Magnavox A531 Germanium Console Amp Reborn as a Vintage Stand-Alone Hi-Fi Component
- By wparks
- Solid State
- 15 Replies
Magnavox A531 Germanium Console Amp Reborn as a Vintage Stand-Alone Hi-Fi Component
Germanium transistor amplifiers are fascinating. They were proudly the first solid state designs, yet are an almost forgotten footnote lost between the chapters of vacuum tubes and silicon transistors. But germanium is worth exploring- in the same way that previously outmoded vacuum tube amplifiers are worth exploring, even though they too, had obvious design short-comings compared to the venerable silicon transistor. The germanium sound has been compared frequently with tube sound, and most of this sonic "coloration" comes from the same ingredient as tube amps- audio transformers in the signal path. Transformers provide for a fat warm bass, well defined, punchy but non-fatiguing midrange, and a delicate, silky high end. This treatment can be very beneficial when paired with modern digital sources, which are often described as harsh, technical, or sterile. I find the germanium sound to be very pleasant, and with the right music intoxicating. Those brave enough to explore germanium I think will end up giving it a welcome place among the pallet of flavors we chose from in our day to day listening.
This thread covers the restoration of a 1962 Magnavox germanium console/record player amplifier chassis to turn it into an attractive stand-alone, dare I say, "high fidelity" amplifier component. This, the first part, will cover cosmetic and chassis restoration, and the second part soon to come will cover the electrical restoration, transistor testing, and circuit details.
I have been tinkering lately with the 12V germanium amplifiers found in affordable 8-track car players from the late 60's and early 70's. They can be found almost anywhere, from garage sales to Ebay for under $30 including shipping. These really are hidden gems- because they include all of the impossible to find parts (the interstage transformers, thermistors, and matching sets of germanium pre and power transistors) already in one functional package ready for your study and redesign. Typically being of Japanese design, they are generally high quality amplifiers in a very small package. However, they are pretty low power- With only 12-14V to work with, a class AB can only generate about 4-5 Watts per channel even into 4 Ohm speakers. This is perfect for near-field listening on a desk top or bookshelf, but is not for general full-room listening. A fun detailed example of one of these that I reworked into a small stand-alone test amplifier is detailed in my "Germanium Bake King" project.
I needed something with a more power, in the 15 to 30 Watt per channel range to drive my larger vintage 3-way speakers for full room listening, and a console amplifier chassis seemed just the ticket. I had previously rebuilt a Magnavox 9300 series 6BQ5/EL84 push-pull tube amplifier chassis to be stand-alone, and thanks to the amazing Dave Gillespie redesign of this chassis posted on AudioKarma it became quite the audiophile contender and my favorite amplifier. Reworking a Magnavox germanium amp would be a perfect compliment in my collection.
When Magnavox first released their new solid state "Astro Sonic" line of consoles in the early 60's, they used germanium power transistor output stages, driven through interstage signal transformers. As these consoles age and are discarded, they provide a ready source for workable examples that can either be converted directly to stand-alone, or harvested for otherwise impossible to find parts to be reused. Many of the later models incorporated the power amplifiers into the radio chassis so they are bulky and not readily converted to stand-alone, but are a good source of parts. There are only a few designs that used a stand-alone amplifier chassis separate from the radio, primarily from the early 60's, such as the one I chose for this project.
I found this 1962 germanium amp chassis from a Magnavox record player for sale on ebay. The seller offered it for $25 plus $25 shipping, and I just could not resist. It looked pretty nasty, but would be a perfect fit if I could restore it. The seller said it did work, so I knew the bones were good, so it probably just needed a full re-cap and some minor upgrades. This is a Magnavox chassis model A531-01-00, which used the same chassis box as it's bigger brother, the A551-01-00. (In Magnavox chassis numbers, A is for Amp, A531 is the model, -01 is the version, and the -00 is revision) The more powerful A551 was used in larger full size Astro Sonic consoles with both radio and phono and was rated at 25 Watts per channel. It had a larger power transformer and used 47P1B transistors, and larger filter and output capacitors.
An example of the bigger A551:
My A531 chassis, with the smaller power transformer and the 38P1C transistors, was used in smaller stereo record player only consoles of unspecified output power. Given the supply voltage is -38V instead of the A551's -44V, I estimate about 18 Watts per channel or so. Still plenty big enough for what I need, and a good companion to the 15 Watt per channel 9300 series 6BQ5 tube amp. The interstage transformers were stamped 1386235, the 138 meaning Stancore manufactured, so excellent transformers, and the date code of work week 35 of 1962. The power transformer was also Stancore and had a similar date code work week 31. The transistors looked pretty roached- badly darkened and corroded, but they did work. The chassis still had the original molex type connector to the radio/phonograph, and the spade type connectors for speakers and pilot lamp.
To begin the cosmetic restoration, I first documented everything with photographs and notes, especially under the chassis. I disconnected and removed the power transformer discarding the really ugly looking screws and sheet metal nuts, then carefully removed and stored the transistors and heat sink to clean everything up. The only thermal paste present under the transistors was a thin oily residue, and dirt had made it's way under the transistors and the mica slips were in bad condition. This is an important area to attend to in older equipment with exposed transistors, which can benefit greatly from new mica slips and modern thermal paste.
What I feared was heavy corrosion on the nickel plated chassis turned out to be only a light fuzzy haze of corrosion, mixed with baked on dust. I tried cleaning first- alcohol, mineral spirits, and even acetone hardly made a dent. I found the fuzz was most easily removed by scraping- with the sharp edge of several wooden clothes pins that did not scratch the nickel. It was slow going, inch at a time, swapping out clothes pins as the edge dulled and started to grind into the nickel. That was followed by a vigorous rub-down with a terrycloth rag soaked in white vinegar to dissolve what I could, dried, then cleaned thoroughly with a water damp rag to remove the acid from the vinegar. While the nickel took on a nice reflective shine, it was still hazy-cloudy where corroded. At this point I could have started using metal polish like Brasso to grind down through the haze, but I don't like the shabby-schick look of over-polished nickel- it never looks right. I am reminded that with most of my projects, it's about what's under the hood and preserving it's original vintage character, not how fancy it's decorated that I really care about. It's vintage, and a bare knuckle nuts and bolts chassis, so let it be what it is in humble and dignified authenticity.
The remaining light surface rust spots on the nickel plate, rivets, and tops of the transformers came off pretty easily using a fine brass bristle brush from Harbor Freight. The brass did not scratch the steel or nickel, but removed the vinegar-softened rust down to a really nice looking patina with no damage. Be careful around the cloth covered wires and the paper/plastic wrapping on the audio transformer windings, as they damage easily even with the brush. I clipped the wires and disconnected the molex connectors, drilled out the rivets holding the the phenolic spade connector strips for the speaker and pilot connections.
I see a lot of different ways of dealing with extraneous holes in the chassis, some not very pretty. I find the most attractive treatment is to tack sheet metal patches from the inside. I keep a stash of vintage sheet metal pieces from the junk chassis I cannibalize, to cut patches for the holes. Vintage cadmium and nickel plated is excellent for soldering and is the easiest, but galvanized will work in a pinch. Fortunately I have an old monster 250W soldering gun from the thrift store that works wonders for soldering terminal strips and patches directly to the steel chassis, but a regular 140W Weller will work if you are patient. First clean the underside surface around the chassis hole with a scrap of sand paper or green scrubbie (don't use steel wool unless you like random shorts!), then add a few drops or dabs of soldering rosin. Once the plates are tacked in place, you can drill new holes for a power switch or input connectors, etc. I prefer to have the new device sit within the confines of the hole- Overlapping over the outside looks tacky to me.
The original standard Magnavox RCA input connectors are very close together, preventing you from using almost all RCA patch cables. I have found that the easiest and most attractive way to remedy this is to remove them, put in a patch plate, then drill for two new individual RCA connectors that are spread apart as far as possible while still fitting inside the original opening. This will allow enough space to use all but the fattest RCA cables.
I really liked how the appearance worked out on my 9300 tube amplifier, which kept very clean and understated, and put on an oak plinth with brushed nickel drawer pull handles, so I did the same thing here. The oak came from the center of a $3 used cabinet door from our local Habitat for Humanity which I cut down, sanded, and treated with the Natural shade of Watco Danish Oil. I really love that stuff! The drawer pulls were the most plain jane brushed nickel from Home Depot. I cut a sheet metal shield plate to sit between the chassis and plinth from some HVAC scrap also from habitat. The shield is held down flat on the oak with two small screws near the center to keep it from bowing up and touching something. For speaker outputs I chose the same type of small profile panel mount 4mm banana jacks as I did with the 9300. I really love the vintage understated look, and prefer ease of banana plugs for most of my speaker cables.
Stay tuned for part 2 coming soon: Electrical restoration, transistor testing, and circuit details
Germanium transistor amplifiers are fascinating. They were proudly the first solid state designs, yet are an almost forgotten footnote lost between the chapters of vacuum tubes and silicon transistors. But germanium is worth exploring- in the same way that previously outmoded vacuum tube amplifiers are worth exploring, even though they too, had obvious design short-comings compared to the venerable silicon transistor. The germanium sound has been compared frequently with tube sound, and most of this sonic "coloration" comes from the same ingredient as tube amps- audio transformers in the signal path. Transformers provide for a fat warm bass, well defined, punchy but non-fatiguing midrange, and a delicate, silky high end. This treatment can be very beneficial when paired with modern digital sources, which are often described as harsh, technical, or sterile. I find the germanium sound to be very pleasant, and with the right music intoxicating. Those brave enough to explore germanium I think will end up giving it a welcome place among the pallet of flavors we chose from in our day to day listening.
This thread covers the restoration of a 1962 Magnavox germanium console/record player amplifier chassis to turn it into an attractive stand-alone, dare I say, "high fidelity" amplifier component. This, the first part, will cover cosmetic and chassis restoration, and the second part soon to come will cover the electrical restoration, transistor testing, and circuit details.
I have been tinkering lately with the 12V germanium amplifiers found in affordable 8-track car players from the late 60's and early 70's. They can be found almost anywhere, from garage sales to Ebay for under $30 including shipping. These really are hidden gems- because they include all of the impossible to find parts (the interstage transformers, thermistors, and matching sets of germanium pre and power transistors) already in one functional package ready for your study and redesign. Typically being of Japanese design, they are generally high quality amplifiers in a very small package. However, they are pretty low power- With only 12-14V to work with, a class AB can only generate about 4-5 Watts per channel even into 4 Ohm speakers. This is perfect for near-field listening on a desk top or bookshelf, but is not for general full-room listening. A fun detailed example of one of these that I reworked into a small stand-alone test amplifier is detailed in my "Germanium Bake King" project.
I needed something with a more power, in the 15 to 30 Watt per channel range to drive my larger vintage 3-way speakers for full room listening, and a console amplifier chassis seemed just the ticket. I had previously rebuilt a Magnavox 9300 series 6BQ5/EL84 push-pull tube amplifier chassis to be stand-alone, and thanks to the amazing Dave Gillespie redesign of this chassis posted on AudioKarma it became quite the audiophile contender and my favorite amplifier. Reworking a Magnavox germanium amp would be a perfect compliment in my collection.
When Magnavox first released their new solid state "Astro Sonic" line of consoles in the early 60's, they used germanium power transistor output stages, driven through interstage signal transformers. As these consoles age and are discarded, they provide a ready source for workable examples that can either be converted directly to stand-alone, or harvested for otherwise impossible to find parts to be reused. Many of the later models incorporated the power amplifiers into the radio chassis so they are bulky and not readily converted to stand-alone, but are a good source of parts. There are only a few designs that used a stand-alone amplifier chassis separate from the radio, primarily from the early 60's, such as the one I chose for this project.
I found this 1962 germanium amp chassis from a Magnavox record player for sale on ebay. The seller offered it for $25 plus $25 shipping, and I just could not resist. It looked pretty nasty, but would be a perfect fit if I could restore it. The seller said it did work, so I knew the bones were good, so it probably just needed a full re-cap and some minor upgrades. This is a Magnavox chassis model A531-01-00, which used the same chassis box as it's bigger brother, the A551-01-00. (In Magnavox chassis numbers, A is for Amp, A531 is the model, -01 is the version, and the -00 is revision) The more powerful A551 was used in larger full size Astro Sonic consoles with both radio and phono and was rated at 25 Watts per channel. It had a larger power transformer and used 47P1B transistors, and larger filter and output capacitors.
An example of the bigger A551:
My A531 chassis, with the smaller power transformer and the 38P1C transistors, was used in smaller stereo record player only consoles of unspecified output power. Given the supply voltage is -38V instead of the A551's -44V, I estimate about 18 Watts per channel or so. Still plenty big enough for what I need, and a good companion to the 15 Watt per channel 9300 series 6BQ5 tube amp. The interstage transformers were stamped 1386235, the 138 meaning Stancore manufactured, so excellent transformers, and the date code of work week 35 of 1962. The power transformer was also Stancore and had a similar date code work week 31. The transistors looked pretty roached- badly darkened and corroded, but they did work. The chassis still had the original molex type connector to the radio/phonograph, and the spade type connectors for speakers and pilot lamp.
To begin the cosmetic restoration, I first documented everything with photographs and notes, especially under the chassis. I disconnected and removed the power transformer discarding the really ugly looking screws and sheet metal nuts, then carefully removed and stored the transistors and heat sink to clean everything up. The only thermal paste present under the transistors was a thin oily residue, and dirt had made it's way under the transistors and the mica slips were in bad condition. This is an important area to attend to in older equipment with exposed transistors, which can benefit greatly from new mica slips and modern thermal paste.
What I feared was heavy corrosion on the nickel plated chassis turned out to be only a light fuzzy haze of corrosion, mixed with baked on dust. I tried cleaning first- alcohol, mineral spirits, and even acetone hardly made a dent. I found the fuzz was most easily removed by scraping- with the sharp edge of several wooden clothes pins that did not scratch the nickel. It was slow going, inch at a time, swapping out clothes pins as the edge dulled and started to grind into the nickel. That was followed by a vigorous rub-down with a terrycloth rag soaked in white vinegar to dissolve what I could, dried, then cleaned thoroughly with a water damp rag to remove the acid from the vinegar. While the nickel took on a nice reflective shine, it was still hazy-cloudy where corroded. At this point I could have started using metal polish like Brasso to grind down through the haze, but I don't like the shabby-schick look of over-polished nickel- it never looks right. I am reminded that with most of my projects, it's about what's under the hood and preserving it's original vintage character, not how fancy it's decorated that I really care about. It's vintage, and a bare knuckle nuts and bolts chassis, so let it be what it is in humble and dignified authenticity.
The remaining light surface rust spots on the nickel plate, rivets, and tops of the transformers came off pretty easily using a fine brass bristle brush from Harbor Freight. The brass did not scratch the steel or nickel, but removed the vinegar-softened rust down to a really nice looking patina with no damage. Be careful around the cloth covered wires and the paper/plastic wrapping on the audio transformer windings, as they damage easily even with the brush. I clipped the wires and disconnected the molex connectors, drilled out the rivets holding the the phenolic spade connector strips for the speaker and pilot connections.
I see a lot of different ways of dealing with extraneous holes in the chassis, some not very pretty. I find the most attractive treatment is to tack sheet metal patches from the inside. I keep a stash of vintage sheet metal pieces from the junk chassis I cannibalize, to cut patches for the holes. Vintage cadmium and nickel plated is excellent for soldering and is the easiest, but galvanized will work in a pinch. Fortunately I have an old monster 250W soldering gun from the thrift store that works wonders for soldering terminal strips and patches directly to the steel chassis, but a regular 140W Weller will work if you are patient. First clean the underside surface around the chassis hole with a scrap of sand paper or green scrubbie (don't use steel wool unless you like random shorts!), then add a few drops or dabs of soldering rosin. Once the plates are tacked in place, you can drill new holes for a power switch or input connectors, etc. I prefer to have the new device sit within the confines of the hole- Overlapping over the outside looks tacky to me.
The original standard Magnavox RCA input connectors are very close together, preventing you from using almost all RCA patch cables. I have found that the easiest and most attractive way to remedy this is to remove them, put in a patch plate, then drill for two new individual RCA connectors that are spread apart as far as possible while still fitting inside the original opening. This will allow enough space to use all but the fattest RCA cables.
I really liked how the appearance worked out on my 9300 tube amplifier, which kept very clean and understated, and put on an oak plinth with brushed nickel drawer pull handles, so I did the same thing here. The oak came from the center of a $3 used cabinet door from our local Habitat for Humanity which I cut down, sanded, and treated with the Natural shade of Watco Danish Oil. I really love that stuff! The drawer pulls were the most plain jane brushed nickel from Home Depot. I cut a sheet metal shield plate to sit between the chassis and plinth from some HVAC scrap also from habitat. The shield is held down flat on the oak with two small screws near the center to keep it from bowing up and touching something. For speaker outputs I chose the same type of small profile panel mount 4mm banana jacks as I did with the 9300. I really love the vintage understated look, and prefer ease of banana plugs for most of my speaker cables.
Stay tuned for part 2 coming soon: Electrical restoration, transistor testing, and circuit details
Leak TL12 Restoration
- By bigbrowncow
- Tubes / Valves
- 18 Replies
Hi everyone,
I’m working on restoring my father in law’s TL12s and would love some input and advice. I have two amps and a spare third chassis with missing ironware and a mix of new and old components. There is also a Point One preamp and Troughline tuner but I am not looking at those.
The amps were last tested 20 years ago but were almost certainly in storage before that.
I have a multimeter and new digital LCR meter, and old (untested) CRT oscilloscope but no other proper test equipment.
What I’ve done so far:
Questions and next steps:
1. The 4uF+8uF+4uF capacitors in the can show no signs of leakage. The LCR meter shows nominal values (3600nF-4100nF, 7800-7820nF and Vloss 0.1% ESR 0.5 Ohms for each). What else do I need to do to test if these are ok to use? Or should I just bypass them with modern caps?
2. I am planning to replace the 5 coupling capacitors in each amp with 0.27uF 630V polypropylene from Cornell Dubelier. I can’t find a reliable source of high voltage 0.25uF capacitors anywhere. Is this a sensible choice?
3. I will replace all the electrolytics with identical values, and any resistors that are out of tolerance according to the list on 44bx.com
4. How can I further test the ironware? I am getting very low resistances (MM shows about 0.5 Ohm) on the mains transformer low voltage secondaries which makes sense to me. I am also getting very low resistances on the outputs secondaries (about 0.5 Ohm).
5. The output transformers are wired for 8 Ohms impedance, but the associated resistor/capacitors are the 32 Ohms options. Maybe the transformers were rewired at some point? Is this a problem?
6. One amp has no R23 in the circuit going to the cap of the preamp valve. It just has a wire going direct to the valve cap. Should I change that? The other amp has a potentiometer in the input circuit and I haven’t worked out what is going on there yet.
5. What advice is there on powering up safely once the steps above (and any others) have been addressed?
6. What else have I missed
I’m working on restoring my father in law’s TL12s and would love some input and advice. I have two amps and a spare third chassis with missing ironware and a mix of new and old components. There is also a Point One preamp and Troughline tuner but I am not looking at those.
The amps were last tested 20 years ago but were almost certainly in storage before that.
I have a multimeter and new digital LCR meter, and old (untested) CRT oscilloscope but no other proper test equipment.
What I’ve done so far:
- read the very helpful advice at 44bx.com
- remove the ironware and test for DC continuity with multimeter. One of the chokes has gone open circuit but luckily there is a spare in the box of stuff I was given.
- clean up the amp chassis
- test the capacitors and resistors in circuit using an LCR meter.
Questions and next steps:
1. The 4uF+8uF+4uF capacitors in the can show no signs of leakage. The LCR meter shows nominal values (3600nF-4100nF, 7800-7820nF and Vloss 0.1% ESR 0.5 Ohms for each). What else do I need to do to test if these are ok to use? Or should I just bypass them with modern caps?
2. I am planning to replace the 5 coupling capacitors in each amp with 0.27uF 630V polypropylene from Cornell Dubelier. I can’t find a reliable source of high voltage 0.25uF capacitors anywhere. Is this a sensible choice?
3. I will replace all the electrolytics with identical values, and any resistors that are out of tolerance according to the list on 44bx.com
4. How can I further test the ironware? I am getting very low resistances (MM shows about 0.5 Ohm) on the mains transformer low voltage secondaries which makes sense to me. I am also getting very low resistances on the outputs secondaries (about 0.5 Ohm).
5. The output transformers are wired for 8 Ohms impedance, but the associated resistor/capacitors are the 32 Ohms options. Maybe the transformers were rewired at some point? Is this a problem?
6. One amp has no R23 in the circuit going to the cap of the preamp valve. It just has a wire going direct to the valve cap. Should I change that? The other amp has a potentiometer in the input circuit and I haven’t worked out what is going on there yet.
5. What advice is there on powering up safely once the steps above (and any others) have been addressed?
6. What else have I missed
Attachments
Sunvalley SV-Pre1616D Point to Point Project
Sunvalley SV-Pre1616D 115/230 version (point to point pre-amp project)
Made in Japan (Nagoya)
SunValley SV-Pre1616D Tube Line Stage Kit Review | Wall of Sound | Audio and Music Reviews
AVAILABLE now $975.00
Assembled by Sunvalley with 2X VCAP ODAM 4.7uf x 2 $1,525.00
EQ1616D Phono Amp
- 12 AX 7 JJ ECC 82/12 AU 7
- 12 AX 7 GD 12 AU 7
- Mullard CV 4003/12 AU 7 (3 matched) SOVTEK 5 AR 4
You can use the following combination
① 12 AX 7 - 12 AX 7 - 12 AX 7 (Sharp and high contrast)
* Standard combination (SV - 722 Marantz type and same circuit)
② 12 AX 7 - 12 AX 7 - 12 AU 7 (Skeletal feeling and entity feeling of medium low range)
* SV - 722 Mckin type sound image Reproduced
③ 12 AU 7 - 12 AU 7 - 12 AU 7 (round and resonate rich)
※ Featuring a rich overtone feeling of the SV - 310 series
Input: 4 lines [Input 4 can be changed to USB input (option)]
Input Volume: Yes
frequency response: 15 Hz ~ 70 kHz (-3 dB)
gain: 15 dB
size: 250W, 225D, 135H (mm ) ※ including protrusions
weight: 3.6 kg
[
Made in Japan (Nagoya)
SunValley SV-Pre1616D Tube Line Stage Kit Review | Wall of Sound | Audio and Music Reviews
AVAILABLE now $975.00
Assembled by Sunvalley with 2X VCAP ODAM 4.7uf x 2 $1,525.00
EQ1616D Phono Amp
- 12 AX 7 JJ ECC 82/12 AU 7
- 12 AX 7 GD 12 AU 7
- Mullard CV 4003/12 AU 7 (3 matched) SOVTEK 5 AR 4
You can use the following combination
① 12 AX 7 - 12 AX 7 - 12 AX 7 (Sharp and high contrast)
* Standard combination (SV - 722 Marantz type and same circuit)
② 12 AX 7 - 12 AX 7 - 12 AU 7 (Skeletal feeling and entity feeling of medium low range)
* SV - 722 Mckin type sound image Reproduced
③ 12 AU 7 - 12 AU 7 - 12 AU 7 (round and resonate rich)
※ Featuring a rich overtone feeling of the SV - 310 series
Input: 4 lines [Input 4 can be changed to USB input (option)]
Input Volume: Yes
frequency response: 15 Hz ~ 70 kHz (-3 dB)
gain: 15 dB
size: 250W, 225D, 135H (mm ) ※ including protrusions
weight: 3.6 kg
[
Hi Everyone First post — Want to learn more about old amps and repairs
- By Sonic5208
- Solid State
- 24 Replies
Attachments
Hartley "boffle" improvement with CLD material
Over the years I read here and there about a old speaker type called a boffle.
It consists of a open backed box with many felt curtains with different sized holes behind the driver. Here are some images to illustrate what it looks like
The idea is to "eat away the back wave" to emulate a infinite baffle.
My question is this, wouldn't it be better to use CLD material (constrained layer damping) in stead of felt curtains......or CLD material covered in felt?
In my mind CLD dividers would suck more energy out of the back wave, especially at low frequencies. I could make sheets from bitumen sandwiched between thin metal plates covered with thin automotive felt....
Is it worth a try?
http://p10hifi.net/tlinespeakers/forum/boffle-RadioElectronics.pdf
It consists of a open backed box with many felt curtains with different sized holes behind the driver. Here are some images to illustrate what it looks like
The idea is to "eat away the back wave" to emulate a infinite baffle.
My question is this, wouldn't it be better to use CLD material (constrained layer damping) in stead of felt curtains......or CLD material covered in felt?
In my mind CLD dividers would suck more energy out of the back wave, especially at low frequencies. I could make sheets from bitumen sandwiched between thin metal plates covered with thin automotive felt....
Is it worth a try?
http://p10hifi.net/tlinespeakers/forum/boffle-RadioElectronics.pdf
Very low MID-bass in TDA7293
okay guys,
i did tda on a veroboard today. there is less than 20mv DC in the output. i used the circuit picked up from Rod's site, with minor modifications
1)added 2uf mkp input capacitor as he doest have one, which is necessary.😀
On the basis of following page, made other few changes
Avoiding TDA7293 pitfalls
2)changed the bootstrap capacitor (as suggested in pitfalls of tda) to 100uf
3)changed the NFB cap to 100uf.
NOTE-the decoupling caps are smaller in comparison to datasheet on the rod eliotts site, and i have used ceramic 100nf ones alongwith them.
The problem is, i did a side by side comparison to tda2050 on 18v rails. but! i am really disappointed by the bass tda7293 puts out on my speakers.
can someone lend me an insight?
i did tda on a veroboard today. there is less than 20mv DC in the output. i used the circuit picked up from Rod's site, with minor modifications
1)added 2uf mkp input capacitor as he doest have one, which is necessary.😀
On the basis of following page, made other few changes
Avoiding TDA7293 pitfalls
2)changed the bootstrap capacitor (as suggested in pitfalls of tda) to 100uf
3)changed the NFB cap to 100uf.
NOTE-the decoupling caps are smaller in comparison to datasheet on the rod eliotts site, and i have used ceramic 100nf ones alongwith them.
The problem is, i did a side by side comparison to tda2050 on 18v rails. but! i am really disappointed by the bass tda7293 puts out on my speakers.
can someone lend me an insight?
Attachments
Fabric Dome Tweeter 96db - altern. to Glockenklang phenol 99db (based to RCF TW116)?
- Multi-Way
- 19 Replies
Attachments
-
RCF TW116.jpg -
RCF TW116-II.jpg -
RCF TW116 datasheet.jpg -
RCF TW116-VII.jpg -
RCF TW116 -VI.jpg -
RCF TW116-III.jpg -
RCF TW116 strip down-II.jpg -
RCF TW116 strip down.jpg -
RCF TW116recone kit.jpg -
RCF TW116 recone-kit-II.jpg -
RCF TW116 recone-kit-IV.jpg -
RCF TW116 recone-kit-V.jpg -
RCF TW116 recone-kit-III.jpg -
img_20190204_132230.jpg -
img_20190204_131901.jpg
Tapped horn. Lonely TH15 Pro
- By Type1
- Subwoofers
- 78 Replies
Hello
I'd like to share a relatively new tapped horn design with you all. It's called Lonely TH15 Pro and developed
by Viktor Stoll from Germany. I stumbled upon Viktors TH designs in a German DIY audio Facebook group, he
has done quite a few tapped horn designs ranging from 6 - 18".
I had a Paraflex Type O 2x15 subwoofer for my garage setup wich was quite impressive, but very big and hard to place.
I didn't fancy building another one just to tackle the problems I had with room modes. I found the Lonely TH15 wich was
about half the size of my Paraflex, and figured that two smaller subwoofers willbe better than one big.
Having built a BFM Table Tuba a long time ago and liking the sound of it, I didn't hesitate to build a tapped horn again.
The Lonely TH15 was designed around Thomanns inexpensive The Box 15LB075-UW4, I asked Viktor if I could use The Box 15LB100-8W instead?
He promptly answered that the box can be built narrower with a stronger driver. Didn't take him many days to come back with a new design suited
for stronger PA drivers and even adjusting the plans for 18mm BB-ply that I had on hand, what a champ! 🙂
These are easy to build, not too big and I really like the way it sounds. The cabinet tunig is 42Hz, but to me it reallysound deeper.
For the kind of music I listen to ranging from blues, rock to metal (even some EDM now and then) I can't say that I'm missing anything
in the low end. What I really like about them is how musical it is, no one note bass and really nice sounding upper bass. What's also
to like is how efficient it is and the way it's present from low volume.
I have compare it to the Marty Cube loaded with a Lavoce WAF 154.00 wich is tuned quite a bit lower with an F3 of 27Hz if I remeber correctly.
The Marty is impressive at high volumes and sure it goes lower. But the Lonely TH sound so effortless and musical that for me it's a
no brainer which one to keep. The Paraflex is of course even more efficient than the TH, having two drivers and being double the size,
but the TH still is more HiFi and sound better higher up in the register to me.
Now I only need to build another one! Hope this inspire some one who want to build a great subwoofer.
Here are links to Viktors posts with simulations, measurements and building plans on the German HiFi forum.
Lonely TH15 Pro, simulations and construction plans in english available at the end of the post.
http://www.hifi-forum.de/viewthread-159-11222.html
And here is the regular Lonely TH15, where you can find the simulation and also the real world measurements.
http://www.hifi-forum.de/viewthread-159-11218.html
Easy to build, single row bracing.
From the left Marty Cube, Lonely TH15 Pro, Paraflex Type O 2x15
I'd like to share a relatively new tapped horn design with you all. It's called Lonely TH15 Pro and developed
by Viktor Stoll from Germany. I stumbled upon Viktors TH designs in a German DIY audio Facebook group, he
has done quite a few tapped horn designs ranging from 6 - 18".
I had a Paraflex Type O 2x15 subwoofer for my garage setup wich was quite impressive, but very big and hard to place.
I didn't fancy building another one just to tackle the problems I had with room modes. I found the Lonely TH15 wich was
about half the size of my Paraflex, and figured that two smaller subwoofers willbe better than one big.
Having built a BFM Table Tuba a long time ago and liking the sound of it, I didn't hesitate to build a tapped horn again.
The Lonely TH15 was designed around Thomanns inexpensive The Box 15LB075-UW4, I asked Viktor if I could use The Box 15LB100-8W instead?
He promptly answered that the box can be built narrower with a stronger driver. Didn't take him many days to come back with a new design suited
for stronger PA drivers and even adjusting the plans for 18mm BB-ply that I had on hand, what a champ! 🙂
These are easy to build, not too big and I really like the way it sounds. The cabinet tunig is 42Hz, but to me it reallysound deeper.
For the kind of music I listen to ranging from blues, rock to metal (even some EDM now and then) I can't say that I'm missing anything
in the low end. What I really like about them is how musical it is, no one note bass and really nice sounding upper bass. What's also
to like is how efficient it is and the way it's present from low volume.
I have compare it to the Marty Cube loaded with a Lavoce WAF 154.00 wich is tuned quite a bit lower with an F3 of 27Hz if I remeber correctly.
The Marty is impressive at high volumes and sure it goes lower. But the Lonely TH sound so effortless and musical that for me it's a
no brainer which one to keep. The Paraflex is of course even more efficient than the TH, having two drivers and being double the size,
but the TH still is more HiFi and sound better higher up in the register to me.
Now I only need to build another one! Hope this inspire some one who want to build a great subwoofer.
Here are links to Viktors posts with simulations, measurements and building plans on the German HiFi forum.
Lonely TH15 Pro, simulations and construction plans in english available at the end of the post.
http://www.hifi-forum.de/viewthread-159-11222.html
And here is the regular Lonely TH15, where you can find the simulation and also the real world measurements.
http://www.hifi-forum.de/viewthread-159-11218.html
Easy to build, single row bracing.
From the left Marty Cube, Lonely TH15 Pro, Paraflex Type O 2x15
Attachments
FunKenya Chinese 300B Monoblocks
- By PeteAugello
- Tubes / Valves
- 44 Replies
Hi everyone!
I just got a pair of Chinese 300b Monoblocks from eBay and have some questions and comments, and wonder if anyone who knows what they are doing has looked at them.
The amps that I got are sold by a bunch of different people but they all look the same. There is very little actual identifying labeling, the vendor that I chose has a funKenya banner on the pictures.
I got the version that came with PSVane 300bs and Russian rectifier and driver tubes. It only took two weeks to get to Pennsylvania from Hong Kong! It was very well packaged and the packaging and contents were undamaged.
There was no manual of any sort included, but I don't read Chinese so that isn't a great loss. The case has no identifying markings at all but there is a sticker on the bottom.
The first thing that I did was peal off the warranty stickers over two of the screws holding the side panels so that I could verify which socket is for the driver and which one gets the rectifier. The case is labeled 110 volts in several places so I checked the heater voltage for the 300b and it was almost 6 volts. I built power cords with 10 volt bucking transformers and reduced my line voltage from 123v to 110v and the heater voltage to 5 volts.
I tested them out on the workbench with small speakers and they appeared to be operating properly, so I brought them upstairs and hooked them up to the big system.
Right off the bat they sounded pretty darn good. Not really competitive with my big VTL monoblocks, but they had something to offer over the Skunkie Designs modified A12 that I had hooked up yesterday. After a couple of hours, they really started to sound pretty darn good!
I brought them downstairs and put them back on the bench with the small speakers out of phase and pushed up against each other, and the Sheffield Labs burn-in track running on repeat. I'm going to hook them back up shortly, after 4 hours or so.
My questions:
Has anyone who knows what they are doing looked at these things? They seem more "engineered" than the A12 but I still wonder if the circuit is actually properly designed and implemented.
I would love to get rid of the Russian tubes and use more common types. It comes with a 5U4M rectifier and obviously a 5AR4 would give me more choice and availability, similarly with the 6H8C driver tube, a 6SN7 is a lot easier to come by. I'm pretty sure that I can't just use the "equivalent" tube types, lol.
There is a multi-turn potentiometer on the back but no exposed test point that I can find. Does it seem possible that this amp is configured with adjustable bias? That raises several other questions.
I'm about ready to bite the bullet and order some better 300b's for it but if I can do something about the others while I'm at it that would be great.
Thanks,
Pete
I just got a pair of Chinese 300b Monoblocks from eBay and have some questions and comments, and wonder if anyone who knows what they are doing has looked at them.
The amps that I got are sold by a bunch of different people but they all look the same. There is very little actual identifying labeling, the vendor that I chose has a funKenya banner on the pictures.
I got the version that came with PSVane 300bs and Russian rectifier and driver tubes. It only took two weeks to get to Pennsylvania from Hong Kong! It was very well packaged and the packaging and contents were undamaged.
There was no manual of any sort included, but I don't read Chinese so that isn't a great loss. The case has no identifying markings at all but there is a sticker on the bottom.
The first thing that I did was peal off the warranty stickers over two of the screws holding the side panels so that I could verify which socket is for the driver and which one gets the rectifier. The case is labeled 110 volts in several places so I checked the heater voltage for the 300b and it was almost 6 volts. I built power cords with 10 volt bucking transformers and reduced my line voltage from 123v to 110v and the heater voltage to 5 volts.
I tested them out on the workbench with small speakers and they appeared to be operating properly, so I brought them upstairs and hooked them up to the big system.
Right off the bat they sounded pretty darn good. Not really competitive with my big VTL monoblocks, but they had something to offer over the Skunkie Designs modified A12 that I had hooked up yesterday. After a couple of hours, they really started to sound pretty darn good!
I brought them downstairs and put them back on the bench with the small speakers out of phase and pushed up against each other, and the Sheffield Labs burn-in track running on repeat. I'm going to hook them back up shortly, after 4 hours or so.
My questions:
Has anyone who knows what they are doing looked at these things? They seem more "engineered" than the A12 but I still wonder if the circuit is actually properly designed and implemented.
I would love to get rid of the Russian tubes and use more common types. It comes with a 5U4M rectifier and obviously a 5AR4 would give me more choice and availability, similarly with the 6H8C driver tube, a 6SN7 is a lot easier to come by. I'm pretty sure that I can't just use the "equivalent" tube types, lol.
There is a multi-turn potentiometer on the back but no exposed test point that I can find. Does it seem possible that this amp is configured with adjustable bias? That raises several other questions.
I'm about ready to bite the bullet and order some better 300b's for it but if I can do something about the others while I'm at it that would be great.
Thanks,
Pete
Acoustic Guitar *Mounted* Microphone
- By jjasniew
- PA Systems
- 5 Replies
I think my acoustic guitar sounds best Mic'd. I mean, tip 'o the hat to all the piezo bridge transducers and sound hole mounted mag pickups, but I play nylon, so one of those options isnt viable. It's easier for the sound guy to just plug in an instrument, when changing players / guitars...
I'd like to mount the mic - in an easily removable fashion - directly on the guitar body. This will allow freedom of movement while maintaining a consistent distance to the capsule. That's problematic, as the guitar has sound vibration happening everywhere on its body, including the neck block / tail block. Put that with there's limited space for it to physically go, due to right hand playing style.
The microphone, of course, is as adept at picking up vibration as it is sound, so what you get for your "sound" is the sum / difference between the acoustic sound and mechanically conducted body vibrations. A hard mount to the side of the guitar would be worst case.
The microphone itself cannot be gigantic - no one's going to put an SM57 on standard gooseneck plumbing with a flange screwed to the top or side of their guitar. Though Dan Hicks did exactly that and went on TV with it.
I've been using a dynamic mic from a Shure headset. It's small and light, picks up sound from both sides like a ribbon and its plumbing diameter is small; almost looks the part. The trouble lies mostly in mounting it to the guitar somehow. It must be easily removable and quickly set up upon pulling the guitar from its case.
This is what works best so far. Basically a cylinder of soft foam Velcro mounted to the side of the guitar, in a spot where my hand wont hit it while grabbin' those strings. (Neodymium magnets would be a "stage 2" development - a pair glued to the inside of the guitar, a pair on whatever it is getting attached) The foam - apparently - works as both an isolator and damper within which the microphone floats. As opposed to a hard mount, where the mic and its plumbing stem would go tong-tong-tong upon plucking the capsule end. Another nice arbitrary resonance to add / subtract from the guitar's sound.
I'm tempted to get one of those camera microphone "shock-mounts" with the o-ring bands, but I'm afraid it'll be an instant fail endeavor. One can actually buy the foam cylinders off epay, in 65 and 100 mm diameter, for more than what the aluminum camera shock mount costs! Whatever material / scheme it is, it has to hold the mic in place during reasonable standing position stage movement and isolate, damp, isolate. This prototype performs adequately, just looks like crap. Hey, I dont have a CNC waterjet or laser, so machining precise features into light density open cell foam - I'm lucky to make a somewhat square to the part hole in it at all.
Any other material suitable? The ubiquitous Sorbothane, but I've never seen it as a foam. I suppose it'd be possible to layup a few discs of the stuff into a cylindrical shape - if I can get discs in the "shore" that'd work for this application. I wouldnt trust metal springs, as there's no damping at all in such an arrangement. A "rollup" of Sorbo sheet with thin foam filling, like a pastry?
I'd like to mount the mic - in an easily removable fashion - directly on the guitar body. This will allow freedom of movement while maintaining a consistent distance to the capsule. That's problematic, as the guitar has sound vibration happening everywhere on its body, including the neck block / tail block. Put that with there's limited space for it to physically go, due to right hand playing style.
The microphone, of course, is as adept at picking up vibration as it is sound, so what you get for your "sound" is the sum / difference between the acoustic sound and mechanically conducted body vibrations. A hard mount to the side of the guitar would be worst case.
The microphone itself cannot be gigantic - no one's going to put an SM57 on standard gooseneck plumbing with a flange screwed to the top or side of their guitar. Though Dan Hicks did exactly that and went on TV with it.
I've been using a dynamic mic from a Shure headset. It's small and light, picks up sound from both sides like a ribbon and its plumbing diameter is small; almost looks the part. The trouble lies mostly in mounting it to the guitar somehow. It must be easily removable and quickly set up upon pulling the guitar from its case.
This is what works best so far. Basically a cylinder of soft foam Velcro mounted to the side of the guitar, in a spot where my hand wont hit it while grabbin' those strings. (Neodymium magnets would be a "stage 2" development - a pair glued to the inside of the guitar, a pair on whatever it is getting attached) The foam - apparently - works as both an isolator and damper within which the microphone floats. As opposed to a hard mount, where the mic and its plumbing stem would go tong-tong-tong upon plucking the capsule end. Another nice arbitrary resonance to add / subtract from the guitar's sound.
I'm tempted to get one of those camera microphone "shock-mounts" with the o-ring bands, but I'm afraid it'll be an instant fail endeavor. One can actually buy the foam cylinders off epay, in 65 and 100 mm diameter, for more than what the aluminum camera shock mount costs! Whatever material / scheme it is, it has to hold the mic in place during reasonable standing position stage movement and isolate, damp, isolate. This prototype performs adequately, just looks like crap. Hey, I dont have a CNC waterjet or laser, so machining precise features into light density open cell foam - I'm lucky to make a somewhat square to the part hole in it at all.
Any other material suitable? The ubiquitous Sorbothane, but I've never seen it as a foam. I suppose it'd be possible to layup a few discs of the stuff into a cylindrical shape - if I can get discs in the "shore" that'd work for this application. I wouldnt trust metal springs, as there's no damping at all in such an arrangement. A "rollup" of Sorbo sheet with thin foam filling, like a pastry?
Headphone amplifier using 4P1L - my version of DHT filament power supply
- By dariusbv
- Tubes / Valves
- 4 Replies
Attachments
An analog active crossover for embedding in speakers
- By tcpip
- Analog Line Level
- 19 Replies
Attachments
Apcl 3001D
attempting to repair it I rubbed the pad off of the tl074 pin 2 inverted input on the second board. Where can I tap into to get the signal? Is it even used thanks
For Sale Neurochrome Modulus 86 (x4) & Power 686 (x1)
Hey there all,
Hoping to part ways with a few (mostly) populated PCBs from Neurochrome!
I planned to make a four-channel amp for some LX Minis but never ended up finishing the project sadly.
The boards are fully populated aside from the ICs (which are all included here) and built using good quality parts from Mouser.
If you've been looking for an easy project to finish here you go! 🙂
Just looking for the price I paid for all the parts + shipping (located in Calgary, Canada): $960cad / $700usd + shipping to you
Hoping to part ways with a few (mostly) populated PCBs from Neurochrome!
I planned to make a four-channel amp for some LX Minis but never ended up finishing the project sadly.
The boards are fully populated aside from the ICs (which are all included here) and built using good quality parts from Mouser.
If you've been looking for an easy project to finish here you go! 🙂
Just looking for the price I paid for all the parts + shipping (located in Calgary, Canada): $960cad / $700usd + shipping to you
Interfacing a vibration transducer to Focusrite Scarlett Solo instrument input
- By kesh
- Electronic Design
- 17 Replies
Hi all,
I'm trying to put together a recording system where I can simultaneously record a mic input and the signal generated by a vibration transducer Knowles BU-27135-141, which is attached to the speaker's neck. This has been done in the voice research field to estimate the aerodynamic pressure close to the vocal folds. Anyway, I've been researching for the simplest way to implement this and converging on using a Scarlett Solo as the A/D solution. However, I'm not 100% sure if it's as simple as I'm making it and wondering if anybody here could comment on the validity before I spend money on it.
From the linked datasheet above, the signal range is +/-1.5 V with the spectral response:
The vibration is lowpass and is expected to roll off steadily from the first harmonic of the voice. So the >3 kHz amplification shouldn't hurt.
The circuit shown on the datasheet is pretty darn simple, the sensor is driven by one AA battery, and the vibration (with dc bias) is measured across the sensor output.
Because the Scarlett Solo's input appears to be AC coupled (freq range 20-20kHz), can I simply hook up these output terminal directly to the Scarlett Solo's instrument input? I think I want to use the instrument mode to keep the battery drainage minimal. But, I really don't know a whole lot about for anything analog circuit or audio recording.
I'd greatly appreciate any inputs. Thanks! -Kesh
I'm trying to put together a recording system where I can simultaneously record a mic input and the signal generated by a vibration transducer Knowles BU-27135-141, which is attached to the speaker's neck. This has been done in the voice research field to estimate the aerodynamic pressure close to the vocal folds. Anyway, I've been researching for the simplest way to implement this and converging on using a Scarlett Solo as the A/D solution. However, I'm not 100% sure if it's as simple as I'm making it and wondering if anybody here could comment on the validity before I spend money on it.
From the linked datasheet above, the signal range is +/-1.5 V with the spectral response:
The vibration is lowpass and is expected to roll off steadily from the first harmonic of the voice. So the >3 kHz amplification shouldn't hurt.
The circuit shown on the datasheet is pretty darn simple, the sensor is driven by one AA battery, and the vibration (with dc bias) is measured across the sensor output.
Because the Scarlett Solo's input appears to be AC coupled (freq range 20-20kHz), can I simply hook up these output terminal directly to the Scarlett Solo's instrument input? I think I want to use the instrument mode to keep the battery drainage minimal. But, I really don't know a whole lot about for anything analog circuit or audio recording.
I'd greatly appreciate any inputs. Thanks! -Kesh
simple headphone buffer
- By No ideas
- Headphone Systems
- 0 Replies
hi i "designed" this little headphone buffer amplifier im intrested if its of any use and should i lower the voltage, also if i could add an extra gain stage that i could turn on/pass the signal through with a switch. and also dac recommendations.
