hi everyone,
My amp sound good, but there's a lack of musical nuance and low level details that get annoying, Also, the bass is exagerated meaning its a bit too loud.
Compared to a couple of class d I have, the class d has more air, more defined soundstage, more details, more coherancy from bass to low.
however, tube amp has more dynamic, better attack, much better tone and a bigger and fuller sound. the real problem is a too emphasized bass and not enough details.
Ive attached the schematic.
Measurments show no apparent problem, they are not malfunctionning, simply I think the circuit is really simple and could/should be improved for better resolution.
The output transformer and the output transformer are the dynaco a 470. Maybe I should get better OPT?
1- I have been recommended to add a small amount of negative feedback. That would likely help the bass
2- I also been suggested to:
''Might also go with independent cathode resistors (and cathode bypass caps if you end up using them) for the paralleled input triode. I have had some problems with tubes fighting each other if the sections were not perfectly matched. (Symptoms less gain, more distortion, etc.) ''
Any input would be greatly appreciated.
thanks
My amp sound good, but there's a lack of musical nuance and low level details that get annoying, Also, the bass is exagerated meaning its a bit too loud.
Compared to a couple of class d I have, the class d has more air, more defined soundstage, more details, more coherancy from bass to low.
however, tube amp has more dynamic, better attack, much better tone and a bigger and fuller sound. the real problem is a too emphasized bass and not enough details.
Ive attached the schematic.
Measurments show no apparent problem, they are not malfunctionning, simply I think the circuit is really simple and could/should be improved for better resolution.
The output transformer and the output transformer are the dynaco a 470. Maybe I should get better OPT?
1- I have been recommended to add a small amount of negative feedback. That would likely help the bass
2- I also been suggested to:
''Might also go with independent cathode resistors (and cathode bypass caps if you end up using them) for the paralleled input triode. I have had some problems with tubes fighting each other if the sections were not perfectly matched. (Symptoms less gain, more distortion, etc.) ''
Any input would be greatly appreciated.
thanks
Attachments
The choke is too small for choke input from your voltages. If it's the Dynaco choke, it's definitely too small. Poor supply regulation results.
I assume you have the 6B4 heaters wired in-phase for hum cancellation. DC heaters could help. You might try an eternal supply and see.
There are better current sources than the 317. If there's enough gain, you can try some negative feedback.
I assume you have the 6B4 heaters wired in-phase for hum cancellation. DC heaters could help. You might try an eternal supply and see.
There are better current sources than the 317. If there's enough gain, you can try some negative feedback.
There are a few fellows saying you want less resistance in the power supply for more dynamics so a low DCR choke is in order like 23 ohms or less and 1-2H will do in PP. Edcor has affordable one in 300 mA or so.
Maybe the Williamson circuit maybe better for detail and bass while eliminating the need for SS as no LTP.
Maybe the Williamson circuit maybe better for detail and bass while eliminating the need for SS as no LTP.
problem with this amp, is that it was bought used. All the information I have is written on the schematic.
The power transformer is:
Vintage Tube Amp Power Transformer 512-23629A Baldwi (04/07/2011)...
I do not have any information on the choke. Maybe I'm better off getting another choke?
The power transformer is:
Vintage Tube Amp Power Transformer 512-23629A Baldwi (04/07/2011)...
I do not have any information on the choke. Maybe I'm better off getting another choke?
If you unplug the 5AR4 you can measure the DCR of the full transformer secondary on pins 6 & 4 of the tube socket.
You can get the DCR of the primary: Unplug the power cord from AC power, measure across the line and neutral of the AC plug with the power switch on.
You'll have to disconnect one side of choke to measure the DCR. Are there any part numbers at all on the choke? Can you post a photo?
It would really help to know what you already have before just guessing and purchasing a new choke.
You can get the DCR of the primary: Unplug the power cord from AC power, measure across the line and neutral of the AC plug with the power switch on.
You'll have to disconnect one side of choke to measure the DCR. Are there any part numbers at all on the choke? Can you post a photo?
It would really help to know what you already have before just guessing and purchasing a new choke.
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This amplifier has a choke input filter. For this filter to work properly critical inductance must be met by the choke. Lcrit = Vdc / Ima so in this case critical inductance = 383V / 122mA or 3H. Now the 2H / 300mA choke is probably about 3H at 125mA, but why use a part that is marginal? If this were my amp I would go for a properly sized choke so that the choke-input filter loads the rectifier enough that current flows into the filter almost continuously, reducing ripple and giving the PS stability.
While it is fashionable to aim for a super low impedance PS, I would be much more inclined to choose a choke based upon its inductance rather than the DCR; which is to say that I would choose the Edcor CXC100-7H-150mA. It is properly rated at 7H at 150mA with a DCR of just 104R. This choke will provide plenty of filtering and provide a low impedance power supply. This power supply change may not take you to the ultimate sound you are looking for, but I doubt that a 80R difference in the PS will be audible and you will have a properly engineered supply and a stable foundation upon which to build a circuit that does meet your expectations sound wise.
While it is fashionable to aim for a super low impedance PS, I would be much more inclined to choose a choke based upon its inductance rather than the DCR; which is to say that I would choose the Edcor CXC100-7H-150mA. It is properly rated at 7H at 150mA with a DCR of just 104R. This choke will provide plenty of filtering and provide a low impedance power supply. This power supply change may not take you to the ultimate sound you are looking for, but I doubt that a 80R difference in the PS will be audible and you will have a properly engineered supply and a stable foundation upon which to build a circuit that does meet your expectations sound wise.
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Conveniently enough, a 6DJ8 should drop right into the input stage socket, which would double the gain. (6DJ8 or ECC88 has same pinout as 6GU7, and almost identical operating points at that voltage, load, etc.) Then there'd be enough gain to add up to about -10dB of global NFB from the output transformer secondary to the first tube's cathode.
But I'm not sure a lack of NFB is the cause of the problem.
Does the amp hum?
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The Harman Kardon Citation II used a low DCR PS with about a 1H choke and even lower DCR. It is a highly liked amp and Jim McShane whom sells upgrade kit does offer a second choke to use with the other channel so maybe that would be a great improvement while keeping the DCR low.
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This amp will go with a decapo 3a reference speaker in my secondary system, so I want this amp to perform really good. However, I'm not willing to spend 300$ on this project. I would like to get the best sound with what I have.
I will get the choke you recommend (Edcor CXC100-7H-150mA), as im sure the choke I have is not even close to ideal...
what else should be absolutely modified?
theres a slight slight hum, but nothing alarming, just like normal behavior. I can surely not hear it from the listening position...
Are you sure that adding NFB to the williamson circuit will result in better sound? Ive been told that the Williamson circuit sounds better without NFB...
Yes, that's possible and the Citation II power supply is a voltage doubler which means that it is a capacitor input supply. The capacitors provide the voltage doubling: that's how it works.
The OP has a very different beast: it is a choke input power supply. As has already been explained, for this filter to work properly critical inductance must be met by the choke. Lcrit = Vdc / Ima so in this case critical inductance = 383V / 122mA or 3H.
A power supply needs to be properly engineered to work effectively. Spend a few weeks modeling power supplies with PUSD II and see what power supplies are all about.
That being said, it would be advantageous to know what the OP has now in terms of choke and PT in order to engineer the best alternative. I modeled my best guess in PSUD2 using the 7H 104R choke. It looks like his B+ will drop significantly, with about 1V P-P ripple after the 100uF cap.
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