed something up in the schematic?

My experience with the 2134 is that it doesn't like being used as a unity gain buffer. It is perfectly happy as a unity gain inverter (like in tone control circuits). I also used it in a non-inverting gain stage with a voltage gain of 1.4 with no problems.

I have successfully configured it as a unity gain buffer with a few extra parts (couple of resistors and ceramic capacitors).

I built a prototype of this circuit Project 99 - Subsonic Filter with op amp sockets. I tested three op amps in the circuit: NE5532, LM4562, and OPA2134.

NE5532 worked great but DC offset was 45 mV.

LM4562 worked great and DC offset was 3 mV 😎

OPA2134 oscillated. I tried using one 2134 and one 4562 and it oscillated.

To me, the 4562 should be the touchiest, with its 50 mHz GBP. But it seems that's not the case.

I have configured the 5532 as a follower with 0.1 to 0.2 mV DC offset, but obviously this isn't doable in a whole lot of circuits.

So has anyone else had a similar experience? I'm always looking for new tricks. 😉

Hello all,

Thinking of putting a little OB project together and cant help but ask regarding exit holes - see attached a la Emerald Physics - I would believe that the smaller exit is designed to "front load" the driver - but is it advised?

I admit, I am one LAZY SOB, and I have a 6" Hole Saw, and I hate using my jigsaw, as it always ends up looking like Stevie Wonder used it.

Application (with DCX2496) - pair of Eminence Alpha 15A mounted to front of 1-1/2" thick Baffle, or to backside with 6" exit hole...

Yes, No, or Hell No?

Go!

I have studied these funny Bertagni speakers which consist of a magnet / voice coil and a polystyrene plate.
But I can not really figure out if the polystyrene is completely attached to the frame or if there is some kind of surround foam

Does the polystyrene move more at the voice coil than out at the edge of the frame?

I think it's a fun speaker and would love to try make something similar



Video = (See 11:30 and 21:10 in the video)

Bertagni Electroacoustic Systems - Caixas de som planas (Plain Speaker Systems) - YouTube

Hi hope someone can help , i have a DENSEN DM-10 with problem of burning some resistors and bridge rectifier but can not solve without schematisc , so if someone can point me on where to find it.

Kind regards

I have some 2SK170bl lying around and want to make an amp for my Denon DL103 to go into the MM input on my Copland. I have an SUT but wanted to try SS. I'm looking for a simple circuit that has the option of gain switching to allow for lower output MCs further down my MC road.

Anyone know of a cct diag, preverably running off a 9v supply.

No RIAA eq needed.

I built a couple of DIY speakers (Quark and Speedster), and I really enjoy how much value you can get for not much money.

One day I'd like to build a bigger/better multi-way speaker using something like Hypex Fa123, but I have too much to learn before I start spending real money.

I was thinking of starting with something much cheaper to get into active crossover and active speaker designs, using a ADAU1701 board and cheap chip amplifiers.

I looked at some of the Sure offerings, e.g. WONDOM | STORE or even WONDOM | STORE which will allow to build a 2-way design with just a power supply. Or WONDOM | STORE for both speakers.

But I've read mixed feedback on the Sure modules, so I'm wondering if there are better boards I should consider. Any advice in how to get started is welcome

There are about 5 things to consider when going for the evil twin of the Aleph 3. After the changes are made we will find that our A3s have specs similar to its older brother the Aleph 5. We get to keep the toasty DC bias of the A3 only toastier. I think this is what keeps the magic in the Aleph 3. Here’s how we can do it:

1. We need to have a beefier PS transformer. About 600-800VA; 2-28V secondary CT. This will deliver about +/-34Vdc loaded with the A3Turbo.

2. We need to increase the built-in current limiter’s current limit. As called in the A3 schematic, the limit is about 4Aac. We will increase this to about 5Aac. The limiter circuit is made up of Q104, R109 and R110. By lowering R110 to about 75Ù the current limit increases to about 5Aac. How it works: At lower load impedances, by virtue of Nelson Pass’s another paradox the Aleph dynamic constant current source, higher voltages and currents develop across and through the output devices and their Source resistors. At about 5Aac the voltage across R122 increases to about 2.35Vac. The voltage divider circuit that includes R109 will drop some of this voltage while about 0.6V develops across R110. 0.6V across the B-E of Q104 will be enough to turn it on limiting input currents to the Gates of the output MOSFETs thereby setting their output currents to a maximum of 5Aac.

3. For the positive going signal to keep up with the increase in negative going signal as the current limit was increased, the 66% of AC current gain (ACIG) as set by R114 will have to be increased. We will set the ACIG to about 78% by replacing R114 with about 634Ù of resistance. Both + and – signals will now start to distort almost at the same time.

4. If we are going to load up our A3Turbo with speakers that dip to 4Ù or 2 Ù at a bunch of frequencies in the audio band you might want to monitor your Source resistors if they heat up rapidly. We should replace them with a higher wattage ones if it did. Start with 5W.

5. As we did with the Source resistors, monitor our heatsinks. The touch and go method as explained by Mr. Pass is effective as it is.

Let’s fire it up. Oops! Nice output signal. That’s SIMetrix though. I’ve tried this at home but only on a computer. You can put into hardware if you find it appealing.

Please feel free to add to it if I'm missing something.



_____________

"For sounding good, I'll take the heat."

Split from 6JN6 screen-drive (g2 driven) plate curves?

Hello, the voltage current transfer curve of a tube driven at a negative grid is non linear. The usual way to minimize the distortions caused by this non linearity is neagtive feedback and/or compensation of this non linearity, e.g. push pull. These methodes are used in solid state devices too. Thus the result is not much different. If you don't want these usual linearisation methods there is another option. The triode. It makes a self linearisation caused by the influence of the anode voltage in the electric field between cathode and grid. Same takes place in the so called "Ultralinear Circuit". It is the change of the g2 voltage that makes this influence. A positive grid ideally eliminates the influence of the following electrodes in the electric field surrounding the cathode. Thus a triode with positive grid voltage is getting more and more pentode like, the positiver the grid is. A pentode (and tetrode) driven at g2 is still a pentode because the g2 is positive and eliminates the influence of the anode in the electric field between cathode and g1. Thus the name "enhanced triode mode" is wrong here. There is a strong similarity between a bipolar transistor and a pentode driven at g2 and you can say it is a pentode in the bipolar mode. #16 All applications I have seen suffer with the problem that the voltage to current conversation at the positive g2 is still non linear. Some people accept this nonlinearity😉 and reduce it in the usual way as explained at the beginning. You can see this non linearity in the change of the spacing of the horizintal output curves of the pentode .#6 It is possible to make the g2 voltage drive linear and the spacing equal. #21 I'll explain this in the next post.🙂

Kind regards, Darius

I have a Meridian 557 that I bought new with a balanced Meridian stack around 1998 (502, 500, 566-24, 557) but it's refusing to power up now. It goes through the soft start sequence, stays on for a couple of seconds then you hear one of the protection relays click and it does a power down. I haven't been able to find a Meridian expert that knows their classic audio components in the Seattle area and the local "official Meridian support" folks are a home theater showroom/installation place that thought I was confused because they didn't know what a 557 was.

I had the local MacIntosh expert check it out for me (reluctantly) and he said the bias is too high on the right channel and that is what is causing the shutdown to trigger. He said it appears to have an auto bias system with no settings (does anyone know if that's true?). He was pretty impressed once he opened the top and said he could probably fix it but would need to see a schematic first. I have found a Meridian 556 schematic but no 557 schematic.

Has anyone seen an issue similar to this in the past and hopefully know what the cause is? I'm an EE/CS with some analog knowledge but I would not attempt to repair this myself. However, I can pass along any detailed information to Mr. MacIntosh who has 25+ years experience fixing high quality amps and other components.

Thanks,

Dean

for sales Acoustic Revive rtp-4 ultimate power strip/conditioner US socket

1500USD free worldwide shipping

Acoustic Revive Rtp-4 Ultimate US | eBay

Closed.... all gone.

Before I throw these in the bin, someone might be able to use these. Two TPA3116 mono modules (1 with volume pot and other without) and one TPA3118 mono module. All are working and are typical of most of these type with a bit of hiss and can have a turn on thump with some power supplies.

I'll cover postage in Australia and are supplied as a bundle only (all three).

Hi all.

Forgive me if this is the wrong sub-forum...

I have a NAD 1240 preamp with a broken headphone jack. It is a solderable PCB-type, I believe the part # from the service manual is

L451Y017H01 PCB TYPE 9 PIN JACK HEADPHONE

This is the actual part that is broken (I stepped on something, lost balance and steadied myself on the first thing I found--the 1/4" heaphone plug sticking out of the preamp). Unfortunately, signal to power amplifier goes through this jack and the accompanying PC-board (# L241A066H12), so not good!

I doubt NAD stocks these, as I purchased the preamp new in 1987...

Does anyobody know where I can get a hold of such a phone jack? I can look for a similar vintage dead amp/preamp, but these are scarce here... Let me know. Cheers!

--Christian

I want to connect my Polytone MiniBrute IV combo to a Polytone Pro Series Cabinet I found.

My question is, is my plan good, how to improve my plan? Thank you.

MY PLAN:
cut and resolder/shrinktube the 4 wires that make up the existing parallel circuit to the internal 15" and the EXT OUT jack, from that junction add a new pair of leads for the SERIES loop to the internal 15" and a NEW JACK w/SHUNT (1/4" switchcraft w/shunt). I will leave the HEADPHONE jack wired, but will stow it securely inside the box. The NEW JACK will go in the hole labeled HEADPHONE. I will add a label that says SERIES OUT.

I don't know why, move more air, fill out the tone, or just because it seems like these two old PTs belong together and there are some funk parties on the horizon



Some calculations (courtesy geoffthegreygeek) show the most effecient (and safe) way to plug them all in would be to connect in:


Is this a good idea?
Thank you

I have a pair of flange-mounted Eminence horns and a set of Dayton H6512 waveguides to compare sound for a 2-way speaker. I will mount both in a simple chipboard prototype box and see how they measure and sound to my ears before I advance to the final routed cabinet.

Despite the quality Eminence screw-on adapter EB 2 SA there is naturally a small but pronounced gap between the aluminum adapter and the waveguide's plastic. I made some pictures for you, the gap is only thin, but I think it has to be filled and also the plastic to be smoothed where it protrudes, for which a file can be used. But what do you use to fill/modify the surface of waveguides/horns? Here it should stick to the waveguide I think. Can you name some suggestions which I can buy preferably in Europe or give the technical term for a brand product which may only be available on your continent?

Regards

I'm new here, so please correct me if this belongs in the software tools or live sound areas... I'm posting here because a ported guitar or bass cabinet is essentially a full-range speaker in that it's got one driver that you're trying to get the most of. It's just that the sonic end goal for a guitar cabinet is different from the Hi-Fi goal.

There are a lot of speaker cabinet calculators out there, but the ones I've seen all seem to assume you're trying to build a system for Hi-Fi. They don't seem flexible enough. Any recommendations for cabinet calculators (preferably web-based) that might offer enough flexibility for this application?

FWIW, I'm hoping to use a Jensen Mod5-30 driver that I happen to have on-hand.

Hello!

I need some help deciphering a schematic I found online for a JMP 2204. Plan use whatever applicable parts I have from my amp to make a combo. I have a decent electrical background and am starting to branch into sound/electronics.

1) From what I can understand, the blue resistors are variable, called potentiometers (volume, bass, treble, gain, etc.) I believe I got them all listed in this schematic. Am I correct in this understanding?

2) I'm new to speakers, and I thought the representation for them was straight forward, or maybe they aren't listed, but I used a pink circle for where I believe they would go on the schematic. Is this also correct? Or am I missing where they go?


3) At first, I believed the speakers to be what I highlighted as green. But then I believe I figured out that they are the diodes. Is this also correct?


These are my main 3 questions before I start looking more deeply into the diagram and construction. Any help you may provide would be greatly appreciated. I'm not looking for a perfect amp, by any means. Just one I can make myself as a project and save money. I currently only have SS and would like to upgrade on a budget on my free time.

Thank you!
Alex

Item: Empirical Audio Off-Ramp 5 USB-Audio Interface, S/PDIF Hynes Reg, with BNC-BNC cable
Location: Sydney
Price: $1,750AUD + shipping
Item Condition: Excellent
Reason for selling: Not used
Payment Method: Pickup - Cash, Paypal

Extra Info:
One of the best USB-audio interfaces out there; pair it with a quality DAC.

I purchased this new from Empirical Audio in March 2014; it has spent most of its life sitting at my Mum's house gathering dust. It's as new; I'd estimate it has had way less than 50 hours of use. It has the S/PDIF Hynes Regulator upgrade and a very good BNC-BNC cable that Empirical Audio also supplied. It comes with a standard wall-wart power supply; I highly recommend pairing it with a high-quality power supply, it transforms the device into something even more spectacular. I can provide a 2-channel Keces PSU for an additional $AUD250 (purchased for $400), which is also in excellent condition with hardly any use.

At the current exchange rate, you'd be paying about $2675+shipping for the Off-Ramp 5 in this configuration (new).

.F.S. New Mark Audio & Fostex drivers (Updated selling info).

Good morning everyone. I am cleaning house and I have a ton of new Mark Audio drivers and Fostex drivers for sale and a pair of ribbon tweeters new as well from fountek. I have most of the current mark audio drivers out today for sale. I have 2 of the fostex Fe sigma series for sale in some FF drivers for sale and a few Fe drivers for sale current drivers as well. Important note: the buyer pays all pay pal fee's and shipping. I will lower the price because of this. I can run the zip code to give you a price on the shipping?Again these are all brand new drivers never used still in the box just cleaning house. If the drivers are on sale at Madisound I will match the price. Please make offers and I will reach back to you. Please e.mail me at jeffmarch076@gmail.com for any questions and pictures. Thanks Jeff


These are the Fostex drivers I have for sale in pairs brand new.
1..FE83NV, FE103NV,FE126EN,FF85WK, FF225WK,FE108EZ, E208EZ + 1 for extra. I will give it away if you buy the pair of these drivers.
I have 3 Fountek 5" inch ribbon tweeters model Number #
$200.00 with shipping NEOCD.22 0M-BLK. I will give away the 3rd one if you buy them as a pair. I also have a Dayton Audio Mini Planner tweeter set as a pair for sale.
Mark Audio drivers I have for sale in brand new Pairs. 1, 6m in gold, 3.CHR 120 in gray, Pluvia 7phd, Pluvia 11 in gray, CHN 120 In gold, CHN 110 in gray, 7MS in Gold, , 11MS in gold, CHN 50 IN Gray, CHR 70a in Gray 2 pairs , CHP70A Natural paper, CHN-70, CHP-70A in black paper drives. The drivers I don't have in my possession to sell is;
The Alpair 12PW, 10 P, and 10 M from Mark Audio.


Thanks for looking. Jeff

I've spent days looking for an answer, but my dense head is just not grokking what must be dead simple for everyone else.

I'll be using a 5AR4 (GZ34) and the schematic shows a 5R4 with apparently six connections. I assume I'd wire AC into pins 4 and 6 on a GZ34, but I'm stumped on what comes out--maybe I use pins 2 and 8, with one of those connecting to the LC network and the other going to to the 5V section of the power transformer/rectifier?

Is this schematic showing a standard convention that "everybody" knows and that I've somehow never seen until now? 😕



Reminds me of when I'm trying solve a chess problem and after a few good runs, I hit a problem that stumps me and in hindsight is dead simple. I can be blind that way sometimes. 😎

Hi,
I am fixing my Orion and need to replace the thermal pad under and above the BJT.
I have thought about using mica and thermal paste, but mica sheets are not easy to find.

What do you use? (economical but safe choice).
Is Kapton okay?

From Italy I generally buy from Rs-component, Mouser, Farnell ..

Thanks for your attention. 🙂

Hello everyone 👋
Can I connect spdif to i2s board to the topping d10s dac ?
I can find the i2s marked pins around the dac chip.

I am going to send in the gerbers to the pcbmanufacturer and make me some of these:'
https://www.diyaudio.com/forums/pass-labs/321925-diyaudio-watt-m2x-post6316096.html

Then I thought maybe somme one else would like some to.
So write if you would like a couple.

Hello,
some speakers (Kef 104, Concerto, etc.) do have the front baffle recessed into the cabinet to acommodate for grille frames. Would it be worth soundwise making the loudspeaker baffle flush with the border side panels? I wonder if it could help somewhat with imaging... I was thinking doing that to my Concerto kit speakers whose baffles are recessed about 1'5 cm into the cab
What do you think?
Thanks

Ok I have acquired a mc368-b150 amplifier and have done a few things with it to share. I haven't really found a lot of info on it so I will start. First of all i ordered this amplifier from china to work with 120vac what i got was a 115/230v version with a 230v power cord but amp was set for 115 vac with appropriate fuse 5 amp. i contacted ming da via email and was told that it will work fine on the 123 vac i have at my receptacle at home. I have a yaqin mc100b that i run at exactly 110v with an apc voltage regulator as its rated 110v ac +/- 10% and 123 vac is out of its upper limit. ming da says the mc 386 b-150 amp i have actually has power transformer wound for 120vac with +/- 10%. I am currently running it at my house 123 vac power. so i open the amp and check a few things. first of all the bias of the amp was a little high so i rebiased the amp for my house power which by the way is suppose to be .4 to .45 vdc across the 10 ohm cathode resistor between ground and pin 8 of the KT150 tube. B+ is too high for my current fluke meter which is rated for 600 v it wont read it so im assuming its above 600v. the 6sn7 and 6sl7 voltages are within specs. and finally the heater voltage was sitting at 6.9v.the heater voltage is rectified via full wave bridge and filtered with large capacitor. so i added a .1 ohm resistor in series with the ac feeding the bridge rectifier and voltage is now 6.3 to 6.4 volts varies with load fluctuations.Also did some power testing using 2 200 watt 4 ohm dummy load resistors and feeding 400 hz signal into the amp with function generator. pushed the amp to signal just before clipping i calculate from rms value and dummy resistor right at 125 watts rms per channel not the 150 watts advertised but still pretty respectable amount of power. also linearity to the point of clipping looks good and balanced. all i have is a oscope and function generator so didn't do any distortion testing. Signal on oscope looked good didn't see any crossover distortion or ringing with a quick audio sweep of my function generator. OK now the sound what about how does it sound? well... I am running some jbl 2800 speakers and i use a fisher eq890 equalizer and at first the amp didn't have very detailed bass but sounded good even running it with flat input sounded decent. after about 3 days of running it and rebiasing it it has opened up and sounds pretty darn good. bass finally came in and even my daughter came out to my garage and said damn that sounds good. she never does that lol. I have pictures of the internals but not sure if i can post them yet as this is my first ever post. I am an electronics tech with a CET and was an electronics instructor for 8 years and have 30 years in. any questions please feel free to ask. as of now i'm not going to do any more with the amp but listen to it. i will post more info on it as it comes Thanks

Looking for a good low distortion 15" driver that will play clean up to a higher than usual xover point ie. 2.5k or so. This will be for a passive studio monitor type speaker that can do light PA duty as well - not wanting to use DSP for this. I have my heart set on the B&C DE250 driver on a JBL JRX/seos type waveguide and don't like the way it sounds at higher volume crossed under 2.5k, so that's why I'm wanting a better LF/midbass driver that will fit the design.

One of the usual culprits I've found are the Eminence 3015HO and B&C 15HPL76 neo drivers, but I was hoping there was something better out there. Most of the 12s and 15s have nasty cone breakup past 1.5k and require lots of xover trickery to flatten out and once you go through a large count of xover components, most of the sensitivity is lost. I'd like to not need more than basic BSC and a zobel other than the basic LP components on the woofer.

Your input is appreciated.

I have a Stetsom EX3000EQ that just stopped playing today. No FETs or outputs blew or shorted, the music simply stopped and the blue Power LED started to flicker and die out and I quickly pulled the power wires to prevent further damage until I got to check it out.

Unable to find anything shorted inside, just not getting +12v at various points inside the amp to allow it to power up. The +5v regulator is only showing 2v on the leg that should have +12v so there is a power interruption somewhere. I have a working one open alongside this one for reference but I just haven't been able to figure out where the interruption is occurring.

I swapped the 5V6 diode(D7) that is in the remote turn on circuit but that component is not defective as the one from the non-working amp, works in the working amp.

Hello diyaudio folks! This is my first post here, so if this is the wrong place for this, please forgive me.
I currently have a Sundown SA12 wired to 1 ohm hooked up to a Sundown SAE1000DV2 @ 1000 watts in a box built to Sundown's website provided box plans. It's pretty much a big ol' square box. I'm planning on building a box with an aeroport for simplicity and a bit different shape to open up some trunk room. The plan so far per Torres...
Height: 14.5"
Width: 24"
Depth: 14.25"
Sub displacement: 0.14 cubes
Gross V: 2.16 cubes
Net V: 1.99 cubes
Port diameter: 3"
Port back/Sub back
Port length per Torres: 5.61"
Port length per WinISD: 6" (so let's say 5.75?)
Tuning: 35Hz

The question: Do those port dimensions look good or would one of you lovely people have a different suggestion on length/diameter/etc?

Although I've been extremely happy with my 26 preamp/DAC, the tweaking bug bit me again so I decided to try out some 01A tubes in place of the 26.
I picked up a nice NOS pair of CX-301A online and set out to make the modification.

It turned out to be much easier than I though it would be, as no modifications were needed to any of the power supplies or even to the biasing arrangement. The 26s were biased with 9V lithium batteries on the grid that actually put out 9.5V with no load (fed through the LL1676 input transformer secondary, so no DC blocking cap needed) and this turned out to be just right to bias the 01A at ~-4.8V given I am running the 01A filament at +4.7V using Coleman regulators. All I needed to do was adjust the plate CCS to 3mA, change R1 in the Coleman regulators to 4.4ohm from 1 ohm, and adjust the Coleman regulators. I soldered a pc-mount terminal block onto the Colemans to make resistor swapping easier in case the bug bit me again (picture 1). The output is taken from the mu output of the CCS to a Bent Audio remote controlled Slagleformer volume control in a lossy parafeed arrangement - the volume control has ~ 150H inductance. Silver wire on a nickel core. No problems driving anything to date.

A few pictures. The preamp as first built (picture 2). Topless shot with the new CX-301A tubes (picture 3). The Buffalo IIISE DAC and Sonore USB input boards are in the top right corner of the box. I have a switch on the back to go from DAC (SPDIF or USB) to preamp (5 line inputs).

So...how does it sound? I've been a staunch supporter of the 26 as a preamp tube, but my first impressions are that the 01A has it beat in terms of detail, air and that certain lush sound, without losing any of the punch or low end. Snare drum shots and massed horns are startling in their intensity. The 26 sounds a bit less precise and a little less "juicy" in comparison. More listening to come but I'm thinking it's going to be hard to go back to the 26 for quite a while...I may also need to get a new faceplate...Max01A maybe?? Or maybe I'll be non-committal and go with MaxDHT.

PS: Rod Coleman was his usual extremely helpful self when I peppered him with questions about his regs and the 01A. Thanks, Rod!

I am new to audio Community, facinated about acoustic impedance maching devices AKA(horns) 🙂.

I am currently planning to build a FLH with vented chamber .

From some knowledge on reading tons of treads on horns, I know that the straight round horn is the best case scenario 😀. But horn gets very long therefore, folding.

So in folding horns, 90 degree bend better than 180 dergree ?.

Does 180 degree bends mess up air flow ?.

Does it creates higher order modes ?.

Causes unwanted turbulence ?.

I have never seen a FLH with 180 degree bend. But a 'TON' of tapped horn with 180 degree bends....
This is my first thread, And english is not my mother tongue. Please forgive me if there is any mistake 🙂. And feel free to correct me .

kind regard🙂.

Hi All

I am a fairly new speaker builder with one project under my belt and I have decided to build another. I thought I would come here first to see if I could receive some advice. I am planning on building a portable Bluetooth speaker with the following components
Woofer: Dayton Audio DSA115-8 4" Designer Series Aluminum Cone Woofer
Tweeter: Dayton Audio ND16FA-4 5/8" Soft Dome Neodymium Tweeter 4 Ohm
Amp: Dayton Audio KAB-250v3 2x50W Class D Audio Amplifier Board with Bluetooth 4.0

I have also made a simple crossover design on Vituixcad2 with the data given from Dayton Audio. I will post a screen shot of the simulation below. Any help with this would be very much appreciated.

The tweeter is 4 ohms and the woofer is 8 ohms and the amp is rated for 4-8 ohms so does this work?

The tweeter also has a Power handling (RMS) of 30 Watts. The amp is 50 Watts. Do I need to worry about this after using a crossover?

Thanks in advance for any help!

Looking for the value of D403 in the remote/power up circuit. It is located at the very end of the preamp daughterboard.

Anyone have a deep understanding of the philips CD control and decoding system? The SAA7341 Decoder IC?

I am trouble shooting a CD player that has a problem with the CD motor control. The CD spin's backwards and won't read a disc(i believe it does not have any PWM motor control). Looking at the Datasheet for the SAA7341 it is a bit cryptic on how it controls the PWM to the CD turntable motor. the datasheet reads as if it ONLY controls the motor on acceleration. but does not give any info if it controls the motor during play?

In the attached photo. pin 28 of the SAA7341 is the PWMA output that is connected to the MC68 Micro controller and the TCA0372 Power opamp that controls the turntable motor.

i am trying to understand the joint operation between the 7341 and the MC68 controllers. I believe one or the other is not putting out the PWM signal to control the motor. one or both IC's may have failed...OR...the problem might be further upstream. is there a Laser/focus/radial error causing a loss of PWM? how do i tell...etc

Is there anyone here that has a solid understanding of these old machines?? Please PM me.

I have this CD player (the older one with tuner) that has a strange problem.
Upon inserting a disc the sled moves to approx. middle portion of the disc and tries to read the TOC from there.... Of course without success, reading: No Disc. (laser works, lens servo works) I tried it with another mechanism (KSS213C) from a working player, but the problem remains. Any idea? No documentation (service manual) is available from anywhere.
There are no adjusting trimmer pots (focus, tracking,etc.) on the PCB....

If I want to add some smaller neodymium magnets as bucking magnets on a midwoofer with a ferrite magnet, where would I place the neodyms, and with which polarity, to achieve the strongest field-increase in the airgap?

I know that a ferrite bucking magnet the same size as the original magnet should be attached just above the original magnet, with opposing field direction. So I guess I could attach the neodyms the same way, above the original magnet and with opposing field direction (they reject each other).

But maybe it would be better to place the small neodyms right at the center of the pole piece, with the same polarity (attracted to the pole piece), so that the field from the neodyms point directly up into the pole piece.

What do you think?

Hello All,

I enjoy the DIY Audio side of electronics and have access to an HP 89410a Vector Signal Analyzer. I see that it can make FR measurements, Phase Noise, Distortion and so many more. Would this be a useful bit of kit for my efforts building amplifiers, speakers and pre-amps? Or is it too cumbersome considering all of the great software available?

I do have an HP 8560E, TEK AA5001 & SG5010, and a 2465b. Would this 89410a be a good addition to the lab and if so what will it add to my current abilities to measure regarding DIY audio tinkering? It is in excellent condition and I would be disappointed to move it along and then find that is EXACTLY what I could have used for anything in my pursuits. But I do not need to simply collect gear for the sake of "cool tools" that are essentially duplicating any that I already have on the bench.

Cheers,

David

I’m looking for a First Watt B5 (Nelson Pass) active crossover for my open baffle loudspeakers.

Remco

Hello

I decided to sale my spare JVC RC-EZ31 ( not EZ35 ) for Shigaclone including the Case. It’s made from Aluminum the Front and backside are not anodizing. The top plate is 10mm thick and the transport and the Display fit perfect in the cutout. Casing dimension are Width: 355mm Deep:340mm Hight:98mm Weight: 10kg The Drive unit, control board, remote control and the puck including (which sits on top of the CD). I have de-assembled the boombox so shipping costs will be relatively low. The Parts are unused and will ship from Germany inside EU I can offer GLS or DHL. Offers are welcome, I want just cover the material cost. I have more pictures available if anyone is interested. The case has been with me for a few years and only takes up space. Please send a PM if you interested.

Regards,

Finwbu

Hi there, wondering if you can perform any upgrades to an HDP Express II DEQX?


Looking for any recommendations, I've heard of people replacing the clock with a abetter one and
using better caps on the output stage. Regards,


Eli

I have 2 mint Shallco 45 positions switch. These are wonderful switches, extremely well-built and large. Used but still in excellent condition. Easily outperformances the DACT or Khozmo.
I will send a BOM for 100K attenuator with Dale resistors for buyers, if interested.
$125/ea plus shipping from Singapore.

Hi,

I'm looking for a pair of BMS 4550 compression drivers i good working order. EU preferred. Looking for low price since i need them for sort of a proof of concept project.

Thanks,
Marijan

The polarity marking of this (probably old but unused) tantalum capacitor seems to be missing:

Any idea what is the polarity of this capacitor? I am guessing the middle lead with the '-52' is the positive side.
Thanks.

Hello Turntable Fans!

I'm selling the original EPA-110 Tonearm unmounted from a Panasonic SL-1100. The Tonearmboard is available as well, as is the Tonearmrest and Lift.

Here are pictures:









The condition ist very good, I have not seen any damage or sign of wear. The arm was in use until recently and was "handled like a raw egg". The Aluminum-Armboard has a few scratches caused by the use of the SL-1100 Dustcover, these may be removable, though. The Lift runs smoothly, no issues.

I'm ready to sell the whole package or in separate chunks, like the Arm with Armrest, the Alu-Board alone, the Arm-Lift mechanics as chunk.

The complete package goes for 270€ plus packaging & shipping, excluding duties. Separate chunks, please PM me for price. Please also PM me with your interest and (reasonably close) price bid.

Advance payment by bank transfer is preferred.
I'll provide proof of shipment, the risk of loss is with the buyer (German law for private deals applies).

Thanks for reading, I'm looking forward to get your bids!
Winfried

Friends, can anyone help with schematics or better service manual for this beast? A-10 or similar. I need to sort out preamp and phono section. Power amp is ok. Yes, I looked at hifiengine, not there. I searched a lot. I am willing to buy it.

Hi all,

Amp came dead. No outputs were bad no power supply fets were bad.
Powered up and was pulling 0.4amps. Checked pin1 voltage which was 5.2v and pin 2 was 5.1v. So I removed the outputs and same issue. I removed main rectifiers same issue.
Removed 4080 same issue.
I lifted the voltage divider resistors connected to pin1 with main rectifiers on board and without 4080 and outputs. Amp came on with 1.3Amps stable. Tried to remove the current limiting resistor and it went upto 4.5amps. Main rail voltage from which voltage divider is connected to go to pin 1 of sg3525 is 87v. Is that current draw normal. And what is the pot in the middle of the board use for?

Good morning HiFis, may I present my plasma loudspeakers here to you? For the amateur handicraftsman somewhat progressed the reproduction might prepare hardly problems. The beginner should only read it. Rel. simple circuit, not expensively, without smell, loud, beautifully. Living room-suited, sense-extending. Not more dangerously than a hair dryer.

Made in Germany.


Dire Straits


Without input


Enough for Living-Rooms


Never heard better.


Best regards
George

Cat 5 and magnet wire - very good speaker cables . . For interconnects, I’ve read that Cat 5 can work very well.

I’m moving my sources & “pre-amp” next to where I sit . . it makes room up the more visible end of the room, for some big speakers

Interconnect lengths will be about 5 m.

I’ve got quite a few to do (including another room o0f similar lengths) so for speed of putting them all together *if sound quality is likely to be about equal, I’d prefer solid core over multi strand (cat 5).

I don’t know if any of this effects things:
the “pre-amp” is a Promitheus Audio transformer volume control (www.promitheusaudio.com/frontpage.html). The TVC’s output impedance depends on the volume setting, but is very low, typically c 2 - 25 R. As TVCs add virtually resistance, the impedance at it’s outputs effectively derives from the source equipment. The source is mostly CD, though in time it will become the PC. The power amps for the foreseeable future will be SS.

So . . would solid core magnet wire work as well as cat 5?

I’m considering a local magnet wire of outer size of 1.25 mm (core = 1.0? mm) ie cross sectional area about 0.8 mm^2. As cross sectional area (CSA) decreases, I think resistance less? Does the TVC’s lower output impedance mean less interconnect CSA is needed?

A search showed that some believe that if the is cables including cat 5 are Teflon-wrapped (C5 plenum grade), it’s better, not sure how. If such a thing might exist, is it worth seeking out Teflon-wrapped magnet wire?

Tho’ if cat 5 is better, how many strands should be enough for that length?


Thanks

I need advice from the experts here.
I want to buy an MC capsule, specifically the famous and renowned Denon DL-103.
This capsule needs a medium to high mass arm, it seems that the higher the mass, the better it behaves from everything I have read.
I have a Micro Seiki MA707 arm that comes supplied with accessories to raise the dough so I can use it with cartridges like the Denon mentioned.
Within my limited budget (and what I'm willing to spend), I had Pro Ject tube phono presets in mind.
But they have presented new and more expensive models, (it is always like that, gg 😀 ) and even the current Tube Box S2 is not suitable for low output MC, only MM and high output MC. The current ideal model would be the Pro-Ject Tube Box DS2, but its price is around 1000 US $, + freight and taxes, so I discard it outright ....😱
So, I abandoned the idea of ​​the pre tubes and found that Musical Fidelity V90-LPS (It's from SS, yes, like the Nad PP2, something cheaper the latter) has good reviews and a price according to what I want to spend.
The question I have is about its pairing with the Denon cartridge
, its output is 0.3 Mv and the pre MF V90-LPS claims 0.4 Mv (400 MicroV) for an output of 300 Mv.
But on the other hand, the input sensitivity of my tube amp is 270 Mv, which would compensate for that very small margin.....

Also my cabinets are high efficiency, 95 DB / 1w / 1m.

I will appreciate any opinion and / or experience, everything is welcome.

DL-103R + V90-LPS = good match?- Vinyl Engine

DL-103


DiaLogue Two — PrimaLuna USA

Musical Fidelity | V90-LPS Phono Stage

I think a picture is worth a thousand words.

I will just say it works beautifully - and I have tested it with signals up to 100Mhz master clocks. 🙂

We have a small qty available very soon, and more to come thereafter.

This cct can be used to switch between DSD sources and PCM or between two PCM sources etc.

The concept is simple. You have a common four channels(A) and two sets of 4 switched channels(B1 and B2). The set that is selected is dependent on the state of the "S" input. The OE(bar) input must be low (jumper to GND) for the output to be enabled.

Pretty easy.

The MUX works with a VCC input of 3.3V to 7V(max) I recommend 5-5.5V the signals that are used should be equal to or less than VCC.

Cheers!
Russ

Hello
Help needed / My sony player never go into mute mode.

It has two relays (RV801 and RV101) - and both relays works correctly.

Can somebody explain this? - and maybe point out what the cause could be.
This turntable should always be muted when the needle is of the record.

BR Benny

hi all, 😉
in this link low-DCR-coils troels describes how to measure low DCR inductance value.

is this method most reliable and accurate then traditional mesurements ?

which is preferable ?

I am in need of two DC blockers for my system, but am not brave enough to build one myself. I've searched the forums and have found so many different circuits that I am not sure which one is best. After reading all the information, I am still very uncomforable with the whole idea of building one of these. I am accident proned enough as it is...

I need one blocker for my subwoofer (JL Fathom F112), which has a 1500W amp in it. The other one I'd like to run on my Forte Audio 1A power amp and receiver. I think the receiver draws about 600W max, and I am not sure about the Forte...

So, would anyone be willing to build a two DC blockers that would fit these requirements for me? Please email me or reply here if you would...

Thank you

Hello!. Would anybody have any information, schematics or bias information on this New Zealand made amplifer?

If so, this information would be usefull.

I have set it up at 150mA p/c (per channel) and it goes well, doesn't run too hot.

Also information on the matching Plinius II preamp would also be nice. Schematic etc.

Thanks on the help with my Playmaster 60/60 on previous posts guys.

Tony.

Hello,
I'm looking for service data of an old 1995 Antileon power amplifier, mainly the alignment procedure.
The schematic would be very welcome aswell. One of the channels takes a little bit longer to come up and I was told it's a common issue with alignment or replacement of certain part...but no one wants say which part.


Many thanks in advance. I am also willing to buy and pay for the schematics.


Regards,
Jan

Hi Thought its about time.. I joined.

Been popping in and out for quite some time looking at the forums. I'm interested in class D amps and about to under take a diy build. Previous projects, digital music player, mains distribution block and some speaker plinth bars (well I sent a drawing to a man and he made them).

Look forward to spending more time on here

Hi, I'm an old fogie, with a lifelong interest in audio, and a range of DIY projects. Despite this, my soldering skills leave a lot to be desired. I seem to spend forever fixing dry joints! I know there are "how to" videos on the web, but they do not seem to help.

A topic close to my heart is the multi-channel reproduction of conventional stereo recordings, and I will raise a separate thread on that subject...

Hi...
I have been reading this amazing forum for a long time, finding several interesting topics and some solutions to my problems.
So I decided to sign up... I write from Rome, Italy.
Thanks for accepting me.

P.s. English is not my language, so forgive me the mistakes I'll surely make...😀

As the title states I am looking to buy the above. Thought I would ask here first before I take the plunge and buy one brand new. I am UK based but open to offers from anywhere.

Cheers!

Hello guys, I'm new here just want to know those have experience with the amplifier PIONEER A9... I replaced the main output transistors, but it keeps on short once the power is initiated... I replaced the complementary pairs 2SA1076/2SC2275 and all drive transistors connected to it, even coupled .47/5W resistors... still it burns out... anyone could give me some idea, is helpful...😉

Hi all, I'm searching for help repairing my old school amplifier. After some minutes listening to music the left channel start to be terribly distorted causing me a lot of pain 🤣.
My board seams to be in good condition, I cleaned and restored the varistors with contact spray and degreased with isopropyl alcohol.

This is the scheme of the board. Hope you can help me, I'm so affectionate to my old school amplifiers! 🙂

Thanks in advance!

hello,

received 8 pins cable by mistake. Any audio-visual use ?

Hi everyone,

For those in Australia, where do you buy your parts from?

Ive been modifying an amp that uses P-P EL84. Ive made a couple of bias-blocks (CCS sub-circuits) along the lines used by Gingertube in his Baby-Huey amp, one per output valve.

Due to the high +B in this amp, Ive reduced bias on the EL84 to 30mA which equals 10.5W per tube at its current +B.

During static testing, I noticed a loss of power over what I had before, so checked cathode-voltages. These (at point of clip) were 25V. The idle voltage was 12.5 to 13V depending on which tube checked.

Ive placed a 14V 5W Zener diode clamp across the bias-block from tube cathode to deck. This has restored the power at full output to near what it was....

Thoughts....?

Pass LabsAudio distortion and feedback - Pass Labs
The link above from Pass Labs say that high-gain NFB (such as Opamps) has lower distortions overall but the output harmonics are more complicated.

A simple triod although has high distortion but mostly 2nd and 3rd order.

I did two simulations using opamp and a simle JFET common emitter and the simulations show that: Opamp has lower overall distortions but it has more harmonics on the output.

On the IMD plot two 10Khz and 11KHz, there is only a single 1KHz on the simple FET, but on the opamp, there are several overtone of the 1KHz tone.

Because of that, opamp tends to sound lean and brittle due to the higher order harmonic.

The harmonic content of an overdriven tube amplifier consists primarily of 2nd order and 3rd order harmonics with some 4th order harmonics. The harmonic content of an overdriven transistor amplifier is primarily 3rd order with suppressed 2nd order harmonics. 2nd and 3rd order harmonics are the most important from a viewpoint of electronic distortion. Musically the 2nd harmonic is an octave above the fundamental and is almost inaudible, yet it adds body to the sound, making it fuller. The 3rd harmonic is a musical 12th. Instead of making the tone fuller, a strong 3rd harmonic makes the tone softer. The odd harmonics (3rd, 5th, etc.) produce a "stopped" or "covered" sound. The even harmonics (2nd, 4th, etc.) produce a "choral" or "singing" sound. Adding a 5th to a strong 3rd harmonic give the sound a metallic quality that gets annoying in character as the amplitude increases. A strong 2nd with a strong 3rd harmonic tends to open the "covered" effect. Adding the 4th and 5th harmonics to this gives an "open horn" character. The higher harmonics, above the 7th, give the tone "edge" or "bite."

Click to expand...