Hi all,
Finally finished my long term project, the Glasshouse 300BSE amp.
I fired it up, checked all the voltages and played some music for the first time.
The issue I have is a very thin sound (no mid/low frequencies) at very low volumes. I'm guessing max volume is 60-70dB
I've attached the schematic and all the voltages check out to a few % except on the anode of V1 & V2 (the EF86). That should be 175V and measures 212V.
The original amp uses a 2.5K output transformer, I'm using a 3.3K OPT.
No noise, pops etc. when turning on and playing. Only thing I thought was weird is I measure 0.2 ohms between the OPT common and 4/8 ohm tabs (while turned off). Is that normal?
Any help is appreciated
Cheers
Finally finished my long term project, the Glasshouse 300BSE amp.
I fired it up, checked all the voltages and played some music for the first time.
The issue I have is a very thin sound (no mid/low frequencies) at very low volumes. I'm guessing max volume is 60-70dB
I've attached the schematic and all the voltages check out to a few % except on the anode of V1 & V2 (the EF86). That should be 175V and measures 212V.
The original amp uses a 2.5K output transformer, I'm using a 3.3K OPT.
No noise, pops etc. when turning on and playing. Only thing I thought was weird is I measure 0.2 ohms between the OPT common and 4/8 ohm tabs (while turned off). Is that normal?
Any help is appreciated
Cheers
Attachments
Have you tested the output transformer alone?
A normal pocket DVM DCR measuring will only reveal a dead short between windings, or total wreckage of the OPT, if that transformer is under suspect it can be externally tested with a low voltage AC supply or with a variac, then please take photos to support your thread it could be any other thing.
A normal pocket DVM DCR measuring will only reveal a dead short between windings, or total wreckage of the OPT, if that transformer is under suspect it can be externally tested with a low voltage AC supply or with a variac, then please take photos to support your thread it could be any other thing.
Pentode plate voltages tend to vary tube to tube. 212V is not wrong here.
Transformer DC resistances should be 10% or less of the nominal Audio impedance. So 0.2r is not wrong for a 4r winding.
"NO" bass suggests a too-small cap or a too-small grid resistor. A popular fault is to put a 1k where a 1Mge should be (resistor stripe colors, or box mix-up).
Transformer DC resistances should be 10% or less of the nominal Audio impedance. So 0.2r is not wrong for a 4r winding.
"NO" bass suggests a too-small cap or a too-small grid resistor. A popular fault is to put a 1k where a 1Mge should be (resistor stripe colors, or box mix-up).
The whole schemo is strangely drawn. Resistors in series, resistors in parallel, and no dots where connections should be. Nobody knows, where wires connect and were not. I can read it with knowledge, but maybe you interpret it different. Thats not the way a schemo is being written, because it could be interpreted different. A schemo should be very clear. With that, nobody can say wether you did faults, because of wrong interpretation. With the wrong interpretation, this could have 20 bugs being made in the amp.
Btw, an EF86 will never make for a fat sounding amp. It will always be a detailled and relative thin sounding one. Thats the sound of this tube and its own character. And thats what every EF86 amp sounds like.
Furthermore, with the wrong speakers, a 300B amp could sound exact the way you describe. It mustn't be a fault in the amp. We don't know anything about whats going on in front and end of this amp. Could easily be a mismatch of components, too.
Most often its not that easy to build an amp, plug it in and it all wows the audience. In most cases, a good sound is a combination with a perfect circuit, which has to be executed and transferred by a known person in a tube amp and this amp has to be perfectly matched to a given electrical environment and room matching. Good sound is all hard work and many knowledge. Without that, most amps fail to deliver its full potential and sound just as you described it.
And good sound doesn't come like switching a light bulb on. It could take days or weeks for the sound to settle in and become better and better. None of my amps sounded good the first hour of listening. They needed to burn in and clever fine tuning to sound good. The result can be heard after many hours.
Btw, an EF86 will never make for a fat sounding amp. It will always be a detailled and relative thin sounding one. Thats the sound of this tube and its own character. And thats what every EF86 amp sounds like.
Furthermore, with the wrong speakers, a 300B amp could sound exact the way you describe. It mustn't be a fault in the amp. We don't know anything about whats going on in front and end of this amp. Could easily be a mismatch of components, too.
Most often its not that easy to build an amp, plug it in and it all wows the audience. In most cases, a good sound is a combination with a perfect circuit, which has to be executed and transferred by a known person in a tube amp and this amp has to be perfectly matched to a given electrical environment and room matching. Good sound is all hard work and many knowledge. Without that, most amps fail to deliver its full potential and sound just as you described it.
And good sound doesn't come like switching a light bulb on. It could take days or weeks for the sound to settle in and become better and better. None of my amps sounded good the first hour of listening. They needed to burn in and clever fine tuning to sound good. The result can be heard after many hours.
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+1. Depending on how you read the schematic, the EF86 is running triode wired and very starved!
1. Many people think to use a small pentode on the input stage is a good thing. I say you will get a bright & lightweight sound especially with an EF86. It will sound weak and thin. Sound-wise to use an EF86 is a bad idea. WE used a pentode on the input but the WE pentode do sound very different than an EF86. I have build 300B monoblocks for over 30 years and think that triodes do sound much better than pentodes on the input. Simple 6SN7 stage will outperform ANY pentode by far. A 6N6P will sound stellar in combo with the 300B.
2. C25/26 is too small. Maybe it is enough to produce low bass but a higher value cap do sound much fuller. Use 0,22uF at least. If you want it even thicker use 2,2 - 4,7uF. Use PIO (Jensen or Arizona Blue Cactus) or Russian hybrid cap K75 (cheap).
3. Use a high quality audio cap on the 300B cathode. At least use a Nichicon VZ or Solen MKP with a smaller cap (Jensen 0,22 PIO) to get rid of the upper mid haze of most cheap MKPs.
4. Use carbon film resistors (KOA/Kiwame or Takman) or at least Mills (now Vishay MRA) or Holco (but only the old UK made, the new US made are magnetic and do sound much brighter and simply unbearable).
4.The drawing is awful.
2. C25/26 is too small. Maybe it is enough to produce low bass but a higher value cap do sound much fuller. Use 0,22uF at least. If you want it even thicker use 2,2 - 4,7uF. Use PIO (Jensen or Arizona Blue Cactus) or Russian hybrid cap K75 (cheap).
3. Use a high quality audio cap on the 300B cathode. At least use a Nichicon VZ or Solen MKP with a smaller cap (Jensen 0,22 PIO) to get rid of the upper mid haze of most cheap MKPs.
4. Use carbon film resistors (KOA/Kiwame or Takman) or at least Mills (now Vishay MRA) or Holco (but only the old UK made, the new US made are magnetic and do sound much brighter and simply unbearable).
4.The drawing is awful.
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BTW, cheap small OTX do sound thin. Lundahl is the best. And what kind of PSU do you have? Tube rectifier do sound fuller and richer. If you use a choke be sure your choke is good quality. Chokes have more effect on the overall sound quality than mains transformer or OTX. So buy a Lundahl choke first before you invest money in better transformer and/or OTX. Except the mains trans and/or OTX is really bad quality. If you use diode rectifiers use only HEXFREDs anything else do sound problematic.
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Are you kidding or haven't you ever seen a correct drawn schemo?
In my university years this looked a little different.
In this schemo, there is never a connection where lines cross but they should be connected. In a serious plan, this is indicated by a dot.
I hate those amateur plans from people who produce massive abilities to have faults in the amp just by thinking they are very clever and don't have to go for standards, instead creating their own standards. Thats exactly what every manufacturer tries to not letting happen: plans with double meanings and multi- interpretations. A free ticket for producing massive faults in every machine which is to build after such a stupid plan.
And exactly that may have happened here.
We may know, how to read this schemo. But that wasn't the question.
Attachments
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Thanks for the replies. A little more info: when I say no bass, I mean literally like only the tweeter of the speaker is playing. Not like in "this amp is not my cup of tea, it sounds thin". The speakers are 90dB+ and max SPL sounds like maybe 60-70dB.
Cathode cap is a 100 uf silmic. Output transformer is a Monolith Magnetics 3.3k.
I agree the schematic is a little ambiguous, but as mentioned, crossing lines have no connection.
I tested C26 and C24, capacitance measurements are good.
Cathode cap is a 100 uf silmic. Output transformer is a Monolith Magnetics 3.3k.
I agree the schematic is a little ambiguous, but as mentioned, crossing lines have no connection.
I tested C26 and C24, capacitance measurements are good.
1. Thats exactly what I wrote. EF86 will never make for a full bodied sound. Always a thin and sterile sounding tube. Look at all those EF86 guitar amps and compare with ECC83. More body, more weight of sound.
WE did it the best way if one want to build a direct pentode driven 300B. No cathode follower is necessary, I would say its complete nonsense if you put the right pentode in it.
And yes, I have heard 300B amps that outperformed triode driven designs by far. But they had a beefy driver in between and no cathode follower.
4. Consensus
You're talking about university so apparently you are clever enough ....
Well done to draw the red dots; however these connections are obvious...no place to go elsewhere.
There are two "crossings" of lines where it might have been better to follow normal drawing protocols but it is obvious enough as it is, at least to be able to read the schematic correctly.
Biggest problem in my view is the 0.015 uF capacitor / 680 k resistor combo, which makes a 15 Hz high pass.
Well done to draw the red dots; however these connections are obvious...no place to go elsewhere.
There are two "crossings" of lines where it might have been better to follow normal drawing protocols but it is obvious enough as it is, at least to be able to read the schematic correctly.
Biggest problem in my view is the 0.015 uF capacitor / 680 k resistor combo, which makes a 15 Hz high pass.
Schemo is OK. So check and double check voltages and wiring. Check signal tracing with a signal generator. You should have a defined signal loss at the output at low freq.
We don't know the PSU. Could be a faulty PSU, too.
Mono Magnetics aren't cheap, so there should be substantial base repro.
Guitar amp with EF86? Jesus... too many stupid idiots on this planet, really!
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