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Author Topic: Fender FRONTMAN 25R amp with LM3886 instead of TDA1514?  (Read 22036 times)

J M Fahey

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Re: Fender FRONTMAN 25R amp with LM3886 instead of TDA1514?
« Reply #15 on: July 19, 2010, 02:27:57 PM »
Hi Jordi.
The nets which I refer to are the "Mute/Standby" ones, where on turn-on they apply a certain voltage on certain IC pins, a couple seconds after turn-on.
They typically are made from a resistor to V+ or V- to said pin(s) plus a 10uF or 22uF capacitor to provide the delay.
Since 3 different ones are suggested: Datasheet 1514; Fender 1514 and Datasheet 3886, I simply reminded you that that's one difference with the original amp, please use the one correct for the actual IC used.
Y sí, soy Argentino, y conozco (y amo) Cataluña, especialmente Barcelona pero sin olvidar lo demás.
Sólo la Catedral ya justifica el viaje, o un simple paseo por la Rambla :tu:.

jordileft

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Re: Fender FRONTMAN 25R amp with LM3886 instead of TDA1514?
« Reply #16 on: July 20, 2010, 05:03:30 AM »
I'm pretty sure that Fender just found out they can buy a huge stock of DPDT switches on a cheaper price than buying also ample inventory of SPST and SPDT switches would have cost. The Double Pole Double Throw -switch can be configured to do the same things as all those other switches, but the other switches can't be made DPDT.

Thanks! You seem to be a real amp enthusiast! then I'll go with an SPST.
I have two more question, these amps uses a reverb can or digital reverb? anyway, what reverb unit should I buy? I can't get that info from nowhere. And about the transformer, I see that (as being from Europe) I would need a 230V to 20V-0-20V, but how many amperes should it stand? Thanks again!

Y sí, soy Argentino, y conozco (y amo) Cataluña, especialmente Barcelona pero sin olvidar lo demás.
Sólo la Catedral ya justifica el viaje, o un simple paseo por la Rambla :tu:.

Me alegro q conozcas cataluña, yo soy de Mataró una ciudad a unos 30km, un saludo!

teemuk

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Re: Fender FRONTMAN 25R amp with LM3886 instead of TDA1514?
« Reply #17 on: July 20, 2010, 12:06:54 PM »
Quote
I have two more question, these amps uses a reverb can or digital reverb?
Can. No idea which model though.
Quote
anyway, what reverb unit should I buy?
What reverb units can you find? If you are thinking about to use a same kind of circuit then there are few criteria: First, the reverb tank must have a high enouh input impedance so a plain OpAmp can drive it. A reasonable estimation is that Zin is higher than at least 600 ohms, but likely more suitable Zin will be in the range of few kilo-ohms. The maximum drive voltage swing will also be limited to about +-14V.

You can, for example, go to Accutronics website, find the spec sheet table of their reverb tanks, and then see what models fit the bill. You can find plenty of other helpful info for aimed for reverb circuit developers from that site as well.

jordileft

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Re: Fender FRONTMAN 25R amp with LM3886 instead of TDA1514?
« Reply #18 on: July 22, 2010, 04:49:29 AM »
What reverb units can you find? If you are thinking about to use a same kind of circuit then there are few criteria: First, the reverb tank must have a high enouh input impedance so a plain OpAmp can drive it. A reasonable estimation is that Zin is higher than at least 600 ohms, but likely more suitable Zin will be in the range of few kilo-ohms. The maximum drive voltage swing will also be limited to about +-14V.

You can, for example, go to Accutronics website, find the spec sheet table of their reverb tanks, and then see what models fit the bill. You can find plenty of other helpful info for aimed for reverb circuit developers from that site as well.

I've been taking a look at Accutronics website, I have some things clear, but I still have some doubts. That's what I have clear:
Digit 1: I would choose 8, for having smaller dimensions.
Digit 4: 2, for medium decay time
Digit 5: C, for having insulated input and grounded output.
Digit 6: 1, no more options.
Digit 7: B, for horizontal open side down, to put it on the floor of the cab.

But what I don't know is the input impedance and output impedance, I rely on you when you tell me Zin should be 600ohm or bigger, but I would like how to calculate that in order to be able to do it for myself the next time. Could you explain me that?

Any help with the transformer current?
Thanks!


phatt

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Re: Fender FRONTMAN 25R amp with LM3886 instead of TDA1514?
« Reply #19 on: July 22, 2010, 09:49:14 AM »
Hi jordy,
             Don't loose sleep it's not an exact science.
As long as the drive end is close to 600 Z.
A DMM Reading should be around 50 to 80 Ohms DC will get you in the zone.

If you want to chase the harder stuff you might find some good reading here.
http://roymal.tripod.com/accutron.htm
Down the bottom is all the rev tanks ,,given in both Z and DCR.
The output (pickup side) transducer can be anywhere above 100 Ohms DC and it will work fine with that circuit.

You might want to consider the reality that the rev circuit in that schematic is not the greatest and an outboard unit might simplify construction and reap far better results anyway.
Having spent far to many years frustrated by onboard rev setups I built my own stand alone unit which is all SS and works like magic.
The beauty of an out-board Rev unit is you can take the reverb signature to *Any other Amp* you use.
Phil.

jordileft

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Re: Fender FRONTMAN 25R amp with LM3886 instead of TDA1514?
« Reply #20 on: July 22, 2010, 10:31:08 AM »
Hi jordy,
             Don't loose sleep it's not an exact science.
As long as the drive end is close to 600 Z.
A DMM Reading should be around 50 to 80 Ohms DC will get you in the zone.

If you want to chase the harder stuff you might find some good reading here.
http://roymal.tripod.com/accutron.htm
Down the bottom is all the rev tanks ,,given in both Z and DCR.
The output (pickup side) transducer can be anywhere above 100 Ohms DC and it will work fine with that circuit.

You might want to consider the reality that the rev circuit in that schematic is not the greatest and an outboard unit might simplify construction and reap far better results anyway.
Having spent far to many years frustrated by onboard rev setups I built my own stand alone unit which is all SS and works like magic.
The beauty of an out-board Rev unit is you can take the reverb signature to *Any other Amp* you use.
Phil.

Ok, I'll go with Accutronics 8EB2C1B. The option about outboard reverb seems really good, how do you connect it? do you used is as a pedal in your chain? maybe I'll try on my next project.
Otherwise, could you help me with the transformer current on the secondary? I think it's the only thing I'm still missing.
I've been talking with people from Fender and they have sent me an updated revision for the Frontman, here it is:

Thanks

alotawatts

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Re: Fender FRONTMAN 25R amp with LM3886 instead of TDA1514?
« Reply #21 on: July 22, 2010, 08:42:42 PM »
Hi, I'm planning to build a Frontman 25R

I going to sound like an amp-snob but ..............................why the time, cost and effort for this amp ?

bry melvin

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Re: Fender FRONTMAN 25R amp with LM3886 instead of TDA1514?
« Reply #22 on: July 22, 2010, 09:12:33 PM »
1.It's not a BAD little amp...
2.It's a FENDER.
3.From a small club stage it can pretty much look (and with a couple of pedals sound) like a 65 Princeton Reissue or Weber/MOJO copy(400-1400 plus the work)
4.And the person wanting to build it is apparently not in the US where they can buy one from Musicians Friend or Sweetwater for $99 with free shipping.

That's my take on it.

jordileft

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Re: Fender FRONTMAN 25R amp with LM3886 instead of TDA1514?
« Reply #23 on: July 23, 2010, 03:50:01 AM »
1.It's not a BAD little amp...
2.It's a FENDER.
3.From a small club stage it can pretty much look (and with a couple of pedals sound) like a 65 Princeton Reissue or Weber/MOJO copy(400-1400 plus the work)
4.And the person wanting to build it is apparently not in the US where they can buy one from Musicians Friend or Sweetwater for $99 with free shipping.

That's my take on it.

I going to sound like an amp-snob but ..............................why the time, cost and effort for this amp ?



Despite all that, I've already built a tube amp (similar to fender blues junior) and some effects pedals, so I wanted to try with a SS amp. Here, in Spain, I could actually buy it for about 120€, but I've played old versions of this amp and they sound great with a medium guitar and doesn't have a much complex schematic, and if you plug it, as I plan, with a MIA Fender Telecaster and a Zendrive (built for me) I'm sure it would make you change your mind. As bry melvin said, it's enough loud for small club gigs and, as any amp builder know, the cost, time and effort on building an amp it worths when you hear it for the first time and every time you see or hear it, you can do some mods if you want, use a different speaker, knobs, wood and finishes,  so when it's finished you would not know what amp is or it's based from. Even giving it a name. And I really enjoy building an amp. For example, the Blues Junior I built it has some mods on EQ section, adding a presence control, upgrading caps, speaker, adding a standby button,... It cost a little bit more than if I would bought it (also due the thing it was my first amp and there was a lot of things I could do for spending much less money I didn't know) but I'm really proud of it, check the video and tell me if you would know it's a Blues junior: http://www.youtube.com/watch?v=_rX-Og3EuXs
For me, it really worth the cost, time and effort

J M Fahey

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Re: Fender FRONTMAN 25R amp with LM3886 instead of TDA1514?
« Reply #24 on: July 23, 2010, 07:15:48 AM »
Hi.
As I see it, jordi is set to build *an amplifier*.
Obviously as a personal project, to learn new skills, to spend a few afternoons doing something he likes, the works.
The fact that it's a Frontman, or anything else, is not that important.
In fact, when somebody who's getting into homebuilding asks me what to do, and wants to start designing from scratch, I usually suggest him to keep it simple , building a straight "Datasheet application" power amp and a simple but good preamp such as Rod Elliot's.
If he wants to go further, I suggest him to copy some relatively simple yet good sounding *commercial* amp.
Hey!!, that Frontman fits the bill !!
Besides, powering that 3886 as the datasheet suggests (+/-28V into 4 ohms or +/- 35V into 8 ohms) will give him a 50 or 60W RMS power amp, which driving a good speaker (Jensen Mod1270) will be a *loud* and quite professional amplifier, well above the original Frontman "25".
Besides, having recently won the FIFA World Cup, the Spaniards are now spirited to conquer the World.  :tu: :tu:
Cuídennos la Copa, la tienen en préstamo ,la próxima nos la llevamos nosotros a casa :lmao:

teemuk

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Re: Fender FRONTMAN 25R amp with LM3886 instead of TDA1514?
« Reply #25 on: July 23, 2010, 07:47:25 AM »
One thing I would do is to build the power amp entirely on a different board than the preamp. If either one proves to be dissapointing in time you can easily throw in something different in there.

Following the datasheet application is (usually) the safest bet, just don't build the bare minimum circuit, which usually omits every stability and reliability ensuring component of which's importance is often discussed further in the datasheets.

BUT, also bear in mind that in case of audio those datasheet circuits are usually HiFi designs with linear frequency response and minimum distortion. Something not neccessarily best for a guitar amp. For example, in case of FM25R, take a look at function of resistor R62 and the additional feedback loop within: This deliberately raises the output impedance of the amp causing the amp's voltage gain (and thus also frequency response) to change in proportion to speaker's different impedance at different frequencies. You will rarely find anything like this from HiFi amps but you'll find that kind of scheme very often from guitar amps because it's a way to mimic characteristics of tube power amps. A datasheet circuit with it's linear frequency response throughout the audio bandwidth will therefore have a very different tone.

In addition, the RC filters in guitar power amps may be configured to deliberately narrow the bandwidth drastically whereas many HiFi-ish designs try to get a linear response from 20 Hz to 20 kHz - something that seldomly benefits a guitar amp. And of course we don't even touch things like soft clipping circuits or tone controlling means incorporated within the power amp: For example, both Peavey Vypyr 30 and Vox AD30VT use a LM3386 chip (and as far as I know, so do some Pritchard amps), yet the external circuitry turns their power amp circuits into something completely different than the generic HiFi application presented in the datasheet of a LM3886.
« Last Edit: July 23, 2010, 07:49:25 AM by teemuk »

jordileft

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Re: Fender FRONTMAN 25R amp with LM3886 instead of TDA1514?
« Reply #26 on: July 23, 2010, 09:58:13 AM »
Hi.
As I see it, jordi is set to build *an amplifier*.
Obviously as a personal project, to learn new skills, to spend a few afternoons doing something he likes, the works.
The fact that it's a Frontman, or anything else, is not that important.
In fact, when somebody who's getting into homebuilding asks me what to do, and wants to start designing from scratch, I usually suggest him to keep it simple , building a straight "Datasheet application" power amp and a simple but good preamp such as Rod Elliot's.
If he wants to go further, I suggest him to copy some relatively simple yet good sounding *commercial* amp.
Hey!!, that Frontman fits the bill !!
Besides, powering that 3886 as the datasheet suggests (+/-28V into 4 ohms or +/- 35V into 8 ohms) will give him a 50 or 60W RMS power amp, which driving a good speaker (Jensen Mod1270) will be a *loud* and quite professional amplifier, well above the original Frontman "25".
Besides, having recently won the FIFA World Cup, the Spaniards are now spirited to conquer the World.  :tu: :tu:
Cuídennos la Copa, la tienen en préstamo ,la próxima nos la llevamos nosotros a casa :lmao:


I can't say that better!
When you talk about output power depending on Vcc, do you say that according to graphic 01183349 Output Power vs Supply Voltage? I think I would feed it with the 27Vdc that TDA1514 has. If you were talking about that graphic it would take about 40W, enough for what I need. I was thinking about changing External-Internal speaker connection so, when a speaker is connected to the External output, the internal speaker keeps sounding driving it parallel, if they are both 8ohm there wouldn't be a problem, is it correct? 'Cause I would like to test combining different speakers with the same output.
Two questions, does anyone know the J4 headphone connector's name? I can't find it anywhere? and some help with transformer secondary current?

One thing I would do is to build the power amp entirely on a different board than the preamp. If either one proves to be dissapointing in time you can easily throw in something different in there.

I appreciate the advice, but I think I will buy it in the same board, I think there will not be any problem with that. In fact, there's no significative changes. The only thing I kept from LM3886 datasheet (which is more hi-fi oriented) is the mute part, which doesn't affect on the sound if it's not open circuit. Otherwise, keeping all in the same board will make much clear for me and simple when mounting on the chassis or cab.  

By the way,  you better get used to Spain winning the FIFA World Cup.  :lmao:

« Last Edit: July 25, 2010, 12:01:17 PM by jordileft »

 

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