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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Fri 23, 2018 7:19 am 
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john8750 wrote:
I like that amp Flip. When are you planning on it? On the 807, where does that top cap connect to? I see you have made some changes to the amp from the original Williamson. Are you planning on using a preamp?
Plans are indefinite now. I had to divert funds to a rash of house problems and there are more on the way. Well, actually, they're already here and just waiting to suck up more money :lol:

The 807 top cap connects to the OPT, as shown on the schematic.

The changes from a classic Williamson were mainly to get more gain. I.e. the 6SL7, instead of a 6SN7, for the front end and my favorite bootstrap gain maximizer/distortion reducer trick. The 6SL7 doesn't have as much heater-cathode withstand voltage, though, so it has to be elevated, which is noted on the schematic. And, of course, the classic Williamson isn't UL whereas I've added that. I also applied the 'bias fix' to the 6SN7 drivers.

I'm not planning on a preamp.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Fri 23, 2018 7:21 pm 
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Flipperhome wrote:
john8750 wrote:
I like that amp Flip. When are you planning on it? On the 807, where does that top cap connect to? I see you have made some changes to the amp from the original Williamson. Are you planning on using a preamp?
Plans are indefinite now. I had to divert funds to a rash of house problems and there are more on the way. Well, actually, they're already here and just waiting to suck up more money :lol:

The 807 top cap connects to the OPT, as shown on the schematic.

The changes from a classic Williamson were mainly to get more gain. I.e. the 6SL7, instead of a 6SN7, for the front end and my favorite bootstrap gain maximizer/distortion reducer trick. The 6SL7 doesn't have as much heater-cathode withstand voltage, though, so it has to be elevated, which is noted on the schematic. And, of course, the classic Williamson isn't UL whereas I've added that. I also applied the 'bias fix' to the 6SN7 drivers.

I'm not planning on a preamp.



OK. I will put this in my 'want to do file'
Would like to build it with you, later on.

I need a preamp. And have a very nice one, Little Prince.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 25, 2018 8:36 pm 
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Maybe I am finally maturing, I kinda like the amp now without a tone control.
Flip, if I get rid of the tone circuit, I will need a balance control. I guess it would go right after the dual volume control pot?
And it would be a single linear pot of about 250K?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 25, 2018 9:08 pm 
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john8750 wrote:
Maybe I am finally maturing, I kinda like the amp now without a tone control.
Flip, if I get rid of the tone circuit, I will need a balance control. I guess it would go right after the dual volume control pot?
And it would be a single linear pot of about 250K?



This is what I figure, looking at other amp circuits.
Attachment:
inputrick.png
inputrick.png [ 172.21 KiB | Viewed 1590 times ]

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 25, 2018 10:05 pm 
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Hi John:
I do n't get how a balance control should be used. The recorded music is rarely ever the same on left and right channels... right?
So unless you feed in a fixed tone from a signal generator to both channels and then adjust the balance... but that too makes no sense since both opamps are set for identical gain of 100 with the opamp feedback resistor.

So... again the balance, I would think, seems to balance the volume from left and right... but the content is not the same left and right so how could you tell?

Confused.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 25, 2018 11:03 pm 
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john8750 wrote:
Maybe I am finally maturing, I kinda like the amp now without a tone control.
Flip, if I get rid of the tone circuit, I will need a balance control. I guess it would go right after the dual volume control pot?
And it would be a single linear pot of about 250K?
Depends on what you want. My normal setup is the 'equal volume' balance control and that would need a second 100k after the volume pot, on the wiper to ground, with 39k from the volume wiper to the source. Input resistance drops to roughly 75 K, though, which is lower than the tube 'minimum' of 100k. To keep it up you have a double all the values and that, then, begins to impact the upper end (due to miller capacitance).

But the main reason I didn't put one there is because it cuts the volume (gain) lower than I'd like so I planned on using the MP3 player's balance control, if necessary.

Gain could be increased 6 dB by lowering feedback to 14 dB instead of 20 dB. Distortion would go up but it's pretty dern low as is, being UL. On the other hand, why, when the source balance can be used?

If I were going to use, say, a tube RIAA phono with it I'd put the balance control in the preamp (like in the Prince John).


Last edited by Flipperhome on Mar Mon 26, 2018 12:09 am, edited 1 time in total.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 25, 2018 11:47 pm 
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I was thinking of not using a preamp for this one. I understand, and don't want, the attenuation with the balance control.
Maybe, an extra buster before, or after the volume/balance section?. The tone amp I just worked on is very strong. Could distort the woofer on some songs. I like a little extra bass, but don't want to shake the plaster off the walls.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 25, 2018 11:51 pm 
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Pbpix wrote:
Hi John:
I do n't get how a balance control should be used. The recorded music is rarely ever the same on left and right channels... right?
So unless you feed in a fixed tone from a signal generator to both channels and then adjust the balance... but that too makes no sense since both opamps are set for identical gain of 100 with the opamp feedback resistor.

So... again the balance, I would think, seems to balance the volume from left and right... but the content is not the same left and right so how could you tell?

Confused.



Nothing to get confused about.
Balance could be affected by room shape, speaker placement, wall design, other things. The balance could be left in the middle if no correction is needed. I would rather have the authority if needed to correct the balance.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Mon 26, 2018 12:36 am 
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john8750 wrote:
I was thinking of not using a preamp for this one. I understand, and don't want, the attenuation with the balance control.
Maybe, an extra buster before, or after the volume/balance section?. The tone amp I just worked on is very strong. Could distort the woofer on some songs. I like a little extra bass, but don't want to shake the plaster off the walls.
I presume you meant a buffer? More accurately it would be a gain amp. Yes, you can always solve a gain problem with more gain, but the question is where to put it. This is a classic "power amp" design and the "volume control" was often called "gain," if it had one at all, because it's really to 'match' the amplifiers gain to the rest of the system. The 'real' volume, balance, and tone controls would be in the preamp. For example, the Williamson, which this amp is based on, has no 'volume pot' (or gain pot) at all. McIntosh amps usually have a (volume) pot on the front end for "gain" adjustment.

In short, this is a "power amp" with enough sensitivity to use an MP3 player, which has a "preamp," with volume, balance, and tone controls, in it. In theory you don't need a 'volume' pot at all but it's more convenient with one and, again, sets the overall gain for whatever MP3 player is used. Once set, so that 'max vol' on the MP3 player drives the amp to 'max power', you generally don't have to fool with it again and think about it. You're going to select the song on the MP3 player so it's simply logical to have the volume, balance, and tone controls there too.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Mon 26, 2018 4:47 am 
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Flipperhome wrote:
john8750 wrote:
I was thinking of not using a preamp for this one. I understand, and don't want, the attenuation with the balance control.
Maybe, an extra buster before, or after the volume/balance section?. The tone amp I just worked on is very strong. Could distort the woofer on some songs. I like a little extra bass, but don't want to shake the plaster off the walls.
I presume you meant a buffer? More accurately it would be a gain amp. Yes, you can always solve a gain problem with more gain, but the question is where to put it. This is a classic "power amp" design and the "volume control" was often called "gain," if it had one at all, because it's really to 'match' the amplifiers gain to the rest of the system. The 'real' volume, balance, and tone controls would be in the preamp. For example, the Williamson, which this amp is based on, has no 'volume pot' (or gain pot) at all. McIntosh amps usually have a (volume) pot on the front end for "gain" adjustment.

In short, this is a "power amp" with enough sensitivity to use an MP3 player, which has a "preamp," with volume, balance, and tone controls, in it. In theory you don't need a 'volume' pot at all but it's more convenient with one and, again, sets the overall gain for whatever MP3 player is used. Once set, so that 'max vol' on the MP3 player drives the amp to 'max power', you generally don't have to fool with it again and think about it. You're going to select the song on the MP3 player so it's simply logical to have the volume, balance, and tone controls there too.



You might be confusing this amp with Peters amp. His will be used for MP3 only. Mine could have a CD or turn table, from the RIAA, input. Actually, I am referring to my next amp build. The one for my Cousin is complete. But I don't want to use the tone section on my next amp. I will start a new thread shortly. So sorry for the confusion :wink: You're probably getting use to it by now :lol:

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Mon 26, 2018 5:35 am 
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john8750 wrote:
Flipperhome wrote:
john8750 wrote:
I was thinking of not using a preamp for this one. I understand, and don't want, the attenuation with the balance control.
Maybe, an extra buster before, or after the volume/balance section?. The tone amp I just worked on is very strong. Could distort the woofer on some songs. I like a little extra bass, but don't want to shake the plaster off the walls.
I presume you meant a buffer? More accurately it would be a gain amp. Yes, you can always solve a gain problem with more gain, but the question is where to put it. This is a classic "power amp" design and the "volume control" was often called "gain," if it had one at all, because it's really to 'match' the amplifiers gain to the rest of the system. The 'real' volume, balance, and tone controls would be in the preamp. For example, the Williamson, which this amp is based on, has no 'volume pot' (or gain pot) at all. McIntosh amps usually have a (volume) pot on the front end for "gain" adjustment.

In short, this is a "power amp" with enough sensitivity to use an MP3 player, which has a "preamp," with volume, balance, and tone controls, in it. In theory you don't need a 'volume' pot at all but it's more convenient with one and, again, sets the overall gain for whatever MP3 player is used. Once set, so that 'max vol' on the MP3 player drives the amp to 'max power', you generally don't have to fool with it again and think about it. You're going to select the song on the MP3 player so it's simply logical to have the volume, balance, and tone controls there too.

You might be confusing this amp with Peters amp. His will be used for MP3 only. Mine could have a CD or turn table, from the RIAA, input. Actually, I am referring to my next amp build. The one for my Cousin is complete. But I don't want to use the tone section on my next amp. I will start a new thread shortly. So sorry for the confusion :wink: You're probably getting use to it by now :lol:
Nah, I'm just explaining how **I** was going to use it, and the 'traditional' design of a power amp. You would apparently need a preamp (details of which are TBD), like Prince John.

Normally I put a balance control on the front (which is fine for everything but RIAA since I don't cotton to tone controls) but we've already gone over why I didn't this time around. I didn't feel there was enough gain and was constrained by wanting to use triodes and octal socket tubes. I.e. the 6SL7 has the most gain in a twin triode octal. You can get gobs more gain out of a pentode preamp but pentodes are not supposed to have as good a sound. That and a pentode preamp has the reverse problem, too much gain (that it's hard to figure out what to do with).

I was shooting for the 'best sounding' amp (within the octal and 807 constraints) with the lowest practical distortion, which is why I wanted triodes and didn't want to reduce the feedback. That left only one solution, no balance control. Which, in turn, is consistent with traditional power amp design.

As is typical of me I have a dozen variations saved (some work and some not so much :lol: ) and one (at least) includes my normal balance control setup. Sensitivity drops from 290 mV to 650 mV (which would probably be fine for a CD player but not an MP3 player/cellphone). That's a loss of 7 dB so to make up for it feedback would have to be reduced to 13 or 14 dB.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Mon 26, 2018 7:16 pm 
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I have nothing near your circuit design capability. The amps I built following your instructions are high quality, and have a reasonable price tag.
So, I will leave the volume and balance control in the preamp. But do like a common gain control in the power amp.
Here's a thought. Could the balance, and/or volume be controlled by a pot in the FB circuit of an opamp?
Was the Williamson amp available as a Heathkit?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Mon 26, 2018 11:55 pm 
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john8750 wrote:
I have nothing near your circuit design capability. The amps I built following your instructions are high quality, and have a reasonable price tag.
So, I will leave the volume and balance control in the preamp. But do like a common gain control in the power amp.
Here's a thought. Could the balance, and/or volume be controlled by a pot in the FB circuit of an opamp?
Was the Williamson amp available as a Heathkit?
Yes, a balance control could be put in the FB circuit of an opamp but then feedback would be different for each setting, not to mention imbalanced (feedback and distortion wise) for everything but the 'center' setting, and a volume control couldn't go to 0 volume. Those functions aren't really suited to that approach and it doesn't solve the gain (sensitivity) problem either. Balance could be implement that way in a pinch, though.

Yes, Heathkit did, in fact, offer a 'Williamson', the W-3M, to be used with the WA-P2 preamp. Here's the PDF of the manual. http://www.mcmlv.org/Archive/HiFi/HeathkitW3M.pdf

Note, sensitivity was 750 mV for 5 Watt out, considerably higher (or lower, depending on how you look at it) than needed for modern line level, much less an MP3 player. Of course, with a preamp the sensitivity doesn't really matter as long as the preamp can drive it. My goal of better than 300 mV sensitivity was so it could be used WITHOUT a preamp or, rather, using an MP3 player as the 'preamp' so the power amp sensitivity needed to match that.

They also offered the W4-AM 'Williamson'. It's sensitivity was 2V for 30 Watt output (although it's rated as 20 Watt amp). It's basically the newer model of the same thing.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Tue 27, 2018 12:37 am 
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Thanks Flip. I just went through the whole manual. I am guessing that the power supply was included in the kit. And two mono blocks, with separate power supply was used for stereo. I would like to build that amp someday.
I noticed, in the power supply, back-back filter caps. Was there a reason for that? To calibrate the cathodes, was a volt meter used to balance with the 100ohm pot?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Tue 27, 2018 12:55 am 
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john8750 wrote:
Thanks Flip. I just went through the whole manual. I am guessing that the power supply was included in the kit. And two mono blocks, with separate power supply was used for stereo. I would like to build that amp someday.
I noticed, in the power supply, back-back filter caps. Was there a reason for that? To calibrate the cathodes, was a volt meter used to balance with the 100ohm pot?
At the time his amp was offered the question would have been "what's stereo?"

The back to back caps are for doubling the voltage rating (two 350 V for 700 V).

Yes, a voltmeter was plugged into the jacks to balance it. (I opted to use the VU meters to do double duty for the same function)


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Tue 27, 2018 8:55 pm 
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Flipperhome wrote:
john8750 wrote:
Thanks Flip. I just went through the whole manual. I am guessing that the power supply was included in the kit. And two mono blocks, with separate power supply was used for stereo. I would like to build that amp someday.
I noticed, in the power supply, back-back filter caps. Was there a reason for that? To calibrate the cathodes, was a volt meter used to balance with the 100ohm pot?
At the time his amp was offered the question would have been "what's stereo?"

The back to back caps are for doubling the voltage rating (two 350 V for 700 V).

Yes, a voltmeter was plugged into the jacks to balance it. (I opted to use the VU meters to do double duty for the same function)



You made some nice improvements Flip. I have a set of those UV meters and driver. I found the OT's for $56 each.
https://www.edcorusa.com/cxpp25-66k
If I build two mono blocks, which choke and PT would be needed X2? Or would it be better on one chassis. Of course we will need powered hydraulics to move it, like the Blumoon.


If you plan on the SS power supply, I wont need chokes.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Fri 30, 2018 7:02 am 
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I still hear some distortion in the mid range area. It seems like harmonic distortion. Only some songs have it, some are very clear. I hear it in both channels. This is the same 6V6 I have built before.
Trying to think of the differences. The IC preamp circuit has changed, along with the NFB circuit. The input coupling capacitor has been removed. The tubes are 6n6c, in substitute of the 6V6.
What could cause this?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Apr Sun 01, 2018 7:57 am 
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So, I took the amp into the shop. With no input connected and headphones I could hear a low end noise. The volume had no control over it. I bypassed the tone amp, which also controls the volume and balance. Totally quiet. Seems like a noisy power supply. I noticed that the power input circuit to the tone amp had no filter. Installing a 100uf ecap took care of the noise. Reconnected it back up in the house. Much better sound now. I notice that the tone controls, both bass and treble are
very responsive. The expansion can be overwhelming. I need to do some more comparing yet. It might just be all in the tone control circuit.
Here is that circuit. I added the cap to the input. It is 13volts.
Attachment:
toneee.jpg
toneee.jpg [ 58.63 KiB | Viewed 1489 times ]

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Apr Sun 01, 2018 11:00 pm 
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I found it. I have a switch to disable the NFB on the rear panel. Just thought I would try it with no NFG. Boy, what a difference. Not able to detect any harmonic distortion now. And the tone controls work normally. The NFG circuit was changed when the opamp circuit was updated. I don't know what else could have such an effect. Anyway, back to pretty decent hi-fi. 8)

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Apr Sun 01, 2018 11:45 pm 
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I noticed there was a change in the NFG circuit from my 6V6 amp, which sounds very good. A .47uf cap was removed, and the resistance was changed from a 470K to a 51K.
But this amp sounds so good now, I will just leave the NFG disconnected.
Might have to do with the tone control circuit. With NFG connected, tone control was erratic.

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